KR101792749B1 - Tri-layered separator for secondary battery, secondary battery comprising the same, and method of preparing the separator - Google Patents

Abstract

The present invention relates to a three-layer separator, an electrochemical device including the same, and a process for producing the separator. According to one aspect of the present invention, there is provided a laminate comprising: a first layer having a plurality of pores, the laminate comprising: 80 to 99 parts by weight of polyethylene and 1 to 20 parts by weight of a high heat resistant polymer; A second layer of polyethylene having a plurality of pores bonded to one side of the first layer and one or more of the pores thereof; And a binder that is applied to at least one of the other side of the second layer and the pores thereof and includes inorganic particles and a binder that is located on some or all of the inorganic particles to connect and fix the inorganic particles therebetween And a third layer having pores. According to another aspect of the present invention, there is provided a method of manufacturing a semiconductor device, comprising the steps of forming a first extruded layer, forming a second extruded layer, forming a first layer and a second layer, forming a slurry layer, A method for producing a battery-use three-layer separation membrane is provided. According to the present invention, the stability of the secondary battery including the separation membrane can be enhanced by greatly improving the heat shrinkage and physical strength of the separation membrane.

Description

TECHNICAL FIELD [0001] The present invention relates to a three-layer separator for a secondary battery, a secondary battery including the same, and a method for manufacturing the separator. BACKGROUND ART < RTI ID = 0.0 >

The present invention relates to a three-layered separator for a secondary battery, specifically, a three-layered separator for a secondary battery in which a porous polyethylene layer mixed with a high heat-resistant polymer is attached to one surface of a porous polyethylene layer and a porous inorganic coating layer is attached to the other surface thereof, And a method for producing the separator.

A secondary battery is a chemical battery which can be used semi-permanently by repeatedly charging and discharging by electrochemical reaction, and can be classified into a lead-acid battery, a nickel-cadmium battery, a nickel-hydrogen battery and a lithium secondary battery. 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 kind of electrolyte, a lithium ion secondary battery using a liquid electrolyte and a solid electrolyte are used Lithium-ion polymer secondary batteries.

The lithium secondary battery includes an anode, a cathode, an electrolyte and a separator. Among these separators, the separator is required to separate the anode and the cathode from each other and electrically insulate the same, while enhancing the permeability of lithium ions based on the high porosity. It is the height.

Polyolefin (PO) films which are advantageous for pore formation and which are excellent in chemical resistance, mechanical properties, and thermal properties, and which are inexpensive, are mainly used as the polymer substrate of the separator which is generally used. However, when the separator is overcharged by overcharging under normal charging conditions or when the positive electrode and the negative electrode of the electrode assembly are short-circuited, the electrolyte in which the lithium salt and the solvent are mixed in the positive electrode is decomposed and lithium metal is precipitated in the negative electrode, Due to the stretching process involved in the production of the separator and the physical properties of the material, an internal short circuit may occur between the anode and the cathode by exhibiting extreme heat shrinkage behavior at a temperature of about 100 ° C or more.

A problem to be solved by the present invention is to provide a separator which can simultaneously satisfy both thermal stability and structural stability.

According to an aspect of the present invention, there is provided a laminate comprising: a first layer having a plurality of pores, which comprises 80 to 99 parts by weight of polyethylene and 1 to 20 parts by weight of a high heat resistant polymer; A second layer of polyethylene having a plurality of pores bonded to one side of the first layer and one or more of the pores thereof; And a binder that is applied to at least one of the other side of the second layer and the pores thereof and includes inorganic particles and a binder that is located on some or all of the inorganic particles to connect and fix the inorganic particles therebetween And a third layer having pores.

According to another aspect of the present invention, there is provided a method for producing a polyurethane foam, which comprises extruding a first mixture containing 80 to 99 parts by weight of polyethylene and 1 to 20 parts by weight of a high heat resistant polymer and a first pore- Forming an extruded layer; Forming a second extruded layer on one side of the first extruded layer by extruding a second mixture comprising polyethylene and a second pore former; Forming a first layer and a second layer by removing the pore-forming agent from the first extruded layer and the second extruded layer, respectively, using a first solvent; Forming a slurry layer on the other surface of the second layer by applying a slurry in which inorganic particles are dispersed in a binder solution of a binder and a second solvent; And removing the second solvent from the slurry layer to form a third layer, thereby forming a laminate including a first layer, a second layer and a third layer, / RTI >

According to the present invention, the stability of the secondary battery including the separation membrane can be enhanced by greatly improving the heat shrinkage and physical strength of the separation membrane.

