KR102005869B1 - Separator for rechargeable battery and rechargeable lithium battery including the same - Google Patents

Abstract

And a heat resistant layer disposed on at least one side of the porous substrate, wherein the heat resistant layer includes a first binder, a second binder, and a filler, wherein the first binder is a core shell structure, Wherein the core of the binder includes a resin having a glass transition temperature of 80 ° C or higher and the shell of the first binder includes a resin having a glass transition temperature of -10 ° C to 10 ° C, A separator, and a lithium secondary battery including the separator.

Description

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

To a separator for a secondary battery and a lithium secondary battery including the same.

The separation membrane for an electrochemical cell is an interlayer which keeps the ion conductivity while keeping the anode and the cathode isolated from each other in the battery, thereby enabling charging and discharging of the battery. However, when the battery is exposed to a high temperature environment due to non-ideal behavior, the membrane is mechanically contracted or damaged due to its melting characteristics at low temperatures. In this case, the positive electrode and the negative electrode come into contact with each other and the battery may be ignited. To overcome this problem, a technique for suppressing the shrinkage of the membrane is required. As a representative method for suppressing the shrinkage of the separator, there is a method of increasing the thermal resistance of the separator by mixing inorganic particles having a high thermal resistance with an adhesive organic binder and coating the separator.

In this unintentional environment, even if the internal temperature of the cell excessively increases, the separation membrane is not shrunk to prevent the direct contact between the anode and the cathode, thereby improving the safety of the battery. At the same time, Research is being actively carried out.

Provided is a separator for a secondary battery having excellent mechanical stability at an elevated temperature, adhesion and workability, and a lithium secondary battery having excellent heat resistance, stability, and life characteristics.

In one embodiment, a porous substrate and a heat resistant layer disposed on at least one side of the porous substrate, wherein the heat resistant layer comprises a first binder, a second binder, and a filler, wherein the first binder is a core shell structure Wherein the core of the first binder comprises a resin having a glass transition temperature of 80 ° C or higher and the shell of the first binder comprises a resin having a glass transition temperature of -10 ° C to 10 ° C, A separation membrane for a secondary battery.

In another embodiment, there is provided a lithium secondary battery including a positive electrode, a negative electrode, and a separator for the secondary battery positioned between the positive electrode and the negative electrode.

The secondary battery separator according to one embodiment is excellent in mechanical stability at high temperature, adhesion and workability, and the lithium secondary battery including the same is excellent in heat resistance, stability, and life characteristics.

FIG. 1 is a cross-sectional view of a separation membrane for a secondary battery according to one embodiment.
2 is an exploded perspective view of a lithium secondary battery according to an embodiment.

Hereinafter, embodiments of the present invention will be described in detail. However, it should be understood that the present invention is not limited thereto, and the present invention is only defined by the scope of the following claims.

Hereinafter, a separator for a secondary battery according to one embodiment will be described. FIG. 1 is a view showing a separation membrane for a secondary battery according to one embodiment. Referring to FIG. 1, a secondary battery separator 10 according to an embodiment includes a porous substrate 20 and a heat resistant layer 30 disposed on one or both surfaces of the porous substrate 20.

The porous substrate 20 has a plurality of pores and may be a substrate that is typically used in an electrochemical device. Examples of the porous substrate include, but are not limited to, polyolefins such as polyethylene and polypropylene, polyesters such as polyethylene terephthalate and polybutylene terephthalate, polyacetals, polyamides, polyimides, polycarbonates, polyetheretherketones, polyaryletherketones, Polyolefins such as polyetherimide, polyamideimide, polybenzimidazole, polyethersulfone, polyphenylene oxide, cyclic olefin copolymer, polyphenylene sulfide, polyethylene naphthalate, glass fiber, Teflon, and polytetrafluoroethylene , Or a polymer membrane formed of at least two kinds of copolymers or mixtures thereof.

The porous substrate may be, for example, a polyolefin-based substrate including a polyolefin, and the polyolefin-based substrate has an excellent shut down function, thereby contributing to safety improvement of the cell. The polyolefin-based substrate may be selected from, for example, a polyethylene single film, a polypropylene single film, a polyethylene / polypropylene double film, a polypropylene / polyethylene / polypropylene triple film and a polyethylene / polypropylene / polyethylene triple film. The polyolefin-based resin may include a non-olefin resin in addition to the olefin resin, or may include a copolymer of an olefin and a non-olefin monomer.

The porous substrate may have a thickness of about 1 탆 to 40 탆 and may have a thickness of, for example, 1 탆 to 30 탆, 1 탆 to 20 탆, 5 탆 to 15 탆, or 5 탆 to 10 탆.

The heat resistant layer 30 according to one embodiment includes a binder and a filler.

