KR20230126985A - Separator, preparing method thereof, and lithium battery comprising the separator - Google Patents

Abstract

porous substrates; And disposed on one or both sides of the porous substrate,
a binder containing at least one selected from a water-based cross-linking reactive acrylamide-based copolymer and a cross-linked product of the water-based cross-linking reactive acrylamide-based copolymer; and inorganic particles, and a first coating layer containing a crosslinked product of the composition for forming the first coating layer; containing, a fluorine-based polymer and a (meth)acrylic resin on top of the first coating layer. and a second coating layer, wherein the composition for forming the first coating layer includes a binder including an aqueous cross-linking reactive acrylamide-based copolymer; inorganic particles; and water, wherein the water-based crosslinking-reactive acrylamide-based copolymer contains two or more crosslinkable crosslinkable reactive groups, a separator, a manufacturing method thereof, and a lithium secondary battery including the same are provided.

Description

Separator, method for manufacturing the same, and lithium battery including the same {Separator, preparing method thereof, and lithium battery comprising the separator}

It relates to a separator, a manufacturing method thereof, and a lithium battery including the same.

In order to meet the miniaturization and high performance of various devices, miniaturization and weight reduction of lithium batteries are becoming important. In addition, the discharge capacity, energy density and cycle characteristics of lithium batteries are becoming important in order to be applied to fields such as electric vehicles. In order to meet the above usage, a lithium battery having high discharge capacity per unit volume, high energy density, and excellent lifespan characteristics is required.

In a lithium battery, a separator is disposed between an anode and a cathode to prevent a short circuit. An electrode assembly including a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode is wound to have a jelly roll shape, and the jelly roll is rolled to improve adhesion between the positive electrode/negative electrode and the separator in the electrode assembly.

Olefin-based polymers are widely used as separators for lithium batteries. Olefin-based polymers have excellent flexibility, but have low strength when immersed in an electrolyte solution, and may cause a short circuit of a battery due to rapid thermal contraction at a high temperature of 100 ° C. or higher. In order to solve this problem, for example, a separator having a shutdown function added using polyethylene wax on a porous olefin-based polymer substrate has been proposed.

However, this separator has insufficient battery stability at high temperatures and needs to be improved.

One aspect is to provide a separator having improved stability at high temperatures as well as improved electrode plate adhesion and heat resistance.

Another aspect is to provide a method for manufacturing the separation membrane.

Another aspect is to provide a lithium battery including the separator.

According to one aspect,

porous substrates; And an aqueous cross-linking reactive acrylamide-based copolymer disposed on one side or both sides of the porous substrate,

a binder containing at least one selected from crosslinking products of water-based crosslinking-reactive acrylamide-based copolymers; And inorganic particles; containing a first coating layer comprising,

Containing a fluorine-based polymer and (meth)acrylic resin on top of the first coating layer

Including a second coating layer,

The water-based crosslinking-reactive acrylamide-based copolymer contains two or more crosslinkable crosslinkable reactive groups, the separator is provided.

According to another aspect,

A binder comprising an aqueous crosslinking-reactive acrylamide-based copolymer on one side or both sides of the porous substrate; inorganic particles; And water; forming a first coating layer on the porous substrate by coating a composition for a first coating containing and drying it; and

Separation film comprising the step of obtaining the above-described separator including the step of forming a second coating layer by coating and drying a composition for forming a second coating layer containing a fluorine-based polymer, a (meth)acrylic resin, and water on top of the first coating layer A manufacturing method is provided.

According to another aspect,

anode;

cathode; and

A lithium battery including the separator disposed between the positive electrode and the negative electrode is provided.

According to one aspect, it is possible to manufacture a separator capable of realizing electrode plate adhesion and having improved heat resistance. A lithium battery with improved lifespan characteristics can be manufactured by using such a separator.

1 is a schematic cross-sectional view of a separation membrane according to an embodiment.
2 is a schematic diagram of a lithium battery including an electrode assembly wound in a flat jelly roll shape according to an embodiment.
3 is a schematic diagram of a lithium battery including an electrode assembly wound in a cylindrical jelly roll shape according to an embodiment.

Since the present inventive concept described below can be applied with various transformations and can have various embodiments, specific embodiments are illustrated in the drawings and described in detail in the detailed description. However, this is not intended to limit the present creative idea to a specific embodiment, and should be understood to include all transformations, equivalents, or substitutes included in the technical scope of the present creative idea.

Terms used below are only used to describe specific embodiments, and are not intended to limit the present inventive idea. Singular expressions include plural expressions unless the context clearly dictates otherwise. Hereinafter, terms such as “comprise” or “have” are intended to indicate that there is a feature, number, step, operation, component, part, component, material, or combination thereof described in the specification, but one or the other It should be understood that the presence or addition of the above other features, numbers, steps, operations, components, parts, components, materials, or combinations thereof is not precluded. "/" used below may be interpreted as "and" or "or" depending on the situation.

In the drawings, the thickness is enlarged or reduced to clearly express various layers and regions. Like reference numerals have been assigned to like parts throughout the specification. Throughout the specification, when a part such as a layer, film, region, plate, etc. is said to be "on" or "above" another part, this includes not only the case directly on top of the other part, but also the case where there is another part in the middle thereof. . Throughout the specification, terms such as first and second may be used to describe various components, but the components should not be limited by the terms. Terms are used only to distinguish one component from another.

In this specification, reference to any monomer(s) generally refers to a monomer that can be polymerized with another polymerizable component, such as another monomer or polymer. Unless otherwise indicated, it is to be understood that once a monomeric component reacts with another component to form a compound, the compound will contain residues of such component.

As used herein, the term “polymer” is intended to refer to prepolymers, oligomers, homopolymers, copolymers, and blends or mixtures thereof.

As used herein, “combination thereof” may mean a mixture of constituents, copolymers, blends, alloys, composites, reaction products, and the like.

Hereinafter, a separator according to embodiments, a manufacturing method thereof, and a lithium battery employing the separator will be described in more detail.

Recently, as the demand for improved current density and higher capacity of lithium batteries mounted in line with technological development and increased demand for automobile batteries continues, the need for thin film separators is on the rise. Accordingly, there is a gradual increase in demand for a separator having high strength, high heat resistance, and excellent adhesion without deterioration in safety.

The present inventors have completed the invention of a separator that meets the above requirements.

A separator according to an embodiment includes a porous substrate; and disposed on one side or both sides of the porous substrate, the porous substrate; and a binder containing at least one selected from a water-based cross-linking reactive acrylamide-based copolymer and a crosslinked product of the water-based cross-linking reactive acrylamide-based copolymer disposed on one or both surfaces of the porous substrate. and inorganic particles, and a second coating layer containing a fluorine-based polymer and a (meth)acrylic resin on the top of the first coating layer.

The first coating layer is, for example, a water-based crosslinking reactive acrylamide-based copolymer,

It may contain crosslinking products of water-based crosslinking reactive acrylamide-based copolymers, or combinations thereof. In the present specification, the “crosslinking product of the water-based crosslinking-reactive acrylamide-based copolymer” refers to a product obtained by reacting the crosslinking-reactive group of the water-based crosslinking-reactive acrylamide-based copolymer through the crosslinking reaction of the water-based crosslinking-reactive acrylamide-based copolymer. indicate

The separator has a structure in which a second coating layer, which is an adhesive layer, is laminated on one surface of a first coating layer disposed on a porous substrate. Due to the presence of such a second coating layer, excellent adhesion of the separator to the electrode plate can be secured.

The fluorine-based polymer is, for example, from the group consisting of polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride, hexafluoropropylene, tetrafluoroethylene, chlorotetrafluoroethylene and perfluoromethylvinyl ether. It is a copolymer of two or more selected monomers, or a combination thereof.

Examples of the copolymer include vinylidene fluoride-hexapropylene copolymer and the like.

The (meth)acrylic resin is, for example, polymethylmethacrylate, polybutylacrylate, (meth)acrylic copolymer or a combination thereof.

For example, the (meth)acrylic copolymer may include (i) a (meth)acrylate-derived repeating unit, and (ii) a monomer-derived repeating unit containing a polymerizable unsaturated group.

The (meth)acrylate-derived repeating unit may be, for example, a conjugate base of (meth)acrylic acid, a (meth)acrylate, or a derivative thereof. The (meth)acrylate-derived repeating unit may be represented by, for example, Formula 1, Formula 2, Formula 3, or a combination thereof.

[Formula 1] [Formula 2] [Formula 3]

In Formulas 1 to 3, R ¹ , R ² and R ³ are each independently hydrogen or a methyl group, and M in Formula 2 is an alkali metal.

The alkali metal may be, for example, lithium, sodium, potassium, rubidium or cesium.

The repeating unit derived from the (meth)acrylate or (meth)acrylic acid is present in an amount of 10 mol% to 70 mol%, such as 20 mol% to 60 mol%, 30 mol% to 60 mol%, based on the total amount of the (meth)acrylic copolymer. , or 40 mol% to 55 mol%.

