KR101674917B1 - Method of preparing porous polyolefin separator, porous polyolefin separator therefrom, and lithium secondary battery comprising the separator - Google Patents

Abstract

The present invention relates to a process for producing a porous polyolefin separator, a porous polyolefin separator prepared by the process, and a lithium secondary battery comprising the porous polyolefin separator. According to an aspect of the present invention, there is provided a method for producing a polyolefin resin, which comprises extruding a polyolefin resin having a melt flow rate (MFR) of 0.1 to 10 g / 10 min to form an extruded film, annealing the extruded film, ) 0.0190 to 0.0280, and uniaxially stretching the extruded film of the birefringence index (n) to form a porous separator membrane. According to the present invention, porosity and air permeability can be greatly improved while maintaining the tensile strength and the piercing strength of the porous polyolefin separator, thereby providing a lithium secondary battery with high capacity and high output characteristics.

Description

TECHNICAL FIELD The present invention relates to a porous polyolefin separator, a porous polyolefin separator, and a lithium secondary battery comprising the porous polyolefin separator.

The present invention relates to a process for producing a porous polyolefin separator, and more particularly, to a process for producing a porous polyolefin separator having an extruded film as an intermediate product of a polyolefin resin having a specific range of birefringence (? N, birefringence), a porous polyolefin separator And a lithium secondary battery comprising the same.

A secondary battery is classified into a lead-acid battery, a nickel-cadmium battery, a nickel-hydrogen battery, and a lithium secondary battery, which can be used semi-permanently by repeatedly charging and discharging by electrochemical reaction. Among them, lithium secondary batteries are superior to other batteries in terms of high voltage and energy density characteristics, leading the secondary battery market. Depending on the types of electrolytes, lithium ion secondary batteries using liquid electrolytes and solid electrolytes Lithium-ion polymer secondary battery.

Lithium secondary batteries are composed of an anode, a cathode, an electrolyte, and a separator. Among them, the lithium secondary battery separator has required properties such as separating the anode and the cathode, electrically isolating the battery, and high permeability of lithium ion, To increase ionic conductivity. Polyolefin (PO), which is advantageous for pore formation and has excellent chemical resistance, mechanical properties and thermal properties, is mainly used as a polymer substrate of a separator which is generally used. In recent years, in order to produce a porous separator from a polyolefin (PO), a dry method including a step of extruding, annealing, stretching and heat setting a polyolefin resin is widely used. In order to increase the air permeability in the polyolefin membrane produced through such a dry method, a method of increasing elongation has been used, but there is a limit to lower the strength of the membrane.

A problem to be solved by the present invention is to produce a porous polyolefin separator having enhanced porosity and air permeability as well as tensile strength and piercing strength.

According to one aspect of the present invention, there is provided a method of manufacturing a polyolefin resin sheet, comprising: extruding a polyolefin resin having a melt flow rate (MFR) of 0.1 to 10 g / 10 min to form an extruded film; forming an extruded film having an anneal birefringence (Δn) of 0.0190 to 0.0280, and forming a porous separator by uniaxially stretching the extruded film having the birefringence index (Δn), comprising the steps of: providing a porous polyolefin separator do.

According to the present invention, porosity and air permeability can be greatly improved while maintaining the tensile strength and the piercing strength of the porous polyolefin separator, thereby providing a lithium secondary battery with high capacity and high output characteristics.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate preferred embodiments of the invention and, together with the description of the invention given above, serve to better understand the spirit of the invention. And should not be construed as limiting.
1 is a process flow chart for producing a porous polyolefin separator according to an embodiment of the present invention.
FIG. 2 is a schematic diagram illustrating refraction of light in a medium having a density difference. FIG.
3 is an electron micrograph (X10,000 times) of an extruded film produced according to Example 3. Fig.
4 is an electron micrograph (X10,000 times) of the extruded film produced according to Comparative Example 3. Fig.

The terms used in the specification and claims should not be construed as limited to ordinary or dictionary terms and the inventor may properly define the concept of a term to describe its invention in its best possible way And should be construed in accordance with the principles and meanings and concepts consistent with the technical idea of the present invention. Accordingly, the configurations disclosed in the embodiments disclosed herein are merely one preferred embodiment of the present invention and are not intended to represent all of the technical ideas of the present invention, so that various equivalents And variations are possible.

The method for producing a porous polyolefin separator according to an aspect of the present invention includes the steps of (S1) forming an extruded film, (S2) forming an extruded film having a specific birefringence, and (S3) forming a porous separator.