By including the filler, the heat resistant layer is improved in heat resistance, and it is possible to prevent the separation membrane from shrinking or deforming rapidly due to temperature rise. The filler may be, for example, an inorganic filler, an organic filler, an inorganic filler, or a combination thereof. The inorganic filler may be a ceramic material capable of improving heat resistance, and may include, for example, a metal oxide, a metalloid oxide, a metal fluoride, a metal hydroxide, or a combination thereof. The inorganic filler may be selected from the group consisting of Al ₂ O ₃ , SiO ₂ , TiO ₂ , SnO ₂ , CeO ₂ , MgO, NiO, CaO, GaO, ZnO, ZrO ₂ , Y ₂ O ₃ , But are not limited to, SrTiO ₃ , BaTiO ₃ , Mg (OH) ₂ , boehmite, or combinations thereof. The organic filler may include, but is not limited to, an acrylic compound, an imide compound, an amide compound, or a combination thereof. The organic filler may have a core shell structure, but is not limited thereto.

The filler may be spherical or plate-like. The average particle size of the filler may be from about 1 nm to 2500 nm, and may be within the range of from 100 nm to 2000 nm, or from 100 nm to 1000 nm, for example from about 200 nm to 800 nm. The average particle diameter of the filler may be a number average particle diameter measured using a laser particle size analyzer or an electric resistance particle size analyzer. By using a filler having an average particle diameter in the above range, the heat resistant layer can be provided with appropriate strength to improve the heat resistance, durability and stability of the separator. The fillers may be used in a mixture of two or more different types or different sizes.

The filler may be contained in an amount of 50% by weight to 99% by weight with respect to the heat-resistant layer. In one embodiment, the filler may comprise from 70% to 99% by weight of the adhesive layer, for example from 80% to 99%, from 85% to 99%, from 90% to 99% Or 90% to 95% by weight. When the filler is included in the above range, the secondary battery separator according to one embodiment may exhibit excellent heat resistance, durability, and stability.

The binder serves to fix the filler on the porous substrate and may provide an adhesive force so that the heat resistant layer adheres well to the porous substrate and the electrode.

In one embodiment, the binder comprises a first binder and a second binder.

The first binder is a core shell structure including a core and a shell surrounding the core. The core of the first binder includes a resin having a glass transition temperature of 80 ° C or higher, and the shell of the first binder includes a resin having a glass transition temperature of -10 ° C to 10 ° C. The first binder has excellent adhesive strength, excellent heat resistance and electrochemically stable characteristics. Specifically, the first binder can effectively prevent an increase in resistance in the battery due to swelling of the binder due to electrolyte impregnation, And the thermal stability of the separator can be realized even at a high temperature of 200 ° C. Further, the first binder may be an aqueous binder, and is advantageous in that it is environmentally friendly.

The glass transition temperature of the resin contained in the core of the first binder may be 80 占 폚 or higher, for example 85 占 폚 or higher, 90 占 폚 or higher, or 95 占 폚 or higher, 150 占 폚 or lower, 140 占 폚 or lower, . The glass transition temperature of the resin contained in the shell of the first binder is in the range of -10 ° C to 10 ° C, and in the range of -9 ° C to 9 ° C, -8 ° C to 8 ° C, -7 ° C to 7 ° C, To 6 占 폚, or from -5 占 폚 to 5 占 폚, and the like.

The first binder may be a structure that is physically stable and includes a hard core and a soft shell.

The resin contained in the core of the first binder and the resin contained in the shell of the first binder are not limited to the same kind as long as they satisfy the respective glass transition temperatures, Based polymer, an olefin-based polymer, a urethane-based polymer, a copolymer thereof, or a combination thereof, and examples thereof include polystyrene, styrene-butadiene copolymer, ethylene propylene diene copolymer (Meth) acrylate, polyacrylonitrile, polyester, polyethylene, polypropylene, ethylene propylene copolymer, polytetrafluoroethylene (polytetrafluoroethylene) , Chlorosulfonated polyethylene, polyethylene oxide, polyvinyl alcohol, polyvinylpyrrolidone, poly Vinylpyridine, polyphosphazenes, epoxy resin, latex, copolymers thereof, derivatives thereof, or a combination thereof. Where alkyl may be, for example, C1 to C30 alkyl, C1 to C15 alkyl, C1 to C10 alkyl, or C1 to C5 alkyl.

For example, the resin included in the core of the first binder and the resin included in the shell may be independently a copolymer of a diene-based monomer and an aromatic vinyl monomer. The diene monomer may be a conjugated diene monomer such as 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 2-ethyl-1,3-butadiene, 1,3-pentadiene, chloroprene, Or non-conjugated diene monomers such as vinylnorbornene, dicyclopentadiene, and 1,4-hexadiene. The aromatic vinyl monomer may be styrene, C1 to C10 alkyl substituted styrene, halogen substituted styrene, or a combination thereof. Examples of the alkyl substituted styrene include o-ethylstyrene, m-ethylstyrene, p- -Methylstyrene, and the like.

As another example, the resin included in the core of the first binder and the resin included in the shell may be, for example, a rubbery polymer, and examples thereof include butadiene rubber, styrene-butadiene rubber, acrylated styrene- Acrylonitrile-butadiene rubber, acrylonitrile-butadiene-styrene rubber, isoprene rubber, isobutylene-isoprene rubber, ethylene-propylene rubber, ethylene-propylene-diene rubber, polyorganosiloxane- Rubber, fluororubber, or a combination thereof.