When the (meth)acrylate or repeating unit derived from (meth)acrylic acid is included in the above range, the acrylic heat-resistant binder and the separation membrane 10 including the same may exhibit excellent adhesive strength, heat resistance, air permeability, and oxidation resistance.

For example, the structural unit derived from (meth)acrylate or (meth)acrylic acid may include a repeating unit represented by Chemical Formula 2 and a structural unit represented by Chemical Formula 3, in which case the structural unit represented by Chemical Formula 2 The repeating unit and the repeating unit represented by Formula 3 may be included in a molar ratio of 10:1 to 1:1, or 5:1 to 1:1.

The monomer containing a polymerizable unsaturated group may be at least one selected from a styrenic monomer, an acid-derived monomer, or a combination thereof.

More specifically, the styrene-based monomer may be one or more selected from methyl styrene, bromo styrene, chloro styrene, or a combination thereof, as well as styrene.

More specifically, the acid-derived monomer includes a substituent corresponding to -COOH, and may be one or more selected from itaconic acid, acrylic acid, or a combination thereof. At this time, the (meth)acrylic resin may be a crosslinking type or a non-crosslinking type. In order to prepare a crosslinking type (meth)acrylate resin, a crosslinking agent may be further added in the polymerization step. The crosslinking agent may be at least one selected from divinylbenzene, divinylsulfone, divinylether, or a combination thereof.

The (meth)acrylic resin may be, for example, a styrene-ethylhexyl acrylate copolymer. In the styrene-ethylhexyl acrylate copolymer, the mixing molar ratio of the styrene monomer and the ethylhexyl acrylate monomer is 1:9 to 9:1 or 2:8 to 8:2.

The fluorine-based polymer and the (meth)acrylic resin may be, for example, a particulate binder.

The particulate binder may have an average particle diameter of 100 nm to 500 nm, or 150 nm to 500 nm, 200 nm to 500 nm, 50 nm to 500 nm, 100 nm to 400 nm, 150 nm to 300 nm, or 150 nm to 250 nm. The average particle diameter of the particulate binder can be adjusted by controlling the amount of initiator added, the amount of emulsifier added, reaction temperature and stirring speed during polymer production.

The average particle diameter, for example, may be a particle size (D ₅₀ ) at 50% by volume in a cumulative size-distribution curve. When the particulate binder has the average particle diameter, it is easier to control the thickness of the second coating layer when forming the second coating layer, which is an adhesive layer, on the separator by a coating method.

When the fluorine-based polymer is a particulate binder, the average particle diameter (d50) is 150 nm to 300 nm, for example 250 nm, and when the acrylic resin is a particulate binder, the average particle diameter (d50) is 100 nm to 500 nm, eg 500 nm.

The weight average molecular weight of the fluorine-based polymer is 100,000 g / mol to 1,000,000 g / mol, for example, 200,000 g / mol to 900,000 g / mol, for example, 300,000 g / mol to 800,000 g / mol, for example, 400,000 g / mol mol to 800,000 g/mol. When the weight average molecular weight of the fluorine-based polymer satisfies the above range, the separator can exhibit excellent adhesion, heat resistance, air permeability, and oxidation resistance.

The weight average molecular weight of the (meth)acrylic resin is 50,000 g/mol to 1,500,000 g/mol, 100,000 g/mol to 1,200,000 g/mol, or 200,000 g/mol to 1,000,000 g/mol, respectively. When the weight average molecular weight of the (meth)acrylic resin satisfies the above range, the separator having the second coating layer containing the (meth)acrylic resin can exhibit excellent adhesion, heat resistance, air permeability, and oxidation resistance. The weight average molecular weight may be a polystyrene reduced average molecular weight measured using gel permeation chromatography.

When the (meth)acrylic resin has a glass transition temperature, the glass transition temperature is 35°C to 80°C. In this range, not only the electrode adhesion is excellent, but also the ionic conductivity is good.

The second coating layer may further include an adhesive binder. The adhesive binder may be a polyvinyl alcohol-based binder. When the adhesive layer further includes an adhesive binder, adhesion between the separator and the electrode may be further improved.

The thickness of the first coating layer is 1 um to 10 um, 1 um to 6 um, 1 um to 5 um, or 1 um to 3 um. The thickness of the second coating layer is 0.5 um to 5 um, or 0.5 um to 3 um. Here, the thickness of the first coating layer and the second coating layer represents the total thickness of the first coating layer and the second coating layer, respectively. For example, when the first coating layer and the second coating layer are each coated only on the end surface of the porous substrate, the total thickness of the first coating layer and the second coating layer represents the cross-sectional thickness. And when the first coating layer and the second coating layer are coated on both sides of the porous substrate, respectively, the total thickness of the first coating layer and the second coating layer represents the thickness of both sides.

When the thickness of the above-described second coating layer is within the above range, adhesion to the electrode is excellent and air permeability is excellent.

And the thickness of the first coating layer is less than 25% of the total thickness of the coating separator. The thickness of the first coating layer is, for example, 10 to 25%, or 15 to 25% of the total thickness of the separator. When the thickness of the first coating layer is within the above range, excellent heat resistance at high temperatures is secured.

According to one embodiment, the total thickness of the coating separator having the first coating layer and the second coating layer is 6 to 20 um, or 7 to 15 um.

The mixing weight ratio of the fluorine-based polymer and the (meth)acrylic resin in the second coating layer is 1:1 to 5:1, 1:1 to 4:1, for example 2:1 to 4:1.

According to one embodiment, the first coating layer and the second coating layer are sequentially disposed on one side of the porous substrate, and the second coating layer including a fluorine-based polymer and a (meth)acrylic resin is disposed on the other side of the porous substrate. can

According to another embodiment, one or more selected from the first coating layer, the second coating layer, and the third coating layer may be disposed on the other surface of the porous substrate. The first coating layer and the second coating layer are as described above, and the third coating layer may contain at least one selected from inorganic particles having high heat resistance and fluorine-based polymers having excellent adhesion.

The separator can realize electrode plate adhesion compared to conventional separators when manufacturing batteries, and has high heat resistance. In addition, a separator manufactured using the same can improve lifespan characteristics of a lithium battery.

In the separator according to an embodiment, the water-based crosslinking-reactive acrylamide-based copolymer contains two or more crosslinkable crosslinkable reactive groups. A first coating layer is formed using such a copolymer.

The composition for forming the first coating layer includes an aqueous crosslinkable acrylamide-based copolymer as a binder, and the acrylamide-based copolymer includes two or more crosslinkable crosslinkable groups.

The composition for forming the first coating layer includes an aqueous crosslinking-reactive acrylamide-based copolymer, so that it can be used in a one-component type without a crosslinking agent, and the two or more crosslinking reactive groups can cause a crosslinking reaction with each other through a self-condensation reaction. Through this, a separator coating layer can be formed, and a separator having high heat resistance characteristics can be provided compared to conventional separators.

According to one embodiment, the crosslinking reactive group may include at least one first functional group selected from a carboxyl group, an amine group, and an isocyanate group; and at least one second functional group selected from a hydroxyl group, an epoxy group, and an oxazoline group, and a cross-linking reaction occurs between the first functional group and the second functional group to be bonded. For example, a carboxyl group and a hydroxyl group may be included as the crosslinking reactive group.

According to one embodiment, the equivalent ratio of the first functional group and the second functional group may be in the range of 30:70 to 70:30. The equivalent ratio of the first functional group and the second functional group may be, for example, in the range of 35:65 to 65:35, 40:60 to 60:40, or 45:55 to 55:45, for example about It can be in the 50:50 range. Within this range, a crosslinking reaction between the first functional group and the second functional group may occur smoothly.

According to one embodiment, the acrylamide-based copolymer includes a (N-substituted) amide-based monomer, and the (N-substituted) amide-based monomer includes (meth)acrylamide, N,N-dimethyl(meth)acryl Amide, N,N-diethyl(meth)acrylamide, N,N-dipropyl(meth)acrylamide, N,N-diisopropyl(meth)acrylamide, N,N-di(n-butyl)( N,N-dialkyl(meth)acrylamides such as meth)acrylamide, N,N-di(t-butyl)(meth)acrylamide, N-ethyl(meth)acrylamide, N-isopropyl(meth) Acrylamide, N-butyl (meth)acrylamide, N-n-butyl (meth)acrylamide, N-methylol (meth)acrylamide, N-ethylol (meth)acrylamide, N-methylolpropane (meth)acrylamide 1 selected from the group consisting of amide, N-methoxymethyl (meth)acrylamide, N-methoxyethyl (meth)acrylamide, N-butoxymethyl (meth)acrylamide, and N-acryloylmorpholine May include more than one species.

The content of the (N-substituted) amide-based monomer may be in the range of 30 to 90 mol% based on the total mole of the monomer components constituting the acrylamide-based copolymer, for example, 40 to 80 mol%, 50 to 80 mol% %, can be By using the acrylamide-based copolymer having the (N-substituted) amide-based monomer in the above range, a decomposition temperature characteristic of 200 ° C. or higher may be exhibited.

