KR20180063649A - Separator for rechargeable battery and rechargeable battery including the same - Google Patents

Abstract

The present invention relates to a separator for a rechargeable battery, a method for manufacturing the separator for a rechargeable battery, and a lithium rechargeable battery including the separator having excellent ionic conductivity. The separator for a rechargeable battery comprises: a porous substrate; and a binder layer disposed on at least one surface of the porous substrate. The binder layer includes latex and an acrylate compound including a repeating unit represented by chemical formula 1.

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 [0002]

A separator for a secondary battery, and a lithium secondary battery including the separator.

The separator 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.

BACKGROUND ART [0002] In recent years, there has been a demand for a light-weight and miniaturization of a battery and a high-output large-capacity battery for use in an electric automobile.

One embodiment provides a separator for a secondary battery having excellent adhesive properties, cycle characteristics, and ionic conductivity.

Another embodiment provides a method of manufacturing the separator.

Another embodiment provides a secondary battery comprising the separator.

According to one embodiment, there is provided a separator for a secondary battery comprising a porous substrate and a binder layer disposed on at least one surface of the porous substrate, wherein the binder layer comprises a latex comprising a repeating unit represented by the following formula Lt; / RTI >

[Chemical Formula 1]

The latex comprising the repeating unit represented by Formula 1 may be a polyvinylidene fluoride latex.

The polyvinylidene fluoride latex may be an aqueous polyvinylidene fluoride latex.

The binder layer has a core-shell structure, the core includes a latex containing a repeating unit represented by the formula (1), and the shell may include the acrylate compound.

The core may have a particle size of 1 nm to 200 nm.

The core-shell structure may be a latex core comprising the repeating unit represented by the formula (1) and a structure in which the core surface is modified with an acrylate group.

The binder layer may include a latex containing a repeating unit represented by the formula (1) and two types of acrylate compounds having different glass transition temperatures.

The acrylate compound may include an acrylate compound having a glass transition temperature of -80 ° C to -20 ° C and an acrylate compound having a glass transition temperature of 30 ° C to 90 ° C.

The binder layer may be a single layer.

The binder layer may contain 50% by weight to 80% by weight of the latex containing the repeating unit represented by the formula (1) and 20% by weight to 50% by weight of the acrylate compound.

Wherein the acrylate compound comprises 10 to 20% by weight of an acrylate compound having a glass transition temperature of -80 캜 to -20 캜, and 80 to 90% by weight of an acrylate compound having a glass transition temperature of 30 캜 to 90 캜. 90% by weight.

According to another embodiment, there is provided a process for preparing a separator for a secondary battery, comprising the steps of preparing a porous substrate and coating a composition comprising a latex and an acrylate compound containing a repeating unit represented by the following formula 1 on the porous substrate ≪ / RTI >

[Chemical Formula 1]

The composition may have a core-shell structure, the core may include a latex containing a repeating unit represented by the formula (1), and the shell may include the acrylate compound.

The composition may include a latex containing the repeating unit represented by the formula (1) and two types of acrylate compounds having different glass transition temperatures.

According to another embodiment, there is provided a lithium secondary battery comprising a positive electrode, a negative electrode, and the separator positioned between the positive electrode and the negative electrode.

The battery characteristics of the lithium secondary battery can be improved by providing the separator with improved adhesion, cycle characteristics and ionic conductivity.

FIG. 1 is a view showing a separator 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 schematic diagram of a binder having a core-shell structure according to one embodiment.
Figure 4 is a schematic diagram showing a binder according to one embodiment and latex and acrylate compounds located on the binder.

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 separator for a secondary battery according to one embodiment.

Referring to FIG. 1, a separator 10 for a secondary battery according to an embodiment includes a porous substrate 20 and a binder layer 30 disposed on one or both surfaces of the porous substrate 20.