The core and the shell of the first binder may include, for example, a resin of the same kind, and in this case, a resin having a glass transition temperature different from each other depending on the content of the monomers, degree of polymerization, and the like. For example, the core and the shell of the first binder may each include a styrene-butadiene copolymer. In this case, the resin included in the core may contain more styrene monomer than the resin contained in the shell. Thus, for example, the core of the first binder includes a styrene-butadiene copolymer having a glass transition temperature of 80 ° C or higher, and the shell of the first binder is a styrene-butadiene copolymer having a glass transition temperature of -10 ° C to 10 ° C Copolymers. The styrene-butadiene copolymer may be, for example, styrene-butadiene rubber.

The resin included in the core of the first binder and the resin included in the shell may be resins having a structure in which a part of the chain is substituted with a carboxyl group.

The resin contained in the core of the first binder and the resin contained in the shell may be a crosslinked resin or a non-crosslinked resin, and may be, for example, a resin having a crosslinked structure substituted with a carboxyl group.

The average particle size of the first binder may be from 70 nm to 300 nm, for example from 70 nm to 250 nm, or from 100 nm to 200 nm. The average particle size of the core of the first binder may also be from 30 nm to 150 nm, for example from 30 nm to 100 nm, or from 40 nm to 80 nm. When the average particle diameter of the first binder and the average particle diameter of the core satisfy the above range, the first binder can exhibit a good binding force with the filler. Here, the average particle size may be calculated by calculating an arithmetic mean of particle sizes of particles other than the upper 10% and lower 10% particles after measuring the particle diameter of 50 or more particles present in the scanning electron microscopic image .

In the first binder, the distance from the very center of the core shell particle to the core region, that is, the radius of the core is C, and the distance from the outermost boundary of the core region to the outermost side of the core shell particle, When the thickness is S, the ratio of S to C (S / C) may be 1 to 3. In this case, the first binder is suitable for application to the heat resistant layer of the separator, has good compatibility, and does not swell due to the electrolytic solution.

The first binder has a low degree of swelling due to the electrolytic solution, thereby effectively suppressing an increase in resistance in the battery. For example, the degree of swelling of the first binder by the electrolytic solution may be 100% to 150%, for example, 100% to 140%. Here, the degree of swelling by the electrolyte may mean the degree of swelling after the binder is allowed to stand in an electrolytic solution prepared by mixing ethylene carbonate, ethylmethyl carbonate and diethyl carbonate in a volume ratio of 3: 5: 2 at about 70 ° C for about 72 hours have.

The first binder may be prepared by a variety of known methods such as emulsion polymerization, suspension polymerization, massive polymerization, solution polymerization, or bulk polymerization. And can be produced, for example, by an emulsion polymerization method.

The second binder is a cellulose compound and can control the viscosity of the slurry for forming the heat resistant layer of the separation membrane to improve phase stability and dispersibility and can improve the coating property of the slurry, It can contribute to improvement in heat resistance. The second binder may be an aqueous binder, and is advantageous in that it is eco-friendly. The slurry for forming a heat resistant layer means a composition obtained by mixing a first binder, a second binder and a filler in a solvent.

The cellulosic compound may be, for example, carboxymethylcellulose, hydroxypropylmethylcellulose, hydroxypropylcellulose, diacetylcellulose, copolymers thereof, or a combination thereof.

The cellulose-based compound may be substituted with sodium ion (Na ⁺ ) and / or ammonium ion (NH ₄ ⁺ ). In this case, the content of sodium ion and / or ammonium ion in the cellulose compound may be 6 wt% to 10 wt%. The degree of substitution (DS), which is the degree to which the sodium ion and / or the ammonium ion is substituted in the cellulosic compound, may be 0.6 to 0.9. In this case, the second binder can improve the phase stability, dispersibility, coating property, and the like of the slurry for forming the heat resistant layer.

The weight average molecular weight of the second binder may be from 10,000 to 700,000, for example from 100,000 to 700,000, or from 200,000 to 600,000, or from 300,000 to 500,000. If the weight average molecular weight of the second binder satisfies the above range, the second binder not only improves the phase stability, dispersibility, coating property, and the like of the heat resistant layer-forming slurry but also contributes to improvement in heat resistance of the binder. Here, the weight average molecular weight may be an average molecular weight in terms of polystyrene measured by gel permeation chromatography.

The average particle size of the second binder may be from 1 to 500 m, for example from 10 m to 400 m, or from 50 m to 300 m. When the average particle diameter of the second binder satisfies the above range, the second binder can improve the phase stability, dispersibility, coating property, and the like of the heat resistant layer-forming slurry. The definition of the average particle diameter is as described above.

The second binder may be prepared by various known methods such as emulsion polymerization, suspension polymerization, bulk polymerization, solution polymerization, or bulk polymerization.

The secondary battery separator according to an embodiment includes the heat-resistant layer including the filler, the first binder, and the second binder described above, thereby ensuring mechanical stability at a high temperature and exhibiting excellent heat resistance, adhesive strength, air permeability, And so on.