According to one embodiment, the water-based crosslinking reactive acrylamide-based copolymer may include (N-substituted) amide-based monomers; and a carboxyl group-containing monomer, an alkyl (meth)acrylate monomer, a hydroxyl group-containing monomer, an isocyanate group-containing monomer, an oxazoline group-containing monomer, a hydroxyl group-containing monomer, a polyfunctional (meth)acrylate-based monomer, and an acid anhydride group-containing monomer. Monomer, sulfonic acid group-containing monomer, phosphoric acid group-containing monomer, succinimide-based monomer, maleimide-based monomer, itaconimide-based monomer, cyano-containing monomer, (meth)acrylic acid aminoalkyl-based monomer, (meth)acrylic acid alkoxyalkyl-based monomer, epoxy group-containing acrylic monomer, acrylic acid ester monomer having a heterocycle, halogen atom, silicon atom, etc., acryloylmorpholine, (meth)acrylic acid ester having an alicyclic hydrocarbon group, (meth)acrylic acid ester having an aromatic hydrocarbon group, and one or two or more acrylic monomers selected from the group consisting of (meth)acrylic acid esters obtained from alcohols derived from terpene compounds.

Here, two or more kinds of functional groups crosslinkable to each other may be present in the (N-substituted) amide-based monomer and the acrylic monomer, or may be present only in the acrylic monomer.

Specific examples of the acrylic monomer include carboxyl group-containing monomers such as acrylic acid, (meth)acrylic acid, carboxyethyl acrylate, carboxypentyl acrylate, itaconic acid, maleic acid, fumaric acid, crotonic acid, and isocrotonic acid; An alkyl (meth)acrylate monomer having a linear or branched chain alkyl group having 1 to 20 carbon atoms in the ester moiety, specifically, for example, methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth) Acrylate, isopropyl(meth)acrylate, n-butyl(meth)acrylate, isobutyl(meth)acrylate, t-butyl(meth)acrylate, pentyl(meth)acrylate, isopentyl(meth)acrylate Late, hexyl(meth)acrylate, cyclohexyl(meth)acrylate, 2-ethylhexyl(meth)acrylate, heptyl(meth)acrylate, octyl(meth)acrylate, isooctyl(meth)acrylate, nonyl (meth)acrylate, isononyl(meth)acrylate, decyl(meth)acrylate, isodecyl(meth)acrylate, undecyl(meth)acrylate, dodecyl(meth)acrylate, tridecyl(meth)acrylate Acrylates, tetradecyl(meth)acrylate, pentadecyl(meth)acrylate, hexadecyl(meth)acrylate, heptadecyl(meth)acrylate, octadecyl(meth)acrylate, isooctadecyl(meth)acrylate Alkyl (meth)acrylates such as nonadecyl (meth)acrylate, myristyl (meth)acrylate, palmityl (meth)acrylate, stearyl (meth)acrylate, and n-tetradecyl (meth)acrylate based monomer; 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, (meth)acrylate 6-hydroxyhexyl, (meth)acrylate 8-hydroxyoctyl, (meth)acrylate 10-hydroxydecyl, (meth)acrylate 12-hydroxylauryl, (4-hydroxymethylcyclohexyl) hydroxyl group-containing monomers such as hydroxyalkyl (meth)acrylates such as methyl (meth)acrylate; Hexanediol diacrylate (HDDA), tripropylene glycol diacrylate (TPGDA), ethylene glycol diacrylate (EGDA), trimethylolpropane triacrylate (TMPTA), trimethylolpropaneethoxy triacrylate (TMPEOTA), polyfunctional (meth)acrylate-based monomers such as glycerin propoxylated triacrylate (GPTA), pentaerythritol tetraacrylate (PETA), or dipentaerythritol hexaacrylate (DPHA); acid anhydride group-containing monomers such as maleic anhydride and itaconic anhydride; sulfonic acid group-containing monomers such as 2-(meth)acrylamido-2-methylpropanesulfonic acid, (meth)acrylamidopropanesulfonic acid, sulfopropyl (meth)acrylate, and (meth)acryloyloxynaphthalenesulfonic acid; phosphoric acid group-containing monomers such as [2-(2-hydroxyethyl)acryloyl] phosphate; N-(meth)acryloyloxymethylenesuccinimide, N-(meth)acryloyl-6-oxyhexamethylenesuccinimide, N-(meth)acryloyl-8-oxyhexamethylenesuccinimide, etc. A succinimide-based monomer of; maleimide monomers such as N-cyclohexylmaleimide, N-isopropylmaleimide, N-laurylmaleimide, and N-phenylmaleimide; N-methyl itaconimide, N-ethyl itaconimide, N-butyl itaconimide, N-octyl itaconimide, N-2-ethylhexyl itaconimide, N-cyclohexyl itaconimide itaconimide-based monomers such as mead and N-laurylitaconimide; cyano-containing monomers such as acrylonitrile and (meth)acrylonitrile; Aminoalkyl (meth)acrylate monomers such as aminoethyl (meth)acrylate, N,N-dimethylaminoethyl (meth)acrylate, N,N-dimethylaminoethyl (meth)acrylate, and t-butylaminoethyl (meth)acrylate ; alkoxyalkyl (meth)acrylate monomers such as methoxyethyl (meth)acrylate, ethoxyethyl (meth)acrylate, propoxyethyl (meth)acrylate, butoxyethyl (meth)acrylate, and ethoxypropyl (meth)acrylate; epoxy group-containing acrylic monomers such as glycidyl (meth)acrylate; acrylic acid ester monomers having heterocycles such as tetrahydrofurfuryl (meth)acrylate, fluorine atom-containing (meth)acrylate, and silicone (meth)acrylate, halogen atom, silicon atom, and the like; acryloylmorpholine; (meth)acrylic acid esters having alicyclic hydrocarbon groups such as cyclopentyl (meth)acrylate, cyclohexyl (meth)acrylate, isobornyl (meth)acrylate, and dicyclopentanyl (meth)acrylate; (meth)acrylic acid esters having aromatic hydrocarbon groups such as phenyl (meth)acrylate and phenoxyethyl (meth)acrylate; (meth)acrylic acid ester obtained from terpene compound derivative alcohol; etc. can be mentioned. The acrylamide-based copolymer may be used alone or in combination of two or more of the aforementioned acryl-based monomers.

According to one embodiment, the molar ratio of the (N-substituted) amide-based monomer and the acryl-based monomer may be in the range of 1:99 to 99:1. For example, the molar ratio of the (N-substituted) amide-based monomer and the acrylic monomer may be in the range of 20:80 to 80:20, 30:70 to 70:30, 40:60 to 60:40, or 50:50. there is. Within the above range, a separator coating layer having improved heat resistance may be formed.

The weight average molecular weight of the acrylamide-based copolymer may be 100,000 to 1,000,000 g/mol. For example, the weight average molecular weight of the acrylamide-based copolymer may be 150,000 to 800,000 g/mol, specifically, for example, 200,000 to 700,000 g/mol, and more specifically, for example, 300,000 to 800,000 g/mol. 600,000 g/mol. Within this range, it is possible to manufacture a coating separator having a low shrinkage rate when stored at a high temperature. For example, within the above range, when stored at 150° C. for 1 hour, a coating separator having a shrinkage rate of 5% or less may be manufactured.

The acrylamide-based copolymer may have a glass transition temperature of 150°C or higher. For example, the glass transition temperature of the acrylamide-based copolymer may be 150 °C to 300 °C, specifically, for example, 170 °C to 280 °C, and more specifically, for example, 190 °C to 250 °C. A separator coating layer having high heat resistance may be formed within the above range.

According to one embodiment, the acrylamide-based copolymer may be a water-based cross-linking reactive polyacrylamide-acrylic acid-hydroxyethyl acryl-based copolymer.

According to one embodiment, the acrylamide-based copolymer may further include one or more types of non-acrylic monomers. By further including one or more non-acrylic monomers in the acrylamide-based copolymer, the copolymer's heat resistance and binding force to the porous substrate of the separator can be further improved.

Non-acrylic monomers included in the acrylamide-based copolymer may be used without particular limitation as long as they are copolymerizable monomers other than the aforementioned acrylic monomers. Examples of copolymerizable non-acrylic monomers include vinyl esters, nitrogen-containing heterocyclic monomers, N-vinylcarboxylic acid amides, lactam monomers, olefin monomers, vinyl ether monomers, aromatic vinyl compounds, and olefins. or dienes, vinyl ethers, vinyl chloride, sulfonic acid group-containing monomers, imide group-containing monomers, isocyanate group-containing monomers, and the like, and one or more types may be selected from these.