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 cross-sectional view of a three-layer separator for a secondary battery according to an embodiment of the present invention.
2 is a schematic flowchart of a process for manufacturing a three-layer separator for a secondary battery according to an embodiment of the present invention.

Hereinafter, the present invention will be described in detail. Prior to this, terms and words used in the present specification and claims should not be construed as limited to ordinary or dictionary terms, and the inventor may designate the concept of a term appropriately in order to describe its own invention in the best way possible. It should be interpreted as meaning and concept consistent with the technical idea of the present invention. Therefore, the constitution described in the embodiments of the present invention is merely an embodiment of the present invention, and does not represent all the technical ideas of the present invention, so that various equivalents and modifications It should be understood.

1 is a cross-sectional view of a three-layer separator for a secondary battery according to an embodiment of the present invention.

Referring to FIG. 1, a three-layered separator for a secondary battery according to an embodiment of the present invention has a three-layer structure. That is, it is a laminate having a three-layer structure in which a first layer, a second layer and a third layer are laminated in order.

The first layer comprises polyethylene (PE) and a high heat resistant polymer. Since polyethylene (PE) has a melting point of about 105 to 140 캜, it can give a shutdown function of the separator in case of abnormality. Examples of such polyethylene (PE) include, but are not limited to, one selected from the group consisting of high density polyethylene, linear low density polyethylene, low density polyethylene, ultra high molecular weight polyethylene, or a mixture of two or more thereof.

The high heat-resistant polymer is not limited to polypropylene (PP), polymethylpentene (PMP), polyethylene terephthalate (PET), polyester, polyacetal, polyamide, Polycarbonate, polyimide, polyetheretherketone, polyetherimide (PEI), polyamideimide, polyethersulfone (PES), polyphenylene oxide polyphenylene sulfide, polyphenylene sulfide, polyethylene naphthalene, and mixtures thereof.

The first layer may comprise about 80 to about 99 parts by weight of polyethylene and about 1 to about 20 parts by weight of the high heat resistant polymer. Preferably, about 90 to about 99 parts by weight of polyethylene and about 1 to about 10 parts by weight of the high heat resistant polymer may be included. Thus, when the first layer contains the polyethylene and the high heat-resistant polymer in the above-mentioned range, the thermal stability of the separator can be imparted by raising the melt down temperature. This first layer may have a porous structure by forming a plurality of pores by a wet process known in the art.

The second layer is bonded to one surface of the first layer and at least one of the pores thereof, and is made of polyethylene. Such a second layer can exhibit the shutdown function of the separator due to the inherent characteristics of the polyethylene forming the second layer, so that the stability of the battery can be maintained. Here, the polyethylene of the second layer is the same as described in the description of the polyethylene for the first layer.

The first layer and the second layer may be biaxially stretched. The first layer and the second layer may be independently biaxially stretched in a mechanical direction (MD) and a transverse direction (TD), respectively.

The first and second layers may each independently have a thickness of from about 1 to about 20 microns, preferably from about 2 to about 10 microns. If the first layer and the second layer have a thickness within the above-mentioned range, the problem of heat shrinkage due to overheating can be eliminated.

The third layer is applied to the other side of the second layer that is not in contact with the first layer and to at least one of the pores thereof. The third layer includes inorganic particles, and a binder positioned on at least a part of the inorganic particles to connect and fix the inorganic particles. And the third layer has a porous structure because it has a plurality of pores by the space between the inorganic particles.

The inorganic particles can be more advantageous for securing the safety of an electrochemical device (for example, a secondary battery) by suppressing a short circuit caused by foreign matter, thermal runaway, etc. between the anode and the cathode. The inorganic particles 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, about 0 to about 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, the dissociation of the electrolyte salt, for example, the lithium salt in the liquid electrolyte, can also contribute to enhance the ionic conductivity of the electrolyte.

For the reasons stated above, the inorganic particles may comprise high-permittivity inorganic particles having a dielectric constant of at least about 5, such as at least about 10, inorganic particles having lithium ion transport capability, or mixtures thereof. Nonlimiting examples of inorganic particles having a dielectric constant of about 5 or more include BaTiO ₃ , Pb (Zr, Ti) O ₃ (PZT), Pb _{1 -x} La _x Zr _{1 -y} Ti _y O ₃ (PLZT) 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.