The porous substrate 20 may have a plurality of pores and may be a porous substrate that can be used in an electrochemical device. Examples of the porous substrate 20 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, Polyetherimide, polyetherimide, polybenzimidazole, polyether sulfone, polyphenylene oxide, cyclic olefin copolymer, polyphenylene sulfide, polyethylene naphthalate, glass fiber, tetrafluoroethylene (TEFLON) And polytetrafluoroethylene (PTFE), or a polymer membrane formed of a mixture of two or more thereof. Specifically, the porous substrate 20 may be a polyolefin-based substrate, and the polyolefin-based substrate is excellent in a shut down function and contributes to improvement of the safety of the battery. The polyolefin-based substrate may be selected from the group consisting of, 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. Further, 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 may have a thickness of about 1 占 퐉 to 40 占 퐉 and may 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, and 5 占 퐉 to 10 占 퐉.

The binder layer (30) comprises a latex and an acrylate compound containing a repeating unit represented by the following formula (1).

[Chemical Formula 1]

Conventionally, a polyvinylidene fluoride copolymer, which is not a latex, was dissolved in a solvent to form a coating layer on a porous substrate, or a coating layer was formed using an acrylate latex to prepare a separator. Separators made of polyvinylidene fluoride copolymer It is difficult to apply an adhesive force to an electrode at room temperature. Since the binder composition must be dissolved and coated, the process cost is high. However, an excessive amount of the acrylate latex causes a deterioration in the ionic conductivity, which shortens the life of the battery.

The latex comprising the repeating unit represented by Formula 1 may be a polyvinylidene fluoride latex, for example, an aqueous polyvinylidene fluoride latex. Conventionally, non-aqueous polyvinylidene fluoride is generally used as a latex in a binder used in a separator. However, in one embodiment, by using an aqueous polyvinylidene fluoride latex, wet adhesion can be facilitated. In manufacturing a basic polymer cell, the cell is deformed due to shrinkage and expansion of the electrode plate during its lifetime, thereby preventing deformation of the cell and securing the long-life characteristics. In order to overcome this technical problem, the material is coated on the separator, and the adhesion force between the material to be coated and the separator is referred to as bond strength. When a step of attaching an electrode plate and a separator is required for manufacturing a stack cell, it is necessary to secure the adhesive force in a state in which the electrolyte solution is not immersed. The adhesive force is called a dry adhesive force. In addition, to prevent cell deformation during cell durability and cell lifetime after immersing the electrolyte solution, the electrode plate and separator are bonded again. This adhesion force is called wet adhesion force.

For example, the binder layer may have a core-shell structure, the core may include a latex containing a repeating unit represented by the formula (1), and the shell may include the acrylate compound. Since the binder layer has a core-shell structure, compared with the binder layer having no core-shell structure, ion conductivity by swelling of the electrolyte in the core structure of PVDF is improved while maintaining the binding force of acrylate, Can be improved.

The core may have a particle size of 1 nm to 200 nm. When the core has a particle diameter of less than 1 nm, surface modification with acrylate is difficult, and when the core has a particle diameter exceeding 200 nm, it is difficult to secure a desired wet adhesion with the pole plate.

As shown in FIG. 3, the core-shell structure may be a structure in which the latex core containing the repeating unit represented by Formula 1 and the core surface are modified with an acrylate group.

For example, as shown in FIG. 4, the binder layer may include a latex containing a repeating unit represented by Formula 1 and two acrylate compounds having different glass transition temperatures. That is, the binder layer is composed of a latex containing the repeating unit represented by the formula (1), an acrylate compound having a high glass transition temperature of -80 ° C to -20 ° C and an acrylate compound having a low glass transition temperature of 30 ° C to 90 ° C Lt; / RTI > compounds.

By including the acrylate compound having a high glass transition temperature of 30 DEG C to 90 DEG C, dry binding becomes easier and the acrylate compound having a low glass transition temperature of -80 DEG C to -20 DEG C is contained, It becomes easier to make a connection with the apparatus. By coating the material having two glass transition temperatures, not only the processability of the separator coating can be secured, but also the cell manufacturing processability can be secured by improving the binding characteristics between the electrode plate and the separator in the production of the stack cell.

The binder layer may be a single layer rather than a multi-layer. In this case, since it is possible to secure both of the two properties (base binder and dry binder) by a single coating, there is an advantageous effect in terms of process cost.