Specific examples of copolymerizable non-acrylic monomers include vinyl esters such as vinyl acetate and vinyl propionate; N-vinyl-2-pyrrolidone, N-methylvinylpyrrolidone, N-vinylpyridine, N-vinylpiperidone, N-vinylpyrimidine, N-vinylpiperazine, Nvinylpyrazine, N-vinylpyrrole, N-vinylimidazole, N-vinyloxazole, N-(meth)acryloyl-2-pyrrolidone, N-(meth)acryloylpiperidine, N-(meth)acryloylpyrrolidine , N-vinylmorpholine, N-vinyl-2-piperidone, N-vinyl-3-morpholinone, N-vinyl 2-caprolactam, N-vinyl-1,3-oxazin-2-one, N nitrogen-containing heterocyclic monomers such as -vinyl-3,5-morpholinedione, N-vinylpyrazole, N-vinylisoxazole, N-vinylthiazole, N-vinylisothiazole, and N-vinylpyridazine; N-vinyl carboxylic acid amides; lactam-based monomers such as N-vinyl caprolactam; olefinic monomers such as isoprene, butadiene, and isobutylene; vinyl ether monomers such as methyl vinyl ether and ethyl vinyl ether; Aromatic vinyl compounds, such as vinyltoluene and styrene; olefins or dienes such as ethylene, butadiene, isoprene, and isobutylene; vinyl ethers such as vinyl alkyl ether; vinyl chloride; sulfonic acid group-containing monomers such as styrene sulfonic acid, allyl sulfonic acid and sodium vinyl sulfonate; imide group-containing monomers such as cyclohexyl maleimide and isopropyl maleimide; isocyanate group-containing monomers such as 2-isocyanate ethyl (meth)acrylate; etc. can be mentioned. These non-acrylic monomers can be used individually by 1 type or in combination of 2 or more types.

The content of the non-acrylic monomer included in the acrylamide-based copolymer is not particularly limited and can be used within a range that does not impair the water-based crosslinking reaction characteristics of the acrylamide-based copolymer and high heat resistance characteristics of the separator. For example, the non-acrylic monomer may be included in the range of 0.1 to 30 mol% based on the total mole of the monomer components constituting the acrylamide-based copolymer. Within the above range, it is possible to provide an acrylamide-based copolymer with improved heat resistance and substrate binding ability of the polymer.

The content of the acrylamide-based copolymer may be 10 to 100% by weight based on the total weight of the binder. For example, the content of the acrylamide-based copolymer may be 30 to 95% by weight, 50 to 90% by weight, or 60 to 80% by weight based on the total weight of the binder. Within the above range, it is possible to provide a composition for coating a separator having improved heat resistance and substrate binding ability.

The composition for forming the first coating layer for the separator may further include an aqueous binder commonly used in the art as a binder. Typical water-based binders include, for example, polyvinyl alcohol, polyvinyl acetate, polyacrylic acid, polyacrylic acid ester, polymethacrylic acid, polymethacrylic acid ester, poly-N-vinylcarboxylic acid amide, and polyacrylonitrile. , Polyether, Polyamide, Ethylene Vinyl Acetate Copolymer, Polyethylene Oxide, Cellulose Acetate, Cellulose Acetate Butyrate, Cellulose Acetate Propionate, Cyanoethyl Pullulan, Cyanoethyl Polyvinyl Alcohol, Cyanoethyl Cellulose, Cyano It may include at least one selected from ethyl sucrose, pullulan, carboxyl methyl cellulose, acrylonitrile styrene butadiene copolymer, and polyimide.

The inorganic particles included in the composition for forming the first coating layer for a separator are included in the coating layer of the separator formed from the composition, thereby reducing the possibility of short circuit between the positive electrode and the negative electrode, thereby improving battery stability. The inorganic particles included in the separator coating composition may be a metal oxide, a metalloid oxide, or a combination thereof. Specifically, inorganic particles include alumina, titania, boehmite, barium sulfate, calcium carbonate, calcium phosphate, amorphous silica, crystalline glass particles, kaolin, talc, silica-alumina composite oxide particles, calcium fluoride, lithium fluoride, zeolite, It may be molybdenum sulfide, mica, magnesium oxide or the like. Inorganic particles are, for example, Al ₂ O ₃ , SiO ₂ , TiO ₂ , SnO ₂ , CeO ₂ , NiO, CaO, ZnO, MgO, ZrO ₂ , Y ₂ O ₃ , It may be SrTiO ₃ , BaTiO ₃ , MgF ₂ , Mg(OH) ₂ or a combination thereof. Considering the crystal growth and economical efficiency of the vinylidene fluoride-hexafluoropropylene copolymer, the inorganic particles may be alumina, titania, boehmite, barium sulfate, or a combination thereof. Inorganic particles may be spherical, plate, fibrous, etc., but are not limited to these, and any form usable in the art is possible. Plate-like inorganic particles include, for example, alumina and boehmite. In this case, reduction in the area of the separator at high temperature can be further suppressed, a relatively large porosity can be secured, and characteristics can be improved during penetration evaluation of a lithium battery. When the inorganic particles are plate-shaped or fibrous, the inorganic particles may have an aspect ratio of about 1:5 to 1:100. For example, the aspect ratio may be about 1:10 to about 1:100. For example, the aspect ratio may be about 1:5 to about 1:50. For example, the aspect ratio may be about 1:10 to about 1:50. On the flat surface of the plate-shaped inorganic particles, the length ratio of the major axis to the minor axis may be 1 to 3. For example, the length ratio of the major axis to the minor axis on the flat surface may be 1 to 2. For example, the ratio of the length of the major axis to the minor axis on the flat surface may be about 1. The aspect ratio and the ratio of the length of the major axis to the minor axis can be measured using a scanning electron microscope (SEM). Shrinkage of the separator may be suppressed, relatively improved porosity may be secured, and penetration characteristics of a lithium battery may be improved in the aspect ratio and the length range of the short axis to the long axis. When the inorganic particles are in the form of a plate, the average angle of the flat surface of the inorganic particles with respect to one surface of the porous substrate is 0 to 30 ° C. For example, the angle of the flat surface of the inorganic particles with respect to one surface of the porous substrate may converge to 0 degrees. That is, one surface of the porous substrate and the flat surface of the inorganic particles may be parallel. For example, when the average angle of the flat surface of the inorganic compound with respect to one surface of the porous substrate is in the above range, thermal contraction of the porous substrate can be effectively prevented, and a separator with reduced shrinkage can be provided. The organic particles may be cross-linked polymers. The organic particles may be highly cross-linked polymers having no glass transition temperature (Tg). When a highly crosslinked polymer is used, heat resistance is improved and shrinkage of the porous substrate at high temperatures can be effectively suppressed.

In the composition for forming the first coating layer for the separation membrane, the total weight of the binder and the weight ratio of the inorganic particles may be 0.1:99.9 to 50:50. For example, the total weight of the binder and the weight ratio of the inorganic particles may be 1:99 to 20:80 or 3:97 to 30:70. Within the above range, it is possible to provide a composition for forming a first coating layer for a separator having excellent substrate binding force and excellent heat resistance.

The composition for forming the first coating layer for the separation membrane may further include organic particles. Organic particles include, for example, styrene-based compounds and derivatives thereof, methyl methacrylate-based compounds and derivatives thereof, acrylate-based compounds and derivatives thereof, diallyl phthalate-based compounds and derivatives thereof, polyimide-based compounds and derivatives thereof, and polyimide-based compounds and derivatives thereof. It may include a urethane-based compound and a derivative thereof, a copolymer thereof, or a combination thereof, but is not limited thereto, and any organic particle that can be used in the art is possible. For example, the organic particles may be crosslinked polystyrene particles or crosslinked polymethylmethacrylate particles. The particles may be secondary particles formed by aggregation of primary particles. In the separator including secondary particles, the porosity of the coating layer is increased, so that a lithium battery having excellent high power characteristics can be provided.

The composition for forming the first coating layer may be provided in a slurry form by including water as a solvent capable of dispersing the above-described components. The composition for forming the first coating layer may further include an organic solvent as long as the water-based properties are not impaired. The organic solvent may be an alcohol-based organic solvent. For example, the organic solvent may include one or more selected from the group consisting of methanol, ethanol, propanol, and butanol. By using an alcohol-based organic solvent, it is possible to provide a composition for forming a first coating layer that is harmless to the body and has excellent drying properties, thereby securing mass productivity without reducing productivity. According to one embodiment, water and the organic solvent may be included in a volume ratio of 100:0 to 60:40. For example, water and the organic solvent may be included in a volume ratio of 95:5 to 80:20, specifically, for example, may be included in a volume ratio of 85:15 to 70:30. Within the above range, it is possible to provide a composition for forming a first coating layer of a separator having improved drying properties.

The solvent is volatilized through drying after coating the composition for forming the first coating layer for the separator, so that it does not exist in the coating layer of the finally obtained separator.

A separator manufacturing method according to an embodiment includes a binder including an aqueous cross-linking reactive acrylamide-based copolymer on one side or both sides of a porous substrate; inorganic particles; And water; forming a first coating layer on the porous substrate by coating a composition for a first coating containing and drying it; and forming a second coating layer by coating and drying a composition for forming a second coating layer containing a fluorine-based polymer, a (meth)acrylic resin, and water on top of the first coating layer to obtain a separator.

