KR20200078010A - Composition for porous heat-resistance layer, separator for rechargeable lithium battery including heat-resistance layer formed therefrom and rechargeable lithium battery including the same - Google Patents

Abstract

The present invention relates to a porous heat-resistant layer composition comprising: a hyperbranched oligomer containing 20 to 200 crosslinkable functional groups; a polymerization initiator; inorganic particles; and a solvent, a heat-resistant layer formed therefrom, a separator for a lithium secondary battery including the same, and a lithium secondary battery including the same.

Description

Porous heat-resistant layer composition, separator for lithium secondary battery comprising heat-resistant layer formed therefrom, and lithium secondary battery comprising same {COMPOSITION FOR POROUS HEAT-RESISTANCE LAYER, SEPARATOR FOR RECHARGEABLE LITHIUM BATTERY INCLUDING HEAT-RESISTANCE LAYER FORMED THEREFROM AND RECHARGEABLE LITHIUMBATTER THE SAME}

It relates to a porous heat-resistant layer composition, a separator for a lithium secondary battery comprising a heat-resistant layer formed therefrom, and a lithium secondary battery comprising the same.

The separator for an electrochemical cell is an intermediate film that allows charging and discharging of the battery by continuously maintaining ion conductivity while isolating the positive and negative electrodes in the battery. However, when the battery is exposed to a high-temperature environment due to non-ideal behavior, the separator is mechanically contracted or damaged due to melting characteristics at a low temperature. In this case, a phenomenon in which the battery ignites due to the contact between the anode and the cathode may occur. In order to overcome this problem, there is a need for a technology capable of suppressing shrinkage of the separator and securing battery stability.

Provided is a separator for a lithium secondary battery having improved membrane resistance and heat resistance while securing excellent air permeability and adhesive properties, and a lithium secondary battery comprising the same.

In one embodiment, a hyperbranched oligomer comprising 20 to 200 crosslinkable functional groups; Polymerization initiators; Inorganic particles; And it provides a porous heat-resistant layer composition comprising a solvent.

In another embodiment, the porous substrate; And a heat resistant layer located on at least one surface of the porous substrate, wherein the heat resistant layer is formed from the porous heat resistant layer composition described above, and provides a separator for a lithium secondary battery.

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

A lithium secondary battery including a separator for a lithium secondary battery having improved membrane resistance and heat resistance can be implemented while securing excellent air permeability and adhesive properties.

1 is an exploded perspective view of a lithium secondary battery according to an embodiment.
2 is a schematic view of a coin symmetric battery manufactured to evaluate the membrane resistance.

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 thereby, and the present invention is only defined by the scope of claims to be described later.

In the present specification, unless otherwise defined,'substituted' means that the hydrogen atom in the compound is a halogen atom (F, Br, Cl or I), a hydroxy group, an alkoxy group, a nitro group, a cyano group, an amino group, an azido group, or an amidino group. Group, hydrazino group, hydrazono group, carbonyl group, carbamyl group, thiol group, ester group, carboxyl group or salt thereof, sulfonic acid group or salt thereof, phosphoric acid or salt thereof, C1 to C20 alkyl group, C2 to C20 alkenyl group, C2 to C20 alkynyl group, C6 to C30 aryl group, C7 to C30 arylalkyl group, C1 to C4 alkoxy group, C1 to C20 heteroalkyl group, C3 to C20 heteroarylalkyl group, C3 to C30 cycloalkyl group, C3 to C15 cycloalkenyl group, C6 to It means substituted with a substituent selected from C15 cycloalkynyl group, C2 to C20 heterocycloalkyl group, and combinations thereof.

In addition, unless otherwise defined in the present specification,'hetero' means one or three hetero atoms selected from N, O, S, and P.

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

The separator for a lithium secondary battery according to an embodiment includes a porous substrate and a heat resistant layer located on one or both sides of the porous substrate.

The porous substrate has a large number of pores and may be a substrate commonly used in electrochemical devices. Porous substrates include, but are not limited to, polyolefins such as polyethylene and polypropylene, polyesters such as polyethylene terephthalate and polybutylene terephthalate, polyacetal, polyamide, polyimide, polycarbonate, polyether ether ketone, polyaryl ether ketone, Polyetherimide, polyamideimide, polybenzimidazole, polyethersulfone, polyphenylene oxide, cyclic olefin copolymer, polyphenylene sulfide, polyethylene naphthalate, glass fiber, teflon, and polytetrafluoroethylene It may be any one polymer selected from the group, or a polymer film formed of two or more of these copolymers or mixtures.

The porous substrate may be, for example, a polyolefin-based substrate including polyolefin, and the polyolefin-based substrate may have an excellent shutdown function, thus contributing to the improvement of battery safety. 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. 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 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, or 10 μm to 15 μm.

The heat-resistant layer according to one embodiment includes a hyperbranched oligomer comprising 20 to 200 crosslinkable functional groups; Polymerization initiators; Inorganic particles; And it may be formed from a porous heat-resistant layer composition comprising a solvent.