The first binder may be contained in an amount of 30 wt% to 99 wt%, and the second binder may be contained in an amount of 1 wt% to 70 wt%, based on the total amount of the first binder and the second binder. For example, the first binder may comprise from 40 wt% to 99 wt%, or from 50 wt% to 99 wt%, or from 50 wt% to 95 wt%, based on the total amount of the first binder and the second binder, The second binder may comprise from 1 wt% to 60 wt%, or from 1 wt% to 50 wt%, or from 5 wt% to 50 wt%, or from 10 wt% to 50 wt% %. ≪ / RTI > In other words, the content ratio of the first binder and the second binder may be 99: 1 to 30:70, and the ratio may be 95: 5, 90:10, 80:20, 70:30, 60:40, : 50, or 40:60. When the content of the first binder and the second binder satisfies the above range, the heat resistant layer may have excellent heat resistance, adhesion, air permeability, etc., and the slurry for heat resistant layer has excellent phase stability, Sex, and the like.

The total content of the first binder and the second binder with respect to the heat resistant layer may be 1 wt% to 30 wt%, for example, 1 wt% to 25 wt%, 1 wt% to 20 wt%, 1 wt% % To 15 wt%, 1 wt% to 10 wt%, or 5 wt% to 10 wt%, and the like. When the first binder and the second binder are included in the above range with respect to the heat resistant layer, the heat resistant layer can have excellent heat resistance, adhesive force, air permeability and the like, and the heat resistant layer forming slurry can exhibit excellent phase stability .

The heat resistant layer may further include one or more binders in addition to the first binder and the second binder.

The heat resistant layer may further include, for example, a crosslinked binder having a crosslinked structure. The crosslinking binder may be obtained from monomers, oligomers and / or polymers having a curable functional group capable of reacting with heat and / or light, for example a polyfunctional monomer having at least two curable functional groups, a polyfunctional oligomer and / Polymer. The curable functional group may include a vinyl group, a (meth) acrylate group, an epoxy group, an oxetane group, an ether group, a cyanate group, an isocyanate group, a hydroxyl group, a carboxyl group, a thiol group, an amino group, an alkoxy group, , But is not limited thereto.

The crosslinking binder may be obtained by curing a monomer, an oligomer and / or a polymer having at least two (meth) acrylate groups, and examples thereof include ethylene glycol di (meth) acrylate, propylene glycol di (meth) Acrylates such as polyethylene glycol di (meth) acrylate, polypropylene glycol di (meth) acrylate, butanediol di (meth) acrylate, hexamethylene glycol di (meth) acrylate, trimethylolpropane tri (Meth) acrylate, pentaerythritol tetra (meth) acrylate, diglycerin hexa (meth) acrylate, or a combination thereof.

For example, the crosslinking binder can be obtained by curing monomers, oligomers and / or polymers having at least two epoxy groups, and examples thereof include bisphenol A diglycidyl ether, bisphenol F diglycidyl ether, hexahydrophthalic acid glycidyl Ester or a combination thereof.

For example, the crosslinking binder may be obtained by curing a monomer, an oligomer and / or a polymer having at least two isocyanate groups, and examples thereof include diphenylmethane diisocyanate, 1,6-hexamethylene diisocyanate, 2,2,4 (2 , 2,4) -trimethylhexamethylene diisocyanate, phenylene diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, 3,3'-dimethyldiphenyl-4,4'-diisocyanate, xylene diisocyanate, Naphthalene diisocyanate, 1,4-cyclohexyl diisocyanate, or a combination thereof.

The heat resistant layer may further include, for example, a non-crosslinked binder. The non-crosslinked binder includes, for example, vinylidene fluoride polymers such as polyvinylidene fluoride homopolymer and polyvinylidene fluoride-hexafluoropropylene copolymer, polyvinylidene fluoride polymers such as polymethyl methacrylate, polyacrylonitrile, polyvinyl Polyvinyl acetates, polyethylene-vinyl acetate copolymers, polyethylene oxide, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethylpullulan, cyanoethylpolyvinyl alcohol, cyanoethylcellulose, Styrene-butadiene copolymer, acrylonitrile-styrene-butadiene copolymer, or a combination thereof, but is not limited thereto.

The heat resistant layer may have a thickness of about 0.01 탆 to 20 탆, and may have a thickness within the range of about 1 탆 to 10 탆, or about 1 탆 to 5 탆.

The ratio of the thickness of the heat resistant layer to the thickness of the porous substrate may be 0.05 to 0.5, for example, 0.05 to 0.4, or 0.05 to 0.3, or 0.1 to 0.2. In this case, the separation membrane including the porous substrate and the heat resistant layer can exhibit excellent air permeability, heat resistance, adhesion, and the like.

Stacking density of the heat-resistant layer may be 0.5 g / cm ³ to 5.0 g / cm ³ days, for example 0.5 g / cm ³ to ^{4.0 g / cm 3, 0.5 g} / cm 3 to 3.0 g / cm ^3, or Lt; ³ > to 2.0 g / cm < ³ >. In this case, the separation membrane can exhibit excellent air permeability, heat resistance, adhesion and the like.