The binder layer may contain 50 wt% to 80 wt% (for example, 60 wt% to 70 wt%) of the latex containing the repeating unit represented by Formula 1 and 20 wt% to 50 wt% 30% to 40% by weight). When the content of the acrylate compound is within the above range, the base adhesion strength and the dry adhesion strength are greatly increased, thereby ensuring fairness. However, when the content of the acrylate compound is out of the above range, the wet adhesion ability may be lowered.

For example, the acrylate compound may include 10 to 20% by weight of an acrylate compound having a glass transition temperature of -80 캜 to -20 캜 and 80% by weight of an acrylate compound having a glass transition temperature of 30 캜 to 90 캜 % To 90% by weight. In this case, as the content of the acrylate compound having a high glass transition temperature is increased, the dry adhesion force is improved and the processability of the battery is easily secured. However, only the acrylate compound having a high glass transition temperature is contained alone or an acrylate having a high glass transition temperature When the compound content is more than 90% by weight or less than 80% by weight based on the total amount of the acrylate compound, the base adhesion force is decreased, and the coating material may fall off from the base material when the separator is manufactured.

The binder layer may further include a filler.

The filler may be, for example, an inorganic filler, an organic filler, an organic 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 , 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 having a size of about 1 nm to 2000 nm, and may have a size of about 100 nm to 1000 nm within the range, and within the range of about 100 nm to 500 nm . Here, the size may be an average particle size or a long diameter. By using a filler having a size within the above range, appropriate strength can be given to the binder layer 30. The fillers may be used in a mixture of two or more different types or different sizes. By including the filler, the heat resistance is improved, and it is possible to further prevent the separator from being rapidly shrunk or deformed due to the temperature rise.

The acrylate compound may be a compound containing an acrylate group. For example, the acrylate compound may be selected from the group consisting of acrylic acid, methacrylic acid, alkyl acrylate, alkyl methacrylate, hydroxyalkyl acrylate, hydroxyalkyl methacrylate, carboxyalkyl acrylate, carboxyalkyl methacrylate, acryloyloxyalkyl Succinic acid, methacryloyloxyalkylsuccinic acid, acryloyloxyalkylphthalic acid, methacryloyloxyalkylphthalic acid, or a combination thereof, but is not limited thereto.

The acrylate compound may more specifically include methyl methacrylate, but is not limited thereto.

The binder layer may further include one or more kinds of binders.

The binder may further comprise, for example, a crosslinking binder having a crosslinking 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. For example, the crosslinking binder may have from 2 to 30 curable functional groups, within this range from 2 to 20 curable functional groups, and within this range from 3 to 15 curable functional groups.

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.

For example, the crosslinking binder may contain at least two vinyl groups, (meth) acrylate groups, epoxy groups, oxetane groups, ether groups, cyanate groups, isocyanate groups, hydroxyl groups, carboxyl groups, thiol groups, amino groups, Oligomers, and / or polymers comprising the same.

For example, the crosslinking binder can 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) (Meth) acrylate, trimethylolpropane tri (meth) acrylate, glycerin tri (meth) acrylate, trimethylolpropane tri (meth) acrylate, ) Acrylate, pentaerythritol tetra (meth) acrylate, diglycerin hexa (meth) acrylate, or a combination thereof.

For example, the crosslinking binder can be obtained by curing a monomer, an oligomer and / or a polymer 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 can be obtained by curing a monomer, oligomer and / or 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 crosslinking binder may have a weight average molecular weight of 50 g / mol to 80,000 g / mol, and may have a weight average molecular weight of 100 g / mol to 60,000 g / mol within the above range. By including a crosslinking binder having a weight average molecular weight in the above range, heat resistance can be secured.

The binder may further include, for example, a non-crosslinkable binder.

The non-crosslinked binder includes, for example, vinylidene fluoride polymers such as polyvinylidene fluoride (PVdF) homopolymer and polyvinylidene fluoride-hexafluoropropylene (PVdF-HFP) copolymer, polymethyl methacrylate, poly Polyvinyl pyrrolidone, polyvinyl acetate, polyethylene-vinyl acetate copolymer, polyethylene oxide, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethylpullulan, cyanoethylpolulan, Vinyl alcohol, cyanoethyl cellulose, cyanoethyl sucrose, pullulan, carboxymethyl cellulose, acrylonitrile-styrene-butadiene copolymer, or a combination thereof, but is not limited thereto.