Hereinafter, each component included in the porous heat-resistant layer composition will be described in more detail.

(a) Hyperbranched Oligomer

The hyperbranched oligomer may contain 20 to 200 crosslinkable functional groups in its structural unit, such as 100 to 200.

For example, the hyperbranched oligomer may include a crosslinkable functional group at the terminal, and a crosslinking structure may be formed by crosslinking reaction through the terminal crosslinkable functional group. These are cured by a polymerization initiator, which will be described later, so that physical and chemical bonds between oligomers are generated, adhesion to the substrate is improved, and a solid heat-resistant layer can be formed, and thus a separation membrane with improved thermal shrinkage can be realized.

The crosslinkable functional group may be at least one selected from the group consisting of (meth)acrylate group, vinyl group, hydroxy group, epoxy group, oxane group, oxetane group, ester group, cyanate group and isocyanate group, and the crosslinkable functional group The hyperbranched oligomer containing may be, for example, represented by Formula 1 below.

[Formula 1]

In Chemical Formula 1,

A core (CORE) is substituted with a functional group which can be combined with R ¹ or unsubstituted C3 to C60 aliphatic hydrocarbon group, substituted with a functional group which can be combined with R ¹ or unsubstituted C3 to C60 heterocyclic aliphatic hydrocarbon ring, R ¹ A substituted or unsubstituted C6 to C60 aromatic hydrocarbon having a functional group capable of being bonded with, a substituted or unsubstituted C3 to C60 hetero aromatic hydrocarbon having a functional group capable of being bonded to R ¹ , or a combination thereof,

R ¹ to R ³ are each independently substituted or unsubstituted C1 to C60 aliphatic hydrocarbon, substituted or unsubstituted C3 to C60 hetero aliphatic hydrocarbon, substituted or unsubstituted C6 to C60 aromatic hydrocarbon, substituted or unsubstituted C3 to C60 heteroaromatic hydrocarbon or a combination thereof,

E ₁ and E ₂ are each independently an ester bond,

X ¹ to X ⁴ are each independently a (meth)acrylate group, a vinyl group, a hydroxyl group, an epoxy group, an oxane group, an oxetane group, an ester group, a cyanate group, an isocyanate group, or a combination thereof,

m1 and m2 are each independently an integer from 1 to 10,

n is an integer from 5 to 20.

For example, the crosslinkable functional group may be a (meth)acrylate group, and the hyperbranched oligomer may be, for example, represented by Formula 2 below.

[Formula 2]

In Chemical Formula 2,

A core (CORE) is substituted with a functional group which can be combined with R ¹ or unsubstituted C3 to C60 aliphatic hydrocarbon group, substituted with a functional group which can be combined with R ¹ or unsubstituted C3 to C60 heterocyclic aliphatic hydrocarbon ring, R ¹ A substituted or unsubstituted C6 to C60 aromatic hydrocarbon having a functional group capable of being bonded with, a substituted or unsubstituted C3 to C60 hetero aromatic hydrocarbon having a functional group capable of being bonded to R ¹ , or a combination thereof,

R ¹ to R ³ are each independently substituted or unsubstituted C1 to C60 aliphatic hydrocarbon, substituted or unsubstituted C3 to C60 hetero aliphatic hydrocarbon, substituted or unsubstituted C6 to C60 aromatic hydrocarbon, substituted or unsubstituted C3 to C60 heteroaromatic hydrocarbon or a combination thereof,

E ₁ and E ₂ are each independently an ester bond,

m1 and m2 are each independently an integer from 1 to 10,

n is an integer from 5 to 20.

Substituted or unsubstituted C3 to C60 aliphatic hydrocarbons constituting the core in Formulas 1 and 2 mean substituted or unsubstituted C3 to C60 alkanes, for example, substituted or unsubstituted C3 to C40 alkanes or C3 to C30 alkanes. Substituted or unsubstituted C3 to C60 heteroaliphatic hydrocarbons may be substituted or unsubstituted C3 to C60 heteroalkanes, for example substituted or unsubstituted C3 to C40 heteroalkanes or substituted or unsubstituted C3 to C30 alkanes. And substituted or unsubstituted C6 to C60 aromatic hydrocarbons, substituted or unsubstituted C6 to C60 arenes, for example, substituted or unsubstituted C6 to C40 arenes or substituted or unsubstituted C6 to C30 arenes Meaned, substituted or unsubstituted C3 to C60 heteroaromatic hydrocarbon is substituted or unsubstituted C3 to C60 heteroarene, for example, substituted or unsubstituted C3 to C40 heteroarene or substituted or unsubstituted C3 to C30 It can mean a hetero arene.

The hetero alkane means to include at least one hetero atom in the main chain of the alkane, and the hetero arene means that at least one of the carbon atoms constituting the arene is substituted with a hetero atom.

