KR101838659B1 - A separator with porous coating layer comprising polyolefin binder polymer and a method of making the same - Google Patents

Abstract

The present invention relates to a separator for a secondary battery in which a porous coating layer containing inorganic particles / organic particles is formed on at least one surface of a porous polymer film, wherein the separator comprises a polyolefin wax as a binder polymer for intergranular binding in a porous coating layer, And a method for producing the same.

Description

TECHNICAL FIELD [0001] The present invention relates to a separator having a porous coating layer comprising a polyolefin-based binder polymer, and a separator having a porous coating layer containing a polyolefin-

The present invention relates to a separator in which a porous coating layer comprising a polyolefin-based binder polymer is formed and a method for producing the same. More particularly, the present invention relates to a separator having a porous coating layer comprising inorganic particles / organic particles on at least one surface of a porous polymer film. The present invention relates to a separator in which a polyolefin wax is used as a binder polymer for intergranular binding in a porous coating layer and a method for producing the same.

Recently, the utilization ratio of secondary batteries is gradually increasing in various fields such as small household appliances, medium and large sized vehicles, and electric power storage devices, and demand for polyolefin compounds widely used as separator materials for secondary batteries is also increasing.

As the separator of the secondary battery, a so-called composite separator is known in which a porous coating layer containing inorganic particles / organic particles is coated on at least one surface of a porous polymer film to improve mechanical and thermal safety as well as a separator made of only a polyolefin film.

In the separator in which such a porous coating layer is formed, an acrylic resin or a modified fluororesin is used as a binder polymer for binding inorganic particles / organic particles used in the porous coating layer. However, these resins are easily swollen or decomposed in the electrolyte solution, As a result, there is a problem that adversely affects the cycle life of the battery.

In order to solve this problem, a method of using a polyolefin-based compound such as polyethylene or polypropylene, which is the same material as the separator material and has no side reaction with the electrolyte, has been studied as a binder polymer for the porous coating layer. However, The binder polymer can function as a binder by melting the binder polymer in the drying process. However, there is a problem in that the temperature of the drying process can not be set to be higher than the melting point of the polyolefin compound in the current window of the porous coating layer formation.

SUMMARY OF THE INVENTION The present invention provides a separator in which a porous coating layer containing a binder polymer to be melted at a heat fixing temperature is formed, in an embodiment of the present invention.

The present invention also provides a separator in which a porous coating layer containing a binder polymer having a small degree of swelling even when an electrolyte solution is impregnated is formed.

To this end, another embodiment of the present invention is to provide a method of manufacturing a separator that enables a wax comprising a polyolefin compound to be used as a binder polymer of a porous coating layer.

It is to be understood that other objects and advantages of the present invention can be understood by the following description and that the objects and advantages of the present invention can be realized by the means or method described in the claims, Will be.

According to one embodiment of the present invention, there is provided a separator having a porous coating layer formed on at least one surface of a porous polymer film, the porous coating layer comprising inorganic particles, organic particles, or both, and a binder polymer, There is provided a separator for a secondary battery comprising a polyolefin-based resin as a binder polymer for binding inorganic particles, organic particles or both in a coating layer.

The porous polymer film may be a polyolefin-based porous substrate.

The binder polymer may be at least one selected from the group consisting of polyethylene polymers such as ethylene homopolymer and ethylene- alpha -olefin copolymer, polypropylene polymers such as propylene homopolymer and propylene- alpha -olefin copolymer, 4-methylpentene-1 polymer, -1) and an ethylene-vinyl acetate copolymer. The polyolefin-based resin may be one or a mixture of two or more selected from the group consisting of ethylene-

The binder polymer may be in the form of a wax.

The inorganic particles, the organic particles, or both of them and the binder polymer may be included in the porous coating layer in a composition ratio of 50:50 to 99: 1 by weight.

According to another embodiment of the present invention, there is provided a process for producing a separator for a secondary battery, wherein a porous coating layer comprising inorganic particles, organic particles or both and a binder polymer is formed on at least one surface of the porous polymer film, Preparing a film; (S2) preparing a slurry for forming a porous coating layer comprising a polyolefin wax as a binder polymer containing inorganic particles, organic particles or both and binding these particles; (S3) applying the slurry for forming a porous coating layer to at least one surface of the porous polymer film; And (S4) heat-fixing the separator.