Particularly, the above-mentioned BaTiO ₃ , Pb (Zr, Ti) O ₃ (PZT), Pb _{1 -x} La _x Zr _{1 -y} Ti _y O ₃ (PLZT), PB (Mg ₃ Nb _2/3 ) O ₃ -PbTiO ₃ (PMN-PT) and hafnia (HfO ₂ ) exhibit a high permittivity characteristic with a permittivity constant of 100 or more. In addition, when a certain pressure is applied, a charge is generated when being tensioned or compressed. It is possible to prevent internal short-circuiting of both electrodes due to an external impact, thereby improving the safety of the electrochemical device. Further, when the above-mentioned high-permittivity inorganic particles and inorganic particles having lithium ion transferring ability are mixed, their synergistic effect can be doubled.

The inorganic particles having the lithium ion transferring ability refer to inorganic particles that contain a lithium element but do not store lithium but have a function of moving lithium ions. The inorganic particles having lithium ion transferring ability exist in the particle structure It is possible to transfer and move lithium ions due to a kind of defect, so that the lithium ion conductivity in the battery is improved, thereby improving the performance of the battery. Examples of the inorganic particles having lithium ion transferring ability include lithium phosphate (Li ₃ PO ₄ ), lithium titanium phosphate (Li _x Ti _y (PO ₄ ) ₃ , 0 <x <2, 0 <y < (Li _x Al _y Ti _z (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 as such (LiAlTiP) _x O _y series glass (0 <x <4, 0 <y <13), lithium lanthanum titanate _{(Li x La y TiO 3,} 0 <x <2, 0 <y <3 _{), Li 3.25 Ge 0.25 P 0.75} S 4 lithium germanate Mani help thiophosphate _{(Li x Ge y P z S} w, 0 <x <4, 0 <y <1, 0 <z <1, 0 <w , such as < 5), Li ₃ N lithium nitride _{(Li x N y, 0 <} x <4, 0 <y <2), Li 3 PO 4 SiS 2 family, such as _{-Li 2 S-SiS 2 glass (} Li x such as _{Si y S z, 0 <x} <3, 0 <y <2, 0 <z <4), LiI-Li 2 SP 2 S 5 P 2 S 5 based glass (Li _x P _y S _z, such as 0 < x <3, 0 <y <3, 0 <z <7), or mixtures thereof.

The size of the inorganic particles is not limited, but for uniform layer thickness formation and adequate porosity, the average particle size of the inorganic particles may be as low as possible from about 0.01 to about 5 microns, or from about 0.05 to about 1.0 microns. When the size of the inorganic particles satisfies the above range, the dispersibility is improved, the physical properties of the separator can be easily controlled, the thickness of the third layer is increased, and the mechanical properties are deteriorated or excessively large, The problem of the occurrence of an internal short circuit can be prevented.

Non-limiting examples of the binder include polyvinylidene fluoride-co-hexafluoropropylene (PVDF-co-HFP), polyvinylidene fluoride-co-trichloroethylene ), Polyvinylidene fluoride-co-chlorotrifluoroethylene, polymethyl methacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylpyrrolidone, But are not limited to, polyvinylacetate, polyethylene-co-vinyl acetate, polyethylene oxide, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate (cellulose acetate propionate), cyanoethylpullulan lan, 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 is located on part or all of the inorganic particles to connect and fix the inorganic particles.

The composition ratio of the inorganic particles and binder in the third layer applied according to one embodiment of the present invention may be, for example, from about 50:50 to about 99: 1, preferably from about 60:40 to about 95: 5. The thickness of the third layer composed of the inorganic particles and the binder is not particularly limited, but may be in the range of about 0.01 to about 20 mu m. The pore size and porosity are also not particularly limited, but the pore size may range from about 0.01 to about 10 μm, and the porosity may range from about 5 to about 90%.

The separation membrane according to an embodiment of the present invention may further include other additives as the third layer component in addition to the inorganic particles and the binder described above to improve the function and stability.

As described above, the three-layered separator can provide effective shutdown and thermal stability together with structural stability.

According to an embodiment of the present invention, there is also provided an electrochemical device, such as a secondary battery, including a positive electrode, a negative electrode, and the above-described three-layered separator for a secondary battery sandwiched between the positive electrode and the negative electrode. The electrochemical device according to one aspect of the present invention includes all devices that perform an electrochemical reaction, and specific examples thereof include capacitors such as all types of primary cells, secondary cells, fuel cells, solar cells, or super capacitor devices ). In particular, 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 may be included in the secondary battery.