1 is a process flow chart for producing a porous polyolefin separator according to an embodiment of the present invention. Referring to FIG.

In step S1, the polyolefin resin is extruded to form an extruded film.

The polyolefin resin may be one or two or more polymers or copolymers selected from the group consisting of ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene and 1-octene, But not limited to, water.

In addition, the polyolefin resin has a melt flow rate (MFR) of from about 0.1 to about 10 g / 10 min, or from about 0.5 to about 5.0 g / 10 min. The melt flow rate (MFR) of the polyolefin resin is related to the molecular weight of the resin. Usually, when the melt flow rate (MFR) is lowered, the molecular weight tends to increase. The molecular weight of the polyolefin resin is not critical if it can be molded into a film or a sheet, but in the case of applications requiring strong physical properties such as separation membranes for secondary batteries, the larger the molecular weight, the better. In this case, the weight average molecular weight of the polyolefin resin may be at least about 1 x 10 ⁵ , preferably about 2 x 10 ⁵ to about 1 x 10 ⁶ , more preferably about 3 x 10 ⁵ to about 7 x 10 ⁵ .

During the extrusion process, it can be heated to form a single phase, which is carried out through an extruder, which may be a single or twin screw extruder. The heating temperature will vary depending on the type of polyolefin resin used. Further, the extrusion temperature may be about 170 to about 280 캜. If the extrusion temperature exceeds 280 DEG C, the formed extruded film may be deteriorated, which is undesirable.

Further, after the extrusion process, the casting process can be performed. This casting process is carried out at a temperature of about 120 DEG C or less. Preferably, it can be carried out at a temperature of about 100 DEG C or less. In addition, the casting step may be a method of contacting with a cooling medium, or a method of contacting a refrigerant-cooled roll or press. The cooling roll is not particularly limited in its kind and form. The geometry of the die is also not particularly limited, and examples thereof include, but are not limited to, a sheet-forming die having a rectangular orifice, a double-cylinder hollow die, an inflation die, T-die) or the like. A gap of about 0.5 to about 5.0 mm, or about 1 to about 4 mm, is suitable for the die. This gap determines the casting speed of the cooling roll to form the final product thickness. In addition, it may be advantageous to increase the casting speed to increase the crystallization speed. Further, for example, the temperature difference between the cooling roll and the die may be made small, which may be advantageous in increasing the degree of crystallization of the separation membrane and forming a uniform pore size.

In step S2, the extruded film formed in step S1 is annealed. The annealing process stabilizes the crystal structure of the porous polyolefin separator. The annealing process may be conducted at a temperature of about 100 to about 165 < 0 > C. During the annealing process, it may be carried out in an oven at about 100 to about 165 DEG C, or about 125 to about 160 DEG C for a retention time of about 1 to about 60 minutes, or about 3 to about 30 minutes. Thus, the extruded film formed by staying at a constant temperature has an increased degree of crystallinity, and such a crystallized portion is advantageous in forming a desired pore in the stretching process.

Through this annealing process, an extruded film having a specific birefringence (n), for example, an extruded film having a birefringence (n) of about 0.0190 to about 0.0280, or about 0.0200 to about 0.0270 is formed. Thereafter, the extruded film having the birefringence index DELTA n in the above-described range has the desired physical properties of the final porous polyolefin separating film through stretching, e.g., uniaxial stretching, and / or heat fixation.

In general, when light passes through two or more media having different optical densities, the direction of light changes (except when the angle of incidence is 90 degrees), so that light travels in a medium having a high optical density This slows down and changes the direction of light travel. When light of a certain wavelength passes through two or more contacted media having different optical densities, the sin of the incident angle maintains a constant ratio with the sin of the refracting angle (Snell's law). When light travels from a medium with a low optical density to a medium with a high optical density, the light refracts toward the normal, while the opposite refracts away from the normal. Therefore, the greater the difference in optical density between two or more media having different optical densities from each other, the closer the refracted light ray is to the normal side.

Refraction of light can be defined as (speed of light under vacuum) / (speed of light in high optical density medium). Such a refractive index, as seen on the basis of FIG. 2, is defined as a point (A) in contact with a low optical density medium, a point (B) in contact with a low optical density medium and a high optical density medium, C), whereby the refractive index can be expressed as sin i / sin r (where sin i is b / n and sin r is b 1 / n 1).

