WO2016003094A1 - Porous polyolefin-based separation membrane and preparation method therefor - Google Patents

Abstract

The present invention relates to a method for preparing a polyolefin-based separation membrane and a polyolefin-based separation membrane prepared by the method, the method comprising: forming a sheet by melt blending a composition comprising a polyolefin-based resin and a plasticizer and extruding the same; carrying out a first drawing in which the sheet drawn by E₁ times at a temperature of T₁ in the longitudinal direction and drawing the same by E₂ times at a temperature of T₂ in the width direction; extracting the plasticizer from the drawn sheet; and carrying out a second drawing of the sheet, from which the plasticizer is extracted, to a final elongation of 1.25-1.5 times thereof in the width direction, wherein, in the first drawing, the temperature conditions are 100°C < T₁ < 115°C, 100°C < T₂ < 115°C and T₂ ≥ T₁, and the magnification condition is E₁×E₂ = 60-80.

Description

Porous Polyolefin-based Membrane and Method for Producing the Same

The present invention relates to a porous polyolefin-based separator and a method for producing 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. In the case of such a battery separator, high air permeability, thin film thickness, and strong mechanical strength are required. In addition, in order to improve the productivity of the high output battery, it is required to be excellent in shape stability due to high heat or high tension. Therefore, there is a need to develop a separator suitable for use in high power batteries, while having high air permeability and porosity, excellent mechanical strength, and small pore shape and size strain.

The present invention is to provide a separator having excellent air permeability and porosity while having a strong strength and a low strain rate of the shape or size of the pores of the separator.

According to one embodiment of the present invention, a composition comprising a polyolefin resin and a plasticizer is melt-kneaded and extruded to form a sheet, and the sheet is elongated at a temperature T ₁ in the longitudinal direction by an E ₁ times and at a temperature T _{2 in the} width direction. Performing a first stretching of E ₂ times stretching, extracting a plasticizer from the stretched sheet, and second stretching of the sheet from which the plasticizer has been extracted so that the final stretching ratio is 1.25 to 1.5 times in the width direction; The polyolefin system wherein the temperature conditions at the time of the first stretching are 100 ° C. <T ₁ <115 ° C., 100 ° C. <T ₂ <115 ° C., and T ₂ ≧ T ₁ , and the magnification condition is E ₁ × E ₂ = 60-80. A method for producing a separator is provided.

According to another embodiment of the present invention, a polyolefin containing a polyolefin-based resin, the average point pressure (psi) / bubble point pressure (psi) in the wet and dry curve of the separator measured by capillary flow porosimeter is 1.8 to 2.4 A system separator is provided.

Separation membrane according to an embodiment of the present invention has a higher electrolyte hygroscopicity by the form of pores of the membrane.

The separator according to an embodiment of the present invention also has a strong mechanical strength while having excellent air permeability and porosity by controlling the size distribution of the pores of the separator.

1 is a graph of capillary flow porometer (Pillary flow porometer) of PMI measured for the separator according to an embodiment of the present invention. The pressure at the starting point at which the curve is drawn in the wet graph is called bubble point pressure (psi), and the pressure at the point where the wet curve meets the virtual straight line where the slope of the straight line is 1/2 in the dry graph This is called the mean point pressure (psi). The bubble point pressure and the average point pressure reflect the maximum pore size and the average pore size of the separator, respectively.

In the method of manufacturing a porous polyolefin-based separator according to an embodiment of the present invention, a melt-kneaded and extruded composition comprising a polyolefin-based resin and a plasticizer to form a sheet, the sheet is stretched E ₁ times at a temperature T ₁ in the longitudinal direction And performing a first stretching of E ₂ times in the width direction at a temperature of T ₂ , extracting a plasticizer from the stretched sheet, and making the final stretch ratio in the width direction of the sheet from which the plasticizer is extracted to be 1.25 times to 1.5 times. The second stretching, wherein the temperature conditions at the first stretching are 100 ° C. <T ₁ <115 ° C., 100 ° C. <T ₂ <115 ° C., and T ₂ ≧ T ₁ , and the magnification condition is E ₁ × E ₂ = 60 to 80.