In Formulas 1 and 2, R ¹ to R ³ are specifically substituted or unsubstituted C1 to C60 alkylene, substituted or unsubstituted C3 to C60 heteroalkylene, substituted or unsubstituted C6 to C60 arylene, substituted Or unsubstituted C3 to C60 heteroarylene or combinations thereof, for example, substituted or unsubstituted C1 to C40 alkylene, substituted or unsubstituted C3 to C40 heteroalkylene, substituted or unsubstituted C6 To C40 arylene, substituted or unsubstituted C3 to C40 heteroarylene, or a combination thereof. Specific examples include substituted or unsubstituted C1 to C30 alkylene, substituted or unsubstituted C3 to C30 heteroalkylene, It may be a substituted or unsubstituted C6 to C30 arylene, a substituted or unsubstituted C3 to C30 heteroarylene, or a combination thereof.

The hetero alkylene means that at least one hetero atom is included in the main chain of the alkylene, and the hetero arylene means that at least one of the carbon atoms constituting arylene is substituted with a hetero atom.

As a specific example, the oligomer may have a structure in which CORE, R ¹ , E, and R ² are hyperbranched as shown in Chemical Formula 3, and the (meth)acrylate functional group surrounds the CORE, R ¹ , E, and R ² . have.

[Formula 3]

In Chemical Formula 3, CORE, E ₁ , E ₂ and R ¹ to R ³ are as described above.

For example, a hyperbranched oligomer containing a (meth)acrylate group can be synthesized by a conventional method by a Diels-Alder reaction or an ester condensation reaction. This can be easily carried out by those skilled in the art to which the present invention pertains.

In one embodiment, a polyester having a trifunctional to hexafunctional hydroxy group and a monomer having a carboxylic acid and two hydroxy groups at the same time undergo ester condensation reaction to prepare a highly functional polyester polyol. Then, it can be synthesized by introducing (meth)acrylic acid into the prepared high-functionality polyester polyol.

The monomer having a trifunctional to hexafunctional hydroxy group may preferably include trimethyl propanol, pentaaryl tritol, dipentaeryl tritol, and the like. Dimethylpropanoic acid, dimethylbutanoic acid, and the like are preferably used as the monomer having the carboxylic acid and two hydroxy groups at the same time. In addition, the (meth) acrylic acid may be acrylic acid or methacrylic acid.

In addition, the hyperbranched oligomer containing 20 to 200 (meth)acrylate groups is readily commercially available. For example, UNIDIC V 6830 manufactured by DIC CORPORATION can be used, but is not limited to these.

In addition, the viscosity of the hyperbranched (meth)acrylate oligomer may range from 100 to 400 cps at 25°C.

The oligomer may be included in 1% to 20% by weight, specifically 2% to 10% by weight based on the solid content of the porous heat-resistant layer composition.

(b) polymerization initiator

The polymerization initiator may induce a crosslinking reaction between oligomers containing a crosslinkable functional group.