The double refraction of light represents a phenomenon in which light is refracted in two directions in an anisotropic material, where the light refracting in two directions is called an ordinary ray (ω) and an extraordinary ray (ε) . The phase ray is light refracted while Snell's law is applied, and the abnormal ray is light refracting in accordance with Snell's law.

Birefringence (birefringence) is the refractive index obtained by subtracting the value of the refractive index (n _ε) of the extraordinary ray from the (n _ω) of the ordinary ray means a refractive index difference between the ordinary ray and the extraordinary ray, and - a (n _ω n _ε), represented by Δn do.

This birefringence can be measured without limitation by an ellipsometry method, a prism coupling method, a minimum deviation angle method, an Abbe's refraction method, a single wavelength interferometer method, a diffraction grating method, a surface plasmon resonance method, a Fabry- , A ring resonator method, a cutoff wavelength method, a confocal electron microscope method, and a Fizeau interferometer method.

The present inventors have found that when the birefringence of the porous polyolefin separator falls within a specific range as described above, the intended properties of the separator for a (lithium) secondary battery, such as porosity, air permeability, tensile strength and puncture strength, And has achieved the process for producing the porous polyolefin separator of the present invention.

In step S3, the extruded film having the specific birefringence formed in step S2 may be uniaxially stretched.

The extruded film having a specific birefringence formed in the step S2 may be uniaxially stretched in the longitudinal direction (MD) and stretched in the longitudinal direction (MD) to about 150 to about 800%, preferably about 150 to about 600% have. The extruded film can be typically subjected to longitudinal (MD) stretching alone (i.e., uniaxially stretched) according to a stretching process.

Optionally, in step S3, the stretched extruded film may be heat set at a predetermined temperature for about 5 to about 300 seconds. In particular, the stretched extruded film is subjected to heat fixation to reduce the shrinkage of the final porous separator by removing residual stresses.

The heat fixation is to fix the porous separator and force the extruded film to shrink by applying heat to remove the residual stress. If the temperature of heat setting is high, it is advantageous for lowering the shrinkage rate, but if it is too high, the extruded film is partially melted, so that the formed pores are clogged and the permeability is lowered.

Here, the heat fixing time should be relatively short when the heat fixing temperature is high, and may be relatively long when the heat fixing temperature is low. Preferably about 10 to about 120 seconds. Most preferably, the temperature is in the range of about 10 to about 120 seconds, and in the temperature range in which the change in the air permeability (sec / 100 cc) of the membrane is increased by about 10 to about 20% Seconds are reasonable.

Alternatively, a porous coating layer may be formed on the porous substrate as the porous polyolefin separating membrane. The porous coating layer is coated on at least one surface of the porous substrate or at least one surface of the porous substrate and a region of the pores of the porous substrate, and includes inorganic particles and a binder polymer. The binder polymer is located on a part or all of the inorganic particles, and functions to connect and fix the inorganic particles.

The inorganic particles may be inorganic particles having a dielectric constant of about 5 or more, or inorganic particles having a lithium ion transporting ability (in the case of a lithium secondary battery), either singly or in combination. The average particle size of the inorganic particles is not particularly limited, but may range from about 0.001 탆 to about 10 탆 for the formation of a porous coating layer of uniform thickness and proper porosity. When the average particle diameter of the inorganic particles satisfies the above range, the dispersibility of the inorganic particles can be prevented from decreasing, and the porous coating layer can be adjusted to an appropriate thickness.

Non-limiting examples of the binder polymer include polyvinylidene fluoride-co-hexafluoro propylene (PVDF-co-HFP), polyvinylidene fluoride-co-trichloro ethylene, polyvinylidene fluoride-co-chlorotrifluoroethylene, polymethyl methacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylpyrrolidone, Polyvinylacetate, polyethylene-co-vinyl acetate, polyethylene oxide, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, Cellulose acetate propionate, cyanoethylpyrrolidone, ethylpullulan, cyanoethylpolyvinylalcohol, cyanoethyl cellulose, cyanoethyl sucrose, pullulan, carboxyl methyl cellulose (CMC), acrylic Acrylonitrile-styrene-butadiene copolymer, polyimide, polyvinylidenefluoride, polyacrylonitrile, and styrene butadiene rubber (SBR). , Or a mixture of two or more thereof.

The binder polymer may be contained in an amount of about 0.1 to about 20 parts by weight, preferably about 1 to about 5 parts by weight, based on 100 parts by weight of the total amount of the binder polymer and the inorganic particles.