The electrode to be applied together with the separator according to an aspect of the present invention is not particularly limited, and the electrode active material may be bound to an electrode current collector according to a conventional method known in the art. Examples of the cathode active material include, but are not limited to, lithium manganese oxide, lithium cobalt oxide, lithium nickel oxide, lithium iron oxide, or a combination thereof A lithium complex oxide may be used. As a non-limiting example of the negative electrode active material, a conventional negative electrode active material that can be used for a negative electrode of an electrochemical device can be used. In particular, lithium metal or a lithium alloy, carbon, petroleum coke, activated carbon, Lithium adsorbing materials such as graphite or other carbon-based materials and the like can be used. Non-limiting examples of the positive current collector include aluminum, nickel, or a combination thereof. Examples of the negative current collector include copper, gold, nickel, or a copper alloy or a combination thereof Foil to be manufactured, and the like.

The electrolyte that can be used in the electrochemical device according to one aspect of the present invention is a salt having a structure such as A ⁺ B ^- , where A ⁺ is an alkali metal cation such as Li ⁺ , Na ⁺ , K ⁺ And B ^- is a metal ion such as 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 -, C (CF 2 SO}} 2) 3 - anion, or a salt containing an ion composed of a combination of propylene carbonate (PC) such as, ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC ), Dimethyl carbonate (DPC), dimethylsulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, tetrahydrofuran, N-methyl-2-pyrrolidone (NMP), ethylmethyl carbonate (G-butyrolactone), or an organic solvent composed of a mixture thereof, but is not limited thereto It is not.

The electrolyte injection may be performed at an appropriate stage of the battery manufacturing process, depending on the manufacturing process and required properties of the final product. That is, it can be applied before assembling the cell or at the final stage of assembling the cell.

As a process for applying a separator according to an aspect of the present invention to a battery, a lamination, stacking and folding process of a separator and an electrode can be performed in addition to a conventional winding process.

2 is a schematic flowchart of a process for manufacturing a three-layer separator for a secondary battery according to an embodiment of the present invention. 2, forming the first extruded layer S1, forming the second extruded layer S2, forming the first and second layers S3, and forming the second extruded layer according to another aspect of the present invention, A step (S4) of forming a slurry layer and a step (S5) of forming a laminate are provided.

In the step S1, the first extruded layer is formed by extruding the first mixture. The first mixture comprises polyethylene, a high heat resistant polymer and a first pore former. The types and contents of the polyethylene and the high heat-resistant polymer are as described in the description of the separator in the present invention.

A pore-forming agent is a substance that is dispersed in a polymer, exhibits a heterogeneity of a layer produced by extrusion, drawing, etc., and is subsequently removed from such a layer. Thus, the site of the pore-forming agent in the polymer of the layer remains in the form of pores. The pore former is preferably a liquid material in the extrusion process, but a material that maintains a solid state may be used.

The pore-forming agent may be an aliphatic hydrocarbon-based solvent such as liquid paraffin, paraffin oil, mineral oil or paraffin wax; Vegetable oils such as soybean oil, sunflower oil, rapeseed oil, palm oil, palm oil, coconut oil, corn oil, grape seed oil, cotton seed oil and the like; Or a plasticizer such as a dialkyl phthalate. In particular, the plasticizer is selected from the group consisting of di-2-ethylhexyl phthalate (DOP), di-butyl phthalate (DBP), di- isononyl phthalate Di-isodecyl phthalate (DIDP), butyl benzyl phthalate (BBP), and the like.

Also, the content of such pore-former may be from about 50 to about 80 wt% based on the total amount of polymer and pore-former. If the content of the pore-forming agent falls within this limited range, pores are produced in a desired range, for example, at a pore size of about 40% or more and / or a thickness of 20 m or less and a pore size of about 400 sec / 100 cc or less.

The first mixture is extruded, for example, through an extruder well known in the art. The extruder is not particularly limited, and may be an extruder commonly used in the art, for example, an extruder having a T-die or a tubular die without limitation. The extrusion process may be carried out at conventional extrusion temperatures, but may preferably be from about 150 to about 250 캜. Through this extrusion process, an extruded layer (e.g., a sheat) is formed.