The polymerization initiator acts as a curing agent that generates free radicals by heating or light, and may be appropriately selected according to the type of the oligomer. For example, the polymerization initiator may be a thermal polymerization initiator such as peroxide-based, azo-based, amine-based, imidazole-based or isocyanate-based, or photopolymerization initiator such as onium salt and organometallic salt. Examples of peroxide-based initiators include t-butyl peroxylaurate, 1,1,3,3-t-methylbutylperoxy-2-ethyl hexanonate, 2,5-dimethyl-2,5-di( 2-ethylhexanoyl peroxy) hexane, 1-cyclohexyl-1-methylethyl peroxy-2-ethyl hexanonate, 2,5-dimethyl-2,5-di(m-toluoyl peroxy) hexane, t-butyl peroxy isopropyl monocarbonate, t-butyl peroxy-2-ethylhexyl monocarbonate, t-hexyl peroxy benzoate, t-butyl peroxy acetate, dicumyl peroxide, 2,5,-dimethyl- 2,5-di(t-butyl peroxy) hexane, t-butyl cumyl peroxide, t-hexyl peroxy neodecanoate, t-hexyl peroxy-2-ethyl hexanonate, t-butyl peroxy- 2-2-ethylhexanonate, t-butyl peroxy isobutylate, 1,1-bis(t-butyl peroxy)cyclohexane, t-hexyl peroxy isopropyl monocarbonate, t-butyl peroxy-3 ,5,5-trimethyl hexanonate, t-butyl peroxy pivalate, cumyl peroxy neodecanoate, di-isopropyl benzene hydroperoxide, cumene hydroperoxide, isobutyl peroxide, 2,4-dichloro Benzoyl peroxide, 3,5,5-trimethyl hexanoyl peroxide, octanoyl peroxide, lauryl peroxide, stearoyl peroxide, succinic peroxide, benzoyl peroxide, 3,5,5-trimethyl hexanoyl peroxide Oxide, benzoyl peroxy toluene, 1,1,3,3-tetramethyl butyl peroxy neodecanoate, 1-cyclohexyl-1-methyl ethyl peroxy nodecanoate, di-n-propyl peroxy di Carbonate, di-isopropyl peroxy carbonate, bis(4-t-butyl cyclohexyl) peroxy dicarbonate, di-2-ethoxy methoxy peroxy dicarbonate, di(2-ethyl hexylperoxy) dicarbonate, Dimethoxy butyl peroxy dicarbonate, di(3-methyl-3-methoxy butyl peroxy) dicarbonate, 1,1-bis(t-hexyl peroxy)-3,3,5-trimethyl cyclohexane, 1, 1-bis(t-hexyl peroxy) cyclohexane, 1,1-bis(t-butyl peroxy)-3,3,5-trimethyl cyclohexane, 1,1-(t-butyl Peroxy) cyclododecan, 2,2-bis(t-butyl peroxy)decane, t-butyl trimethyl silyl peroxide, bis(t-butyl) dimethyl silyl peroxide, t-butyl triallyl silyl peroxide, bis (t-butyl) diallyl silyl peroxide, tris(t-butyl) aryl silyl peroxide, and the like. Examples of the azo-based polymerization initiator include 2,2'-azobis (4-methoxy-2,4-dimethyl valeronitrile), dimethyl 2,2'-azobis (2-methyl propionate), 2, 2'-azobis (N-cyclohexyl-2-methyl propionide), 2,2-azobis (2,4-dimethyl valeronitrile), 2,2'-azobis (2-methyl butylonitrile ), 2,2'-azobis[N-(2-propenyl)-2-methylpropionide], 2,2'-azobis(N-butyl-2-methyl propionide), 2,2 '-Azobis[N-(2-propenyl)-2-methyl propionide], 1,1'-azobis (cyclohexane-1-carbonitrile), 1-[(cyano-1-methylethyl )Azo] formamide and the like. As an example of the isocyanate-based polymerization initiator, a polyisocyanate-based initiator may be used, and aliphatic polyisocyanate, alicyclic polyisocyanate, aromatic aliphatic polyisocyanate, aromatic polyisocyanate, and derivatives or modified products thereof may be used. For example, trimethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, pentamethylene diisocyanate, 1,2-propylene diisocyanate, 1,2-butylene diisocyanate, 2,3-butylene diisocyanate, 1, 3-butylene diisocyanate, 2,4,4- or 2,2,4-trimethylhexamethylene diisocyanate, 2,6-diisocyanate methyl caproate, lysine ester triisocynet, 1,4,8-triisocyanate octane , 1,6,11-triisocyanateundecane, 1,8-diisocyanate-4-isocyanatemethyloctane, 1,3,6-triisocyanatehexane, 2,5,7-trimethyl-1,8-diisocyanate- 5-isocyanate methyl octane or the like can be used. Other thermal polymerization initiators, for example, benzophenone (BZP from Aldrich), 2,6-bis(azidobenzylidene)-4-methylcyclohexanone (bisazido from Aldrich), 2,2-dimethoxy-2- Phenylacetophenone, 1-benzoyl-1-hydroxycyclohexane, 2,4,6-trimethylbenzoyldiphenylphosphine oxide, 3-methyl-2-butenyltetramethylenesulfonium hexafluoroantimonate salt, Ytterbium trifluoromethenesulfonate salt, samarium trifluoromethenesulfonate salt, erbium trifluoromethenesulfonate salt, dysprosium trifluoromethenesulfonate salt, lanthanum trifluoromethenesulfonate salt, tetrabutylphosphonium Methenesulfonate salt, ethyltriphenylphosphonium bromide salt, benzyldimethylamine, dimethylaminomethylphenol, triethanolamine, 2-methylimidazole, 2-ethyl-4-methylimidazole, 1,8-diaza- Bicyclo(5,4,0)undecene-7, triethylenediamine, and tri-2,4-6-dimethylaminomethylphenol, and the like can be used.

Examples of the photopolymerization initiator are aryl sulfonium hexafluoroantimonate salt, diphenyldiodonium hexafluorophosphate salt, diphenyldiodonium hexaantimonium salt, ditolylododonium hexafluorophosphate Salts, and 9-(4-hydroxyethoxyphenyl) cyanrenium hexafluorophosphate salts.

The polymerization initiator may be 0.01 wt% to 10 wt%, specifically 0.1 wt% to 5 wt%, such as 0.1 wt% to 3 wt%, based on the total weight of the porous heat-resistant layer composition.

(c) inorganic particles

The heat-resistant layer improves heat resistance by including inorganic particles, thereby preventing the separator from rapidly contracting or deforming due to an increase in temperature. The inorganic particles are, 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 , boehmite, or a combination thereof, but is not limited thereto. The inorganic particles may be spherical, plate-shaped, cubic, or amorphous. The average particle diameter of the filler may be about 1 nm to 2500 nm, within this range may be 100 nm to 2000 nm, or 200 nm to 1000 nm, for example, about 300 nm to 800 nm. The average particle diameter of the inorganic particles may be a particle size (D ₅₀ ) at 50% by volume ratio in a cumulative size-distribution curve. By using inorganic particles having an average particle diameter in the above range, appropriate strength is imparted to the heat-resistant layer, and the heat resistance, durability, and stability of the separator can be improved.

