KR20170129646A - Separator for rechargeable battery and rechargeable lithium battery including the same - Google Patents

Abstract

The present invention provides a separator for a secondary battery having high heat resistance and strong adhesion, and provides a lithium secondary battery which includes the same and has improved heat resistance, stability, life properties, rate properties, and oxidation resistance. The separator for a secondary battery comprises a porous substrate and a heat resistance layer located at one surface of the porous substrate. The heat resistance layer includes an acrylic copolymer, an alkali metal, and a filler. The acrylic copolymer includes a unit induced from (meta) acrylate or (meta) acrylic acid, a cyano group-containing structural unit, and a sulfonate group-containing structural unit.

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. In order to overcome this problem, there is a need for a technique capable of suppressing the shrinkage of the separator and ensuring the stability of the battery.

In this connection, 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 on the separator is known. However, the conventional method can not sufficiently secure the desired adhesive strength, and it is difficult to apply it to the separator having various sizes and shapes. Therefore, it is necessary to develop a separation membrane having high heat resistance and excellent adhesion.

Disclosed is a separator for a secondary battery having a high heat resistance and a strong adhesion, and a lithium secondary battery having improved heat resistance, stability, life characteristics, rate characteristics, oxidation resistance, and the like.

In one embodiment, the porous substrate includes a porous substrate and a heat resistant layer disposed on at least one side of the porous substrate, wherein the heat resistant layer includes an acrylic copolymer, an alkali metal, and a filler, and the acrylic copolymer is a (meth) A separator for a secondary battery comprising a unit derived from (meth) acrylic acid, a cyano group-containing unit, and a sulfonate group-containing unit.

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 heat resistance and adhesion, and the lithium secondary battery including the same has excellent heat resistance, stability, life characteristics, rate characteristics and oxidation resistance.

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.
3 is a graph showing lifetime characteristics of a lithium secondary battery according to Production Example 1-1, Comparative Production Example 1 and Comparative Production Example 2. FIG.
4 is a graph showing the rate characteristics of a lithium secondary battery according to Production Example 1-1, Comparative Production Example 1 and Comparative Production Example 2. FIG.
5 is a graph showing the oxidation resistance of the acrylic binder and the polyvinylidene fluoride binder prepared in Synthesis Example 1, Comparative Synthesis Example 1,

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.

"Substituted" as used herein, unless otherwise defined, means that the hydrogen in the compound is a C1 to C30 alkyl group, a C2 to C30 alkynyl group, a C6 to C30 aryl group, a C7 to C30 alkylaryl group, a C1 to C30 alkoxy A C3 to C30 cycloalkenyl group, a C6 to C30 cycloalkynyl group, a C2 to C30 heterocycloalkyl group, a halogen atom, a C1 to C30 heteroalkyl group, a C3 to C30 heteroalkylaryl group, a C3 to C30 cycloalkyl group, (F, Cl, Br, or I), hydroxyl group (-OH), nitro (-NO _2), cyano (-CN), amino group (-NRR 'where R and R' are independently from each other hydrogen or a C1 to C6 alkyl group), a sulfonyl beta popular _{^{(-RR'N + (CH2) n SO3}} -), beta carboxy popular _{^{(-RR'N + (CH2) n COO}} - where R and R 'are independently C1 to C20 alkyl groups each (-NH ₂ ), an aldehyde group (-C (= NH) NH ₂ ), a hydrazino group (-NHNH ₂ ), an azido group (-N ₃ ), an amidino group = O) H), car Carbamoyl group (carbamoyl group, -C (O) NH _2), thiol (-SH), an ester group (-C (= O) OR, where R is C1 to C6 alkyl group or a C6 to C12 aryl group), carboxyl group ( -COOH) or a salt thereof (-C (= O) OM, wherein M is an organic or inorganic cation), sulfonic acid (-SO ₃ H) or a salt thereof (-SO ₃ M, (-PO ₃ H ₂ ) or a salt thereof (-PO ₃ MH or -PO ₃ M ₂ , where M is an organic or inorganic cation), and combinations thereof. do.

Hereinafter, The C1 to C3 alkyl group means a methyl group, an ethyl group, or a propyl group. The C1 to C10 alkylene group may be, for example, a C1 to C6 alkylene group, a C1 to C5 alkylene group, a C1 to C3 alkylene group, and may be, for example, a methylene group, an ethylene group or a propylene group. The C3 to C20 cycloalkylene group may be, for example, a C3 to C10 cycloalkylene group, or a C5 to C10 alkylene group, and may be, for example, a cyclohexylene group. The C6 to C20 arylene group may be, for example, a C6 to C10 arylene group and may be, for example, a benzylene group or a phenylene group. The C3 to C20 heterocyclic group may be, for example, a C3 to C10 heterocyclic group, and may be, for example, a pyridine group.

"Hetero" means one or more heteroatoms selected from N, O, S, Si, and P.

Hereinafter, the "combination thereof" may mean a mixture, a copolymer, a blend, an alloy, a composite, a reaction product, and the like of the constituent.

In the formulas, an asterisk indicates an atom, a group, or a part connected to a unit.

Hereinafter, the term "alkali metal" refers to an element belonging to group 1 of the periodic table, and refers to lithium, sodium, potassium, rubidium, cesium, or francium, and may exist in a cationic or neutral state.

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 usually used in an electrochemical device. The porous substrate 20 includes, but is not limited to, polyolefins such as polyethylene, polypropylene and the like, polyesters such as polyethylene terephthalate and polybutylene terephthalate, polyacetals, polyamides, polyimides, polycarbonates, polyetheretherketones, Polyetherimide, polyetherimide, polybenzimidazole, polyether sulfone, polyphenylene oxide, cyclic olefin copolymer, polyphenylene sulfide, polyethylene naphthalate, glass fiber, Teflon, and polytetrafluoro Ethylene, or a copolymer or mixture of two or more of the above polymers.