In step S2, the second extruded layer is formed by extruding the second mixture on one surface of the first extruded layer formed in step S1. The second mixture comprises polyethylene and a second pore-former. The kind and content of polyethylene are as described in the description of the separator in the present invention. The second pore forming system is as described in the description of the first pore forming agent in the step S1. The formation of the second extruded layer may be the same as or similar to that described in the description of the first extruded layer in the step S1.

The formation of the second extruded layer may be carried out sequentially after formation of the first extruded layer or simultaneously with formation of the first extruded layer. The formation of the first extruded layer and the second extruded layer sequentially must be performed immediately after the formation of the first extruded layer so that a sufficient bonding force between the first extruded layer and the second extruded layer is maintained. Simultaneous formation of the first extruded layer and the second extruded layer can be achieved by a co-extrusion method or the like, and such simultaneous formation is preferable from the viewpoint of maintaining a high bonding force.

In the forming of the first extruded layer and the second extruded layer, the content of the first pore former and the second pore former may be about 50 to about 80 wt%, respectively, based on the first mixture or the second mixture .

In step S3, the first and second layers are formed by removing the pore-forming agent from the first extruded layer and the second extruded layer formed in steps S1 and S2, respectively. The pore-forming agent is removed by a method commonly used in the art, for example, by using a first solvent to form a plurality of pores in the layer. The principle of such pore formation is as previously described in the description of the separator here.

The pore-forming agent present in the extruded layer is extracted and dried, for example, by using a first solvent. The first solvent usable in the present invention is not particularly limited and any solvent capable of extracting the pore forming agent used for extrusion can be used. Preferably, the solvent is methyl ethyl ketone, methylene chloride, Hexane, and the like, or a mixture thereof.

The extraction method can be used in combination with all common solvent extraction methods such as immersion method, solvent spray method, ultrasonic method and the like. The amount of pore-forming agent remaining in the extraction should not be more than 1% by weight. If the residual pore former exceeds 1 wt%, the physical properties are lowered and the permeability of the membrane is decreased.

In step S4, a slurry in which inorganic particles are dispersed in a binder solution of a binder and a second solvent is coated on the other surface of the second layer formed in step S3 to form a slurry layer. The inorganic particles and binders are as previously described in the description of the separator herein.

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

The content of the second solvent may be about 40 to about 95 wt%, preferably about 60 to about 90 wt% of the slurry. If the content of the second solvent falls within the above-mentioned range, it can help maintain the pore structure of the second layer while securing the wettability of the slurry to the second layer in the subsequent coating.

In step S5, the second solvent used in step S4 is removed to form a third layer. The removal of the second solvent is usually carried out by drying. Due to the removal of the second solvent, a third layer is formed in at least one of the other side of the second layer and the pores. Thus, a laminate including the first layer, the second layer and the third layer is formed.

Alternatively, before the step S4, that is, before the formation of the third layer, it may further include a stretching and / or heat fixing step.

The stretching process is carried out by a stretching method commonly used in the art. This stretching method may include a low temperature stretching and / or a high temperature stretching using a stretcher commonly used in the art. Non - limiting examples of such stretching machines include axial differential stretchers and the like. The film thus stretched can have, for example, improved mechanical strength.

The stretching process is carried out in machine direction (MD), machine direction, longitudinal direction) and / or transverse direction (TD), vertical direction. The tensile strength in the stretching direction is increased by the stretching process in all of these, or one of them. If desired, the separator of the present invention can be subjected to longitudinal (MD) stretching and / or transverse (TD) stretching alone (e.g., uniaxially stretching), simultaneously or sequentially (e.g., biaxially stretching) .

Prior to step S4, i.e., prior to formation of the third layer, the first and second layers may be biaxially stretched to about 10 to about 200% of the initial length in the longitudinal (MD) and transverse (TD) directions.

Alternatively, it may further comprise a step of heat setting after the forming steps of the first layer and the second layer. For example, the step of fixing the laminate including the first layer and the second layer or the layers by heat treatment may be further included. By this heat setting, a separation membrane having the desired air permeability is finally obtained. In particular, the layer stretched by the preceding process undergoes heat setting to reduce the shrinkage of the final layer by removing the residual residual stress.