The inorganic particles may be included in 80% by weight to 99% by weight relative to the heat-resistant layer. For example, it may be included as 85% to 99% by weight or 90% to 99% by weight. When the inorganic particles are included in the above range, the separator for a lithium secondary battery according to an embodiment may exhibit excellent heat resistance, durability and stability.

(d) solvent

The porous heat-resistant layer composition is the oligomer described above; Polymerization initiators and suitable solvents for dispersing the inorganic particles.

The solvent is not particularly limited, and alcohols having 1 to 15 carbon atoms, aliphatic hydrocarbons, alicyclic hydrocarbons, hydrocarbon solvents such as aromatic hydrocarbons, halogenated hydrocarbon solvents, ethers such as aliphatic ethers and alicyclic ethers, mixtures thereof, etc. Can be illustrated. For example, ketones such as acetone, methyl ethyl ketone, methyl butyl ketone, methyl isobutyl ketone, cyclohexanone, or ethers such as ethyl ether, dioxane, tetrahydrobutane, or methyl acetate, ethyl acetate, and propyl acetate , Esters such as isopropyl acetate, butyl acetate, isobutyl acetate, pentyl acetate, isopentyl acetate, or alcohols such as butanol, 2-butanol, isobutyl alcohol, isopropyl alcohol, ethanol, methanol, or dichloromethane, Halogenated hydrocarbons such as chloroform, dichloroethane, trichloroethane, tetrachloroethane, dichloroethylene, trichloroethylene, tetrachloroethylene, and chlorobenzene, n-hexane, cyclohexanol, methylcyclohexanol, benzene, toluene, etc. And hydrocarbons.

Meanwhile, the heat-resistant layer may further include a non-crosslinking binder. The non-crosslinking binder is, for example, vinylidene fluoride polymer, polymethyl methacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinyl acetate, polyethylene-vinyl acetate copolymer, polyethylene oxide, cellulose acetate, cellulose Acetate butyrate, cellulose acetate propionate, cyanoethyl pullulan, cyanoethylpolyvinyl alcohol, cyanoethylcellulose, cyanoethyl sucrose, pullulan, carboxymethylcellulose, acrylonitrile-styrene-butadiene copolymers or these It may be a combination of, but is not limited thereto.

The vinylidene fluoride-based polymer may be a homopolymer containing only units derived from vinylidene fluoride monomer, or a copolymer of a unit derived from vinylidene fluoride and another monomer. Specifically, the copolymer may be at least one of vinylidene fluoride-derived units and units derived from chlorotrifluoroethylene, trifluoroethylene, hexafluoropropylene, ethylene tetrafluoride, and ethylene monomer, but is not limited thereto. 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.

For example, the non-crosslinking binder may include 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 and the heat-resistant layer is improved, and the stability of the separator and the impregnation property of the electrolyte can be improved, thereby improving the charge/discharge characteristics of the battery and the like.

The heat-resistant layer may have a thickness of about 1 μm to 5 μm, for example, 1.5 μm to 3 μm.

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

The separator for a lithium secondary battery according to an embodiment may exhibit excellent air permeability and less than 30 sec/100cc·1 μm per unit thickness, for example, 20 sec/100 cc·1 μm or less, or 10 sec/100 cc·1 μm or less Can also have a value. Here, the air permeability means a time (second) for 100 cc of air to pass through the unit thickness of the separator. The air permeability per unit thickness can be obtained by measuring the air permeability of the entire thickness of the membrane and dividing it by the thickness.

The separator for a lithium secondary battery according to an embodiment may be manufactured by various known methods. For example, the separator for a lithium secondary battery may be formed by applying a composition for forming a heat-resistant layer on one or both surfaces of a porous substrate and then drying it.

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

The separator for a lithium secondary battery may be manufactured by methods such as lamination and coextrusion in addition to the above-described method.

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

Lithium secondary batteries may be classified into lithium ion batteries, lithium ion polymer batteries, and lithium polymer batteries according to the type of separator and electrolyte used, and may be classified into cylindrical, square, coin, pouch, etc. , It can be divided into bulk type and thin film type according to the size. The structure and manufacturing method of these batteries are well known in the art, so detailed descriptions thereof are omitted.

Here, as an example of the lithium secondary battery, a rectangular lithium secondary battery will be described as an example. 1 is an exploded perspective view of a lithium secondary battery according to an embodiment. Referring to FIG. 1, the lithium secondary battery 100 according to an embodiment includes an electrode assembly 60 and an electrode assembly 60 wound through a separator 10 between the positive electrode 40 and the negative electrode 50. It includes a built-in case (70).

The electrode assembly 60 may be, for example, 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 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 electrode active material layer may include a positive electrode active material, a binder, and optionally a conductive material.

Aluminum, nickel, or the like may be used as the positive electrode current collector, but is not limited thereto.

As the positive electrode 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 combination of metals and lithium or a complex phosphorus oxide of lithium may be used. For example, the positive electrode 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 material particles well to each other, but also serves to adhere the positive electrode active material to the positive electrode current collector, and specific examples include polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, and polyvinyl chloride. , Carboxylated polyvinylchloride, polyvinylfluoride, ethylene oxide-containing polymer, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, Acrylate-styrene-butadiene rubber, epoxy resin, nylon, and the like, but is not limited thereto. These may be used alone or in combination of two or more.