The solvent is similar in solubility index to the binder polymer to be used, and preferably has a low boiling point. This is because the mixing can be made uniform and then the solvent can be easily removed. Non-limiting examples of the solvent include acetone, tetrahydrofuran, methylene chloride, chloroform, dimethylformamide, N-methyl-2-pyrrolidone (N- methyl-2-pyrrolidone, NMP), cyclohexane, water or mixtures thereof.

The selective formation of the porous coating layer may be achieved by dispersing inorganic particles in a binder solution of a binder polymer and a solvent to prepare a slurry, coating the slurry on a porous substrate, and removing the solvent do. As the coating method, a conventional method can be used, and various methods such as dip coating, die coating, roll coating, comma coating, or a mixing method thereof can be used.

According to one embodiment of the present invention, the air permeability of the porous polyolefin separator having a thickness of 20 mu m is about 450 sec / 100cc or less. The term "permeability " used in the separator of the present invention means the time for 100 cc of air to permeate through the separator having a thickness of 20 mu m, and as a unit thereof, sec / And is usually indicated by a Gurely value or the like.

According to one embodiment of the present invention, the porosity of the porous polyolefin separator is at least about 40%. The term "porosity " used in the separation membrane of the present invention means the ratio of the volume occupied by the pores to the volume of the separation membrane, and is used as a unit thereof in terms of porosity and porosity. And in a secondary battery such as a lithium secondary battery, pores must be large enough to prevent an internal short circuit.

According to one embodiment of the present invention, the porous polyolefin separator has a puncture strength of about 200 gf or more. The term "puncture strength " as used in the separator of the present invention means the resistance of the separator against external hazards, for example, penetration of an external object, using gf as its unit, In general, the higher the value, the lower the internal short-circuit defect rate of the separator.

In the porous polyolefin separator, if the porosity is about 40% or more and the air permeability of 20 탆 thick is about 450 sec / 100cc or less, the content of the electrolyte impregnated and wetted in the separation membrane due to the high porosity is increased, So that a high capacity and a high output characteristic can be provided to the battery. In addition, according to the present invention, if the puncture strength is about 200 gf or more, the risk of short circuit due to external impact is greatly reduced, and the defect rate of the battery can be remarkably reduced.

Further, according to one embodiment of the present invention, the longitudinal (MD) tensile strength of the porous polyolefin separator may be about 1,500 kg / cm ^{2 or} more. The tensile strength of the membrane is one of the properties that have a large effect on processes such as winding or unwinding.

The porous polyolefin separator of the present invention is characterized in that it is uniaxially stretched in machine direction (MD), machine direction, longitudinal direction). The porous polyolefin separator is uniaxially stretched at about 150 to about 800%, or about 150 to about 600%. Therefore, the longitudinal stretching process of the present invention not only increases the strength in the stretching direction, but also enhances the desired physical properties of the above-described (lithium) secondary battery separator, such as porosity, air permeability, tensile strength, May have a desired range.

In another embodiment, the present invention provides a lithium secondary battery comprising a positive electrode, a negative electrode, and the above-described porous polyolefin separator interposed between the positive electrode and the negative electrode.

The anodes, cathodes, electrolytes, etc. used in the present invention are commercially available or can be prepared by processes and / or methods known in the art.

The positive electrode is manufactured by binding a positive electrode active material to a positive electrode collector according to a conventional method known in the art, and performs a function of intercalating and deintercalating lithium ions. As the cathode active material, a conventional cathode active material that can be used for a cathode of a conventional secondary battery can be used, and examples thereof include LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , Li (Ni _a Co _b Mn _{c) O 2 (0 <a} <1, 0 <b <1, a + b + c = 1), LiNi 1 - Y Co Y O 2, LiCo 1 - Y Mn Y O 2, LiNi 1 -Y Mn Y O ₂ (where, 0≤Y <1), Li ( Ni a Co b Mn c) O 4 (0 <a <2, 0 <b <2, a + b + c = 2), LiMn 2 - Z Ni _Z O ₄ , LiMn _{2 -Z} Co _Z O ₄ (where 0 <Z <2), LiCoPO ₄ , LiFePO _4, and mixtures thereof. As the positive electrode collector, aluminum, nickel, or a foil produced by a combination of these may be used.