The binder layer 30 may have a thickness of about 0.01 탆 to 20 탆 and may have a thickness of about 1 탆 to 10 탆 within the above range and have a thickness of about 1 탆 to 5 탆 within the above range .

Another embodiment of the present invention is a method for manufacturing a separator for a secondary battery, comprising the steps of preparing a porous substrate, and coating a composition comprising a latex and an acrylate compound containing the repeating unit represented by Formula 1 on the porous substrate to provide.

That is, the separator for a secondary battery can be formed, for example, by applying a composition for a binder layer to one surface or both surfaces of the porous substrate 20 and drying the same.

For example, the composition may have a core-shell structure, the core may include a latex comprising the repeating unit represented by Formula 1, and the shell may include the acrylate compound.

For example, the composition may include a latex including the repeating unit represented by Formula 1 and two acrylate compounds having different glass transition temperatures.

The composition for a binder layer includes a latex and an acrylate containing a repeating unit represented by the formula (1), and may further include the binder, filler, initiator, and / or solvent described above.

The initiator may be, for example, a photoinitiator, a thermal initiator, or a combination thereof. The photoinitiator may be used when curing by photopolymerization using ultraviolet rays or the like. Examples of the photoinitiator include diethoxyacetophenone, 2-hydroxy-2-methyl-1-phenylpropan-1-one, benzyldimethylketal, 1- hydroxycyclohexyl- Morpholine (4-thiomethylphenyl) propan-1-one; Benzoin ethers such as benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether and benzoin isobutyl ether; Benzophenone, methyl o-benzoylbenzoate, 4-phenylbenzophenone, 4-benzoyl-4'-methyldiphenylsulfuric acid, 4-benzoyl-N, Phenyloxy) ethyl] benzenethanaminium bromide, and (4-benzoylbenzyl) trimethylammonium chloride; Thioxanthones such as 2,4-diethylthioxanthone and 1-chloro-4-dichlorothioxanthone; 2,4,6-trimethylbenzoyldiphenylbenzoyloxide, etc. These may be used alone or in combination of two or more. The thermal initiator may be used when curing by thermal polymerization. As the thermal initiator, an organic peroxide free radical initiator such as diacyl peroxides, peroxyketals, ketone peroxides, hydroperoxides, dialkyl peroxides, peroxyesters and peroxydicarbonates can be used And there may be mentioned, for example, lauroyl peroxide, benzoyl peroxide, cyclohexanone peroxide, 1,1-bis (t-butylperoxy) -3,3,5-trimethylcyclohexane, Oxides, etc. may be used alone or in combination of two or more.

The solvent is not particularly limited as long as it can dissolve or disperse the above-mentioned binder and the filler described above. The solvent may be, for example, acetone, methyl ethyl ketone, ethyl isobutyl ketone, tetrahydrofuran, dimethyl formaldehyde, cyclohexane or mixtures thereof, but is not limited thereto.

The application may be, for example, spin coating, dip coating, bar coating, die coating, slit coating, roll coating, inkjet printing, and the like, 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 ° C to 120 ° C, and may be performed at a temperature of, for example, about 80 ° C to 100 ° C for about 5 seconds to 60 seconds, .

The curing may be performed by a method of photo-curing, thermosetting or a combination thereof. The photo-curing can be performed, for example, by irradiating ultraviolet (UV) light of 150 to 170 nm for 5 to 300 seconds. The thermal curing may be carried out at a temperature of, for example, 60 캜 to 120 캜 for 1 hour to 36 hours, for example, at a temperature of 80 캜 to 100 캜 for 10 hours to 24 hours.

The separator for a secondary battery may be manufactured by a method such as lamination, coextrusion or the like in addition to the above-described method.

The lithium secondary battery including the above-described separator for a secondary battery will be described below.

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 the separator and the electrolyte used. The lithium secondary battery 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, the lithium secondary battery 100 according to an embodiment includes an electrode assembly 60 and an electrode assembly 60 wound between the anode 40 and the cathode 50 with the separator 10 interposed therebetween. 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.

