KR102290852B1 - Separator for rechargeable battery and rechargeable battery including the same - Google Patents

Abstract

A separator for a secondary battery comprising a porous substrate and a binder layer positioned on at least one surface of the porous substrate, wherein the binder layer includes a latex and an acrylate compound including a repeating unit represented by the following Chemical Formula 1, and the secondary battery separator It relates to a method and a lithium secondary battery including the separator.

Description

Separator for secondary battery and lithium secondary battery including same

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

A separator for an electrochemical battery is an interlayer that enables charging and discharging of a battery by continuously maintaining ionic conductivity while isolating the positive and negative electrodes within the battery.

In recent years, as the trend of weight reduction and miniaturization of batteries and the need for high-output large-capacity batteries for use in electric vehicles, etc., not only high-capacity but also improvement of adhesion characteristics and cycle characteristics are required.

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

Another embodiment provides a method of manufacturing the separator.

Another embodiment provides a secondary battery including the separator.

According to one embodiment, a separator for a secondary battery comprising a porous substrate and a binder layer positioned on at least one surface of the porous substrate, wherein the binder layer includes a latex and an acrylate compound including a repeating unit represented by the following Chemical Formula 1 provides

[Formula 1]

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

The polyvinylidene fluoride latex may be a water-based polyvinylidene fluoride latex.

The binder layer may have a core-shell structure, the core may include latex including the repeating unit represented by Chemical Formula 1, and the shell may include the acrylate compound.

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

The core-shell structure may be a latex core including the repeating unit represented by Formula 1 and a structure in which a surface of the core is modified with an acrylate group.

The binder layer may include latex including the repeating unit represented by Chemical 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 include 50 wt% to 80 wt% of the latex including the repeating unit represented by Chemical Formula 1 and 20 wt% to 50 wt% of the acrylate compound.

The acrylate compound includes 10 wt% to 20 wt% of an acrylate compound having a glass transition temperature of -80 °C to -20 °C, and 80 wt% to an acrylate compound having a glass transition temperature of 30 °C to 90 °C 90% by weight.

According to another embodiment, preparing a porous substrate and preparing a separator for a secondary battery comprising the step of coating a composition comprising a latex and an acrylate compound including a repeating unit represented by the following Chemical Formula 1 on the porous substrate provide a way

[Formula 1]

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

The composition may include a latex including a repeating unit represented by Formula 1 and two types of acrylate compounds having different glass transition temperatures.

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

By providing a separator with improved adhesion characteristics, cycle characteristics, and ionic conductivity, battery characteristics of a lithium secondary battery can be improved.

1 is a view showing a separator for a secondary battery according to an exemplary 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 an embodiment.
4 is a schematic diagram showing a binder and a latex and an acrylate compound positioned on the binder according to an embodiment.

Hereinafter, embodiments of the present invention will be described in detail. However, this is presented as an example, and the present invention is not limited thereto, and the present invention is only defined by the scope of the claims to be described later.

Hereinafter, a separator for a secondary battery according to an embodiment will be described.

1 is a view showing a separator for a secondary battery according to an exemplary embodiment.

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

The porous substrate 20 has a plurality of pores and may be a porous substrate that can be used in a conventional 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, and polyaryls. Ether ketone, polyetherimide, polyamideimide, polybenzimidazole, polyethersulfone, polyphenylene oxide, cyclic olefin copolymer, polyphenylene sulfide, polyethylene naphthalate, glass fiber, tetrafluoroethylene (TEFLON), and polytetrafluoroethylene (PTFE) may be a polymer film formed of any one polymer selected from the group consisting of or a mixture of two or more thereof. Specifically, the porous substrate 20 may be a polyolefin-based substrate, and the polyolefin-based substrate has an excellent shut-down function, thereby contributing to the improvement of battery safety. The polyolefin-based substrate may be, for example, selected from the group consisting of a polyethylene single layer, a polypropylene single layer, a polyethylene/polypropylene double layer, a polypropylene/polyethylene/polypropylene triple layer, and a polyethylene/polypropylene/polyethylene triple layer. In addition, the polyolefin-based resin may include a non-olefin resin in addition to the olefin resin, or a copolymer of an olefin and a non-olefin monomer.