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

The polyolefin-based resin is a resin containing a polyolefin, for example, a 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 It may include one or two or more selected from. In another example, the polyolefin resin may include other resin in addition to the polyolefin. Examples of other resins include polyimide, polyester, polyamide, polyetherimide, polyamideimide, polyacetal, and the like. In the case of including other resins, the polyolefin resin composition may be prepared by blending the polyolefin resin and the other resin in an appropriate solvent. 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 ultrahigh molecular weight polyethylene may be used in an amount of 30% by weight or less based on the weight of the polyolefin resin, and for example, a viscosity average molecular weight of 1 × 10 ⁵ g / mol to 9 × 10 ⁵ g / Polyolefin resins containing 70% by weight or more of high density polyethylene, which is mol, and 30% by weight or less of ultra high molecular weight polyethylene having a viscosity average molecular weight of 9 × 10 ⁵ g / mol or more can be used. The polyolefin resin is advantageous because it can produce a high strength separator. In addition, when it contains two or more types of said polyolefin resin, it is good to mix using 1 or more types chosen from the group which consists of a Henschel mixer, a Bambari mixer, and a French mixer.

The plasticizer may be an organic compound that forms a single phase with the polyolefin-based resin at an extrusion temperature. Examples of plasticizers usable in the present invention include aliphatic or cyclic hydrocarbons such as nonane, decane, decalin, liquid paraffin (or paraffin oil), 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, liquid paraffin can be preferably used. Liquid paraffin is harmless to the human body, has a high boiling point and low volatile components, making it suitable for use as a plasticizer in the wet process.

Melting and kneading the composition comprising the polyolefin-based resin and the plasticizer herein may use a method known to those skilled in the art, and may be melt-kneading the polyolefin-based resin and the plasticizer at a temperature of 150 ° C to 250 ° C. The melt-kneaded composition may be injected into a twin screw extruder to extrude at 150 ° C to 250 ° C. Thereafter, the extruded polyolefin resin is 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, the sheet in the longitudinal direction is carried out first stretch of E ₂ times longer in the temperature T ₂ to the E ₁ times and then stretched widthwise at a temperature T _1. The stretching temperature conditions at the time of stretching are 100 ° C <T ₁ <115 ° C, 100 ° C <T ₂ <115 ° C, and T ₂ ≥ T ₁ . When both the MD direction stretching temperature (T ₁ ) and the TD direction stretching temperature (T ₂ ) are less than 115 ° C., the porosity can be increased, and the MD direction stretching temperature (T ₁ ) is lower than the TD direction stretching temperature (T ₂ ). Or the same stretching may cause a difference in the length of stretching for each part, and after stretching in the TD direction can be formed in the separation membrane of two or more different pore size. Of the two or more kinds of pores of different sizes, relatively small pores are advantageous in terms of heat shrinkage, strength, and pore strain, and relatively large pores are advantageous in terms of air permeability, electrolyte wettability, and battery capacity. The stretching ratio condition during the stretching may be E ₁ × E ₂ = 60 ~ 80. Furthermore, E ₁ ≧ 7.5, and E ₂ ≧ 8. In the draw ratio, the MD direction draw ratio (E ₁ ) and the TD direction draw ratio (E ₂ ) are 7.5 times and 8 times or more, respectively, and the draw surface ratio (E ₁ × E ₂ ) is 60 to 80, which is high. Due to the stretched surface magnification, it is possible to minimize the strain of the shape and size of the pores due to the external pressure of the separator to improve battery stability.

The present invention can minimize the strain of the shape and size of the pores by the external pressure while ensuring the porosity required for the separation membrane by stretching under the conditions of the stretching temperature and the draw ratio as described above. The MD stretching temperature T ₁ may be 2 ° C. or more lower than the TD stretching temperature T ₂ . For example, it may be lower than 3 ° C, or higher than 5 ° C.

In one example, MD direction draw ratio E ₁ is 7.5 times, TD direction draw ratio E ₂ is 8 times; MD direction draw ratio E ₁ is 8 times, TD direction draw ratio E ₂ is 8 times; MD direction draw ratio E ₁ is 8 times, TD direction draw ratio E ₂ is 8.5 times; Alternatively, the MD direction draw ratio E ₁ may be 8.5 times, and the TD direction draw ratio E ₂ may be 8.5 times. The draw ratios in the width direction and the longitudinal direction may be the same or different. Specifically, the ratio of E ₁ / E ₂ may be 0.85 to 1. If it is the range of the said extending | stretching ratio, the dispersion | variation effect of the extending | stretching length for each site | part created by making MD and TD direction extending | stretching temperature different can be strengthened further.