For example, the permeability of the separator may be 90 sec / 0.1L to 150 sec / 0.1L, and 100 sec / 0.1L to 140 sec / 0.1L or 100 sec / 0.1L to 130 sec / 0.1L. The air permeability means the time (seconds) in which 0.1 L of air passes through the separator.

Further, the separation membrane can exhibit excellent air permeability despite the thickness of the heat resistant layer. For example, the increase rate of the air permeability of the separator depending on the thickness of the heat resistant layer may be 20 sec / 탆 or less, for example, 15 sec / 탆.

The separator exhibits excellent thermal stability. For example, even when the separator is left at 200 DEG C or higher, the separator can be maintained in a stable state without being ruptured or deformed in shape.

The secondary battery separator according to one embodiment can be manufactured by various known methods. For example, the secondary battery separator may be formed by applying a slurry for forming a heat resistant layer on one side or both sides of the porous substrate and drying the same.

The slurry for forming the heat resistant layer may include the filler, the first binder, the second binder, and the solvent. The solvent is not particularly limited as long as it can dissolve or disperse the first binder, the second binder and the filler. The solvent may be water, alcohol, or a combination thereof, for daily use. Alternatively, the solvent may be a low-boiling solvent having a boiling point of 80 DEG C or lower, and may be, for example, acetone, methyl ethyl ketone, ethyl isobutyl ketone, tetrahydrofuran, dimethylformaldehyde, cyclohexane or a mixture thereof.

The slurry for forming a heat resistant layer can exhibit excellent phase stability. Specifically, the slurry for forming a heat resistant layer can exhibit a stable state without causing a phase separation phenomenon even after being left for about 48 hours.

The application may be performed by, for example, spin coating, dip coating, bar coating, die coating, slit coating, roll coating, inkjet printing, etc., but is not limited thereto.

The drying can be performed by, for example, a method of drying by natural drying, hot air, hot air or low-humidity wind, vacuum drying, far-infrared ray, electron beam, etc., but is not limited thereto. The drying process may be performed at a temperature of, for example, 25 to 120 ° C.

The secondary battery separator may be manufactured by a method such as lamination or co-extrusion.

Hereinafter, a lithium secondary battery including the separator for a secondary battery will be described.

The lithium secondary battery can be classified into a lithium ion battery, a lithium ion polymer battery, and a lithium polymer battery according to the type of separation membrane and electrolytic solution used, and can be classified into a cylindrical shape, a square shape, a coin shape, Depending on the size, it can be divided into bulk type and thin type. The structure and the manufacturing method of these cells are well known in the art, and detailed description thereof will be omitted.

Here, a prismatic lithium secondary battery is exemplarily described as an example of a lithium secondary battery. 2 is an exploded perspective view of a lithium secondary battery according to an embodiment. 2, a lithium secondary battery 100 according to an embodiment includes an electrode assembly 60 and an electrode assembly 60 wound around a separator 10 between an anode 40 and a cathode 50 And includes a built-in case 70.

The electrode assembly 60 may be in the form of a jelly roll formed by winding the anode 40 and the cathode 50 with the separator 10 interposed therebetween.

The anode 40, the cathode 50 and the separator 10 are impregnated with an electrolyte (not shown).

The anode 40 may include a cathode current collector and a cathode active material layer formed on the cathode current collector. The cathode active material layer may include a cathode active material, a binder, and optionally a conductive material.

As the positive electrode collector, aluminum, nickel, or the like may be used, but the present invention is not limited thereto.

As the cathode active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. Concretely, at least one of cobalt, manganese, nickel, aluminum, iron or a composite oxide or composite phosphorus of a metal and lithium in combination thereof may be used. For example, the cathode active material may be lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate or a combination thereof.

The binder not only adheres the positive electrode active materials to each other well but also adheres the positive electrode active material to the positive electrode current collector. Specific examples thereof include polyvinyl alcohol, carboxymethylcellulose, hydroxypropylcellulose, diacetylcellulose, polyvinyl chloride , Carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide containing polymer, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, Acrylated styrene-butadiene rubber, epoxy resin, nylon, and the like. These may be used alone or in combination of two or more.

The conductive material imparts conductivity to the electrode. Examples of the conductive material include, but are not limited to, natural graphite, artificial graphite, carbon black, carbon fiber, metal powder, and metal fiber. These may be used alone or in combination of two or more. The metal powder and the metal fiber may be metals such as copper, nickel, aluminum, and silver.

The cathode 50 may include a negative electrode collector and a negative electrode active material layer formed on the negative collector.

The negative electrode current collector may be copper, gold, nickel, copper alloy, or the like, but is not limited thereto.

The negative electrode active material layer may include a negative electrode active material, a binder, and optionally a conductive material. Examples of the negative electrode active material include a material capable of reversibly intercalating and deintercalating lithium ions, a lithium metal, an alloy of lithium metal, a material capable of doping and dedoping lithium, a transition metal oxide, Can be used.