The conductive material is to impart conductivity to the electrode, and examples thereof include natural graphite, artificial graphite, carbon black, carbon fiber, metal powder, and metal fiber, but are not limited thereto. 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 negative electrode 50 may include a negative electrode current collector and a negative electrode active material layer formed on the negative electrode current collector.

Copper, gold, nickel, copper alloy, and the like may be used as the negative electrode current collector, but is not limited thereto.

The negative active material layer may include a negative active material, a binder, and optionally a conductive material. The negative active material includes a material capable of reversibly intercalating and deintercalating lithium ions, a lithium metal, a lithium metal alloy, a material capable of doping and dedoping lithium, a transition metal oxide, or a combination thereof. Can be used.

Examples of a material capable of reversibly intercalating and deintercalating the lithium ions 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-shape, flake, spherical or fibrous natural graphite or artificial graphite. Examples of the amorphous carbon include soft carbon or hard carbon, mesophase pitch carbide, and calcined coke. The lithium metal alloy is lithium and Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn. Alloys of the metal of choice can be used. Materials capable of doping and dedoping the lithium include Si, SiO _x (0<x<2), Si-C composite, Si-Y alloy, Sn, SnO ₂ , Sn-C composite, and Sn-Y. It can also be used, and it can also be used by mixing at least one of them and SiO ₂ . The elements Y are 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, Se, Te, Po, and combinations thereof. Examples of the transition metal oxide include vanadium oxide and lithium vanadium oxide.

The type of the binder and the conductive material used in the negative electrode 50 may be the same as the binder and the conductive material used in the positive electrode 40 described above.

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. 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, detailed description thereof will be omitted.

The electrolyte 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. Dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, methylethyl carbonate, ethylene carbonate, propylene carbonate, butylene carbonate, etc. may be used as the carbonate-based solvent, and as the ester-based solvent Methyl acetate, ethyl acetate, n-propyl acetate, 1,1-dimethylethyl acetate, methyl propionate, ethyl propionate, γ-butyrolactone, decanolide, valerolactone, mevalonolactone (mevalonolactone), caprolactone, etc. may be used. Dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, and the like may be used as the ether-based solvent, and cyclohexanone may be used as the ketone-based solvent. have. In addition, ethyl alcohol, isopropyl alcohol, or the like may be used as the alcohol-based solvent, and R-CN (R is a C2 to C20 straight-chain, branched or cyclic hydrocarbon group as the aprotic solvent). Amides such as nitriles and dimethylformamide, and dioxolanes such as 1,3-dioxolane, and the like, and sulfolanes.

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

The lithium salt is a material that dissolves in an organic solvent, acts as a source of lithium ions in the battery, enables basic lithium secondary battery operation, and promotes the movement of lithium ions between the positive electrode and the negative electrode. Examples of the lithium salt, 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 However, it is not limited to this.

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, since the electrolyte has an appropriate conductivity and viscosity, it can exhibit excellent electrolyte performance, and lithium ions can effectively move.

Hereinafter, 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 are not intended to limit the scope of the present invention.

Manufacturing example : Porous Heat-resistant layer Preparation of the composition

Manufacturing example One :

The hyperbranched oligomer (DIC CORPORATION, UNIDIC V 6830) was diluted to 30% by weight in acetone, and stirred for 1 hour at 25°C using a stirrer to prepare a first polymer solution.

In addition, after alumina (Al ₂ O ₃ , Nippon Light Metal Co., Japan) was pulverized through a bead mill, 25% by weight of crushed alumina and 75% by weight of acetone were mixed at 40° C. for 4 hours to obtain an inorganic dispersion. .

After mixing the first polymer solution and the inorganic dispersion so that the alumina weight ratio was 97%, Irgacure-184 (Ciba) as a photopolymerization initiator was added in an amount of 3 parts by weight based on 100 parts by weight of the binder solids, followed by 2 hours at 25°C with a power mixer. During stirring, a porous heat-resistant layer composition was prepared.

Manufacturing example 2 :

A porous heat-resistant layer composition was prepared in the same manner as in Preparation Example 1, except that the first polymer solution and the inorganic dispersion were mixed so that the alumina weight ratio was 92%.

Comparative manufacturing example One :

A porous heat-resistant layer composition was prepared in the same manner as in Preparation Example 1, except that the polyfunctional urethane acrylate resin (Miwon Specialty Chemicals, SC2152) having a weight average molecular weight of about 20,000 g/mol was diluted to 30% by weight in acetone. Did.

Comparative manufacturing example 2 :

A porous heat-resistant layer composition was prepared in the same manner as in Preparation Example 2, except that the polyfunctional urethane acrylate resin having a weight average molecular weight of about 20,000 g/mol (Miwon Specialty Chemicals, SC2152) was diluted to 30% by weight in acetone. Did.