The cathode current collector may be aluminum (Al), nickel (Ni) or the like, but 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. More specifically, 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 may be used.

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 made of 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 (Cu), gold (Au), nickel (Ni), 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-like, 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 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 separator 10 is as described above.

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. Specific examples thereof may be selected from a carbonate-based solvent, an ester-based solvent, an ether-based solvent, a ketone-based solvent, an alcohol-based solvent and an aprotic solvent.

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 (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC) EC), propylene carbonate (PC), and butylene carbonate (BC) may be used. As the ester solvent, methyl acetate, ethyl acetate, n-propyl acetate, 1,1-dimethyl ethyl acetate, methyl propionate , Ethyl propionate,? -Butyrolactone, decanolide, valerolactone, mevalonolactone, caprolactone and the like can 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 nitriles such as dimethylformamide, and dioxolanes such as 1,3-dioxolane, sulfolanes, and the like can be used.

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.

The lithium secondary battery including the separator described above can be operated at a high voltage of 4.2 V or higher, and thus a high capacity lithium secondary battery can be realized without deteriorating the life characteristics.

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.

Separator  Produce

Example  One

An aqueous PVDF latex having a core-shell structure with a size of 200 nm and whose surface was modified with an acrylate group, 5 wt% of an acrylate having a glass transition temperature of -50 DEG C, and an acrylate having a glass transition temperature of 60 DEG C 28.5% by weight were added to a stirrer and stirred at 1500 rpm for 1 hour to prepare a slurry. The prepared slurry was coated on both sides by a gravure coating method on a separator of 9 mu m and hot air dried at 80 DEG C to prepare a separator having a thickness of 10 mu m.

Example  2

66.5% by weight of an aqueous PVDF latex (without core-shell structure) having a size of 200 nm, 5% by weight of an acrylate having a glass transition temperature of -50 DEG C and 28.5% by weight of an acrylate having a glass transition temperature of 60 DEG C And the mixture was stirred at 1500 rpm for 1 hour to prepare a slurry. The prepared slurry was coated on both sides by a gravure coating method on a separator of 9 mu m and hot air dried at 80 DEG C to prepare a separator having a thickness of 10 mu m.

Comparative Example  One

66.5% by weight of a non-aqueous PVDF latex having a core-shell structure having a size of 200 nm, 5% by weight of an acrylate having a glass transition temperature of -50 캜, and 28.5% by weight of an acrylate having a glass transition temperature of 60 캜, And the mixture was stirred at 1500 rpm for 1 hour to prepare a slurry. The prepared slurry was coated on both sides by a gravure coating method on a separator of 9 mu m and hot air dried at 80 DEG C to prepare a separator having a thickness of 10 mu m.

Comparative Example  2

A water-based PVDF latex having a core-shell structure with a size of 200 nm or an aqueous PVDF latex with a surface modified with HFP, 66.5% by weight of water-based PVDF latex having a glass transition temperature of -50 DEG C and 5% Was added to a stirrer and stirred at 1500 rpm for 1 hour to prepare a slurry. The prepared slurry was coated on both sides by a gravure coating method on a separator of 9 mu m and hot air dried at 80 DEG C to prepare a separator having a thickness of 10 mu m.

Comparative Example  3

66.5% by weight of a non-aqueous PVDF latex (without core-shell structure) having a size of 200 nm, 5% by weight of an acrylate having a glass transition temperature of -50 DEG C and 28.5% by weight of an acrylate having a glass transition temperature of 60 DEG C, Was placed in a stirrer and stirred at 1500 rpm for 1 hour to prepare a slurry. The prepared slurry was coated on both sides with a gravure coating method on a separator of 9 탆 and hot air dried at 80 캜 to prepare a separator having a thickness of 10 탆

Comparative Example  4

66.5% by weight of an aqueous PVDF latex (having no core-shell structure) having a size of 200 nm and 33.5% by weight of an acrylate having a glass transition temperature of 60 DEG C were added to a stirrer and stirred at 1500 rpm for 1 hour to prepare a slurry. The prepared slurry was coated on both sides by a gravure coating method on a separator of 9 mu m and hot air dried at 80 DEG C to prepare a separator having a thickness of 10 mu m.