Examples of the material capable of reversibly intercalating and deintercalating lithium ions include carbonaceous materials, and examples thereof include crystalline carbon, amorphous carbon, and combinations thereof. Examples of the crystalline carbon include amorphous, plate-shaped, flake-shaped, spherical or fibrous natural graphite or artificial graphite. Examples of the amorphous carbon include soft carbon or hard carbon, mesophase pitch carbide, fired coke and the like. As the lithium metal alloy, a lithium-metal alloy may be selected from the group consisting of lithium, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, An alloy of a selected metal may be used. As the material capable of doping and dedoping lithium, Si, SiO _x (0 <x <2), Si-C composite, Si-Y alloy, Sn, SnO ₂ , Sn-C composite, Sn- And at least one of them may be mixed with SiO ₂ . The element Y may be at least one element selected from the group consisting of Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Tl, Ge, P, As, Se, Te, Po, and combinations thereof. Examples of the transition metal oxide include vanadium oxide, lithium vanadium oxide, and the like.

The kind of the binder and the conductive material used for the cathode may be the same as the binder and the conductive material used in the anode.

The positive electrode 40 and the negative electrode 50 can be produced by mixing each of the active materials and the binder with a conductive material in a solvent to prepare each active material composition and applying the active material composition to each current collector. The solvent may be N-methyl pyrrolidone or the like, but is not limited thereto. The method of manufacturing the electrode is well known in the art, and therefore, a detailed description thereof will be omitted herein.

The electrolytic solution includes an organic solvent and a lithium salt.

The organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can move. As the organic solvent, for example, a carbonate-based, ester-based, ether-based, ketone-based, alcohol-based or aprotic solvent may be used. Examples of the carbonate solvent include dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, methyl ethyl carbonate, ethylene carbonate, propylene carbonate, butylene carbonate and the like. Methyl acetate, ethyl acetate, n-propyl acetate, 1,1-dimethyl ethyl acetate, methyl propionate, ethyl propionate,? -Butyrolactone, decanolide, valerolactone, mevalonolactone mevalonolactone, caprolactone, and the like may be used. Examples of the ether solvent include dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, and tetrahydrofuran. As the ketone solvent, cyclohexanone may be used have. As the alcoholic solvent, ethyl alcohol, isopropyl alcohol and the like can be used. As the aprotic solvent, R-CN (R is a C2 to C20 linear, branched or cyclic hydrocarbon group, An amide such as nitrile, dimethylformamide, etc., which may contain a linking aromatic ring or an ether bond, a dioxolane such as 1,3-dioxolane, sulfolane, and the like.

The organic solvents may be used alone or in combination of two or more. When two or more of them are used in combination, the mixing ratio may be appropriately adjusted according to the performance of the desired cell.

The lithium salt is dissolved in an organic solvent to act as a source of lithium ions in the battery to enable operation of a basic lithium secondary battery and accelerate the movement of lithium ions between the positive electrode and the negative electrode. For example the lithium salt _{is, LiPF 6, LiBF 4, LiSbF} 6, LiAsF 6, LiN (SO 3 C 2 F 5) 2, LiN (CF 3 SO 2) 2, LiC 4 F 9 SO 3, LiClO 4, LiAlO 2 , LiAlCl ₄ , LiN (C _x F _{2x + 1} SO ₂ ) (C _y F _{2y + 1} SO ₂ ) where x and y are natural numbers, LiCl, LiI, LiB (C ₂ O ₄ ) _2, But the present invention is not limited thereto.

The concentration of the lithium salt can be used within the range of 0.1M to 2.0M. When the concentration of the lithium salt is within the above range, the electrolytic solution has an appropriate conductivity and viscosity, and thus can exhibit excellent electrolytic solution performance, and lithium ions can effectively move.

Hereinafter, the aspects of the present invention described above will be described in more detail through examples. However, the following examples are for illustrative purposes only and do not limit the scope of the invention.

Example : Preparation of Membrane

Example  One

A styrene-butadiene rubber having a core shell structure including a styrene-butadiene shell having a glass transition temperature of -80 占 폚 or higher and a glass transition temperature of -10 占 폚 to 10 占 폚 Particle diameter 150 nm) is used. Carboxymethylcellulose (Japan Paper) having a weight average molecular weight of 360,000 is used as the second binder, and boehmite having an average particle diameter of about 300 nm is used as a filler. In a water solvent, 90 weight% of the first binder and 10 weight% of the second binder were mixed and 1500 weight parts of the filler was added to 100 weight parts of the total weight of the first binder and the second binder to prepare 800 占 퐉 zirconia balls And mixed in a paint shaker for 2 hours or more, followed by filtering only the mixed liquid to prepare a slurry for forming a heat resistant layer.

The slurry for forming the heat resistant layer was coated on the polyethylene base material having a thickness of 12 탆 in a blade or bar coating manner, followed by drying at 80 캜 to prepare a secondary battery separator.

Example  2

A slurry for forming a heat resistant layer and a separation membrane for a secondary battery were prepared in the same manner as in Example 1, except that 75 wt% of the first binder and 25 wt% of the second binder were mixed.