The porous substrate 20 may be, for example, a polyolefin-based material including a polyolefin, and the polyolefin-based material may have an excellent shut-down function, thereby contributing to safety improvement of the battery. 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 20 can have a thickness of about 1 占 퐉 to 40 占 퐉 and can have a thickness of, for example, 1 占 퐉 to 30 占 퐉, 1 占 퐉 to 20 占 퐉, 5 占 퐉 to 15 占 퐉, or 10 占 퐉 to 15 占 퐉 .

The heat resistant layer 30 according to one embodiment includes an acrylic copolymer, an alkali metal, and a filler.

The heat resistance of the heat resistant layer 30 is improved by including the filler, 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, plate-like, cubic, or amorphous. The average particle size of the filler can be from about 1 nm to 2500 nm, and can be from 100 nm to 2000 nm, or from 200 nm to 1000 nm, within the range, for example, from about 300 nm to 800 nm. The average particle size of the filler may be a particle size (D ₅₀ ) at 50% by volume in a cumulative size-distribution curve. By using a filler having an average particle diameter in the above range, appropriate strength is given to the heat resistant layer 30, and heat resistance, durability and stability of the separation membrane 10 can be improved. 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 (30). In one embodiment, the filler may comprise from 70% to 99% by weight, for example from 80% to 99%, from 85% to 99%, from 90% to 99% By weight, or from 95% by weight to 99% by weight. When the filler is included in the above range, the secondary battery separator 10 according to one embodiment may exhibit excellent heat resistance, durability, oxidation resistance, and stability.

The alkali metal may be in the form of a cation, for example, lithium, sodium, potassium, rubidium, or cesium. The alkali metal may be present in the form of a salt in combination with an acrylic copolymer to be described later. The alkali metal can help the synthesis of the acrylic copolymer in the aqueous solvent, improve the adhesion of the heat resistant layer 30, and improve the heat resistance, air permeability and oxidation resistance of the separation membrane 10.

The alkali metal may be contained in an amount of 1 wt% to 40 wt%, for example, 1 wt% to 30 wt%, or 1 wt% to 20 wt% based on the total weight of the alkali metal and the acrylic copolymer, or 10% by weight to 20% by weight.

The alkali metal may be contained in an amount of 0.1 to 1.0 mol% based on the total amount of the alkali metal and the acrylic copolymer.

When the alkali metal is included in the above range, the heat resistant layer 30 can have excellent adhesion, and the separator 10 including the alkali metal can exhibit excellent heat resistance, air permeability, and oxidation resistance.

The acrylic copolymer includes a unit derived from (meth) acrylate or (meth) acrylic acid, a cyano group-containing unit, and a sulfonate group-containing unit. The acrylic copolymer serves to fix the filler on the porous substrate 20 and may provide an adhesive force so that the heat resistant layer 30 adheres well to the porous substrate 20 and the electrode, Heat resistance, air permeability and oxidation resistance.

In the unit derived from (meth) acrylate or (meth) acrylic acid, the (meth) acrylate may be a conjugated base of (meth) acrylic acid, a (meth) acrylate or a derivative thereof. The unit derived from (meth) acrylate or (meth) acrylic acid may be represented by, for example, the following formula 1, formula 2, formula 3, or a combination thereof.

[Chemical Formula 1] (2)   (3)

In the above Chemical Formulas 1 to 3, R ¹ , R ² , and R ³ are each independently hydrogen or a methyl group, and in Formula 2, M is an alkali metal. The alkali metal may be, for example, lithium, sodium, potassium, rubidium, or cesium.

For example, the unit derived from (meth) acrylate or (meth) acrylic acid may include a unit represented by the formula (2) and a unit represented by the formula (3). In this case, May be contained in a molar ratio of from 10: 1 to 1: 2, or from 10: 1 to 1: 1, or from 5: 1 to 1: 1.

The unit derived from (meth) acrylate or (meth) acrylic acid may be contained in an amount of 10 mol% to 70 mol%, for example, 20 mol% to 60 mol%, or 30 mol% 60 mol%, or 40 mol% to 55 mol%. When the unit is included in the above range, the acrylic copolymer and the separation membrane 10 including the acrylic copolymer can exhibit excellent adhesion, heat resistance, air permeability and oxidation resistance.

The cyano group-containing unit may be represented by, for example, the following formula (4).

[Chemical Formula 4]

In Formula ^4, R 4 is hydrogen or C1 to C3 alkyl group, L ¹ is -C (= O) -, -C (= O) O-, -OC (= O) -, -O-, or - C (= O) NH-, x is an integer of 0 to 2, L ² is a substituted or unsubstituted C1 to C10 alkylene group, a substituted or unsubstituted C3 to C20 cycloalkylene group, a substituted or unsubstituted C6 Or a substituted or unsubstituted C3 to C20 heterocyclic group, and y is an integer of 0 to 2.

The cyano group-containing unit may be, for example, a unit derived from (meth) acrylonitrile, alkenitrile, cyanoalkyl (meth) acrylate, or 2- (vinyloxy) alkanonitrile. Wherein the alkene may be a C1 to C20 alkene, a C1 to C10 alkene, or a C1 to C6 alkene, wherein the alkyl may be a C1 to C20 alkyl, a C1 to C10 alkyl, or a C1 to C6 alkyl, C20 alkane, a C1 to C10 alkane, or a C1 to C6 alkane.