The plasticizer may be extracted after the first stretching. The plasticizer extraction may be performed using an organic solvent, and in particular, the longitudinally stretched and the widthwise stretched separator 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 is preferably 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.

Subsequently, the second drawing may be performed such that the sheet from which the plasticizer has been extracted is stretched in the width direction such that the final draw ratio is 1.25 to 1.5 times. The stretching in the width direction is a heat setting step for removing the residual stress of the film to reduce the shrinkage of the final film, and can adjust the heat shrinkage rate, transmittance, etc. of the film according to the temperature and fixation ratio during the heat setting. Specifically, the heat setting may be performed in the width direction of the drawing in a range of 1.25 times to 2 times of the 2-1 stretching, and relaxed to 70% to 100% of the stretched width direction so that the final drawing ratio is 1.25 times to 1.5 times. Can be. The heat setting in the arrangement has the effect of improving the air permeability by adjusting the deviation of the pores generated during the biaxial stretching. The heat setting may be performed at 100 to 150 ° C., for example, may be performed at 120 to 135 ° 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 polyolefin-based separator prepared by the method for producing a polyolefin-based separator according to the above examples.

The polyolefin separator may have an average point pressure (psi) / bubble point pressure (psi) of about 1.8 to about 2.4 in a wet curve of the separator measured by a capillary flow porosimeter.

If the ratio of the average point pressure (psi) / bubble point pressure (psi) in the capillary flow pore meter wetting and drying curves is within this range, the pore size is varied so that the porosity required for the membrane, eg, 40% or more It is possible to provide a separator having excellent air permeability and excellent electrolyte wettability and strength while achieving.

The bubble point pressure (psi) refers to the pressure of the starting point at which the wet curve is drawn in the capillary flow pore meter. Specifically, when the membrane sample is soaked in the solution, the pore is filled with the solution, and the air is increased while the air is blown while increasing the pressure. The solution filled inside moves under pressure first, and the pressure at this time is called bubble point pressure. Referring to FIG. 1, the bubble point pressure refers to the pressure at the time when the flow velocity is maintained at 0 and starts to increase in the graph of the flow rate change with increasing pressure of the capillary flow pore meter.

The average point pressure (psi) refers to the pressure at the point where the wet straight line meets the imaginary straight line and the wet curve in which the slope is 1/2 in the dry straight line in the capillary flow pore meter. Specifically, when the air is blown while increasing the pressure while the membrane sample is not wetted with the solution, a graph having a linear shape in which the flow rate increases in proportion to the pressure increase is obtained. Referring to FIG. 1, when a virtual straight line (half dry graph in FIG. 1) having a slope is 1/2 in the straight graph (dry graph in FIG. 1), the virtual straight line and the wet curve are The pressure at the point of meeting is called the average point pressure.

The polyolefin-based separator according to an embodiment of the present invention may have a porosity of 40% to 50% and a permeability of 50 sec / 100 cc to 200 sec / 100 cc. In the present specification, air permeability refers to the time at which 100 cc of air passes through the separator. Specifically, the air permeability may be 60 sec / 100cc to 150 sec / 100cc.

In the polyolefin-based separator according to an embodiment of the present invention, the ratio of tensile strength (kg / cm ² ) / elongation (%) in the longitudinal and width directions of the separator is 15 to 28 {(kg / cm ² ) /%}, respectively. Can be. If the tensile strength / elongation ratio is in the range, the excellent separator has a mechanical strength while the pores or the membrane has a low strain, thereby minimizing deformation due to external force or impact. In addition, the polyolefin-based separator according to an embodiment of the present invention may have a tensile strength of 1700 kg / cm ² or more in the longitudinal direction of the membrane, a tensile strength of 1800 kg / cm ^{2 or} more in the width direction, elongation and Elongation in the width direction may be 100% or less, more specifically 98% or less. When the elongation is in the range, a separation membrane having improved stability against deformation of the pore size and shape may be provided. The polyolefin-based separator according to an embodiment of the present invention may have a water droplet contact angle of the separator 107 ° or less, for example, 95 ° to 107 °, specifically, 100 ° to 106 °. When the contact angle is in the above range, the electrolyte wettability is good, and thus battery performance may be improved.