The solvent of the slurry for forming a porous coating layer may be water.

The heat setting may be carried out at a temperature ranging from 128 to 140 캜.

The polyolefin wax can be melted in the heat setting step.

According to another embodiment of the present invention, in the secondary battery comprising the cathode, the anode, the electrolyte and the separator, the separator may be the above-described separator for a secondary battery.

The secondary battery may be a lithium secondary battery.

The separator manufactured according to one embodiment of the production method of the present invention can be used as a binder polymer since the polyolefin-based resin used in the porous coating layer can be melted in the heat-setting process to bind inorganic particles / organic particles do.

Accordingly, in the present invention, the binder polymer may exhibit a binding effect in a different manner from that exhibiting a binding function by swelling the acrylic or modified fluoropolymer binder polymer.

Also, in one embodiment of the present invention, since the degree of swelling of the binder polymer contained in the porous coating layer is not large when the separator is impregnated with the electrolyte, adverse effects on cycle life due to swelling of the binder polymer upon electrolyte impregnation may be eliminated or reduced.

Further, since the porous polymer film and the binder polymer of the porous coating layer are composed of the same or similar compound components, the binding force between the porous polymer film and the porous coating layer can be further improved.

The terms or words used in the present specification and claims should not be construed to be limited to ordinary or dictionary terms and the inventor shall properly define the concept of the term in order to best explain its invention The present invention should be construed in accordance with the meaning and concept consistent with the technical idea of the present invention.

Therefore, the configurations shown in the embodiments described herein are merely the most preferred embodiments of the present invention and are not intended to represent all of the technical ideas of the present invention. Therefore, various equivalents And variations are possible.

A separator for a secondary battery according to an embodiment of the present invention is a separator in which a porous coating layer comprising inorganic particles, organic particles or both and a binder polymer is formed on at least one surface of a porous polymer film, , And a polyolefin-based resin as a binder polymer for binding organic particles or both of them.

According to another aspect of the present invention, there is provided a method of manufacturing a separator for a secondary battery, comprising the steps of: (S1) preparing a porous polymer film; (S2) preparing a slurry for forming a porous coating layer comprising a polyolefin wax as a binder polymer containing inorganic particles, organic particles or both and binding these particles; (S3) applying the slurry for forming a porous coating layer to at least one surface of the porous film; And (S4) performing heat fixing.

The porous polymer film to be used in the present invention is a porous film formed of various polymers and can be used in any planar porous substrate commonly used in an electrochemical device. For example, a polyolefin porous film used as a separator of an electrochemical device, particularly, a lithium secondary battery, or a nonwoven fabric made of polyethylene terephthalate fiber may be used. The material and the shape may be variously selected depending on the purpose. For example, high density polyethylene (HDPE), low density polyethylene (LDPE), linear low density polyethylene (LLDPE), ultra high molecular weight polyethylene (UHMWPE), polypropylene, polyethylene terephthalate, polybutyleneterephthalate, Polyester, polyester, polyacetal, polyamide, polycarbonate, polyimide, polyetheretherketone, polyethersulfone, polyphenylene oxide, polyphenylene sulfide, polyphenylene sulfide, polyethylenenaphthalene, or mixtures and copolymers thereof, and the like, but are not limited thereto.

The porous polymer film may be prepared by the following process without being thermally set after the film formation, but the present invention is not limited thereto.

a) A polyolefin-based resin and a pore-forming agent are mixed while stirring.

b) The mixture is then introduced into an extruder and heated to melt at high temperature.

c) The melt is fed to a T-die and extruded into a film in sheet form.

d) The film obtained in the above step is solidified using a casting roll or the like.

e) The solidified film is uniaxially stretched in the longitudinal direction at low temperature and biaxially stretched in the transverse direction.

f) removing the pore-forming agent from the stretched film using a solvent to obtain a porous polymer film.

In the above, e) may be performed after step f).

The porous polymer film may further contain additives such as a stabilizer, a flame retardant, a lubricant, an antioxidant, a pore-forming agent, a dispersant, and an antistatic agent within a range permissible for use as a separator substrate.