The negative electrode is manufactured by binding an anode active material to an anode current collector according to a conventional method known in the art, and performs a function of intercalating and deintercalating lithium ions in the same manner as the anode. At this time, the negative electrode active material may be carbon such as non-graphitized carbon or graphite carbon; _{Li x Fe 2 O 3 (0} = x = 1), Li x WO 2 (0 = x = 1), Sn x Me 1 -x Me 'y O z (Me: Mn, Fe, Pb, Ge; Me' : A metal complex oxide of Al, B, P, Si, group 1, group 2, group 3 elements of the periodic table, halogen, 0? X = 1; y = 3; Lithium metal; Lithium alloy; Silicon-based alloys; Tin alloy; _{SnO, SnO 2, PbO, PbO} 2, Pb 2 O 3, Pb 3 O 4, Sb 2 O 3, Sb 2 O 4, Sb 2 O 5, GeO, GeO 2, Bi 2 O 3, Bi 2 O 4, Bi ₂ O ₅ and the like; Conductive polymers such as polyacetylene; Li-Co-Ni-based materials and the like can be used. On the other hand, as the negative electrode collector, stainless steel, nickel, copper, titanium or an alloy thereof can be used.

Also, the electrolyte that can be inserted between the electrode and the separator is a salt having a structure such as A ⁺ B ^- , where A ⁺ includes an alkali metal cation such as Li ⁺ , Na ⁺ , K ⁺ and B ^- is _{^{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 - (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), and the like, and salts containing anions such as C (CF ₂ SO ₂ ) ₃ ^- But are not limited to, dipropyl carbonate (DPC), dimethylsulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, tetrahydrofuran, N-methyl-2-pyrrolidone (NMP), ethylmethyl carbonate (? -butyrolactone), or a mixture thereof, but is not limited thereto All.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail with reference to examples. However, the embodiments according to the present invention can be modified into various other forms, and the scope of the present invention should not be construed as being limited to the above-described embodiments. The embodiments of the present invention are provided so that those skilled in the art can explain the present invention more clearly and completely.

 [Example 1]

The polypropylene (PP) used as a starting material has a melt flow rate (MFR) of about 3 g / 10 min. The polypropylene (PP) was extruded at about 220 DEG C using a single-screw extruder. The extrudate was passed through a T-die having a gap of 1.5 mm and then passed through a cooling roll at 80 DEG C An extruded film having a thickness of 20 mu m was formed. The extruded film thus formed was annealed in an oven at about 150 캜 for a retention time of 5 minutes to obtain an extruded film having a birefringence (Δn) of 0.0190. The extruded film of the birefringence index n was stretched by about 200% in the machine direction using a uniaxial stretching machine. The longitudinal (MD) stretching temperature was about 130 占 폚. The stretched extruded film was heat-set at about 140 캜 to obtain a final separator. The physical properties of the obtained membranes are shown in Table 1 below.

 [Example 2]

The film was passed through a T-die having a gap of 2.5 mm under the same extrusion conditions as in Example 1, and then passed through a cooling roll at 80 DEG C to form an extruded film having a thickness of 20 mu m. The extruded film thus formed was annealed in an oven at about 150 캜 for a retention time of 10 minutes to obtain an extruded film having a birefringence (Δn) of 0.0220. A final separation membrane was prepared under the same conditions as in Example 1. The physical properties of the obtained membranes are shown in Table 1 below.

[Example 3]

After passing through a T-die of 2.0 mm gap under the same extrusion conditions as in Example 1, the film was passed through a cooling roll at 80 DEG C to form an extruded film having a thickness of 20 mu m. The extruded film thus formed was annealed in an oven at about 160 캜 for a retention time of 20 minutes to obtain an extruded film having a birefringence (Δn) of 0.0270. A final separation membrane was prepared under the same conditions as in Example 1. The physical properties of the obtained membranes are shown in Table 1 below.

[Comparative Example 1]

An extruded film having a thickness of 20 탆 was formed under the same conditions as in Example 1. The extruded film thus formed was annealed in an oven at about 150 캜 for a retention time of 2 minutes to obtain an extruded film having a birefringence (Δn) of 0.0150. A final separation membrane was prepared under the same conditions as in Example 1. The physical properties of the obtained membranes are shown in Table 1 below.

 [Comparative Example 2]

A final separation membrane was produced under the same conditions as in Comparative Example 1, except that the extruded film was extruded so as to have a birefringence (n) of 0.0180. The physical properties of the obtained membranes are shown in Table 1 below.

[Comparative Example 3]

The film was passed through a T-die having a gap of 2.9 mm under the same extrusion conditions as in Example 1, and then passed through a 110 占 폚 cooling roll to form an extruded film having a thickness of 20 占 퐉. The extruded film thus formed was annealed in an oven at about 160 캜 for a retention time of 20 minutes to obtain an extruded film having a birefringence (Δn) of 0.0290. Although the extruded film had a birefringence (n) of 0.0290, the resulting extruded film had a fibril-like structure between the pores (Fig. 3). Due to such a fibril-like structure, a desired final separation membrane could not be produced.