Hereinafter, a polyolefin separator according to another example of the present invention will be described. The separator according to the present embodiment may include a coating layer on one side or both sides of the separator manufactured according to the example of the present invention, the coating layer may include an organic binder, and may further include inorganic particles. have. The organic binder may include, for example, a polyvinylidene fluoride polymer having a weight average molecular weight of 1,000,000 g / mol or more, a polyvinylidene fluoride polymer having a weight average molecular weight of 800,000 g / mol or less, or a mixture thereof. have. For example, polyvinylidene fluoride homopolymer (PVdF), polyvinylidene fluoride-hexapropylene copolymer (PVdF-HFP), and other polyvinylidene fluoride copolymers alone or mixtures thereof Can be used. The inorganic particles there may be mentioned _{Al 2 O 3, SiO 2,} B 2 O 3, Ga 2 O 3, TiO 2, and SnO ₂ and the like. The coating layer may be formed by a dip coating method. The separator having the coating layer may be left in an oven at 105 ° C. for 1 hour, and the heat shrinkage may be 3% or less in the MD and TD directions, respectively. More specifically, it may be 2% or less.

The porous polyolefin-based separator according to 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 polyolefin-based 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.

In addition, the porous polyolefin-based separator or coating separator according to the embodiments of the present invention is cut to 50 × 50 mm in size of the separator prepared in a 120 ℃ oven after shrinking for 1 hour, after which the size of the contracted separator When measuring the shrinkage by reflecting the reduced size, the shrinkage in the longitudinal direction may be 5% or less, the shrinkage in the width direction may be 3% or less, and more specifically, the shrinkage in the longitudinal direction is 4% or less and the shrinkage in the width direction is 2% or less. Can be.

The present invention also provides a battery chemical cell comprising the porous polyolefin-based separator, positive electrode, negative electrode and electrolyte disclosed in the present invention. The type of electrochemical cell is not particularly limited and may be a kind of electricity known in the art. The electrochemical cell of the present invention may preferably be a lithium secondary battery such as a lithium metal secondary battery, a lithium ion 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: The cell can be prepared by placing the separator or coated separator of the present invention between the positive and negative electrodes of the cell and then filling the electrolyte therewith. have. 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. 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 carbon includes 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 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, 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 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), dimethylformamide (Dimethylformamide, DMF), Dipropyl carbonate (DPC), Dimethyl sulfoxide (DMSO), Acetonitrile, Dimethoxyethane, Diethoxyethane, Tetrahydrofuran ( Tetrahydrofuran), N-methyl-2-pyrrolidone (NMP), ethyl methyl carbonate (EMC), or gamma-butyrolactone (-Butyrolactone). 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 Porous Polyolefin Membrane

High-density polyethylene (HDPE; manufactured by Mitsui Chemical) having a viscosity average molecular weight of 600,000 g / mol was fed to a twin screw extruder, and then liquid paraffin (Far East Emulsification) was weighted to polyethylene 30 to liquid paraffin. The extruder was injected into the twin screw extruder in an amount of 70.

After the extrusion, the gel phase obtained through the T-die was manufactured as a sheet-type separator using a cooling roll. The membrane was stretched in the longitudinal direction (Machine Direction, MD) at 110 ° C and in the transverse direction (TD) at 113 ° C (stretch ratio: 8.0 (MD) x 8.0 (TD)).

The stretched polyolefin-based separator was immersed in methylene chloride (Samsung Fine Chemical) to extract liquid paraffin, and then transferred to a drying roll to dry.

Then, the dried film was heat-set in the width direction of the secondary stretching (width direction draw ratio: 1.0 → 1.6 → 1.4, stretching temperature 128 ° C.) to prepare a porous polyolefin separator having a thickness of 12.5 μm.

Example 2: Preparation of Porous Polyolefin-Based Membranes

In Example 1, the stretching was performed in the machine direction (Machine Direction, MD) at 103 ° C and transverse direction (TD) at 105 ° C (stretch ratio: 8.5 (MD) x 8.5 (TD)) In the same manner as in Example 1, a separator having a thickness of 12.3 μm was prepared.