The alkenitrile can be, for example, cyanide allyl, 4-pentenenitrile, 3-pentenenitrile, 2-pentenenitrile, or 5-hexenenitrile. Examples of the cyanoalkyl (meth) acrylate include cyanomethyl (meth) acrylate, cyanoethyl (meth) acrylate, cyanopropyl (meth) acrylate, cyanohexyl . The 2- (vinyloxy) alkanitrile may be, for example, 2- (vinyloxy) ethanenitrile, 2- (vinyloxy) propanenitrile or the like.

The cyano group-containing unit may be contained in an amount of 30 mol% to 85 mol%, for example, 30 mol% to 70 mol%, 30 mol% to 60 mol%, or 35 mol% to 55 mol %. ≪ / RTI > When the cyano group-containing unit is contained in the above range, the acrylic copolymer and the separation membrane 10 including the acrylic copolymer can ensure excellent oxidation resistance and exhibit adhesive strength, heat resistance and air permeability.

The sulfonate group-containing unit may be a unit containing a conjugated base of a sulfonic acid, a sulfonic acid salt, a sulfonic acid, or a derivative thereof. For example, the sulfonate group-containing unit may be represented by the following formula (5), (6), (7), or a combination thereof.

[Chemical Formula 5] [Chemical Formula 6] (7)

R ⁵ , R ⁶ , and R ⁷ are each independently hydrogen or a C 1 to C 3 alkyl group; L ³ , L ⁵ , and L ⁷ are each independently -C (= O) -, (= O) O-, -OC (= O) -, -O-, or -C (= O) NH-, L ⁴ , L ⁶ , and L ⁸ are each independently substituted or unsubstituted A substituted or unsubstituted C3 to C20 cycloalkylene group, a substituted or unsubstituted C6 to C20 arylene group, or a substituted or unsubstituted C3 to C20 heterocyclic group, and a, b, c, d , e, and f are each independently an integer of 0 to 2, and M 'in formula (6) is an alkali metal.

For example, L ^3, L ^5, and L ⁷ are each independently -C (= O) NH-, L 4, L 6, and L ⁸ are each independently a C1 to C10 alkyl, in the following Chemical Formulas 5 to 7 And a, b, c, d, e, and f may be 1.

The sulfonate group-containing unit may include either one of the unit represented by the general formula (5), the unit represented by the general formula (6), and the unit represented by the general formula (7), or two or more kinds thereof. For example, the sulfonate group-containing unit may include a unit represented by the formula (6). In another example, the sulfonate group-containing unit may include a unit represented by the formula (6) and a unit represented by the formula (7).

The sulfonate group-containing units may be, for example, those derived from vinyl sulfonic acid, allylsulfonic acid, styrenesulfonic acid, anetholsulfonic acid, acrylamidoalkanesulfonic acid, sulfoalkyl (meth) acrylate, Lt; / RTI >

Wherein the alkane may be a C1 to C20 alkane, a C1 to C10 alkane, or a C1 to C6 alkane, and wherein the alkyl may be C1 to C20 alkyl, C1 to C10 alkyl, or C1 to C6 alkyl. The salt means a salt composed of the aforementioned sulfonic acid and a suitable ion. The ion may be, for example, an alkali metal ion, in which case the salt may be an alkali metal sulfonate.

The acrylamidoalkanesulfonic acid may be, for example, 2-acrylamido-2-methylpropanesulfonic acid and the sulfoalkyl (meth) acrylate may be, for example, 2-sulfoethyl (meth) Propyl (meth) acrylate, and the like.

The sulfonate group-containing unit may be contained in an amount of 0.1 mol% to 20 mol%, for example, 0.1 mol% to 10 mol%, or 1 mol% to 20 mol%, or 1 mol% 10 mole%. When the unit containing the cellophane group is included in the above range, the acrylic copolymer and the separation membrane 10 including the acrylic copolymer can exhibit excellent adhesion, heat resistance, air permeability and oxidation resistance.

The acrylic copolymer may be represented by the following general formula (11).

(11)

R ¹¹ and R ¹² are each independently hydrogen or a methyl group, R ¹³ and R ¹⁴ are each independently hydrogen or a C 1 to C 3 alkyl group, L ¹ and L ⁵ are each independently -C (= O ) -, -C (= O) O-, -OC (= O) -, -O- or -C (= O) NH-, L ² and L ⁶ are each independently substituted or unsubstituted C1 A substituted or unsubstituted C3 to C20 cycloalkylene group, a substituted or unsubstituted C6 to C20 arylene group, or a substituted or unsubstituted C3 to C20 heterocyclic group, x, y, c, and d And M is an alkali metal such as lithium, sodium, potassium, rubidium, or cesium, and k, l, m, and n mean molar ratios of the respective units.

For example, in formula (11), k + 1 + m + n = 1. Also, for example, 0.1? (K + 1)? 0.5, 0.4? M? 0.85, and 0.001? N? 0.2, for example, 0.1? K? 0.5 and 0?

For example, in Formula 11, x = y = 0, L ⁵ is -C (= O) NH-, L ⁶ is a C1 to C10 alkylene group, and c = d = 1.

The degree of substitution of the alkali metal (M ⁺ ) in the acrylic copolymer may be 0.5 to 1.0 with respect to (k + n), and may be, for example, 0.6 to 0.9 or 0.7 to 0.9. When the degree of substitution of the alkali metal satisfies the above range, the acrylic copolymer and the separation membrane 10 including the acrylic copolymer may exhibit excellent adhesion, heat resistance and oxidation resistance.