Example  3

A slurry for forming a heat resistant layer and a separator for a secondary battery were prepared in the same manner as in Example 1, except that 50 wt% of the first binder and 50 wt% of the second binder were mixed.

Example  4

A slurry for forming a heat resistant layer and a separator for a secondary battery were prepared in the same manner as in Example 1, except that 1000 parts by weight of the filler was added to 100 parts by weight of the total of the first binder and the second binder.

Comparative Example  One

A slurry for forming a heat resistant layer and a separator for a secondary battery were prepared in the same manner as in Example 2 except that a styrene-butadiene rubber having an average particle diameter of 70 nm and a glass transition temperature of 7 캜 and not a core shell structure was used as a first binder do.

Comparative Example  2

A slurry for forming a heat resistant layer and a separator for a secondary battery were prepared in the same manner as in Example 2 except that a styrene-butadiene rubber having an average particle diameter of 320 nm and a glass transition temperature of 5 캜 and not a core shell structure was used as the first binder do.

Comparative Example  3

A slurry for forming a heat-resistant layer and a separator for a secondary battery were prepared in the same manner as in Comparative Example 2, except that carboxymethylcellulose having a weight average molecular weight of 12,500 was used as the second binder.

Comparative Example  4

A slurry for forming a heat-resistant layer and a separation membrane for a secondary battery were prepared in the same manner as in Comparative Example 2, except that carboxymethylcellulose having a weight average molecular weight of 700,000 was used as the second binder.

Comparative Example  5

A slurry for forming a heat-resistant layer and a separation membrane for a secondary battery were prepared in the same manner as in Example 1, except that the second binder was not used.

Comparative Example  6

A slurry for forming a heat resistant layer and a separation membrane for a secondary battery were prepared in the same manner as in Example 1, except that the first binder was not used.

Table 1 below shows kinds and contents of the first binder, second binder and filler used in Examples 1 to 4 and Comparative Examples 1 to 6. In Table 1, the values for the first binder and the second binder represent the weight percentage with respect to the total of the first binder and the second binder, and the numerical values for the fillers are 100 parts by weight for the total of the first binder and the second binder Means the weight of the filler.

Example Comparative Example One 2 3 4 One 2 3 4 5 6 The first binder 150nm core shell 90 75 50 90 - - - - 100 - 70 nm - - - 75 - - - - - 320nm - - - - 75 75 75 - - The second binder 360,000 g / mol 10 25 50 10 25 25 - - - 100 12,500 g / mol - - - - - 25 - - - 700,000 g / mol - - - - - - 25 - - Filler (parts by weight) 1500 1500 1500 1000 1500 1500 1500 1500 1500 1500

Evaluation example  One: Heat resistant layer  Phase stability of the slurry for forming

The slurry for forming the heat resistant layer according to Examples 1 to 4 and Comparative Examples 1 to 6 was stored in a designated position with a 15 mL vial, and the phase separation phenomenon of each slurry was observed over time, and the results are shown in Table 2 below.

Evaluation example  2: Measurement of membrane thickness

The thicknesses of the membranes prepared in Examples 1 to 4 and Comparative Examples 1 to 6 were measured with a precision measuring instrument (TESA-μHite), and the results are shown in Table 2 below.

Evaluation example  3: Air permeability of membrane

For the membranes prepared in Examples 1 to 4 and Comparative Examples 1 to 6, the time (in seconds) during which 100 mL of air was permeated at room temperature was measured with an air permeability meter (Asahi-seiko, EG01-55-1MR) , And the results are shown in Table 2 below.

Evaluation example  4: Adhesion of membrane

With respect to the separation membranes prepared in Examples 1 to 4 and Comparative Examples 1 to 6, the binding force between the porous base and the heat resistant layer is evaluated. Specifically, using a tensile tester (Tinius Olsen, HT400), a separation membrane was attached to an adhesive tape having a width of 10 mm and bent at 180 ° to measure a force (N) required for detaching the tape from the membrane. Are shown in Table 2.

Evaluation example  5: Heat resistance of membrane

Examples 1 to 4 and Comparative Examples 1 to preparing 6 a membrane prepared in each of a size of 5x5 cm ^2, is secured by attaching the separator to the heat-resistant tape to the inside heating plate of 4x4 cm ² with a hole to produce a sample . The sample was placed in an oven and the temperature was raised from room temperature to 220 ° C at a rate of 5 ° C / min. The state of the sample was confirmed, and the results are shown in Table 2 below. As a result of the test, if the separator ruptures, NG is displayed. If the separator does not rupture and is in good condition, it is marked as OK.