First, while moving the porous substrate, the composition for forming the first coating layer for the separator is coated on one or both surfaces of the porous substrate.

The method of coating the composition for forming the first coating layer of the separator on one side or both sides of the moving porous substrate is not particularly limited, and for example, a forward roll coating method, a reverse roll coating method, a micro At least one selected from a gravure (microgravure) coating method and a direct metering (direct metering) coating method may be selected, but is not necessarily limited to these methods. The coating method may be, for example, a direct metering coating method.

Subsequently, the porous substrate coated with the composition for forming the first coating layer is moved into the dryer.

The separator having the coating layer disposed on the porous substrate is prepared by drying the porous substrate coated with the composition for forming the first coating layer for the separator in a dryer by hot air. The porous substrate coated with the composition for forming the first coating layer for the separator is supplied to one side of the dryer, dried by hot air in the dryer, and discharged to the other side of the dryer. In the dryer, hot air is supplied from upper and lower nozzles disposed alternately or symmetrically on the upper and lower parts of the porous substrate coated with the composition for forming the first coating layer for the separator.

The moving speed of the porous substrate in the dryer may be the same as the coating speed. If the moving speed of the porous substrate is too slow, the inorganic particles included in the composition for forming the first coating layer for the separation membrane are mainly distributed at the interface between the coating layer and the porous substrate, thereby deteriorating the binding force between the coating layer and the porous substrate. If the moving speed of the porous substrate is too fast, the inorganic particles in the coating layer are mainly distributed near the surface facing the electrode of the coating layer, and thus the binding force between the separator and the electrode may decrease.

The hot air supply speed in the dryer is, for example, 10 to 50 m/s, 10 to 40 m/s, 10 to 30 m/s, or 10 to 20 m/s, and the drying completion rate may be greater than 15 mpm . By having the hot air supply speed and drying completion speed within these ranges, a separator with improved bending strength and peel strength can be manufactured while improving the production speed. If the hot air supply speed is too slow, the inorganic particles included in the composition for forming the first coating layer for the separation membrane are mainly distributed at the interface between the coating layer and the porous substrate, and thus the binding force between the coating layer and the porous substrate may decrease.

The hot air drying temperature in the dryer is, for example, 30 to 80°C, 35 to 75°C, 40 to 70°C, or 45 to 65°C. By having the hot air temperature in this range, a separator having improved bending strength and peel strength at the same time can be manufactured.

The residence time of the porous substrate in the dryer is, for example, 10 to 50 seconds, 10 to 45 seconds or 10 to 40 seconds, 10 to 35 seconds, or 10 to 30 seconds. By having the residence time in the dryer within this range, a separator having improved bending strength and peel strength at the same time can be manufactured. If the residence time of the porous substrate in the dryer is too short, uniform phase separation may not be achieved. If the residence time of the porous substrate in the dryer is excessively long, the base film may shrink and the pores of the entire membrane may shrink.

During hot air drying in the dryer, the non-solvent supplied into the dryer may be at least one selected from water and alcohol. The non-solvent may be, for example, water vapor. Alcohol can be, for example, methanol, ethanol, propanol, and the like.

A separator according to another embodiment includes a porous substrate; and a first coating layer disposed on one side or both sides of the porous substrate, wherein the coating layer includes a dried cross-linked product of the above-described composition for forming the first coating layer for a separator.

The first coating layer includes a binder and inorganic particles including an aqueous crosslinking-reactive acrylamide-based copolymer by crosslinking and drying the above-described composition for forming the first coating layer for a separator, and includes two types included in the acrylamide-based copolymer. The above cross-linking reactive groups have a cross-linked form with each other.

A step of forming a second coating layer by coating and drying a composition for forming a second coating layer including a fluorine-based polymer, a (meth)acrylic resin, and water on the first coating layer is performed. Here, the coating and drying conditions may be performed in the same manner as the coating and drying conditions at the time of forming the first coating layer described above. In addition, the composition for forming the second coating layer may further include an organic solvent in the same manner as the composition for forming the first coating layer.

An adhesive binder may be further added to the composition for forming the second coating layer.

The heat shrinkage rate of the separator according to one embodiment after storage at 150 ° C. for 1 hour is 15%

or less, and the heat shrinkage rate after storage at 150 ° C. for 10 minutes in the state containing the electrolyte is less than 10%. Here, as the electrolyte, 1M LiBF ₄ dissolved in propylene carbonate (PC) is used. As such, the separator according to one embodiment exhibits high heat resistance.

Also, the electrode adhesion of the separator according to one embodiment is 0.4 gf/mm or more. The evaluation conditions of the electrode adhesive strength were as described in Evaluation Example 4.

The separator may have a basis weight ratio calculated by Equation 1 below of less than 0.6. Specifically, for example, the separator may have a basis weight ratio of 0.55 or less, 0.5 or less, 0.48 or less, 0.47 or less, 0.46 or less, or 0.45 or less. The basis weight ratio of the separator may be at least 0.40 or more. The separator may have a basis weight ratio of, for example, 0.4 to 0.55, and specifically, 0.45 to 0.5.

<Equation 1>

Basis weight ratio = unit weight of coating layer / unit weight of porous substrate

In the case of a conventional coated separator, it was impossible to secure physical properties such as heat resistance at a basis weight ratio of less than 0.6. However, the serafator according to an embodiment uses the above-described composition for forming the first coating layer for a separator, so that heat resistance is desired even at a weight ratio of less than 0.6. It is possible to secure physical properties by improving the level.

The separation membrane including the first coating layer formed from the above-described composition for forming the first coating layer for a separation membrane may have very good physical properties such that the number of black dots per unit area (1 m ² ) is less than 0.04. The number of black dots per unit area (1 m ² ) of the separation membrane may be 0.003 or less, 0.002 or less, or 0.001 or less.

The electrode assembly including the separator disposed between the positive electrode and the negative electrode and wound in a jelly roll form may have a bending strength of 460 N or more and a peel strength of 0.3 N/m or more. . Since the separator exhibits a bending strength of 460 N or more and a peel strength of 0.3 N/m or more, energy density and cycle characteristics of a lithium battery including the separator may be improved.

The porous substrate included in the separator may be a porous membrane including polyolefin. Polyolefin has an excellent short circuit prevention effect and can improve battery stability by a shutdown effect. For example, the porous substrate may be a film made of a resin such as polyolefin, such as polyethylene, polypropylene, polybutene, and polyvinyl chloride, and a mixture or copolymer thereof, but is not necessarily limited thereto and may be used in the art. Any porous membrane is possible. For example, a porous film made of polyolefin resin; Porous membrane woven with polyolefin fibers; Non-woven fabric containing polyolefin; Aggregates of insulating material particles and the like may be used. For example, a porous membrane containing polyolefin has excellent applicability of a binder solution for preparing a coating layer formed on a porous substrate, and it is possible to increase the capacity per unit volume by increasing the ratio of the active material in the battery by thinning the membrane thickness of the separator. .

The polyolefin used as the material of the porous substrate may be, for example, a homopolymer of polyethylene or polypropylene, a copolymer, or a mixture thereof. Polyethylene may be low-density, medium-density, or high-density polyethylene, and from the viewpoint of mechanical strength, high-density polyethylene may be used. In addition, two or more types of polyethylene may be mixed for the purpose of imparting flexibility. The polymerization catalyst used for preparing polyethylene is not particularly limited, and a Ziegler-Natta catalyst, a Phillips catalyst, a metallocene catalyst, or the like can be used. From the viewpoint of achieving both mechanical strength and high permeability, the weight average molecular weight of polyethylene may be 100,000 to 12,000,000, for example, 200,000 to 3,000,000. Polypropylene may be a homopolymer, a random copolymer, or a block copolymer, and may be used alone or in combination of two or more thereof. In addition, the polymerization catalyst is not particularly limited, and a Ziegler-Natta catalyst or a metallocene catalyst may be used. In addition, stereoregularity is not particularly limited, and isotactic, syndiotactic or atactic can be used, but inexpensive isotactic polypropylene can be used. In addition, polyolefins other than polyethylene or polypropylene and additives such as antioxidants can be added to polyolefins within a range that does not impair the effects of the present invention.

The porous substrate included in the separator includes, for example, polyolefin such as polyethylene and polypropylene, and a multilayer film of two or more layers may be used, a polyethylene/polypropylene two-layer separator, a polyethylene/polypropylene/polyethylene three-layer separator, and polypropylene. Mixed multilayer membranes such as /polyethylene/polypropylene three-layer separators may be used, but are not limited thereto, and any material and configuration that can be used as a porous substrate in the art is possible. The porous substrate included in the separator may include, for example, a diene-based polymer prepared by polymerizing a monomer composition including a diene-based monomer. The diene-based monomer may be a conjugated diene-based monomer or a non-conjugated diene-based monomer. For example, the diene monomer is 1,3-butadiene, isoprene, 2-chloro-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 2-ethyl-1,3-butadiene, 1 , 3-pentadiene, chloroprene, vinylpyridine, vinylnorbornene, dicyclopentadiene and 1,4-hexadiene, including but not necessarily limited to one or more selected from the group consisting of diene-based monomers in the art Anything that can be used is possible.