The acrylic copolymer may further include other units in addition to the units described above. For example, the acrylic copolymer may further include a unit derived from an alkyl (meth) acrylate, a unit derived from a diene, a unit derived from a styrene, an ester group containing unit, a carbonate group containing unit, or a combination thereof can do.

The acrylic copolymer may be in various forms such as an alternating polymer in which the units are alternately distributed, a random polymer randomly distributed, or a graft polymer in which some structural units are grafted.

The weight average molecular weight of the acrylic copolymer may be 200,000 to 700,000, for example, 200,000 to 600,000, or 300,000 to 600,000. When the weight average molecular weight of the acrylic copolymer satisfies the above range, the acrylic copolymer and the separation membrane 10 including the acrylic copolymer can exhibit excellent adhesion, heat resistance, air permeability and oxidation resistance. The weight average molecular weight may be an average molecular weight in terms of polystyrene measured by gel permeation chromatography.

The glass transition temperature of the acrylic copolymer may be 200 ° C to 280 ° C, for example, 210 ° C to 270 ° C, or 210 ° C to 260 ° C. When the glass transition temperature of the acrylic copolymer satisfies the above range, the acrylic copolymer and the separation membrane 10 including the acrylic copolymer can exhibit excellent adhesion, heat resistance, air permeability and oxidation resistance. The glass transition temperature may be a value measured by differential scanning calorimetry.

The acrylic copolymer may be produced by various known methods such as emulsion polymerization, suspension polymerization, bulk polymerization, solution polymerization, or bulk polymerization.

The acrylic copolymer may be contained in an amount of 1 to 30 wt%, for example 1 to 20 wt%, or 1 to 15 wt%, or 1 to 10 wt%, based on the heat resistant layer 30. [ % ≪ / RTI > by weight. When the acrylic copolymer is contained in the heat resistant layer 30 in the above range, the separator 10 can exhibit excellent heat resistance, adhesion, air permeability, and oxidation resistance.

On the other hand, the heat resistant layer 30 may further include a crosslinking binder having a crosslinking structure in addition to the acrylic copolymer. 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 30 may further include a non-crosslinked binder in addition to the acrylic copolymer. The non-crosslinked binder may be, for example, a vinylidene fluoride-based polymer, polymethyl methacrylate, polyacrylonitrile, polyvinyl pyrrolidone, polyvinyl acetate, polyethylene-vinyl acetate copolymer, polyethylene oxide, cellulose acetate, cellulose Cellulose acetate propionate, cyanoethylpullulan, cyanoethylpolyvinyl alcohol, cyanoethylcellulose, cyanoethyl sucrose, pullulan, carboxymethylcellulose, acrylonitrile-styrene-butadiene copolymer or the like But is not limited thereto.

The vinylidene fluoride-based polymer may specifically be a homopolymer containing only vinylidene fluoride monomer-derived units, or a copolymer of vinylidene fluoride-derived units and other monomer-derived units. The copolymer may specifically be a unit derived from vinylidene fluoride and at least one unit derived from chlorotrifluoroethylene, trifluoroethylene, hexafluoropropylene, ethylene tetrafluoride and ethylene monomer, It is not. For example, the copolymer may be a polyvinylidene fluoride-hexafluoropropylene (PVdF-HFP) copolymer comprising a unit derived from a vinylidene fluoride monomer and a unit derived from a hexafluoropropylene monomer.

As an example, the non-crosslinked binder may comprise a polyvinylidene fluoride (PVdF) homopolymer, a polyvinylidene fluoride-hexafluoropropylene (PVdF-HFP) copolymer, or a combination thereof. In this case, the adhesion between the porous substrate 20 and the heat resistant layer 30 is improved, and the stability of the separation membrane 10 and the electrolyte impregnability are improved, so that the high rate charge / discharge characteristics of the battery can be improved.

The heat resistant layer 30 may have a thickness of about 0.01 to 20 占 퐉 and may have a thickness within the range of about 1 占 퐉 to 10 占 퐉 or about 1 占 퐉 to 5 占 퐉 or 1 占 퐉 to 3 占 퐉 .

The ratio of the thickness of the heat-resistant layer 30 to the thickness of the porous substrate 20 may be 0.05 to 0.5, and may be, 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 10 including the porous substrate 20 and the heat resistant layer 30 can exhibit excellent air permeability, heat resistance, adhesion, and the like.

The secondary battery separator 10 according to one embodiment has excellent heat resistance. Specifically, the separation membrane 10 may have a shrinkage ratio at high temperature of 5% or less, or 4% or less. For example, the shrinkage percentage in the longitudinal direction and in the transverse direction of the separator 10 measured after the separation membrane 10 is left at 150 ° C for 60 minutes may be 5% or less, or 4% or less, respectively.

Generally, when the heat resistant layer 30 is thick in the separator 10, the shrinkage at high temperature tends to be low. However, the separator 10 according to one embodiment can achieve a high temperature shrinkage ratio of 5% or less, even though the thickness of the heat resistant layer 30 is 1 탆 to 5 탆, or 1 탆 to 3 탆.

In addition, the secondary battery separator 10 according to an embodiment can maintain a stable shape without being broken or deformed even at a high temperature of 200 ° C or more, for example, 200 ° C to 250 ° C.

The secondary battery separator 10 according to one embodiment may exhibit excellent air permeability and may have an air permeability value of, for example, less than 200 sec / 100cc, for example, 190 sec / 100cc or less, or 180 sec / 100cc or less . That is, it may have an air permeability value of less than 40 sec / 100cc 占 1 占 퐉 per unit thickness, for example, 30 sec / 100cc 占 1 占 퐉 or less, or 25 sec / 100cc 占 1 占 퐉 or less. Here, the air permeability means the time (in seconds) taken for 100 cc of air to pass through the unit thickness of the separator. The air permeability per unit thickness can be obtained by dividing the air permeability of the membrane by the thickness.