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

The binder layer 30 includes latex and an acrylate compound including a repeating unit represented by Formula 1 below.

[Formula 1]

Conventionally, a separator was prepared by dissolving a polyvinylidene fluoride copolymer, not latex, in a solvent on a porous substrate to form a coating layer, or by forming a coating layer using acrylate latex. A separator prepared from polyvinylidene fluoride copolymer is difficult to impart adhesion with the electrode at room temperature, and the process cost is high because it has to be coated by dissolving the binder composition. However, excessive adhesion due to excess acrylate latex lowers ionic conductivity, thereby shortening the battery life.

The latex including the repeating unit represented by Formula 1 may be a polyvinylidene fluoride latex, for example, an aqueous polyvinylidene fluoride latex. Conventionally, it is common to use non-aqueous polyvinylidene fluoride as a latex in a binder used in a separator, but in one embodiment, by using an aqueous polyvinylidene fluoride latex, wet binding can be made more easily. In manufacturing a basic polymer cell, the cell is deformed due to the contraction and expansion of the electrode plate during its lifespan. In order to overcome this technical problem, a material is coated on the separator, and the bonding force between the coated material and the separator is called the substrate bonding strength. When a process of attaching an electrode plate and a separator is required to manufacture a stack cell, it is necessary to secure binding force in a state in which the electrolyte is not immersed, and the binding force is called dry binding force. In addition, after immersion in electrolyte, to prevent cell strength and cell deformation during life, the electrode plate and the separator are once again bound. This binding force is called wet binding force.

For example, the binder layer may have a core-shell structure, the core may include latex including the repeating unit represented by Formula 1, and the shell may include the acrylate compound. As the binder layer has a core-shell structure, compared to a binder layer not having a core-shell structure, while maintaining the binding force of the acrylate, the ionic conductivity of the PVDF of the core structure by the electrolyte swelling is improved, thereby improving battery life characteristics. can be improved

The core may have a particle diameter of 1 nm to 200 nm. When the core has a particle diameter of less than 1 nm, it is difficult to modify the surface with acrylate, and when the core has a particle diameter of more than 200 nm, there is a problem in that it is difficult to secure a desired wet binding force with the electrode plate.

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

For example, as shown in FIG. 4 , the binder layer may include latex including the repeating unit represented by Chemical Formula 1 and two types of acrylate compounds having different glass transition temperatures. That is, the binder layer is a latex containing the repeating unit represented by Formula 1, an acrylate compound having a high glass transition temperature of -80°C to -20°C, and an acryl having a low glass transition temperature of 30°C to 90°C. It may contain a rate compound.

By including the acrylate compound having a high glass transition temperature of 30 ° C. to 90 ° C., dry binding becomes easier, and by including the acrylate compound having a low glass transition temperature of -80 ° C. to -20 ° C., the substrate It becomes easier to bind with. By coating a material having two glass transition temperatures in this way, it is possible not only to secure the membrane coating processability, but also to improve the binding characteristics of the electrode plate and the separator when manufacturing the stack cell, thereby securing the cell manufacturing processability at the same time.

The binder layer may be a single-layer rather than a multi-layer. In this case, since both properties (base material binding and dry binding) can be secured with one coating, there is an advantageous effect in terms of process cost.

The binder layer, 50% to 80% by weight (eg, 60% to 70% by weight) of the latex including the repeating unit represented by Formula 1 and 20% to 50% by weight of the acrylate compound (eg, 30% to 40% by weight). When the acrylate compound content is within the above range, the substrate binding force and the dry binding force are greatly increased to ensure fairness. However, when the content of the acrylate compound is out of the above range, wet binding strength may be reduced.

For example, the acrylate compound may include 10 wt% to 20 wt% of an acrylate compound having a glass transition temperature of -80°C to -20°C, and 80 wt% of an acrylate compound having a glass transition temperature of 30°C to 90°C. % to 90% by weight. In this case, as the content of the acrylate compound having a high glass transition temperature increases, the dry binding force is improved, making it easier to secure fairness during battery manufacturing. When the compound content is included in an amount of more than 90% by weight or less than 80% by weight based on the total amount of the acrylate compound, the bonding force to the substrate is reduced, so that the coating material may fall off from the substrate 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-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 is, for example, 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 , bohemite, or a combination thereof may be included, but is not limited thereto. The organic filler may include an acrylic compound, an imide compound, an amide compound, or a combination thereof, but is not limited thereto. The organic filler may have a core-shell structure, but is not limited thereto.