Reference example  One

66.5% by weight of an aqueous PVDF latex (having no core-shell structure) having a size of 200 nm, 5% by weight of an acrylate having a glass transition temperature of 30 DEG C and 28.5% by weight of an acrylate having a glass transition temperature of 60 DEG C, And the mixture was stirred at 1500 rpm for 1 hour to prepare a slurry. The prepared slurry was coated on both sides by a gravure coating method on a separator of 9 mu m and hot air dried at 80 DEG C to prepare a separator having a thickness of 10 mu m.

evaluation

(1) Base adhesion

The substrate adhesion of the separator according to Example 1, Example 2, Comparative Example 1 to Comparative Example 4, and Reference Example 1 was evaluated.

The adhesive strength of the substrate was evaluated in the following manner.

The test was carried out in accordance with Clause 8 of Korean Industrial Standard KS-A-01107 (Test Method for Adhesive Tape and Adhesive Sheet). Specimens of 25 mm in width and 250 mm in length were prepared from the separators according to Example 1, Example 2, Comparative Examples 1 to 4 and Reference Example 1, and the test specimens were prepared by attaching tapes (nitto 31B) to the front and back surfaces . Then, using a pressing roller having a load of 2 kg, it was reciprocated once at a speed of 300 mm / min and pressed. After a lapse of 30 minutes from the pressing, one side of the evaluation specimen was turned 180 ° to peel off about 25 mm. The separator and one side of the tape were attached to the upper clip of the tensile strength device, And the load at the time of pulling off at a tensile speed of 60 mm / min was measured. The tensile strength machine was an Instron Series lX / s Automated materials Tester-3343.

The results are shown in Table 1 below.

(2) Ion conductivity

Ionic conductivities of the separators according to Example 1, Example 2, Comparative Examples 1 to 4, and Reference Example 1 were evaluated.

The ionic conductivity was evaluated by the following method.

(The separator was punched by the 2016 coin cell standard and placed between coin cells in the absence of an electrode plate. Ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) were mixed at a volume ratio of 3: 5: A coin cell was prepared by adding 1.15M LiPF ₆ to a mixed solvent and aging at room temperature for 24 hours. The impedance was measured using a Viologic VSP EIS (Electrochemical Impedance Spectroscopy) meter to calculate the conductivity The measurement conditions were measured at room temperature 25 ℃ and initial frequency was measured from 500KHZ to Final Frequency 1Hz.

The results are shown in Table 1 below.

(3) The lithium secondary battery  Performance evaluation

A lithium secondary battery was manufactured by the following method, and the lithium secondary battery was charged and discharged, and the adhesive force, the thickness change rate, and the capacity retention rate of the separator were evaluated.

LiCoO ₂ , polyvinylidene fluoride and carbon black were added to the N-methylpyrrolidone (NMP) solvent at a weight ratio of 96: 2: 2 to prepare a slurry. The slurry was applied to an aluminum (Al) thin film, dried and rolled to prepare a positive electrode.

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

The electrolytic solution was prepared by adding 1.15M LiPF ₆ to a mixed solvent of ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) in a volume ratio of 3: 5: 2.

A jelly roll type electrode assembly was prepared between the prepared positive electrode and negative electrode through the separator according to Example 1, Example 2, Comparative Examples 1 to 4, and Reference Example 1. Then, the electrode assembly was fixed to the case, and the electrolyte solution was injected and sealed to prepare a lithium secondary battery.

Then, a charge / discharge cycle test was carried out in which the lithium secondary battery was charged with a constant current until the voltage reached 4.2 V by a constant current constant voltage charging method at 60 캜 and then charged to a constant voltage and then discharged to 3.0 V with a constant current of 1C Respectively. The charge-discharge cycle test is performed up to 500 cycles. The higher the capacity retention rate, the smaller the capacity decrease during charging and discharging. The lower the capacity retention rate, the larger the capacity deterioration.

The results are shown in Table 1 below.