The porous polymer base material obtained after thermally fixing the porous polymer film has a thickness of 7 to 30 탆, preferably 7 to 20 탆, more preferably 7 to 15 탆. If the thickness is thinner than the above range, the mechanical strength may be lowered, and as the thickness of the porous polymer film is thicker, the ion conductivity may be lowered. In the case of the separator of the present invention, it is preferable to select a minimum thickness that can provide excellent mechanical strength and maximum ion conductivity. The porous polymer film may have a pore size of 1 탆 or less, 0.01 탆 to 0.5 탆, or 0.02 탆 to 0.1 탆. In addition, the porous polymer film may have a porosity of 40% to 70%.

The polyolefin-based resin used as the binder polymer in the porous coating layer may be a polyolefin-based polymer such as ethylene homopolymer, ethylene-? -Olefin copolymer, polypropylene-based polymer such as propylene homopolymer or propylene- Pentene-1 polymer, poly (butene-1), ethylene-vinyl acetate copolymer and the like. Polyolefins having excellent compatibility with ultrahigh molecular weight polyethylene are preferable, and specific examples include polyethylene resins such as ethylene homopolymers or ethylene-? -Olefin copolymers. These polyolefin-based resins are added in the form of a wax at the time of producing the slurry for forming a porous coating layer, and then melted in the heat-setting process proceeding at a temperature of 128 ° C or more to bind the inorganic particles / organic particles, . This melting temperature is very low compared to the melting temperature of the acrylic binder polymer or the modified fluorine-based binder polymer used as the conventional binder polymer. Thus, the polyolefin wax of the present invention can be melted at a heat fixing temperature.

The inorganic particles used in the slurry for forming the porous coating layer are not particularly limited as long as they are electrochemically stable. That is, the inorganic particles usable in the present invention are not particularly limited as long as oxidation and / or reduction reaction does not occur in the operating voltage range of the applied electrochemical device (for example, 0 to 5 V based on Li / Li ⁺ ). Particularly, when inorganic particles having ion transfer ability are used, the ion conductivity in the electrochemical device can be increased to improve the performance. When inorganic particles having a high dielectric constant are used as the inorganic particles, dissociation of an electrolyte salt, for example, a lithium salt, in the liquid electrolyte is also increased, and ion conductivity of the electrolyte can be improved.

Non-limiting examples of the inorganic particles include high-permittivity inorganic particles having a dielectric constant of 5 or more, preferably 10 or more, inorganic particles having lithium ion transporting ability, or mixtures thereof.

Non-limiting examples of inorganic particles greater than a dielectric constant of 5 is _{BaTiO 3, Pb (Zr, Ti} ) O 3 (PZT), Pb 1-x La x Zr 1-y Ti y O 3 (PLZT), PB (Mg 1 _{/ 3} Nb _2/3 ) O ₃ -PbTiO ₃ (PMN-PT), hafnia (HfO ₂ ), SrTiO ₃ , SnO ₂ , CeO ₂ , MgO, NiO, CaO, ZnO, ZrO ₂ , Y ₂ O ₃ , Al ₂ O ₃ , TiO _2, SiC Or mixtures thereof.

The term "inorganic particle having lithium ion-transferring ability" as used herein refers to an inorganic particle containing a lithium element but not having lithium stored therein and having a function of moving lithium ions. The inorganic particle has a lithium ion- examples include lithium phosphate (Li ₃ PO _4), lithium titanium phosphate _{(Li x Ti y (PO 4} ) 3, 0 <x <2, 0 <y <3), lithium aluminum titanium phosphate (Li _x Al _y Ti _z (LiAlTiP) _x O _y series such as (PO ₄ ) ₃ , 0 <x <2, 0 <y <1, 0 <z <3), 14Li ₂ O-9Al ₂ O ₃ -38TiO ₂ -39P ₂ O ₅ (Li _x La _y TiO ₃ , 0 <x <2, 0 <y <3), Li _3.25 Ge _0.25 P _0.75 S (0 <x <4, 0 <y <13) ₄ lithium such as germanium Mani help thiophosphate lithium such as _{(Li x Ge y P z S} w, 0 <x <4, 0 <y <1, 0 <z <1, 0 <w <5), Li 3 N SiS ₂ series glass (Li _x Si _y S _z , 0 < x < ₂₎ such as nitride (Li _x N _y , 0 <x <4, 0 <y <2), Li ₃ PO ₄ -Li ₂ S- 3, 0 <y <2, 0 <z <4), LiI -Li has a P ₂ S ₅ based _{glass (Li x P y S z} , 0 <x <3, 0 <y <3, 0 <z <7) or a mixture thereof, such as ₂ SP ₂ S _5.