The filler may be spherical, plate-shaped, 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 about 100 nm to 500 nm within the range. can Here, the size may be an average particle diameter or a long diameter. By using a filler having a size within the above range, an appropriate strength may be imparted to the binder layer 30 . The fillers may be of different types or may be used by mixing two or more types having different sizes. By including the filler, heat resistance is improved, and thus, it is possible to further prevent the separator from being rapidly contracted or deformed due to a rise in temperature.

The acrylate compound may be a compound containing an acrylate group. For example, the acrylate compound is 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 combinations thereof.

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

The binder layer may further include one or more binders.

The binder may further include, for example, a crosslinked binder having a crosslinked structure.

The crosslinking binder may be obtained from monomers, oligomers and/or polymers having curable functional groups capable of reacting with heat and/or light, such as polyfunctional monomers, polyfunctional oligomers and/or polyfunctional polymers having at least two curable functional groups. It can be obtained from a polymer. For example, the crosslinking binder may have 2 to 30 curable functional groups, 2 to 20 curable functional groups within the above range, and 3 to 15 curable functional groups within the above range.

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, or a combination thereof. , but is not limited thereto.

For example, the crosslinking binder may include 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, alkoxy groups, or a combination thereof. It can be obtained from monomers, oligomers and/or polymers comprising

For example, the crosslinking binder may be obtained by curing a monomer, oligomer and/or polymer having at least two (meth)acrylate groups, for example, ethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, polyethylene Glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, butanediol di(meth)acrylate, hexamethylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, glycerin tri(meth) ) acrylate, pentaerythritol tetra(meth)acrylate, diglycerin hexa(meth)acrylate, or a combination thereof.

For example, the crosslinking binder may be obtained by curing a monomer, oligomer and/or polymer having at least two epoxy groups, for example, bisphenol A diglycidyl ether, bisphenol F diglycidyl ether, hexahydrophthalic acid glycidyl ester. or by curing a combination thereof.

As an example, the crosslinking binder can be obtained by curing monomers, oligomers and/or polymers having at least two isocyanate groups, such as 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 It can be obtained by curing 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. Heat resistance can be ensured by including a crosslinking binder having a weight average molecular weight in the above range.

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

The non-crosslinked binder is, for example, a vinylidene fluoride-based polymer such as polyvinylidene fluoride (PVdF) homopolymer, polyvinylidene fluoride-hexafluoropropylene (PVdF-HFP) copolymer, polymethyl methacrylate, poly Acrylonitrile, polyvinylpyrrolidone, polyvinyl acetate, polyethylene-vinyl acetate copolymer, polyethylene oxide, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethylpullulan, cyanoethyl poly It may be 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 μm to 20 μm, may have a thickness of about 1 μm to 10 μm within the range, and have a thickness of about 1 μm to 5 μm within the range. can

Another embodiment provides a method for preparing a separator for a secondary battery comprising preparing a porous substrate and coating a composition containing a latex and an acrylate compound including the repeating unit represented by Formula 1 on the porous substrate to provide.

That is, the separator for a secondary battery may be formed by, for example, coating a composition for a binder layer on one or both surfaces of the porous substrate 20 and drying the composition.

For example, the composition may have a core-shell structure, the core may include a latex including a 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 types of acrylate compounds having different glass transition temperatures.

The composition for the binder layer may include latex and acrylate including the repeating unit represented by Chemical Formula 1, and may further include the aforementioned binder, filler, initiator and/or solvent.