Example 1 Example 2 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Reference Example 1 Substrate adhesion
(mN / 25 mm) 0.72 0.63 0.22 0.28 0.24 0.18 0.42 Ion conductivity (mS / cm) 0.306 0.315 0.125 0.288 0.304 0.113 0.189 Shrinkage (%)
@ 120 degrees, 1Hr 3.0 3.2 3.1 3.8 3.0 3.4 3.3 Capacity retention rate (%) 83% 81% 68% 79% 71% 66% 74%

Referring to Table 1, it can be seen that the separator according to Examples 1 and 2 has significantly improved base adhesive strength and ion conductivity as compared with the separator according to Comparative Examples 1 to 4 and Reference Example 1. [ The lithium secondary battery to which the separator according to Example 1 and Example 2 was applied was confirmed to have improved capacity retention ratio after charge and discharge as compared with the lithium secondary battery to which the separator according to Comparative Examples 1 to 4 and Reference Example 1 was applied have. It is to be noted that the separator according to Reference Example 1 is superior to the separator according to Examples 1 and 2 in terms of substrate adhesion and ionic conductivity but is superior to the separator according to Comparative Examples 1 to 4 in terms of substrate adhesion and ion conductivity .

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.

1: Core
2: Shell
3: Water-based polyvinylidene fluoride latex
4: Acrylate having a high glass transition temperature
5: Acrylate having a low glass transition temperature
10: Separator
20: Porous substrate
30: Binder layer
40: anode
50: cathode
60: electrode assembly
70: Case

Claims (15)

The porous substrate and /
A binder layer disposed on at least one surface of the porous substrate,
/ RTI &gt;
Wherein the binder layer comprises a latex and an acrylate compound containing a repeating unit represented by the following formula (1).
[Chemical Formula 1]

The method of claim 1,
Wherein the latex comprising the repeating unit represented by Formula 1 is a polyvinylidene fluoride latex. 3. The method of claim 2,
Wherein the polyvinylidene fluoride latex is an aqueous polyvinylidene fluoride latex. The method of claim 1,
The binder layer has a core-shell structure,
Wherein the core comprises a latex containing a repeating unit represented by the formula (1), and the shell comprises the acrylate compound. 5. The method of claim 4,
Wherein the core has a particle diameter of 1 nm to 200 nm. 5. The method of claim 4,
Wherein the core-shell structure comprises a latex core comprising a repeating unit represented by the formula (1), and a structure in which the core surface is modified with an acrylate group. The method of claim 1,
Wherein the binder layer comprises a latex containing a repeating unit represented by the formula (1) and two kinds of acrylate compounds having different glass transition temperatures. 8. The method of claim 7,
Wherein the acrylate compound comprises an acrylate compound having a glass transition temperature of -80 占 폚 to -20 占 폚 and an acrylate compound having a glass transition temperature of 30 占 폚 to 90 占 폚. 8. The method of claim 7,
Wherein the binder layer is a single layer. 8. The method of claim 7,
The above-
50% by weight to 80% by weight of a latex comprising the repeating unit represented by the formula (1)
20% to 50% by weight of the acrylate compound,
And a separator for a secondary battery. 9. The method of claim 8,
The above-
1% to 10% by weight of an acrylate compound having a glass transition temperature of -80 ° C to -20 ° C and
90% by weight to 99% by weight of an acrylate compound having a glass transition temperature of 30 DEG C to 90 DEG C,
And a separator for a secondary battery. Preparing a porous substrate; and
Coating a composition comprising a latex and an acrylate compound comprising a repeating unit represented by the following formula (1) on the porous substrate
Wherein the separator is made of a thermoplastic resin.
[Chemical Formula 1]

The method of claim 12,
The composition has a core-shell structure,
Wherein the core comprises a latex comprising the repeating unit represented by the formula (1), and the shell comprises the acrylate compound. The method of claim 12,
Wherein the composition comprises a latex comprising the repeating unit represented by the formula (1) and two kinds of acrylate compounds having different glass transition temperatures. anode,
Cathode, and
The lithium secondary battery according to any one of claims 1 to 11, which is positioned between the positive electrode and the negative electrode.

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