Example Comparative Example One 2 3 4 One 2 3 4 5 6
Phase stability Stable until 48 hours Stable until 48 hours Stable until 48 hours Stable until 48 hours Stable until 48 hours Stable until 48 hours Settling within 24 hours Agglomerated / uncoated Settling within 12 hours Stable until 48 hours thickness
(탆) 14 14 14 16 14 14 14 - 14 14 Ventilation
(sec / 0.1L) 120 125 130 140 170 135-170 115 - 116 141 Adhesion
(N) 18 15 14 14 8 7 9 - 16 7 Heat resistance OK OK OK OK NG NG NG - NG NG

Referring to Table 2, it can be confirmed that the phase stability of the heat resistant layer-forming slurry in Examples 1 to 4 is excellent, and the permeability, adhesion and heat resistance of the separator are excellent. On the other hand, in Comparative Examples 1, 2 and 6, the air permeability, adhesive strength and heat resistance of the separator were not good, Comparative Examples 3 and 5 showed poor phase stability of the slurry for forming the heat resistant layer and the permeability, And in Comparative Example 4, the slurry for forming the heat resistant layer was aggregated, indicating that the coating was impossible.

Manufacturing example  1 to 4 and Comparative Manufacturing Example  1 to 6: Preparation of lithium secondary battery

LiCoO ₂ , polyvinylidene fluoride and carbon black were added to the N-methylpyrrolidone solvent in a weight ratio of 96: 2: 2 to prepare a slurry. The slurry was applied to an aluminum foil, dried and rolled to produce a positive electrode.

Graphite, polyvinylidene fluoride and carbon black were added to the N-methylpyrrolidone solvent in a weight ratio of 98: 1: 1 to prepare a slurry. The slurry was applied to a copper foil, dried and rolled to produce a negative electrode.

A jelly roll electrode assembly in the form of a winding was prepared between the prepared anode and cathode through the separation membranes prepared in Examples 1 to 4 and Comparative Examples 1 to 6, respectively. Then, an electrolyte solution containing 1.15M LiPF ₆ was added to a mixed solvent of ethylene carbonate, ethyl methyl carbonate and diethyl carbonate in a volume ratio of 3: 5: 2, and the mixture was sealed to prepare a lithium secondary battery.

Evaluation example  6: Battery life characteristics

The discharge capacity retention rates of the lithium secondary batteries prepared in Production Example 1 and Comparative Production Example 5 were measured according to the cycle, and the results are shown in FIG. Referring to FIG. 3, it can be seen that, in the case of Production Example 1, the life characteristics are remarkably superior to those of Comparative Production Example 5. FIG.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, And falls within the scope of the invention.

10: Membrane
20: Porous substrate
30: Heat resistant layer
40: anode
50: cathode
60: electrode assembly
70: Case

Claims (15)

A porous substrate, and a heat-resistant layer disposed on at least one side of the porous substrate,
Wherein the heat resistant layer comprises a first binder, a second binder, and a filler,
Wherein the first binder comprises a core shell structure and the core of the first binder comprises a resin having a glass transition temperature of 80 ° C or higher and the shell of the first binder comprises a resin having a glass transition temperature of -10 ° C to 10 ° C In addition,
Wherein the second binder is a cellulose compound,
Wherein the second binder is contained in an amount of 10 wt% to 50 wt% based on the total amount of the first binder and the second binder. The method of claim 1,
The resin contained in the core of the first binder and the resin contained in the shell of the first binder are the same or different and each independently selected from the group consisting of a styrene polymer, a diene polymer, an acrylate polymer, an ester polymer, , A urethane-based polymer, a copolymer thereof, or a combination thereof. The method of claim 1,
Wherein the core of the first binder comprises a styrene-butadiene copolymer having a glass transition temperature of 80 ° C or higher, and the shell of the first binder has a glass transition temperature of -10 ° C to 10 ° C. Battery separator. The method of claim 1,
Wherein the average particle diameter of the first binder is 70 nm to 300 nm. The method of claim 1,
Wherein the core of the first binder has an average particle diameter of 30 nm to 150 nm. The method of claim 1,
Wherein the second binder has a weight average molecular weight of 10,000 to 700,000. The method of claim 1,
Wherein the cellulose-based compound is a carboxymethylcellulose, hydroxypropylmethylcellulose, hydroxypropylcellulose, diacetylcellulose, a copolymer thereof, or a combination thereof. The method of claim 1,
And the second binder has an average particle diameter of 1 to 500 m. delete The method of claim 1,
Wherein the total content of the first binder and the second binder with respect to the heat resistant layer is 1 wt% to 30 wt%. The method of claim 1,
Wherein the filler is contained in an amount of 70 wt% to 99 wt% with respect to the heat resistant layer. The method of claim 1,
The filler may be selected from the group consisting of Al ₂ O ₃ , SiO ₂ , TiO ₂ , SnO ₂ , CeO ₂ , MgO, NiO, CaO, GaO, ZnO, ZrO ₂ , Y ₂ O ₃ , SrTiO ₃ , BaTiO ₃ , Mg (OH) ₂ , boehmite, or a combination thereof. The method of claim 1,
Wherein the filler has an average particle diameter of 100 nm to 1000 nm. The method of claim 1,
Wherein the porous substrate comprises a polyolefin. A lithium secondary battery comprising a positive electrode, a negative electrode, and a separator for a secondary battery according to any one of claims 1 to 8 and 10 to 14 positioned between the positive electrode and the negative electrode.

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