The secondary battery separator 10 according to one embodiment can be manufactured by various known methods. For example, the secondary battery separator 10 may be formed by applying a composition for forming a heat resistant layer on one side or both sides of the porous substrate 20 and drying the same.

The composition for forming the heat resistant layer may include the acrylic copolymer, the alkali metal, the filler, and the solvent. The solvent is not particularly limited as long as it can dissolve or disperse the acrylic copolymer and the filler. In one embodiment, the solvent can be water-based daily, including water, alcohol, or a combination thereof, and is advantageous in that it is environmentally friendly.

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 10 may be manufactured by a method such as lamination or coextrusion in addition to the above-described method.

Hereinafter, a lithium secondary battery including the above-described secondary battery separator 10 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, 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 50 may be the same as the binder and the conductive material used in the anode 40 described above.

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.

Synthetic example : Preparation of Acrylic Copolymer

Synthetic example  One

(9600 g), acrylic acid (45.00 g, 0.62 mol), ammonium persulfate (0.54 g, 2.39 mmol, 1500 ppm based on the monomer), 2- Acrylamide-2-methylpropanesulfonic acid (5.00 g, 0.02 mol) and a 5N aqueous sodium hydroxide solution (0.8 equivalents based on the total amount of acrylic acid and 2-acrylamido-2-methylpropanesulfonic acid) , The internal pressure was reduced to 10 mmHg and the internal pressure was returned to normal pressure with nitrogen was repeated three times, and then acrylonitrile (50.00 g, 0.94 mol) was added.

After reacting for 18 hours while controlling the temperature of the reaction solution to be stabilized between 65 ° C and 70 ° C, ammonium persulfate (0.23 g, 1.00 mmol, 630 ppm based on the monomer) was added and then the temperature was raised to 80 ° C And reacted again for 4 hours. After cooling to room temperature, the pH of the reaction solution is adjusted to 7 to 8 using 25% aqueous ammonia solution.

In this manner, poly (acrylic acid-co-acrylonitrile-co-2-acrylamido-2-methylpropanesulfonic acid) sodium salt was prepared. The molar ratio of acrylic acid, acrylonitrile, and 2-acrylamido-2-methylpropanesulfonic acid is 39: 59: 2. About 10 mL of the reaction solution (reaction product) was taken out and the nonvolatile component was measured to be 9.0% (theoretical value: 10%).

Synthetic example  2

Except that acrylic acid (40 g, 0.56 mol), acrylonitrile (50 g, 0.94 mol) and 2-acrylamido-2-methylpropanesulfonic acid (10 g, 0.05 mol) An acrylic copolymer was prepared in the same manner. The molar ratio of acrylic acid, acrylonitrile, and 2-acrylamido-2-methylpropanesulfonic acid is 36: 61: 3. The non-volatile component of the reaction solution was 9.0% (theoretical value: 10%).

Synthetic example  3

Except that acrylic acid (35 g, 0.49 mol), acrylonitrile (50 g, 0.94 mol) and 2-acrylamido-2-methylpropanesulfonic acid (15 g, 0.07 mol) To prepare an acrylic copolymer. The molar ratio of acrylic acid, acrylonitrile, and 2-acrylamido-2-methylpropanesulfonic acid is 32: 63: 5. The non-volatile component of the reaction solution was 9.0% (theoretical value: 10%).

Synthetic example  4

The same procedure as described in Preparation Example 1 was repeated except that acrylic acid (30 g, 0.42 mol), acrylonitrile (50 g, 0.94 mol) and 2-acrylamido-2-methylpropanesulfonic acid (20 g, To prepare an acrylic copolymer. The molar ratio of acrylic acid, acrylonitrile, and acrylamido-2-methylpropanesulfonic acid is 28: 65: 7. The non-volatile component of the reaction solution was 9.0% (theoretical value: 10%).

Synthetic example  5

The same procedure as in Synthesis Example 1 was repeated except for using acrylic acid (32 g, 0.49 mol), acrylonitrile (60 g, 1.13 mol) and 2-acrylamido-2-methylpropanesulfonic acid (5 g, To prepare an acrylic copolymer. The molar ratio of acrylic acid, acrylonitrile, and 2-acrylamido-2-methylpropanesulfonic acid is 30: 69: 1. The non-volatile component of the reaction solution was 9.0% (theoretical value: 10%).

Synthetic example  6

The same procedure as in Synthesis Example 1 (1) was repeated except that acrylic acid (30 g, 0.42 mol), acrylonitrile (60 g, 1.13 mol) and 2-acrylamido- To prepare an acrylic copolymer. The molar ratio of acrylic acid, acrylonitrile, and 2-acrylamido-2-methylpropanesulfonic acid is 26: 71: 3. The non-volatile component of the reaction solution was 9.0% (theoretical value: 10%).

Synthetic example  7

The same procedure as described in Preparation Example 1 was repeated except for using acrylic acid (25 g, 0.35 mol), acrylonitrile (60 g, 1.13 mol) and 2-acrylamido-2-methylpropanesulfonic acid (15 g, To prepare an acrylic copolymer. The molar ratio of acrylic acid, acrylonitrile, and 2-acrylamido-2-methylpropanesulfonic acid is 22: 73: 5. The non-volatile component of the reaction solution was 9.0% (theoretical value: 10%).