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-phenylketone, 2-methyl-2- acetophenones such as morphine (4-thiomethylphenyl) propan-1-one; benzoin ethers such as benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, and benzoin isobutyl ether; Benzophenone, o-benzoylmethylbenzoate, 4-phenylbenzophenone, 4-benzoyl-4'-methyldiphenylsulfite, 4-benzoyl-N,N-dimethyl-N-[2-(1-oxo-2-pro) phenyloxy) ethyl] benzophenones such as benzenemethanaminium blomide and (4-benzoylbenzyl)trimethylammonium chloride; thioxanthone such as 2,4-diethylthioxanthone and 1-chloro-4-dichlorothioxanthone; 2,4,6-trimethylbenzoyldiphenylbenzoyloxide etc. are mentioned, These can be used individually or in mixture of 2 or more types. The thermal initiator may be used when curing by thermal polymerization. As the thermal initiator, organic peroxide free radical initiators such as diacyl peroxides, peroxyketals, ketone peroxides, hydroperoxides, dialkyl peroxides, peroxyesters, and peroxydicarbonates can be used. and, for example, lauroyl peroxide, benzoyl peroxide, cyclohexanone peroxide, 1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane, t-butylhydroperoxide Oxides and the like 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 above-mentioned filler. The solvent may be, for example, acetone, methyl ethyl ketone, ethyl isobutyl ketone, tetrahydrofuran, dimethylformaldehyde, cyclohexane, or a mixed solvent 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 may be carried out by, for example, natural drying, drying by warm air, hot air or low humidity, vacuum drying, far-infrared rays, or electron beam irradiation, but is not limited thereto. The drying process may be performed, for example, at a temperature of 25° C. to 120° C., for example, at a temperature of about 80° C. to 100° C. for about 5 seconds to 60 seconds, and batch or continuous drying is possible. .

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

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

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

Lithium secondary batteries can be classified into lithium ion batteries, lithium ion polymer batteries, and lithium polymer batteries depending on the type of separator and electrolyte used, and can be classified into cylindrical, prismatic, coin-type, pouch-type, etc. according to the shape. , can be divided into bulk type and thin film type according to the size. Since the structure and manufacturing method of these batteries are well known in the art, a detailed description thereof will be omitted.

Here, a prismatic lithium secondary battery will be exemplarily described as an example of the lithium secondary battery.

2 is an exploded perspective view of a lithium secondary battery according to an embodiment.

Referring to FIG. 2 , in the lithium secondary battery 100 according to one embodiment, the electrode assembly 60 and the electrode assembly 60 wound by interposing the separator 10 between the positive electrode 40 and the negative electrode 50 are It includes a built-in case (70).

The electrode assembly 60 may be in the form of, for example, a jelly roll formed by winding the positive electrode 40 and the negative electrode 50 with the separator 10 interposed therebetween.

The positive electrode 40 , the negative electrode 50 , and the separator 10 are impregnated with an electrolyte solution (not shown).

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

Aluminum (Al), nickel (Ni), etc. may be used as the positive electrode current collector, 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. Specifically, at least one of cobalt, manganese, nickel, aluminum, iron, or a composite oxide of lithium and a metal of a combination thereof or a composite phosphate oxide 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 material particles well to each other, but also serves to adhere the positive electrode active material well to the positive electrode current collector, and specific examples include polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride. , carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymer, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, Acrylated styrene-butadiene rubber, epoxy resin, nylon, and the like, but is not limited thereto. These can be used individually or in mixture of 2 or more types.

The conductive material imparts conductivity to the electrode, and examples thereof include natural graphite, artificial graphite, carbon black, carbon fiber, metal powder, metal fiber, and the like, but is not limited thereto. These can be used individually or in mixture of 2 or more types. The metal powder and the metal fiber may use a metal such as copper, nickel, aluminum, silver.

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

The negative electrode current collector may be made of copper (Cu), gold (Au), nickel (Ni), a copper alloy, or the like, but is not limited thereto.

The anode active material layer may include an anode active material, a binder, and optionally a conductive material.

As the negative active material, a material capable of reversibly intercalating and deintercalating lithium ions, lithium metal, an alloy of lithium metal, a material capable of doping and dedoping lithium, a transition metal oxide, or a combination thereof Can be used.