The heat fixation is to fix the layer for a certain period of time in the state of being subjected to the tension at the temperature below the melting point of the polymer to be used and forcing the layer to be shrunk by applying heat to remove the residual stress. Heat fixation is advantageous for lowering the shrinkage rate at high temperatures, but if it is too high, the membrane is partially melted and the formed pores are clogged and the air permeability is lowered. Such a heat-setting temperature may be, for example, but not limited to, the range of "the melting point of the polymer-a temperature of about 80 ° C" to "the melting point of the polymer-a temperature of about 5 ° C".

In the heat setting, uniaxial stretching in the transverse direction (TD) can be further performed. This uniaxial stretching at the time of heat setting can be performed by uniaxially stretching about 0 to about 40% of the first and second layers in the transverse direction (TD) after formation of the first layer and the second layer by simultaneous extrusion And after this stretching can be shrunk again to about 0 to about 20%. On the other hand, uniaxial stretching at the time of heat setting can be uniaxially stretched in the transverse direction (TD) about 0 to about 10% after the formation of the third layer, and after this stretching, . The heat settling time can be about 1 minute or less, preferably about 30 seconds or less.

This shrinkage after the transverse (TD) stretching is easy to control the final thickness of the separator and can increase the thickness uniformity. In addition, the final air permeability can be adjusted and the porosity can be controlled.

Further, the layer assembly comprising the first layer and the second layer, or the laminate comprising the layer assembly and the third layer, is subjected to a conventional aging process at a temperature of about 60 to about 80 DEG C for about 24 hours It can be rough.

Thus, according to the above-described steps, a three-layer separator for a secondary battery having a three-layer structure is produced.

Claims (25)