Comparative Example 1: Preparation of porous polyolefin-based separator

In Example 1, the stretching was performed in the machine direction (Machine Direction, MD) at 120 ° C and in the transverse direction (TD) at 123 ° C (stretch ratio: 8 (MD) x 8 (TD)). Then, a membrane having a thickness of 12.2 μm was prepared in the same manner as in Example 1.

Comparative Example 2: Preparation of Porous Polyolefin-Based Membrane

In Example 2, the same method as in Example 2, except that the stretching direction in the longitudinal direction (MD) and the stretching direction in the transverse direction (TD) were set to 7 (MD) x 7 (TD). 12.3 μm thick membrane was prepared.

Table 1 shows the production conditions of the separators according to Examples 1 and 2 and Comparative Examples 1 and 2.

	Example 1	Example 2	Comparative Example 1	Comparative Example 2
Drawing method	rotor	rotor	rotor	rotor
Stretch ratio (MD x TD)	8 × 8	8.5 × 8.5	8 × 8	7 × 7
MD drawing temperature	110 ℃	103 ℃	120 ℃	103 ℃
TD drawing temperature	113 ℃	105 ℃	123 ℃	105 ℃
2nd TD drawing temperature	128 ℃	128 ℃	128 ℃	128 ℃
2nd TD final draw ratio	1.4	1.4	1.4	1.4

Experimental Example

The porosity, air permeability, tensile strength, elongation, shrinkage rate, bubble point and average point pressure, and droplet contact angle were measured by the measurement methods disclosed below for the separators prepared in Examples 1 and 2 and Comparative Examples 1 and 2, and The results are shown in Table 2.

	Example 1	Example 2	Comparative Example 1	Comparative Example 2
Average point pressure (psi)	258.856	272.12	201.34	282.24
Bubble Point Pressure (psi)	121.675	113.31	121.54	113.35
Average Point Pressure / Bubble Point Pressure	2.13	2.40	1.66	2.49
Porosity (%)	44.5	43	53.1	38.5
Breathability (sec / 100cc)	122	115	95	223
Tensile Strength (kg / cm 2 ) (MD, TD)	2120, 2214	2250, 2305	1653,1622	1742,1783
Elongation (%) (MD, TD)	89, 92	86, 88	95, 110	93, 98
Tensile Strength / Elongation (MD, TD)	23.8, 24.1	26.2, 26.2	17.4, 14.7	18.7, 18.2
Droplet contact angle (°)	102	103	111	111
Shrinkage (%) (MD, TD)	2,0	2,0	8,3	2,0

1.Measure bubble point pressure and average point pressure on capillary flow porosity graph

Each of the separators prepared in Examples and Comparative Examples was sampled into a circle having a diameter of 26 mm. The membrane itself is mounted on a PMI capillary flow pore meter and thoroughly wetted with Galwick ^TM solution (surface tension of 15.9 dyne / cm). Wet up Calc. After setting the mode, draw the wet curve by measuring the flow rate of N ₂ for each pressure. The pressure at which the first bubble is detected in the wet curve is recorded as the bubble point pressure (psi). In addition, each of the separators prepared in Examples and Comparative Examples was sampled in a circle having a diameter of 26 mm and the separator itself was mounted on the device, and then the device was dried. The mode was set, and the flow rate of N ₂ for each pressure was measured and shown as a dry curve graph. In the measured dry curve graph, a straight line extends from the origin to a point having linearity, draws an imaginary straight line that is half of the slope of the straight line, and the pressure at the point where the imaginary straight line and the wet curve meet the average point pressure ( psi).

2. Porosity

Samples of 10 cm × 10 cm of each of the separators prepared in Examples 1 and 2 and Comparative Examples 1 and 2 were cut out to obtain their volume (cm 3) and mass (g), and the volume, mass and Porosity was calculated from the density (g / cm 3) using the following equation.

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

Density of sample = density of polyethylene

3. Aeration

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.

4. Tensile Strength

Each of the membranes prepared in Examples and Comparative Examples was made of 10 samples cut at 10 different points (MD) 10 mm × length (TD) 50 mm, and 20 mm portions were bitten in the UTM. After pulling up and down the strength was measured. The tensile strength of each sample was measured three times, and then the average value was calculated.

5. Elongation

For each of the separators prepared in Examples and Comparative Examples, the value of ((length of break point-20) / 20 mm) x 100 was compared with the original length and the length at the break point when measuring the tensile strength of 4. Is expressed as a percentage.