The porous coating layer may contain organic particles instead of or in combination with the inorganic particles. Organic particles are advantageous in terms of air permeability, heat shrinkability, and peel strength.

Nonlimiting examples of the organic particles include polystyrene, polyethylene, polyimide, melamine resin, phenol resin, cellulose, modified cellulose (such as carboxymethylcellulose), polypropylene, polyester (polyethylene terephthalate, polyethylene naphthalate, poly Butylene terephthalate and the like), polyphenylene sulfide, polyaramid, polyamideimide, and polyimide. The organic particles may be composed of two or more kinds of polymers.

The size of the inorganic particles or the organic particles is not limited, but may be in the range of 0.001 to 10 mu m in terms of forming a coating layer of uniform thickness and having an appropriate porosity.

The inorganic particles / organic particles and the binder polymer prepared as described above may be used in a composition ratio of 50:50 to 99: 1 on the basis of weight to form a slurry for forming a porous coating layer. If the content of the inorganic particles / organic particles exceeds the above-mentioned range, the content of the binder polymer may be too small to reduce the bonding force between the particles. If the content of the inorganic particles / organic particles does not fall within the above range, There is a drawback in that the effect of improving the heat resistance of the thermoplastic resin is insignificant.

The solvent used in the slurry for forming the porous coating layer preferably has a solubility index similar to that of the binder polymer to be used and a low boiling point. This is to facilitate uniform mixing and subsequent solvent removal. Non-limiting examples of usable solvents include acetone, tetrahydrofuran, methylene chloride, chloroform, dimethylformamide, N-methyl-2-pyrrolidone ( N-methyl-2-pyrrolidone, NMP), cyclohexane, water or a mixture thereof. Water is preferable in terms of environmental friendliness.

The slurry for forming a porous coating layer may be applied to a porous polymer film by a process commonly used in the art. The coating method is not particularly limited and may be applied by dip coating, die coating, roll coating, comma coating, or a mixture thereof.

The slurry for forming a coated porous coating layer is present as a porous coating layer as the solvent is removed in a subsequent process. The porous coating layer is formed by bonding inorganic particles / organic particles via a binder polymer, Pores are formed by an interstitial volume. The interstitial volume is a space defined by the inorganic particles / organic particles that are substantially interfaced in the closed packed or densely packed form of the inorganic particles / organic particles. The porous coating layer may be formed on at least one surface of the porous polymer film to a thickness of 1 탆 to 10 탆, preferably 2 탆 to 5 탆.

Then, a heat fixing process is performed.

A polyolefin-based porous substrate for a separator of a secondary cell, which is commonly used at present, is manufactured through an extrusion / stretching / heat fixing process. During this series of processes, the heat setting process has the greatest influence on the final physical properties of the porous separator . In a typical separator manufacturing process, the heat setting temperature is in the range of about 128 占 폚 to about 132 占 폚.

According to a specific embodiment of the present invention, the heat setting may be performed at a temperature of 120 ° C to 150 ° C, preferably 128 ° C to 140 ° C, more preferably 133 ° C to 140 ° C, but is not limited thereto. Particularly, in the present invention, since a porous coating layer is additionally formed on the porous polymer film, heat fixing can be performed at a higher temperature than the conventional one. The heat setting can be carried out using an ordinary drying process in the prior art for applying an oven or hot air, and can be performed under an atmosphere of an inert gas such as argon.

The reason why the heat fixing temperature can not be increased higher than this is because the porous polymer film partially melts due to the hot hot wind, and the surface pores of the porous polymer film are closed and damaged, and the ventilation time is greatly increased. Since the porous polymer film is first exposed to the hot hot air in the heat fixation process and absorbs a large amount of heat, the change of the fibril morphology on the surface is more severe as the heat fixing temperature is higher. This change in surface morphology can affect the electrical resistance / aeration time / flexure of the final separator.

According to another embodiment of the present invention, an electrochemical device including a cathode, an anode, and the above-described separator interposed between the cathode and the anode can be manufactured. The electrochemical device of the present invention includes all devices that perform an electrochemical reaction. Examples of the electrochemical device include capacitors such as all types of primary cells, secondary cells, fuel cells, solar cells, and super capacitors. Particularly, a lithium secondary battery including a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery is preferable among the above secondary batteries.