No. Extruded film Membrane properties Birefringence
(? N) Ventilation
(Sec / 100cc) Porosity
(%) The tensile strength
(kgf / cm ² ) Puncture strength gf N / 탆 Example 1 0.0190 360 39 1,510 213 0.222 Example 2 0.0220 320 40 1,540 219 0.232 Example 3 0.0270 243 48 1,555 289 0.211 Comparative Example 1 0.0150 8,445 16 700 128 0.145 Comparative Example 2 0.0180 1,200 35 1,120 128 0.230 Comparative Example 3 0.0290 677 32 1,570 230 0.210

As shown in Table 1, Examples 1 to 3 exhibited high air permeability of not less than 40% porosity and air permeability of not more than 400 sec / 100 cc, while exhibiting high mechanical strength characteristics of not less than 1,500 kg / cm ² in tensile strength and not less than ²⁰⁰ gf in puncture strength It provides characteristics suitable for high capacity and high output lithium ion secondary batteries.

Claims (15)

Extruding a polyolefin resin having a melt flow rate (MFR) of 0.5 to 10 g / 10 min to form an extruded film,
Annealing the extruded film to form an extruded film having a birefringence (Δn) of 0.0190 to 0.0280, and
And uniaxially stretching the extruded film having the birefringence index (n) to form a porous separation membrane,
Wherein the porous separator has a minimum tensile strength of 1,500 kg / cm &lt; ² &gt;. The method according to claim 1,
Wherein the polyolefin resin has a melt flow rate (MFR) of 0.5 to 5.0 g / 10 min. The method according to claim 1,
Wherein the polyolefin resin is one or two or more polymers or copolymers selected from the group consisting of ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene and 1-octene, Wherein the porous polyolefin separating membrane is water. The method according to claim 1,
Wherein the polyolefin resin is extruded at a temperature of 170 to 280 占 폚. The method according to claim 1,
Wherein the polyolefin resin is extruded through a die having a gap of 0.5 to 5.0 mm and then subjected to a casting process at a temperature of 120 DEG C or less. The method according to claim 1,
Wherein the extruded film is annealed at a temperature of 100 to 165 캜. The method according to claim 1,
Wherein the extruded film is annealed for a retention time of 1 to 60 minutes. The method according to claim 1,
Wherein the extruded film of the birefringence index n is uniaxially stretched in the longitudinal direction (MD). 9. The method of claim 8,
And uniaxially stretching the extruded film having the birefringence index (n) to 150% or more. The method according to claim 1,
And at least one surface of the porous separation membrane or at least one surface of the porous separation membrane and an area of the pores of the porous substrate, wherein the inorganic separation membrane is disposed on at least one surface of the porous separation membrane or at least one surface of the porous separation membrane, Wherein the porous polyolefin separator further comprises a porous coating layer containing a binder polymer for fixing the porous polyolefin separator. 11. The method of claim 10,
Wherein the inorganic particles are selected from the group consisting of inorganic particles having a dielectric constant of 5 or more, inorganic particles having lithium ion transporting ability, and mixtures thereof. 11. The method of claim 10,
Wherein the binder polymer is selected from the group consisting of polyvinylidene fluoride-co-hexafluoropropylene (PVDF-co-HFP), polyvinylidene fluoride-co-trichloroethylene, Polyvinylidene fluoride-co-chlorotrifluoroethylene, polymethyl methacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinyl acetate, polyvinyl pyrrolidone, polyvinylacetate, polyethylene-co-vinyl acetate, polyethylene oxide, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, propionate, cyanoethylpullulan, But are not limited to, polyvinylpyrrolidone, polyvinyl alcohol, cyanoethylpolyvinylalcohol, cyanoethyl cellulose, cyanoethyl sucrose, pullulan, carboxyl methyl cellulose (CMC), acrylonitrile-styrene Acrylonitrile-styrene-butadiene copolymer, polyimide, polyvinylidene fluoride, polyacrylonitrile, and styrene butadiene rubber (SBR). Or a mixture of two or more selected from the above. A porous polyolefin separator produced by the process for producing a porous polyolefin separator according to any one of claims 1 to 12. 13. A lithium secondary battery comprising a positive electrode, a negative electrode, and a porous polyolefin separator interposed between the positive electrode and the negative electrode.
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