The porous substrate included in the separator may have a thickness of 1 μm to 100 μm. For example, the porous substrate may have a thickness of 1 μm to 30 μm. For example, the porous substrate may have a thickness of 5 μm to 20 μm. For example, the porous substrate may have a thickness of 5 μm to 15 μm. For example, the porous substrate may have a thickness of 5 μm to 10 μm. If the thickness of the porous substrate is less than 1 μm, it may be difficult to maintain mechanical properties of the separator, and if the thickness of the porous substrate exceeds 100 μm, the internal resistance of the lithium battery may increase. The porosity of the porous substrate included in the separator may be 5% to 95%. If the porosity is less than 5%, the internal resistance of the lithium battery may increase, and if the porosity is greater than 95%, it may be difficult to maintain mechanical properties of the porous substrate. The pore size of the porous substrate in the separator may be 0.01 μm to 50 μm. For example, the pore size of the porous substrate in the separator may be 0.01 μm to 20 μm. For example, the pore size of the porous substrate in the separator may be 0.01 μm to 10 μm. If the pore size of the porous substrate is less than 0.01 μm, the internal resistance of the lithium battery may increase, and if the pore size of the porous substrate exceeds 50 μm, it may be difficult to maintain mechanical properties of the porous substrate.

The coating layer may be disposed on one side or both sides of the porous substrate. The coating layer is formed from the above-described composition for forming the first coating layer for the separator. The coating layer may have, for example, a single-layer structure or a multi-layer structure. For example, the coating layer may be disposed on only one side of the porous substrate and may not be disposed on the other side. Also, the coating layer may have a multilayer structure. In the multi-layered coating layer, layers selected from organic layers, inorganic layers, and organic-inorganic layers may be arbitrarily disposed. The multi-layer structure may be a two-layer structure, a three-layer structure, or a four-layer structure, but is not necessarily limited to such a structure and may be selected according to required composite separator properties. The coating layer may be respectively disposed on both sides of the porous substrate, for example. The coating layers disposed on both sides of the porous substrate may independently be organic layers, inorganic layers, or organic-inorganic layers, and at least one of them includes the above-described composition for forming the first coating layer for the separator. In addition, at least one of the coating layers respectively disposed on both sides of the porous substrate may have a multilayer structure. In the multi-layered coating layer, layers selected from organic layers, inorganic layers, and organic-inorganic layers may be arbitrarily disposed. The multi-layer structure may be a two-layer structure, a three-layer structure, or a four-layer structure, but is not necessarily limited to such a structure and may be selected according to required composite separator properties.

^The coating layer included in the separator includes, for example, 0.3 to 0.4 pores with an average diameter of 500 nm to 1000 nm per 1 um ² and 0.5 to 1.5 pores with an average diameter of less than 500 nm per 1 um 2 . Pores with an average diameter of 500 nm to 1000 nm per 1 um ² are, for example, large-diameter pores, and pores with an average diameter of less than 500 nm per 1 um ² are, for example, small-diameter pores. As the separator has the number of large-diameter pores and the number of small-diameter pores within these ranges, the composite separator can provide balanced air permeability.

When the number of large-diameter pores included in the separation membrane is less than 0.3 and the number of small-diameter pores is greater than 0.15, the air permeability of the separation membrane is excessively increased. Accordingly, since the internal resistance of the separator impregnated with the electrolyte increases, cycle characteristics of a lithium battery including the separator may deteriorate. If the number of large-diameter pores included in the separation membrane is greater than 0.4 and the number of small-diameter pores is less than 0.5, the air permeability of the separation membrane is excessively low. Therefore, it is difficult for the separator to inhibit the growth of lithium dendrites generated during the charging and discharging process, which increases the possibility of short-circuiting of the lithium battery including the separator. The air permeability is, for example, Gurley air permeability measured by measuring the time required for 100 cc of air to pass through the separator according to JIS P-8117.

The surface of the coating layer included in the separation membrane may have a morphology including, for example, a plurality of pores in the form of islands discontinuously disposed on the polymer membrane. The surface of the coating layer included in the separation membrane may show a morphology in which a plurality of pores are discontinuously disposed on the polymer membrane. The surface of the coating layer is basically made of a polymer film, and may have a morphology in which pores are irregularly arranged in the form of islands on the polymer film. By having the morphology of the coating layer included in the separator, the bending strength and peel strength of the separator may be improved. As a result, the energy density and cycle characteristics of the lithium battery including the separator may be improved. In contrast, the surface of the coating layer included in the conventional separator does not show a polymer film, and shows a morphology in which a plurality of particles are connected to each other to form a porous surface.

The content of the inorganic particles included in the coating layer may be 99% by weight or less, or 98% by weight or less based on the total weight of the coating layer.

The content of the inorganic particles included in the coating layer formed from the composition for forming the first coating layer of the separator may be 50% by weight or more, 55% by weight or more, or 60% by weight or more based on the total weight of the coating layer. The content of the inorganic particles included in the coating layer formed from the composition for forming the first coating layer for the separator is 55% to 99% by weight, 60% to 99% by weight, or 60% to 98% by weight, based on the total weight of the coating layer. or 60% to 96% by weight. By including the particles in this range in the coating layer formed from the composition for forming the first coating layer for the separator, the bending strength and peel strength of the separator may be simultaneously improved.

The average particle diameter of the inorganic particles included in the coating layer is 100 nm to 2 μm, 150 nm to 1.5 μm, and 200 nm to 1.0 μm. The average particle diameter of the inorganic particles is measured using, for example, a laser diffraction method or a dynamic light scattering method measuring device. The average particle diameter of the inorganic particles is measured using, for example, a laser scattering particle size distribution analyzer (e.g., Horiba LA-920), and the median particle diameter (D50) when accumulated by 50% from the small particle side in terms of volume is the value of Both binding force between the coating layer and the porous substrate and binding force between the coating layer and the electrode may be improved by using inorganic particles having an average particle diameter within this range. In addition, by using inorganic particles having an average particle diameter within this range, a separator including a coating layer containing inorganic particles may have an appropriate porosity. If the average particle diameter of the inorganic particles is less than 100 nm, air permeability of the separator may decrease and moisture content may increase.

The thickness of the coating layer is, for example, 0.5 to 4 μm, 0.5 to 2.5 μm, or 0.5 to 2 μm per side. If the thickness of the coating layer per side is too thick, the volume of the rolled electrode assembly may increase. If the thickness of the coating layer per side is too thin, improved bending strength and peel strength may not be obtained. By disposing the coating layer on both sides of the porous substrate, binding force between the coating layer and the electrode is further improved, and as a result, volume change during charging and discharging of the lithium battery can be suppressed. For example, referring to FIG. 1, a first coating layer 12 is disposed on one side of a porous substrate 11 in a separator, a second coating layer 13 is disposed thereon, and the other side of the porous substrate 11 is disposed. A second coating layer 13 is disposed on one surface. A first coating layer 12 may be further disposed between the porous substrate 11 and the second coating layer 13 formed on the other surface of the porous substrate 11 .

The porosity of the coating layer is 30% to 90%, 35% to 80%, or 40% to 70%. When the coating layer has a porosity within this range, an increase in internal resistance of the separator may be prevented, and excellent membrane strength may be provided while having excellent high-rate characteristics. The porosity of the coating layer is the volume occupied by pores in the total volume of the coating layer.

The coating amount of the coating layer is, for example, 1.5 g/m ² to 4.5 g/m ² , 1.7 g/m ² to 4.5 g/m ² , 1.9 g/m ² to 4.5 g/m ² , or 2.1 g/m ² to 4.5 g/m ² . By having the coating amount of the coating layer within this range, the separator including the coating layer can provide improved heat resistance, peel strength, and bending strength at the same time. If the application amount of the coating layer is too low, improved heat resistance, bending strength and peel strength may not be obtained.

The binder included in the coating layer may not have a concentration gradient in which the concentration of the binder increases in a direction from an interface in contact with the porous substrate of the porous layer to a surface facing the electrode. For example, from the interface in contact with the porous substrate of the porous layer toward the surface facing the electrode, it may have a concentration gradient in which the concentration of the binder decreases, or may have a concentration gradient with no tendency to change in concentration.

A lithium battery according to another embodiment includes a positive electrode, a negative electrode, and the above-described separator disposed between the positive electrode and the negative electrode.

According to one embodiment, the lithium battery includes an electrode assembly including a positive electrode, a negative electrode, and the above-described separator disposed between the positive electrode and the negative electrode, and the electrode assembly may have a jelly roll shape. By including the above-mentioned separator in the lithium battery, black spot defects can be reduced and quality can be improved, and since the adhesive force between the electrode (anode and cathode) and the separator increases, volume change during charging and discharging of the lithium battery can be suppressed. . Accordingly, degradation of the lithium battery accompanying a change in volume of the lithium battery may be suppressed, and lifespan characteristics of the lithium battery may be improved.