Cathodes, anodes, and the like can be easily produced by processes and / or methods known in the art. The cathode is manufactured in the form that the cathode active material is bound to the cathode current collector according to a conventional method known in the art. At this time, the cathode active material is capable of a conventional cathode active material that can be used in a cathode of a conventional electrochemical device used, non-limiting examples 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 2} O, 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 include _2-Z Co _Z O ₄ (where, 0 <Z <2), LiCoPO 4, LiFePO 4 , and mixtures thereof. The cathode current collector may be made of aluminum, nickel, or a combination thereof.

The anode is prepared by binding an anode active material to an anode current collector according to a conventional method known in the art. At this time, the anode 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' : Metal complex oxides of Al, B, P, Si, Group 1, Group 2, Group 3 elements of the periodic table, halogen, 0 < x &lt; 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, the anode current collector may be made of stainless steel, nickel, copper, titanium or an alloy thereof.

Also, the electrolyte that can be inserted between the electrode and the separator is a salt having a structure such as A ⁺ B ^- , wherein 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 no.

The electrolyte may be injected at an appropriate stage of the battery manufacturing process, depending on the manufacturing process and required properties of the final product. As a process for applying the separator of the present invention to a battery, lamination, stacking and folding processes of a separator and an electrode are possible in addition to a general winding process.

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 embodiments described below. The embodiments of the present invention are provided to enable those skilled in the art to more fully understand the present invention.

Example 1

Preparation of Porous Polymer Film

3.5 kg of polyethylene and 6.5 kg of liquid paraffin (LP) as a pore former were mixed with stirring. This was put into an extruder, heated and melted at about 210 캜, fed to a T-die, and extruded into a sheet-shaped film. The extruded film was cooled through a casting roll. The cooled film was uniaxially stretched in the longitudinal direction at a low temperature of about 105 캜 and biaxially stretched in the transverse direction. The pore-forming agent was removed from the stretched film using methyl chloride (MC) as a solvent to obtain a porous polymer film.

Formation of Porous Coating Layer

The slurry for forming a porous coating layer was prepared by mixing Boehmite particles / carboxymethylcellulose / polyethylene wax (BYK, AQUACER 1547 (melting point: 125 ° C) / distilled water = 14.05 / 0.05 / 0.9 /

The slurry for forming a porous coating layer prepared above was coated on one side of a porous polymer film to a thickness of 3.5 탆 and heat-set at 130 캜. The total thickness of the obtained separator was 14.5 占 퐉.

Example 2

The slurry for forming the porous coating layer was prepared by mixing Boehmite particles / carboxymethylcellulose / polyethylene wax (BYK, AQUACER 1547 (melting point: 125 ° C) / distilled water = 37.4 / 0.12 / 2.48 / , The total thickness of the obtained separator was 13.0 占 퐉.

Example 3

A separator was prepared in the same manner as in Example 1 except that a slurry for forming a porous coating layer was coated on both sides of a porous polymer film to a thickness of 4.0 탆. The total thickness of the obtained separator was 20 mu m.

Example 4

A separator was prepared in the same manner as in Example 2, except that the slurry for forming the porous coating layer was coated on both sides of the porous polymer film to a thickness of 4.0 탆. The total thickness of the obtained separator was 18.5 占 퐉.

Comparative Example 1

Preparation of Porous Polymer Film

3.5 kg of polyethylene and 6.5 kg of liquid paraffin (LP) as a pore former were mixed with stirring. This was put into an extruder, heated and melted at about 210 캜, fed to a T-die, and extruded into a sheet-shaped film. The extruded film was cooled through a casting roll. The cooled film was uniaxially stretched in the longitudinal direction at a low temperature of about 105 캜 and biaxially stretched in the transverse direction. Next, the stretched film was heat-set at about 130 캜. The pore-forming agent was removed from the stretched film using methyl chloride (MC) as a solvent to obtain a porous polymer film.

Formation of Porous Coating Layer

The slurry for forming a porous coating layer was prepared by mixing Boehmite particles / carboxymethyl cellulose / polyvinylidene fluoride (PVDF) / distilled water = 14.05 / 0.05 / 0.9 / 85 weight ratio.

The slurry for forming a porous coating layer prepared above was coated on one side of a porous polymer film to a thickness of 3.5 탆 and heat-set at 130 캜. The thickness of the obtained separator was 14.5 占 퐉.