A material capable of reversibly intercalating and deintercalating lithium ions may include a carbon-based material, and examples thereof include crystalline carbon, amorphous carbon, or a combination thereof. Examples of the crystalline carbon include amorphous, plate-like, flake-like, spherical or fibrous natural graphite or artificial graphite. Examples of the amorphous carbon include soft carbon or hard carbon, mesophase pitch carbide, calcined coke, and the like. The lithium metal alloy includes lithium and Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al and Sn from the group consisting of Alloys of selected metals may be used. As a 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-Y, etc. In addition, at least one of these and SiO ₂ may be mixed and used. The element Y includes Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Tl, Ge, P, As, Sb, Bi, S, It may be selected from the group consisting of Se, Te, Po, and combinations thereof. Examples of the transition metal oxide include vanadium oxide and lithium vanadium oxide.

The binder and the conductive material used in the negative electrode may be the same as the binder and the conductive material used in the positive electrode.

The positive electrode 40 and the negative electrode 50 may be prepared by mixing each active material and a binder and optionally a conductive material in a solvent to prepare each active material composition, and applying the active material composition to each current collector. In this case, the solvent may be N-methylpyrrolidone or the like, but is not limited thereto. Since such an electrode manufacturing method is widely known in the art, a detailed description thereof will be omitted herein.

The separator 10 is as described above.

The electrolyte 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 carbonate-based solvents, ester-based solvents, ether-based solvents, ketone-based solvents, alcohol-based solvents, and aprotic solvents.

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-based solvent include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), methylethyl carbonate (MEC), ethylene carbonate ( EC), propylene carbonate (PC), butylene carbonate (BC), etc. may be used, and examples of the ester solvent include methyl acetate, ethyl acetate, n-propyl acetate, 1,1-dimethylethyl acetate, and methylpropionate. , ethyl propionate, γ-butyrolactone, decanolide (decanolide), valerolactone, mevalonolactone, caprolactone, etc. may be used. Dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, etc. may be used as the ether-based solvent, and cyclohexanone, etc. may be used as the ketone-based solvent. have. In addition, as the alcohol-based solvent, ethyl alcohol, isopropyl alcohol, etc. may be used, and the aprotic solvent is R-CN (R is a C2 to C20 linear, branched or cyclic hydrocarbon group, nitriles such as nitriles (which may contain an aromatic ring or ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; sulfolanes;

The organic solvent may be used alone or in a mixture of two or more, and when two or more kinds of the organic solvent are mixed and used, the mixing ratio may be appropriately adjusted according to the desired battery performance.

The lithium salt is a material that is dissolved in an organic solvent, serves as a source of lithium ions in the battery, enables basic lithium secondary battery operation, and promotes movement of lithium ions between the positive electrode and the negative electrode. Examples of the lithium salt include 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 ) (x and y are natural numbers), LiCl, LiI, LiB(C ₂ O ₄ ) ₂ or combinations thereof may be mentioned, but is not limited thereto.

The concentration of the lithium salt may be used within the range of 0.1M to 2.0M. When the concentration of the lithium salt is within the above range, since the electrolyte has appropriate conductivity and viscosity, excellent electrolyte performance may be exhibited, and lithium ions may move effectively.

The lithium secondary battery including the above-described separator may be operated at a high voltage of 4.2V or more, and thus, a high-capacity lithium secondary battery may be implemented without deterioration of lifespan characteristics.

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

of separator Produce

Example One

66.5 wt% of a water-based PVDF latex having a core-shell structure having a size of 200 nm and a surface modified with an acrylate group, 5 wt% of an acrylate having a glass transition temperature of -50°C, and an acrylate having a glass transition temperature of 60°C 28.5 wt% was put into 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 9 μm separator and dried with hot air at 80° C. to prepare a 10 μm-thick separator.