A lithium battery can be manufactured, for example, in the following way.

First, an anode active material composition in which an anode active material, a conductive material, a binder, and a solvent are mixed is prepared. The negative electrode active material composition is directly coated on a metal current collector to manufacture a negative electrode plate. Alternatively, the negative active material composition may be cast on a separate support, and then a film separated from the support may be laminated on a metal current collector to manufacture a negative electrode plate. The negative electrode is not limited to the forms listed above and may have forms other than the above forms.

The negative electrode active material may be a non-carbon-based material. For example, the anode active material includes at least one selected from the group consisting of a metal capable of forming an alloy with lithium, an alloy of a metal capable of forming an alloy with lithium, and an oxide of a metal capable of forming an alloy with lithium. can do.

For example, the metal alloyable with lithium is Si, Sn, Al, Ge, Pb, Bi, Sb Si-Y alloy (where Y is an alkali metal, an alkaline earth metal, a Group 13-16 element, a transition metal, a rare earth element, or It is a combination of these elements, but not Si), a Sn-Y alloy (where Y is an alkali metal, an alkaline earth metal, a Group 13 to 16 element, a transition metal, a rare earth element, or a combination thereof, but not Sn), and the like. . The element Y is 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, Ge, P, As, Sb, Bi, S, Se, It may be Te, Po, or a combination thereof.

For example, the transition metal oxide may be lithium titanium oxide, vanadium oxide, or lithium vanadium oxide.

For example, the non-transition metal oxide may be SnO ₂ , SiO _x (0<x<2), or the like.

Specifically, the anode active material is Si, Sn, Pb, Ge, Al, SiOx (0<x≤2), SnOy (0<y≤2), Li ₄ Ti ₅ O ₁₂ , TiO ₂ , LiTiO ₃ , Li ₂ It may be one or more selected from the group consisting of Ti ₃ O ₇ , but is not necessarily limited thereto, and any material used in the art as a non-carbon-based negative electrode active material is possible.

In addition, a composite of the non-carbon-based negative electrode active material and the carbon-based material may be used, and a carbon-based negative electrode active material may be additionally included in addition to the non-carbon-based material.

The carbon-based material may be crystalline carbon, amorphous carbon, or a mixture thereof. The crystalline carbon may be graphite such as non-shaped, plate-shaped, flake-shaped, spherical or fibrous natural graphite or artificial graphite, and the amorphous carbon may be soft carbon (low-temperature calcined carbon) Alternatively, it may be hard carbon, mesophase pitch carbide, calcined coke, or the like.

As the conductive material, acetylene black, ketjen black, natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, metal powder such as copper, nickel, aluminum, silver, metal fiber, etc. may be used. Conductive materials such as polyphenylene derivatives may be used singly or in combination of one or more, but are not limited thereto, and any conductive material that can be used in the art may be used. In addition, the above-described crystalline carbon-based material may be added as a conductive material.

Examples of the binder include vinylidene fluoride/hexafluoropropylene copolymer, polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethyl methacrylate, polytetrafluoroethylene and mixtures thereof, or styrene butadiene rubber-based polymers. It may be used, but is not limited to these, and any that can be used as a binder in the art may be used.

N-methylpyrrolidone, acetone, or water may be used as the solvent, but it is not limited thereto, and any solvent that can be used in the art may be used.

The contents of the negative electrode active material, conductive material, binder, and solvent are at levels commonly used in lithium batteries. At least one of the conductive material, the binder, and the solvent may be omitted depending on the use and configuration of the lithium battery.

Meanwhile, the binder used in manufacturing the negative electrode may be the same as the composition for forming the first coating layer of the separator included in the coating layer of the separator.

Next, a cathode active material composition in which a cathode active material, a conductive material, a binder, and a solvent are mixed is prepared. The cathode active material composition is directly coated on a metal current collector and dried to prepare a cathode plate. Alternatively, the positive electrode active material composition may be cast on a separate support, and then the film separated from the support may be laminated on a metal current collector to manufacture a positive electrode plate.

The cathode active material may include at least one selected from the group consisting of lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, and lithium manganese oxide, but is not necessarily limited thereto, and in the art Any available cathode active material may be used.

For example, Li _a A _1-b B _b D ₂ (wherein 0.90 ≤ a ≤ 1.8, and 0 ≤ b ≤ 0.5); Li _a E _1-b B _b O _2-c D _c (wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05); LiE _2-b B _b O _4-c D _c (wherein 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05); Li _a Ni _1-bc Co _b B _c D _α (wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α ≤ 2); Li _a Ni _1-bc Co _b B _c O _2-α F _α (wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α <2); Li _a Ni _1-bc Co _b B _c O _2-α F ₂ (wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α <2); Li _a Ni _1-bc Mn _b B _c D _α (wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α ≤ 2); Li _a Ni _1-bc Mn _b B _c O _2-α F _α (wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α <2); Li _a Ni _1-bc Mn _b B _c O _2-α F ₂ (wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α <2); Li _a Ni _b E _c G _d O ₂ (wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, 0.001 ≤ d ≤ 0.1); Li _a Ni _b Co _c Mn _d GeO ₂ (wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, 0 ≤ d ≤ 0.5, 0.001 ≤ e ≤ 0.1); Li _a NiG _b O ₂ (wherein 0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1); Li _a CoG _b O ₂ (wherein 0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1); Li _a MnG _b O ₂ (wherein 0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1); Li _a Mn ₂ G _b O ₄ (wherein 0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1); QO ₂ ; QS ₂ ; LiQS ₂ ; V ₂ O ₅ ; LiV ₂ O ₅ ; LiIO ₂ ; LiNiVO ₄ ; Li _(3-f) J ₂ (PO ₄ ) ₃ (0 ≤ f ≤ 2); Li _(3-f) Fe ₂ (PO ₄ ) ₃ (0 ≤ f ≤ 2); A compound represented by any of the chemical formulas of LiFePO ₄ may be used:

In this formula, A is Ni, Co, Mn, or a combination thereof; B is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, a rare earth element, or a combination thereof; D is O, F, S, P, or a combination thereof; E is Co, Mn, or a combination thereof; F is F, S, P, or a combination thereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, or combinations thereof; Q is Ti, Mo, Mn, or a combination thereof; I is Cr, V, Fe, Sc, Y, or a combination thereof; J is V, Cr, Mn, Co, Ni, Cu, or combinations thereof.

Of course, one having a coating layer on the surface of this compound may be used, or a mixture of the compound and a compound having a coating layer may be used. The coating layer may include a coating element compound of an oxide, a hydroxide, an oxyhydroxide of a coating element, an oxycarbonate of a coating element, or a hydroxycarbonate of a coating element. Compounds constituting these coating layers may be amorphous or crystalline. As the coating element included in the coating layer, Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, or mixtures thereof may be used. In the process of forming the coating layer, any coating method may be used as long as the compound can be coated in a method (eg, spray coating, dipping method, etc.) that does not adversely affect the physical properties of the positive electrode active material by using these elements. Since it is a content that can be well understood by those skilled in the art, a detailed description thereof will be omitted.

For example, LiNiO ₂ , LiCoO ₂ , LiMn _x O _2x (x=1, 2), LiNi _1-x Mn _x O ₂ (0<x<1), LiNi _1-xy Co _x Mn _y O ₂ (0 ≤x≤0.5, 0≤y≤0.5), LiFeO ₂ , V ₂ O ₅ , TiS, MoS, and the like may be used.

In the cathode active material composition, the same conductive material, binder, and solvent as in the case of the anode active material composition may be used. Meanwhile, it is also possible to form pores in the electrode plate by further adding a plasticizer to the cathode active material composition and/or the anode active material composition.

The contents of the positive electrode active material, conductive material, general binder, and solvent are at levels commonly used in lithium batteries. Depending on the use and configuration of the lithium battery, one or more of the conductive material, general binder, and solvent may be omitted.

Meanwhile, the binder used in manufacturing the anode may be the same as the composition for forming the first coating layer of the separator included in the coating layer of the separator.

Next, the composite separator described above is disposed between the anode and the cathode.

In an electrode assembly including an anode/separator/cathode, the separator disposed between the anode and the cathode is a porous substrate as described above; and a coating layer disposed on both sides of the porous substrate, wherein the coating layer includes the above-described composition for forming the first coating layer for the separator.

A separator may be prepared separately and disposed between the anode and the cathode. Alternatively, the separator is formed by winding the electrode assembly including the positive electrode/separator/negative electrode into a jelly roll form, then accommodating the jelly roll in a battery case or pouch, and thermally softening the jelly roll under pressure while being accommodated in the battery case or pouch. It can be prepared by undergoing a formation step of pre-charging, hot rolling the filled jelly roll, cold rolling the filled jelly roll, and charging and discharging the filled jelly roll under pressure.