Synthetic example  8

Except that acrylic acid (20 g, 0.28 mol), acrylonitrile (60 g, 1.13 mol) and 2-acrylamido-2-methylpropanesulfonic acid (20 g, 0.10 mol) To prepare an acrylic copolymer. The molar ratio of acrylic acid, acrylonitrile, and 2-acrylamido-2-methylpropanesulfonic acid is 18: 75: 7. The non-volatile component of the reaction solution was 9.0% (theoretical value: 10%).

compare Synthetic example  One

Acrylic acid (50 g, 0.69 mol) and acrylonitrile (50 g, 0.94 mol) and that 2-acrylamido-2-methylpropanesulfonic acid was not used To prepare an acrylic copolymer. The molar ratio of acrylic acid and acrylonitrile is 42:58. The non-volatile component of the reaction solution was 9.0% (theoretical value: 10%).

compare Synthetic example  2

Acrylic acid (50 g, 0.69 mol) and 2-acrylamido-2-methylpropane sulfonic acid (50 g, 0.24 mol) were used and acrylonitrile was not used To prepare an acrylic copolymer. The molar ratio of acrylic acid and acrylamido-2-methylpropanesulfonic acid is 74:26. The non-volatile component of the reaction solution was 9.0% (theoretical value: 10%).

compare Synthetic example  3

An acrylic copolymer was prepared in the same manner as in Synthesis Example 1, except that an aqueous solution of sodium hydroxide was not used.

Table 1 below shows the molar ratios, weight average molecular weight and glass transition temperature of each monomer of the acrylic copolymer prepared in Synthesis Examples 1 to 8 and Comparative Synthesis Examples 1 to 3.

Monomer mole ratio Weight average molecular weight
(g / mol) Glass transition temperature (캜) AA AN AMPS Synthesis Example 1 39 59 2 310,000 280 Synthesis Example 2 36 61 3 302,000 277 Synthesis Example 3 32 63 5 304,000 275 Synthesis Example 4 28 65 7 311,000 271 Synthesis Example 5 30 69 One 285,000 265 Synthesis Example 6 26 71 3 298,000 263 Synthesis Example 7 22 73 5 305,000 232 Synthesis Example 8 18 75 7 314,000 260 Comparative Synthesis Example 1 42 58 - 320,000 278 Comparative Synthesis Example 2 74 - 26 293,000 305 Comparative Synthesis Example 3 39 59 2 161,000 98

In Table 1, AA is acrylic acid, AN is acrylonitrile, and AMPS is 2-acrylamido-2-methylpropanesulfonic acid. The glass transition temperature is a value measured by differential scanning calorimetry.

Example : Preparation of separator for secondary battery

Example  1-1

The acrylic polymer (10 wt% in distilled water) and boehmite (AOH60, average particle diameter 600 nm) manufactured in Synthesis Example 1 were added to a water solvent at a mass ratio of 1:20, And water was added thereto so that the total solid content was 20% by weight to prepare a composition for forming a heat resistant layer. This was coated on the cross section of a polyethylene porous substrate having a thickness of 12.5 占 퐉 (SK Corporation, air permeability: 113 sec / 100 cc, puncture strength: 360 kgf) to a thickness of 3 占 퐉 by die coating method and then dried at 70 占 폚 for 10 minutes, A separator was prepared.

Example  1-2

A separator for a secondary battery was prepared in the same manner as in Example 1-1, except that the acrylic polymer prepared in Synthesis Example 1 and boehmite were added in a weight ratio of 1:40.

Example  1-3

A mixture of 75 wt% of a filler (boehmite AOH 60, average particle diameter: 600 nm) and 25 wt% of boehmite (Nabaltec 200SM, average particle size: 350 nm) The separator for a secondary battery was prepared in the same manner as in Example 1-1, except that the filler was added at a weight ratio of 1:20.

Example  1-4

A polyacrylic dispersant corresponding to boehmite (Nabaltec AOH60, average particle diameter: 600 nm) and 1.0 wt% of the boehmite was added to a water solvent and milled at 25 DEG C for 30 minutes to prepare an inorganic dispersion of 25 wt% first . The acrylic polymer of Synthesis Example 1 was added to the inorganic dispersion solution so that the mass ratio of the acrylic polymer of Synthesis Example 1 to the boehmite ratio was 1:20, and water was added so that the total solid content was 20% by weight, A separator for a secondary battery was prepared in the same manner as in Example 1-1.

Example  2

A separator for a secondary battery was prepared in the same manner as in Example 1-1, except that the acrylic polymer of Synthesis Example 2 was used instead of the acrylic polymer of Synthesis Example 1.

Example  3

A separator for a secondary battery was prepared in the same manner as in Example 1-1, except that the acrylic polymer of Synthesis Example 3 was used instead of the acrylic polymer of Synthesis Example 1.

Example  4

A separator for a secondary battery was prepared in the same manner as in Example 1-1, except that the acrylic polymer of Synthesis Example 4 was used instead of the acrylic polymer of Synthesis Example 1.

Example  5

A separator for a secondary battery was prepared in the same manner as in Example 1-1, except that the acrylic polymer of Synthesis Example 5 was used instead of the acrylic polymer of Synthesis Example 1.

Example  6

A separator for a secondary battery was prepared in the same manner as in Example 1-1, except that the acrylic polymer of Synthesis Example 6 was used instead of the acrylic polymer of Synthesis Example 1.

Example  7

A separator for a secondary battery was prepared in the same manner as in Example 1-1, except that the acrylic polymer of Synthesis Example 7 was used instead of the acrylic polymer of Synthesis Example 1.

Example  8

A separator for a secondary battery was prepared in the same manner as in Example 1-1, except that the acrylic polymer of Synthesis Example 8 was used instead of the acrylic polymer of Synthesis Example 1.