Example 2

66.5 wt% of an aqueous PVDF latex having a size of 200 nm (without a core-shell structure), 5 wt% of an acrylate having a glass transition temperature of -50 °C, and 28.5 wt% of an acrylate having a glass transition temperature of 60 °C Put in 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 9 μm separator and dried with hot air at 80° C. to prepare a 10 μm-thick separator.

comparative example One

66.5 wt% of non-aqueous PVDF latex having a core-shell structure having a size of 200 nm, 5 wt% of an acrylate having a glass transition temperature of -50 °C, and 28.5 wt% of an acrylate having a glass transition temperature of 60 °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 9 μm separator and dried with hot air at 80° C. to prepare a 10 μm-thick separator.

comparative example 2

Water-based PVDF latex having a core-shell structure with a size of 200 nm or water-based PVDF latex having a surface modified with HFP 66.5 wt%, 5 wt% of an acrylate having a glass transition temperature of -50 °C, and a glass transition temperature of 60 °C 28.5% by weight of the acrylate having the acrylate was put into 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 9 μm separator and dried with hot air at 80° C. to prepare a 10 μm-thick separator.

comparative example 3

66.5 wt% of a non-aqueous PVDF latex having a size of 200 nm (without a core-shell structure), 5 wt% of an acrylate having a glass transition temperature of -50 °C, and 28.5 wt% of an acrylate having a glass transition temperature of 60 °C was put into 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 9 μm separator and dried with hot air at 80° C. to prepare a 10 μm-thick separator.

comparative example 4

A slurry was prepared by putting 66.5 wt% of an aqueous PVDF latex having a size of 200 nm (without a core-shell structure) and 33.5 wt% of an acrylate having a glass transition temperature of 60 °C into a stirrer and stirring at 1500 rpm for 1 hour. The prepared slurry was coated on both sides by a gravure coating method on a 9 μm separator and dried with hot air at 80° C. to prepare a 10 μm-thick separator.

Reference example One

66.5 wt% of a water-based PVDF latex having a size of 200 nm (without a core-shell structure), 5 wt% of an acrylate having a glass transition temperature of 30 °C, and 28.5 wt% of an acrylate having a glass transition temperature of 60 °C were mixed with 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 9 μm separator and dried with hot air at 80° C. to prepare a 10 μm-thick separator.

evaluation

(1) Adhesion to substrate

Example 1, Example 2, Comparative Examples 1 to 4, and the substrate adhesive strength of the separators according to Reference Example 1 was evaluated.

The adhesion to the substrate was evaluated in the following manner.

It was tested according to clause 8 of the Korean Industrial Standard KS-A-01107 (Test Methods for Adhesive Tapes and Adhesive Sheets). Examples 1, 2, Comparative Examples 1 to 4, and the separators according to Reference Example 1 were made into specimens having a width of 25 mm and a length of 250 mm, and an evaluation specimen was prepared by attaching a tape (nitto 31B) to the front and back surfaces. . Then, it was compressed by reciprocating once at a speed of 300 mm/min using a compression roller with a load of 2 kg. After 30 minutes have elapsed after compression, one side of the evaluation specimen is turned 180° and peeled off about 25 mm, and the side with the separator and tape on one side is attached to the upper clip of the tensile strength machine, and the tape on the other side is clipped to the lower side of the test plate. The load was measured when it was fixed to the pole and pulled off at a tensile rate of 60 mm/min. For tensile strength, Instron Series lX/s Automated materials Tester-3343 was used.

The results are shown in Table 1 below.

(2) ionic conductivity

The ionic conductivity of the separators according to Examples 1 and 2, Comparative Examples 1 to 4, and Reference Example 1 was evaluated.

The ionic conductivity was evaluated as follows.

(Punching the separator according to the 2016 coin cell standard, put it between the coin cells in a state where there is no electrode plate, and mix ethylene carbonate (EC), ethylmethyl carbonate (EMC) and diethyl carbonate (DEC) in a volume ratio of 3:5:2 Electrolyte prepared by adding 1.15 M of LiPF ₆ to a mixed solvent was added, aged at room temperature for 24 hours, and then impedance was measured using a Viologic VSP EIS (Electrochemical Impedance Spectroscopy) instrument to calculate conductivity The measurement conditions were measured at room temperature of 25°C, and the initial frequency was measured from 500KHZ to the final frequency of 1Hz.

The results are shown in Table 1 below.

(3) lithium secondary battery performance evaluation

A lithium secondary battery was manufactured in the following manner, and after charging and discharging the lithium secondary battery, the adhesive strength, thickness change rate, and capacity retention rate of the separator were evaluated.