80 to 99 parts by weight of polyethylene and 1 to 20 parts by weight of a high heat resistant polymer;
A second layer having a plurality of pores made of polyethylene and bonded to at least one surface of the first layer or at least one surface of the first layer and a pore of the first layer; And
And at least one surface of the second layer, or at least one surface of the second layer and a region of the pores of the second layer, the inorganic particles being disposed on a part or the whole of the inorganic particles, And a third layer having a plurality of pores,
Wherein the high heat resistant polymer is selected from the group consisting of polypropylene (PP), polymethylpentene (PMP), polyethylene terephthalate (PET), polyester, polyacetal, polyamide, poly Examples of the polymer include polycarbonate, polyimide, polyetheretherketone, polyetherimide (PEI), polyamideimide, polyethersulfone (PES), polyphenylene oxide ), Polyphenylenesulfide, and polyethylenenaphthalene. 3. The three-layered separator for a secondary battery according to claim 1, The method according to claim 1,
Wherein the first layer comprises 90 to 99 parts by weight of polyethylene and 1 to 10 parts by weight of a high heat resistant polymer. The method according to claim 1,
Wherein the first layer and the second layer are biaxially stretched. The method of claim 3,
Wherein the first layer and the second layer are biaxially stretched in a machine direction (MD) and a transverse direction (TD). delete The method according to claim 1,
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 transferring ability, and mixtures thereof. The method according to claim 1,
Wherein the binder is selected from the group consisting of polyvinylidene fluoride-co-hexafluoropropylene (PVDF-co-HFP), polyvinylidene fluoride-co-trichloroethylene, polyvinylidene fluoride- Polyvinylidene fluoride-co-chlorotrifluoroethylene, polymethyl methacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinyl acetate (also referred to as polyvinylpyrrolidone), polyvinylpyrrolidone polyvinyl acetate, polyvinylacetate, polyethylene-co-vinyl acetate, polyethylene oxide, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate ), Cyanoethylpullulan, cyano But are not limited to, polyvinyl alcohol, cyanoethylpolyvinylalcohol, cyanoethyl cellulose, cyanoethyl sucrose, pullulan, carboxyl methyl cellulose (CMC), acrylonitrile-styrene-butadiene But are not limited to, those selected from the group consisting of acrylonitrile-styrene-butadiene copolymer, polyimide, polyvinylidenefluoride, polyacrylonitrile, and styrene butadiene rubber (SBR) One or a mixture of two or more thereof. A secondary battery comprising a separator according to any one of claims 1 to 4 and 6 to 7 interposed between an anode and a cathode and between the anode and the cathode. 9. The method of claim 8,
Wherein the secondary battery is a lithium secondary battery. Forming a first extruded layer by extruding a first mixture comprising 80 to 99 parts by weight of polyethylene and 1 to 20 parts by weight of a high heat resistant polymer based on 100 parts by weight of solids content and a first pore former;
Forming a second extruded layer on one side of the first extruded layer by extruding a second mixture comprising polyethylene and a second pore former;
Forming a first layer and a second layer by removing the pore-forming agent from the first extruded layer and the second extruded layer, respectively, using a first solvent;
Forming a slurry layer on the other surface of the second layer by applying a slurry in which inorganic particles are dispersed in a binder solution of a binder and a second solvent; And
Removing the second solvent from the slurry layer to form a third layer, thereby forming a laminate including a first layer, a second layer and a third layer
/ RTI &gt;
Wherein the high heat resistant polymer is selected from the group consisting of polypropylene (PP), polymethylpentene (PMP), polyethylene terephthalate (PET), polyester, polyacetal, polyamide, poly Examples of the polymer include polycarbonate, polyimide, polyetheretherketone, polyetherimide (PEI), polyamideimide, polyethersulfone (PES), polyphenylene oxide ), Polyphenylenesulfide, and polyethylenenaphthalene. 3. The method for producing a three-layered separator for a secondary battery according to claim 1, 11. The method of claim 10,
Wherein the content of the first pore forming agent and the content of the second pore forming agent in the first extruding layer and the second extruding layer is 50 to 80% by weight based on the first mixture or the second mixture, respectively (JP) METHOD FOR MANUFACTURING THREE - 11. The method of claim 10,
Wherein the first pore forming agent and the second pore forming agent are independently selected from the group consisting of aliphatic hydrocarbon solvents, vegetable oils, and plasticizers. 11. The method of claim 10,
Wherein the first layer and the second layer are biaxially stretched by 10 to 200% of the initial length in the longitudinal direction (MD) and the transverse direction (TD) before formation of the third layer . 11. The method of claim 10,
Wherein the formation of the second extruded layer is carried out sequentially after the formation of the first extruded layer or simultaneously with the formation of the first extruded layer. 11. The method of claim 10,
Wherein the first layer and the second layer are thermally fixed after the formation of the first layer and the second layer. 16. The method of claim 15,
Wherein the uniaxially stretching is performed by heat setting. 17. The method of claim 16,
In the uniaxial stretching, after the formation of the first layer and the second layer by simultaneous extrusion, the first layer and the second layer are stretched in the transverse direction (TD) by 0 to 40% of the first layer and the second layer , And further shrinks to 0 to 20%. The method for producing a three-layered separator for a secondary battery according to claim 1, 17. The method of claim 16,
In the uniaxial stretching, after the formation of the third layer, 0 to 10% stretching of the laminate in the transverse direction (TD) is followed by shrinking to 0% again. 11. The method of claim 10,
Wherein the first solvent is methyl ethyl ketone, methylene chloride, hexane or a mixture thereof. 11. The method of claim 10,
Wherein the second solvent is selected from the group consisting of acetone, tetrahydrofuran, methylene chloride, chloroform, dimethylformamide, N-methyl-2-pyrrolidone, 2-pyrrolidone, NMP), and cyclohexane. The method for producing a three-layered separator for a secondary battery according to claim 1, 11. The method of claim 10,
Wherein the first mixture comprises 90 to 99 parts by weight of polyethylene and 1 to 10 parts by weight of the high heat resistant polymer based on 100 parts by weight of the solid content. delete 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 transferring ability, and mixtures thereof. 11. The method of claim 10,
Wherein the binder is selected from the group consisting of polyvinylidene fluoride-co-hexafluoropropylene (PVDF-co-HFP), polyvinylidene fluoride-co-trichloroethylene, polyvinylidene fluoride- Polyvinylidene fluoride-co-chlorotrifluoroethylene, polymethyl methacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinyl acetate (also referred to as polyvinylpyrrolidone), polyvinylpyrrolidone polyvinyl acetate, polyvinylacetate, polyethylene-co-vinyl acetate, polyethylene oxide, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate ), Cyanoethylpullulan, cyano But are not limited to, polyvinyl alcohol, cyanoethylpolyvinylalcohol, cyanoethyl cellulose, cyanoethyl sucrose, pullulan, carboxyl methyl cellulose (CMC), acrylonitrile-styrene-butadiene But are not limited to, those selected from the group consisting of acrylonitrile-styrene-butadiene copolymer, polyimide, polyvinylidenefluoride, polyacrylonitrile, and styrene butadiene rubber (SBR) One or a mixture of two or more thereof. A three-layer separator for a secondary battery produced by the method of any one of claims 10 to 21 and 23 to 24.

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