Comparative Example  One

A separator for a secondary battery was prepared in the same manner as in Example 1-1, except that the acrylic polymer of Comparative Synthesis Example 1 was used instead of the acrylic polymer of Synthesis Example 1.

Comparative Example  2

A separator for a secondary battery was prepared in the same manner as in Example 1-1, except that the acrylic polymer of Comparative Synthesis Example 2 was used in place of the acrylic polymer of Synthesis Example 1.

Comparative Example  3

A separator for a secondary battery was prepared in the same manner as in Example 1-1, except that the acrylic polymer of Comparative Synthesis Example 3 was used instead of the acrylic polymer of Synthesis Example 1.

Evaluation example  1: Airflow

The time (seconds) taken for the air to pass through 100 cc was measured for the secondary battery separating membranes of Examples 1 to 8 and Comparative Examples 1 to 3 using an air permeability measuring device (Asahi Seiko Co., Ltd., EG01-55-1MR) The results are shown in Table 2 below.

Evaluation example  2: Heat shrinkage

The separation membranes for secondary batteries of Examples 1 to 8 and Comparative Examples 1 to 3 were cut out to a size of 8 cm x 8 cm and samples were prepared. A square having a size of 5 cm x 5 cm was drawn on the surface of the sample, and the sample was sandwiched between paper or alumina powder. The sample was taken out of the oven for one hour at room temperature, The shrinkage ratio of each of the direction (MD) and the longitudinal direction (TD) is calculated. The results are shown in Table 2 below.

Evaluation example  3: Thermal break

The separator for secondary batteries of Examples 1 to 8 and Comparative Examples 1 to 3 was cut into a size of 5 cm x 5 cm to prepare a sample. The sample was placed on a corrugated paperboard having a hole of 4 cm x 4 cm in the center using a polyimide film, and then the sample was placed in each oven heated to 200 ° C, 230 ° C, and 250 ° C. After 10 minutes, samples were taken out of the oven to confirm the breakage, and the results are shown in Table 2 below. When it is broken, it is marked with O. If it is not broken, it is marked with X.

The mole ratio of each monomer in the acrylic copolymer The solid content (% by weight) of the heat resistant layer- The mass ratio of the acrylic copolymer to the boehmite Heat resistance layer thickness (탆) Membrane ventilation rate (sec / 100cc) Heat Shrinkage Rate of Membrane (%) Thermal break AA AN AMPS 200 ℃ 230 ℃ 250 ℃ Example 1-1 39 59 2 20 1:20 3 145 MD: 5
TD: 3 X X X Examples 1-2 39 59 2 20 1:40 3 133 MD: 3
TD: 2 X X O Example 1-3 39 59 2 20 1:20 3 135 MD: 2
TD: 2 X X X Examples 1-4 39 59 2 20 1:20 3 146 MD: 4
TD: 3 X X X Example 2 36 61 3 20 1:20 3 151 MD: 4
TD: 3 X X X Example 3 32 63 5 20 1:20 3 137 MD: 4
TD: 3 X X X Example 4 28 65 7 20 1:20 3 143 MD: 4
TD: 3 X X X Example 5 30 69 One 20 1:20 3 142 MD: 4
TD: 3 X X X Example 6 26 71 3 20 1:20 3 152 MD: 4
TD: 3 X X X Example 7 22 73 5 20 1:20 3 143 MD: 4
TD: 3 X X X Example 8 18 75 7 20 1:20 3 138 MD: 4
TD: 3 X X X Comparative Example 1 42 58 - 20 1:20 3 141 MD: 8
TD: 7 X O O Comparative Example 2 74 - 26 20 1:20 3 158 MD: 15
TD: 13 O O O Comparative Example 3 39 59 2 20 1:20 3 171 MD: 25
TD: 22 O O O

Referring to Table 2, the separator prepared in the Example exhibits excellent air permeability of less than 152 sec / 100 cc, exhibits a shrinkage ratio of less than 5% at 150 ° C, and does not break even at 200 ° C to 250 ° C, And the thermal stability is realized. On the other hand, the separator of Comparative Example 1 had a remarkably high heat shrinkage rate after being left at 150 ° C for 1 hour and a problem of breaking at a temperature of 200 ° C or more, so that the heat resistance at high temperature was poor, and the separator of Comparative Examples 2 to 3 had poor air permeability The heat shrinkage rate after leaving at 150 ° C for 1 hour is remarkably high, and it can be seen that a problem of breaking at a temperature of 200 ° C or more has occurred .

Production Examples 1-1 to 1-4 and Production Examples 2 to 8 and Comparative Production Examples 1 to 3 Production 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 jellyroll electrode assembly in the form of a winding was prepared between the prepared anode and cathode through the separator prepared in the above Examples and Comparative Examples. 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  4: Battery life characteristics

The capacity recovery rates according to the number of cycles were evaluated for the batteries of Production Example 1-1 and Comparative Production Examples 1 and 2 to which the separator prepared in Example 1-1 and Comparative Examples 1 and 2 were applied. Respectively.

Charge: CC 1.0C to 4.4V, CV to 0.01C

Discharge: CC 1.0C to 2.75V

Referring to FIG. 3, it can be seen that the life characteristics of the battery manufactured in Production Example 1-1 are remarkably excellent.

Evaluation example  5: Characteristic of battery

The capacity recovery rates according to the C-rate were evaluated for the cells of Production Example 1-1 and Comparative Production Examples 1 and 2 to which the separator prepared in Example 1-1 and Comparative Examples 1 and 2 were applied, Is shown in Fig.