Comparative manufacturing example 3 :

Multifunctional monomer (SK Cytec, DPHA: dipentaerythritol hexaacrylate) was diluted with acetone to 30% by weight, and the inorganic dispersion was the same as in Preparation Example 1, except that the alumina weight ratio was 97%. Porous heat-resistant layer composition was prepared.

Preparation of separator for lithium secondary battery

The prepared porous heat-resistant layer composition was coated on a cross section of a polyethylene single-film base film having a thickness of 12 μm using a meyer bar coater, and then dried at 80° C. for 2 minutes. After drying, a high-pressure mercury lamp was irradiated with ultraviolet light at a quantity of 350 mJ/cm to cure to prepare a 15 μm separator having a 3 μm coating layer thickness.

Each composition is shown in Table 1 below.

Binder (% by weight) Alumina
(weight%) Photoinitiator
(weight%) Hypbranched (meth)acrylate oligomer Urethane acrylate DPHA Example 1 2.9 - - 97 0.1 Example 2 7.7 - - 92 0.3 Comparative Example 1 - 2.9 - 97 0.1 Comparative Example 2 - 7.7 - 92 0.3 Comparative Example 3 - - 2.9 97 0.1

Evaluation example

Evaluation example 1: Aeration

For each of the separators prepared in Examples 1 and 2 and Comparative Examples 1 to 3, the time (seconds) for 100 cc of air to permeate using an air permeability measuring device (Asahi Seiko, EG01-55-1MR) was measured. Measurement was made, and the results are shown in Table 2 below.

Evaluation example 2: description Cohesion

A slurry was prepared by adding LiCoO ₂ , polyvinylidene fluoride and carbon black to a N-methylpyrrolidone solvent in a weight ratio of 96:2:2. The slurry was applied to an aluminum thin film, dried and rolled to prepare an anode.

Slurry was prepared by adding graphite, polyvinylidene fluoride and carbon black to a N-methylpyrrolidone solvent in a weight ratio of 98:1:1. The slurry was applied to a copper foil, dried and rolled to prepare a negative electrode.

The separators prepared in Examples 1 and 2 and Comparative Examples 1 to 3 were positioned between the prepared positive electrode and the negative electrode, and passed through a roll having a pressure of 250 kgf in an 80° C. chamber at a speed of 150 mm/sec. And a separator were adhered. A sample was prepared by cutting the separator bonded to the electrode into a width of 25 mm and a length of 50 mm. After separating the separator from the negative electrode plate about 10 to 20 mm in the sample, the separator was fixed to the upper grip, and the negative electrode plate was fixed to the lower grip so that the gap between the grips was 20 mm, and then tensioned and peeled in the 180° direction. The peeling rate was 20 mm/min, and after peeling, the force required to peel 40 mm was measured three times to calculate the average value, and the results are shown in Table 2 below.

Evaluation example 3: membrane resistance evaluation

The cathode, Examples 1 and 2, and the separators and anodes prepared in Comparative Examples 1 to 3 were sequentially stacked, and 1.5M LiBF ₄ was injected with an electrolyte in EC/EMC/DMC=2/1/7 solvent. Thus, a coin symmetric battery as shown in FIG. 2 was prepared and allowed to stand at room temperature for 24 hours.

2 is a schematic view of a coin symmetric battery manufactured to evaluate the membrane resistance.

The resulting coin symmetric battery was mounted on a resistance meter and then evaluated for resistance, and the results are shown in Table 2 below.

Evaluation example 4: Heat shrinkage rate

The separators for lithium secondary batteries of Examples 1 and 2 and Comparative Examples 1 to 3 were cut 15 cm in the MD direction. The sample is prepared by cutting the sample to a size of 10 cm * 10 cm in all directions. The cut sample is dotted at 50 mm intervals in the MD direction and 50 mm intervals in the TD direction. The median is the point where the two points in the MD direction and the two points in the TD meet vertically.

After standing at 130° C., 150° C., and 200° C. for 1 hour in the oven, and measuring the marked dot spacing, the shrinkage ratio was calculated according to Equation 1 below, and the results are shown in Table 2 below.

[Equation 1]

Shrinkage (%) = [(L0-L1)/L0] * 100

(L0 = initial median interval, L1 = median interval after 1 hour left)

Example 1 Example 2 Comparative Example 1 Comparative Example 2 Comparative Example 3 Number of functional groups 20 or more 20 or more 15 pieces 15 pieces 6 Heat-resistant layer thickness 3㎛ 3㎛ 3㎛ 3㎛ 3㎛ Mineral content 97% 92% 97% 92% 97% Aeration (sec/100cc) 139 147 141 148 149 Base binding force (N/12mm) 0.89 0.81 0.05 0.45 0.03 Membrane resistance (Ω) 0.62 0.68 0.66 0.69 0.71 Shrinkage 130℃/1hr 0% 0% 16% 3% 12% 150℃/1hr 2% 3% >60% 26% >60% 200℃/1hr 3% 3% >60% >60% >60%

Referring to Table 2, it can be seen that the separation membrane according to an embodiment significantly improves substrate binding power and heat shrinkage rate while securing air permeability and membrane resistance of a certain level or higher.