LiCoO ₂ , polyvinylidene fluoride and carbon black were added to an N-methylpyrrolidone (NMP) solvent in 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 an N-methylpyrrolidone (NMP) solvent in a weight ratio of 98:1:1 to prepare a slurry. The slurry was coated on a copper foil (Cu foil), dried and rolled to prepare a negative electrode.

The electrolyte was prepared by adding _{1.15M of LiPF 6} to a mixed solvent in which ethylene carbonate (EC), ethylmethyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 3:5:2.

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

Next, the lithium secondary battery is charged with a constant current until it reaches 4.2 V by the constant current constant voltage charging method at 60 ° C. at 1 C, then charged at a constant voltage, and then discharged to 3.0 V at a constant current of 1 C. A charge/discharge cycle test is performed. did. The charge/discharge cycle test is performed up to 500 cycles, and the higher the capacity retention rate, the less the capacity decrease during charging and discharging, and the lower the capacity retention rate, the greater the capacity decrease.

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 Adhesion to substrate
(mN/25mm) 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 separators according to Examples 1 and 2 have significantly improved substrate adhesion and ionic conductivity compared to the separators according to Comparative Examples 1 to 4 and Reference Example 1. In addition, it can be confirmed that the lithium secondary battery to which the separator according to Examples 1 and 2 is applied has improved capacity retention after charging and discharging compared to the lithium secondary battery to which the separator according to Comparative Examples 1 to 4 and Reference Example 1 is applied. have. In addition, the separator according to Reference Example 1 was inferior to the separators according to Examples 1 and 2 in substrate adhesion and ionic conductivity, but it was confirmed that the substrate adhesion and ionic conductivity were superior to those of the separators according to Comparative Examples 1 to 4 can

Although preferred embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements by those skilled in the art using the basic concept of the present invention as defined in the following claims are also presented. It belongs to 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: positive electrode
50: cathode
60: electrode assembly
70: case

Claims (15)

porous substrate and
A binder layer positioned on at least one surface of the porous substrate
including,
The binder layer comprises 60 wt% to 70 wt% of a latex containing a repeating unit represented by the following formula (1) and 30 wt% to 40 wt% of an acrylate compound,
The acrylate compound includes 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 acrylate compound includes 10 wt% to 20 wt% of an acrylate compound having a glass transition temperature of -80 °C to -20 °C, and 80 wt% to an acrylate compound having a glass transition temperature of 30 °C to 90 °C A secondary battery separator comprising 90% by weight.
[Formula 1]

In claim 1,
The latex containing the repeating unit represented by the formula (1) is a polyvinylidene fluoride latex secondary battery separator. In claim 2,
The polyvinylidene fluoride latex is an aqueous polyvinylidene fluoride latex secondary battery separator. In claim 1,
The binder layer has a core-shell structure,
The core includes a latex including the repeating unit represented by Chemical Formula 1, and the shell includes the acrylate compound. In claim 4,
The core is a separator for a secondary battery having a particle diameter of 1 nm to 200 nm. In claim 4,
The core-shell structure is a secondary battery separator having a latex core including the repeating unit represented by Formula 1 and a structure in which the surface of the core is modified with an acrylate group. delete delete In claim 1,
The binder layer is a single layer separator for a secondary battery. delete delete preparing a porous substrate; and
and coating a composition comprising 60 wt% to 70 wt% of a latex containing a repeating unit represented by the following formula (1) and 30 wt% to 40 wt% of an acrylate compound on the porous substrate,
The acrylate compound includes 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 acrylate compound includes 10 wt% to 20 wt% of an acrylate compound having a glass transition temperature of -80 °C to -20 °C, and 80 wt% to an acrylate compound having a glass transition temperature of 30 °C to 90 °C A method for manufacturing a separator for a secondary battery comprising 90% by weight.
[Formula 1]

In claim 12,
The composition has a core-shell structure,
The core includes a latex including the repeating unit represented by Formula 1, and the shell includes the acrylate compound. delete anode,
cathode, and
A lithium secondary battery comprising the separator according to any one of claims 1 to 6 and 9 positioned between the positive electrode and the negative electrode.

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