6. 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.

7. Droplet contact angle (electrolyte wettability evaluation)

Each of the separators prepared in Examples and Comparative Examples was cut to 20 mm long by 20 mm wide by 20 mm long by TD to prepare five samples. The sample was placed on a contact angle measuring device (DSA-100, Matek Trading Co., Ltd.), and water was dropped by dropper, and then contact angle was measured. The contact angles (°) of the five samples were averaged and calculated.

Claims (16)

1. Melt-kneading and extruding a composition comprising a polyolefin resin and a plasticizer to form a sheet,

   The sheet in the longitudinal direction to perform a first stretch which E ₂ times longer in the temperature T ₂ in the direction E, and _1-fold stretched in the width T ₁ and the temperature,

   Extracting a plasticizer from the stretched sheet,

   Second stretching the sheet from which the plasticizer has been extracted so that the final stretching ratio is 1.25 to 1.5 times in the width direction;

   The polyolefin system wherein the temperature conditions at the time of the first stretching are 100 ° C. <T ₁ <115 ° C., 100 ° C. <T ₂ <115 ° C., and T ₂ ≧ T ₁ , and the magnification condition is E ₁ × E ₂ = 60-80. Method for producing a separator.
2. The method of claim 1, wherein the ratio of E ₁ / E ₂ is 0.85 to 1 under the magnification condition.
3. According to claim 1, wherein the polyolefin resin is a high density polyethylene having a viscosity average molecular weight of 1 × 10 ⁵ g / mol to 9 × 10 ⁵ g / mol and an ultra high molecular weight polyethylene having a viscosity average molecular weight of 9 × 10 ⁵ g / mol or more A manufacturing method comprising a single or a mixture thereof selected from the group consisting of.
4. The manufacturing method according to any one of claims 1 to 3, wherein E ₁ ≧ 7.5 and E ₂ ≧ 8.
5. The method according to any one of claims 1 to 3, wherein the second stretching is from 1.25 times to 2 times in the width direction of 2-1 to 2-1 stretching and from 70% to the length of the 2-1 stretching in the width direction. A method of manufacture comprising relaxing to 100%.
6. The method according to any one of claims 1 to 3, further comprising coating one or both surfaces of the prepared polyolefin-based separator with a coating composition containing an organic polymer and inorganic particles.
7. Containing polyolefin resin,

   A polyolefin-based separator having a ratio of average point pressure (psi) / bubble point pressure (psi) in the wetting and drying curves of the separator measured by a capillary flow porometer.
8. The polyolefin-based separator of claim 7, wherein a ratio of tensile strength (kg / cm ² ) / elongation (%) in the longitudinal direction and the width direction of the separator is 15 to 28, respectively.
9. The polyolefin-based separator of claim 7, wherein the separator has a porosity of 40% to 50%.
10. The polyolefin-based separator of claim 7, wherein the separator has a permeability of 50 sec / 100 cc to 200 sec / 100 cc.
11. The polyolefin-based separator according to claim 7, wherein the droplet contact angle of the separator is 107 ° or less.
12. The high-density polyethylene and the viscosity average molecular weight according to any one of claims 7 to 11, wherein the polyolefin resin has a viscosity average molecular weight of 1 × 10 ⁵ g / mol to 9 × 10 ⁵ g / mol. A polyolefin-based separator comprising a single or a mixture thereof selected from the group consisting of ultra high molecular weight polyethylene of more than ⁵ g / mol.
13. The method according to any one of claims 7 to 11, wherein the polyolefin-based separator is stretched E ₁ times at T ₁ temperature in the longitudinal direction and E ₂ times at T ₂ temperature in the width direction. The conditions are 100 ° C. <T ₁ <115 ° C., 100 ° C. <T ₂ <115 ° C., and T ₂ ≧ T ₁ , and the magnification condition at the time of stretching is E ₁ × E ₂ = 60 to 80, E ₁ ≥ 7.5, and Polyolefin-based membrane, E ₂ ≥ 8.
14. The polyolefin separator of claim 13, wherein the ratio of E ₁ / E ₂ is 0.85 to 1 under the magnification condition.
15. An electrochemical cell comprising the polyolefin separator according to any one of claims 7 to 11.
16. The electrochemical cell of claim 15, wherein the electrochemical cell is a lithium secondary battery.

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