Although the preferred embodiments of the present invention have been described in detail above, the scope of rights of the present invention is not limited thereto, and various modifications and improvements of those skilled in the art using the basic concept of the present invention defined in the following claims are also provided. It belongs to the scope of the invention.

10: separator
40: anode
50: cathode
60: electrode assembly
70: case
100: lithium secondary battery

Claims (13)

A hyperbranched oligomer comprising 20 to 200 crosslinkable functional groups; Polymerization initiators; Inorganic particles; And a porous heat-resistant layer composition comprising a solvent. In claim 1,
The number of crosslinkable functional groups included in the hyperbranched oligomer is 100 to 200 porous heat-resistant layer composition. In claim 1,
The crosslinkable functional group is a (meth) acrylate group, vinyl group, hydroxyl group, epoxy group, oxane group, oxetane group, ester group, cyanate group and at least one selected from the group consisting of a porous heat-resistant layer composition. In claim 1,
The hyperbranched oligomer is represented by the following formula (1), porous heat-resistant layer composition:
[Formula 1]

In Chemical Formula 1,
A core (CORE) is substituted with a functional group which can be combined with R ¹ or unsubstituted C3 to C60 aliphatic hydrocarbon group, substituted with a functional group which can be combined with R ¹ or unsubstituted C3 to C60 heterocyclic aliphatic hydrocarbon ring, R ¹ A substituted or unsubstituted C6 to C60 aromatic hydrocarbon having a functional group capable of being bonded with, a substituted or unsubstituted C3 to C60 hetero aromatic hydrocarbon having a functional group capable of being bonded to R ¹ , or a combination thereof,
R ¹ to R ³ are each independently substituted or unsubstituted C1 to C60 aliphatic hydrocarbon, substituted or unsubstituted C3 to C60 hetero aliphatic hydrocarbon, substituted or unsubstituted C6 to C60 aromatic hydrocarbon, substituted or unsubstituted C3 to C60 heteroaromatic hydrocarbon or a combination thereof,
E ₁ and E ₂ are each independently an ester bond,
X ¹ to X ⁴ are each independently a (meth)acrylate group, a vinyl group, a hydroxyl group, an epoxy group, an oxane group, an oxetane group, an ester group, a cyanate group, an isocyanate group, or a combination thereof,
m1 and m2 are each independently an integer from 1 to 10,
n is an integer from 5 to 20. In claim 1,
The crosslinkable functional group is a (meth) acrylate group, a porous heat-resistant layer composition. In claim 5,
The hyperbranched oligomer is represented by the following formula (2), porous heat-resistant layer composition:
[Formula 2]

In Chemical Formula 2,
A core (CORE) is substituted with a functional group which can be combined with R ¹ or unsubstituted C3 to C60 aliphatic hydrocarbon group, substituted with a functional group which can be combined with R ¹ or unsubstituted C3 to C60 heterocyclic aliphatic hydrocarbon ring, R ¹ A substituted or unsubstituted C6 to C60 aromatic hydrocarbon having a functional group capable of being bonded with, a substituted or unsubstituted C3 to C60 hetero aromatic hydrocarbon having a functional group capable of being bonded to R ¹ , or a combination thereof,
R ¹ to R ³ are each independently substituted or unsubstituted C1 to C60 aliphatic hydrocarbon, substituted or unsubstituted C3 to C60 hetero aliphatic hydrocarbon, substituted or unsubstituted C6 to C60 aromatic hydrocarbon, substituted or unsubstituted C3 to C60 heteroaromatic hydrocarbon or a combination thereof,
E ₁ and E ₂ are each independently an ester bond,
m1 and m2 are each independently an integer from 1 to 10,
n is an integer from 5 to 20. In claim 1,
The inorganic particles are 80 to 99% by weight relative to the total weight of the porous heat-resistant layer composition, porous heat-resistant layer composition. In claim 1,
The polymerization initiator is a porous heat-resistant layer composition, 0.01 to 10% by weight relative to the total weight of the porous heat-resistant layer composition. In claim 1,
The hyperbranched oligomer is 1 to 20% by weight based on the solid content of the porous heat-resistant layer composition, porous heat-resistant layer composition. In claim 1,
The inorganic particles are Al ₂ O ₃ , SiO ₂ , TiO ₂ , SnO ₂ , CeO ₂ , MgO, NiO, CaO, GaO, ZnO, ZrO ₂ , Y ₂ O ₃ , Porous heat-resistant layer composition comprising SrTiO ₃ , BaTiO ₃ , Mg(OH) ₂ , boehmite or a combination thereof. Porous substrates; And
It includes a heat-resistant layer located on at least one surface of the porous substrate,
The heat-resistant layer is formed from the porous heat-resistant layer composition according to any one of claims 1 to 10, lithium secondary battery separator. In claim 11,
The thickness of the heat-resistant layer is 1 ㎛ to 6 ㎛, the separator for a lithium secondary battery. anode; cathode; And Lithium secondary battery comprising a separator for a lithium secondary battery according to claim 11 located between the positive electrode and the negative electrode.

Images