Charge: CC 1.0C to 4.4V, CV to 0.01C

Discharge: CC 1.0 C, 2.0 C, 3.0 C to 2.75 V

Referring to FIG. 4, it can be seen that the rate characteristics of the battery produced in Production Example 1-1 are remarkably excellent.

Evaluation example  6: Linear main dictionary misconduct  (Linear Sweep Voltammetry , LSV ) evaluation

For oxidation resistance evaluation of the binder, with the Synthesis Example 1 and Comparative Synthesis Example 1 and the acrylic binder prepared in 2, and a polyvinylidene fluoride binder (Solvay, Solef ^® 5130), carbon materials (SFG6) 90% by weight And 10 wt% of the binder were coated on a platinum (Pt) electrode to prepare an electrode for oxidation resistance measurement. The oxidation resistance test was conducted using a solution obtained by dissolving 1.3M LiPF ₆ in a solvent mixture of ethylene carbonate / ethyl methyl carbonate / diketyl carbonate in a weight ratio of 30/50/20. The electric potential was varied at 30 DEG C under the condition of 0.005 V / sec to derive a current-potential curve. The results are shown in Fig.

Referring to FIG. 5, the dislocation is changed at 4.65 V in Synthesis Example 1, 4.61 V in Comparative Synthesis Example 1, 4.64 V in Comparative Synthesis Example 2, and 4.63 V in polyvinylidene fluoride binder, It seems to be changing. The change in dislocation indicates that the binder is decomposed. Therefore, it can be confirmed from the above results that the binder of Synthesis Example 1 is excellent in oxidation resistance.

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)

And a heat-resistant layer disposed on at least one side of the porous substrate, wherein the heat-resistant layer includes an acrylic copolymer, an alkali metal, and a filler,
The acrylic copolymer includes a unit derived from (meth) acrylate or (meth) acrylic acid, a cyano group-containing unit, and a sulfonate group-containing unit. 2. The separator for a secondary battery according to claim 1, wherein the units derived from (meth) acrylate or (meth) acrylic acid are represented by the following formulas (1), (2)
[Formula 3] &lt; EMI ID =

In the above Chemical Formulas 1 to 3, R ¹ , R ² , and R ³ are each independently hydrogen or a methyl group, and in Formula 2, M is an alkali metal. The separator for a secondary battery according to claim 1, wherein the cyano group-containing unit is represented by the following formula (4)
[Chemical Formula 4]

In Formula ^4, R 4 is hydrogen or C1 to C3 alkyl group, L ¹ is -C (= O) -, -C (= O) O-, -OC (= O) -, -O-, or - C (= O) NH-, x is an integer of 0 to 2, L ² is a substituted or unsubstituted C1 to C10 alkylene group, a substituted or unsubstituted C3 to C20 cycloalkylene group, a substituted or unsubstituted C6 Or a substituted or unsubstituted C3 to C20 heterocyclic group, and y is an integer of 0 to 2. The separator for a secondary battery according to claim 1, wherein the sulfonate group-containing unit is represented by the following formula (5), (6), (7)
[Chemical Formula 5] &lt; EMI ID =

R ⁵ , R ⁶ , and R ⁷ are each independently hydrogen or a C 1 to C 3 alkyl group; L ³ , L ⁵ , and L ⁷ are each independently -C (= O) -, (= O) O-, -OC (= O) -, -O-, or -C (= O) NH-, L ⁴ , L ⁶ , and L ⁸ are each independently substituted or unsubstituted A substituted or unsubstituted C3 to C20 cycloalkylene group, a substituted or unsubstituted C6 to C20 arylene group, or a substituted or unsubstituted C3 to C20 heterocyclic group, and a, b, c, d , e, and f are each independently an integer of 0 to 2, and M 'in formula (6) is an alkali metal. The separator for a secondary battery according to claim 1, wherein the acrylic copolymer contains the sulfonate group-containing unit in an amount of 0.1 mol% to 20 mol%. The acrylic copolymer according to claim 1, wherein in the acrylic copolymer,
The unit derived from (meth) acrylate or (meth) acrylic acid is contained in an amount of 10 mol% to 70 mol%
The cyano group-containing unit is contained in an amount of 30 mol% to 85 mol%
And the sulfonate group-containing unit is contained in an amount of 0.1 mol% to 20 mol%. The separator for a secondary battery according to claim 1, wherein the weight average molecular weight of the acrylic copolymer is 200,000 to 700,000. The separator for a secondary battery according to claim 1, wherein the acrylic copolymer has a glass transition temperature of 200 ° C to 280 ° C. The separator for a secondary battery according to claim 1, wherein the acrylic copolymer in the heat resistant layer is 1 wt% to 30 wt%. The separator for a secondary battery according to claim 1, wherein the alkali metal is contained in an amount of 1% by weight to 40% by weight based on the total weight of the alkali metal and the acrylic copolymer. The separator for a secondary battery according to claim 1, wherein the filler is contained in an amount of 50 wt% to 99 wt% with respect to the heat resistant layer. The filler according to claim 1, wherein the filler is 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 separator for a secondary battery according to claim 1, wherein the heat resistant layer has a thickness of 1 탆 to 5 탆. The separator for a secondary battery according to claim 1, wherein the secondary battery separator has a shrinkage ratio of 5% or less in the longitudinal direction and the transverse direction, respectively, after the separation membrane for secondary battery is left at 130 ° C to 170 ° C for 20 to 70 minutes. A lithium secondary battery comprising a separator for a secondary battery according to any one of claims 1 to 14, which is positioned between an anode, a cathode, and the anode and the cathode.

Images