Comparative Example 2

The slurry for forming the porous coating layer was prepared by mixing Boehmite particles / carboxymethyl cellulose / polyvinylidene fluoride (PVDF) / distilled water = 37.4 / 0.12 / 2.48 / 60 in weight ratio and heat- , A separator was produced in the same manner as in Comparative Example 1. [ The total thickness of the obtained separator was 13.0 占 퐉.

Comparative Example 3

A separator was prepared in the same manner as in Comparative Example 1, except that the slurry for forming a porous coating layer was coated on both sides of the porous polymer film to a thickness of 4.0 탆. The total thickness of the obtained separator was 20.0 mu m.

Comparative Example 4

A separator was prepared in the same manner as in Comparative Example 2 except that a slurry for forming a porous coating layer was coated on both sides of a porous polymer film to a thickness of 4.0 탆. The total thickness of the obtained separator was 18.5 占 퐉.

Comparative experiment results

The aeration time, tensile strength and heat shrinkage of the separator obtained in Examples 1 to 4 and Comparative Examples 1 to 4 were measured. At this time, the heat shrinkage ratios of Examples 1 and 2 and Comparative Examples 1 and 2 were measured at 120 ° C for 1 hour, and the heat shrinkage ratios of Examples 3 and 4 and Comparative Examples 3 and 4 were measured at 150 ° C for 0.5 hour Respectively. The results are shown in Tables 1 and 2 below.

Example 1 Example 2 Example 3 Example 4 Ventilation time
Sec / 100ml 220 260 320 370 The tensile strength
Kg / cm ² MD 1800 2500 1700 2250 TD 1500 2180 1450 2400 Heat shrinkage MD 5 3 22 5 TD 3 2 14 3

Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Ventilation time
Sec / 100ml 240 1300 400 1300 The tensile strength
Kg / cm ² MD 1750 2400 1750 2350 TD 1450 2100 1500 2200 Heat shrinkage MD 35 8 5 3 TD 25 4 4 2

Claims (11)

A method for producing a separator for a secondary battery, wherein a porous coating layer comprising inorganic particles, organic particles or both and a binder polymer is formed on at least one surface of a porous polyethylene film,
(S1) preparing a porous polyethylene film, wherein the porous polyethylene film is formed but not thermally fixed;
(S2) preparing a slurry for forming a porous coating layer comprising a polyethylene wax as a binder polymer containing inorganic particles, organic particles or both and binding these particles;
(S3) applying the slurry for forming a porous coating layer to at least one surface of the porous polyethylene film; And
(S4) subjecting the porous polyethylene film coated with the slurry for forming a porous coating layer to heat setting at a temperature range of 128 to 140 占 폚;
Wherein the separator is made of a metal.
The method according to claim 1,
Prior to step (S1)
a) mixing the polyethylene-based resin and the pore-forming agent with stirring,
b) feeding the mixed material into an extruder, heating and melting,
c) extruding the molten material into a film in sheet form,
d) solidifying the film using a casting roll,
e) stretching the solidified film, and
f) A step of obtaining a porous polyethylene film by removing the pore-forming agent from the stretched film by using a solvent is carried out.
The method according to claim 1,
Wherein the binder polymer is an ethylene homopolymer, an ethylene -? - olefin copolymer or a mixture thereof.
The method according to claim 1,
Wherein the binder polymer is contained in the form of a wax.
The method according to claim 1,
Wherein the inorganic particles, the organic particles, or both of them and the binder polymer are contained in the porous coating layer in a composition ratio of 50:50 to 99: 1 by weight.
The method according to claim 1,
Wherein the inorganic particles are inorganic particles having a dielectric constant of 5 or more, inorganic particles having lithium ion transferring ability, or mixtures thereof.
The method according to claim 1,
Wherein the solvent of the slurry for forming a porous coating layer is water.
The method according to claim 1,
Wherein the organic particles are selected from the group consisting of polystyrene, polyethylene, polyimide, melamine resin, phenol resin, cellulose, cellulose modified product, polypropylene, polyester, polyphenylene sulfide, polyaramid, polyamideimide and polyimide Wherein the separator is made of a thermoplastic resin.
The method according to claim 1,
Wherein the binder polymer is melted in a heat fixing step.
delete The method according to claim 1,
Wherein the secondary battery is a lithium secondary battery.