Next, the electrolyte is prepared.

The electrolyte may be in a liquid or gel state.

For example, the electrolyte may be an organic electrolyte. Also, the electrolyte may be solid. For example, it may be boron oxide, lithium oxynitride, etc., but is not limited thereto, and any solid electrolyte that can be used in the art can be used. The solid electrolyte may be formed on the negative electrode by a method such as sputtering.

For example, an organic electrolyte solution may be prepared. The organic electrolyte may be prepared by dissolving a lithium salt in an organic solvent.

Any organic solvent that can be used as an organic solvent in the art may be used. For example, propylene carbonate, ethylene carbonate, fluoroethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, methyl isopropyl carbonate, dipropyl carbonate, dibutyl carbonate , benzonitrile, acetonitrile, tetrahydrofuran, 2-methyltetrahydrofuran, γ-butyrolactone, dioxolane, 4-methyldioxolane, N,N-dimethylformamide, dimethylacetamide, dimethyl sulfoxide , dioxane, 1,2-dimethoxyethane, sulfolane, dichloroethane, chlorobenzene, nitrobenzene, diethylene glycol, dimethyl ether, or mixtures thereof.

Any lithium salt can be used as long as it can be used as a lithium salt in the art. For example, LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiClO ₄ , LiCF ₃ SO ₃ , Li(CF ₃ SO ₂ ) ₂ N, LiC ₄ F ₉ SO ₃ , LiAlO ₂ , LiAlCl ₄ , LiN(C _x F _2x+1 SO ₂ )(C _y F _2y+1 SO ₂ ) (provided that x and y are natural numbers), LiCl, LiI, or mixtures thereof.

As shown in FIG. 2 , the lithium battery 1 includes a positive electrode 3 , a negative electrode 2 and a composite separator 4 . After the positive electrode 3, the negative electrode 2, and the separator 4 are wound into an electrode assembly in the form of a flat jelly roll, the pouch 7 is accommodated. Subsequently, an organic electrolyte solution is injected into the pouch 7 and sealed to complete the lithium battery 1 .

As shown in FIG. 3 , the lithium battery 1 includes a positive electrode 3 , a negative electrode 2 and a separator 4 . After the positive electrode 3, the negative electrode 2, and the separator 4 are wound into an electrode assembly in the form of a cylindrical jelly roll, the battery case 5 is accommodated. Subsequently, an organic electrolyte solution is injected into the battery case 5 and sealed with a cap assembly 6 to complete the lithium battery 1 . The battery case may be cylindrical, prismatic, or thin film. The lithium battery may be a lithium ion battery. The lithium battery may be a lithium polymer battery.

Lithium batteries have excellent high-rate characteristics and lifespan characteristics, so they are suitable for electric vehicles (EVs). For example, it is suitable for hybrid vehicles such as plug-in hybrid electric vehicles (PHEVs).

This inventive concept is explained in more detail through the following examples and comparative examples. However, the embodiments are for exemplifying the present creative concept, and the scope of the present creative concept is not limited only to these examples.

(Manufacture of Separator)

Example 1: Water-based crosslinking binder ((N-substituted) amide-based monomer 50 mol%), basis weight ratio 0.45

14.3% by weight of boehmite (ACTILOX 200SM, Nabaltec) with an average particle diameter of 0.3㎛ (D50 by volume) and 0.5% by weight of crosslinkable acrylamide-acrylic acid-hydroxyethyl acryl-based copolymer (Mw 400,000), PVA ( A coating solution 1 for forming a first coating layer was prepared by mixing 0.2% by weight of polyvinyl alcohol) (Daejeong Hwageum, Mw 22,000) and 85% by weight of deionized water. In the cross-linking reactive acrylamide-acrylic acid-hydroxyethyl acryl-based copolymer, the content of the (N-substituted) amide-based monomer is 50 mol% based on the total mole of the monomer components constituting the copolymer.

Separately, 3.64% by weight of polyvinylidene fluoride, 1.2% by weight of acrylic resin, styrene-ethylhexyl acrylate copolymer (molar ratio of styrene and ethylhexyl acrylate = 8:2), 0.16% by weight of PVA (polyvinyl alcohol) , Deionized water (DI water) was mixed with 95% by weight to prepare a coating solution 2 for forming a second coating layer.

The coating liquid 1 for forming the first coating layer was coated on the cross section of a 5.5 μm thick polyethylene porous substrate (CZMZ, NW05535) by bar coating, and then dried under conditions of a temperature of 80 ° C and a wind speed of 15 m / sec to form a first coating layer. Thus, a separator having a first coating layer (thickness: 1.5 um) having a basis weight ratio (coating layer unit weight/porous substrate unit weight) of 0.45 was prepared.

Both sides of the separator having the first coating layer were coated with the coating liquid 2 for forming the second coating layer in a bar coating method on both sides, and then dried under conditions of a temperature of 80 ° C and a wind speed of 15 m / sec to obtain a thickness of 0.5 μm, respectively. A coating separator was prepared by coating a second coating layer (adhesive layer) having a thickness.

The total thickness of the second coating layer (adhesive layer) is 1 μm, and the total thickness of the finally obtained coating separator is 8.0 μm. Therefore, the total thickness of the first coating layer is 19% of the total thickness of the finally obtained coating separator. Here, the total thickness of the second coating layer is the sum of the thicknesses of the second coating layers formed on both sides of the porous substrate.

Example 2: Water-based crosslinking binder ((N-substituted) amide-based monomer 80 mol%), basis weight ratio 0.45

As the cross-linking reactive copolymer in Example 1, the content of the (N-substituted) amide-based monomer is 80 mol% based on the total mole of the monomer components constituting the copolymer. Cross-linking reactive acrylamide-acrylic acid-hydroxyethyl acryl-based copolymer Except for using, the same process was performed to prepare a coating separator.

Comparative Example 1: Application of non-crosslinked CMC binder, basis weight ratio 0.5/thickness of the second coating layer: 1um in total on both sides

D50 0.3㎛ boehmite (ACTILOX 200SM, Nabaltec) 14.3% by weight and Carboxymethylcellulose Sodium Salt (CMC Medium Viscosity, Sigma-Aldrich) 0.5% by weight, PVA (polyvinyl alcohol) (Daejeong Chemical, Mw 22,000) 0.2% by weight and 85% by weight of deionized water were mixed to prepare a coating solution 1.

Separately, coating liquid 2 for forming a second coating layer was prepared by mixing 3.64 wt% of polyvinylidene fluoride (PVdF)-based binder, 1.2 wt% of acrylate-based binder, 0.16 wt% of PVA (polyvinyl alcohol), and 95 wt% of deionized water. manufactured.

The coating solution 1 was coated on a cross section of a 5.5 μm thick polyethylene porous substrate (CZMZ, NW05535) to prepare a coating separator having a first coating layer having a basis weight ratio (coating layer unit weight/porous substrate unit weight) of 0.5.

Both sides of the separator having the first coating layer were coated in a bar coating method using the coating liquid 2 for forming the second coating layer, and then dried under conditions of a temperature of 80 ° C and a wind speed of 15 m / sec, each having a thickness of 0.5 μm. By coating the second coating layer (adhesive layer), a coating separator having a total thickness of 1 μm of the second coating layer (adhesive layer) was prepared. Here, the total thickness of the second coating layer is the sum of the thicknesses of the second coating layers formed on both sides of the porous substrate.

Comparative Example 2: Application of non-crosslinked CMC binder, basis weight ratio 0.6/thickness of the second coating layer: 1um in total on both sides

D50 0.3㎛ boehmite (ACTILOX 200SM, Nabaltec) 14.3% by weight, Carboxymethylcellulose Sodium Salt (CMC Medium Viscosity, Sigma Aldrich) 0.5% by weight, PVA (polyvinyl alcohol) (Daejeong Chemical, Mw 22,000) 0.2% by weight, DI A coating solution 1 was prepared by mixing 85% by weight of water.

Separately, coating liquid 2 for forming the second coating layer was prepared by mixing 3.64 wt% of polyvinylidene fluoride (PVdF)-based binder, 1.2 wt% of acrylate-based binder, 0.16 wt% of PVA (polyvinyl alcohol), and 95 wt% of DI water. manufactured.

The coating solution 1 was coated on a cross section of a polyethylene porous substrate (CZMZ, NW05535) having a thickness of 5.5 μm to prepare a coating separator having a first coating layer having a basis weight ratio (unit weight of coating layer/unit weight of porous substrate) of 0.6.

The coating solution 2 was coated on both sides of the separator having the first coating layer in a bar coating method, and then dried under conditions of a temperature of 80 ° C and a wind speed of 15 m / sec, so that the second coating layer (adhesive layer) each having a thickness of 0.5 μm ) to prepare a coating separator.

The total thickness of the second coating layer (adhesive layer) is 1 μm, and the total thickness of the finally obtained coating separator is 8.8 μm.

Comparative Example 3: application of non-crosslinked polyacrylamide binder, basis weight ratio 0.45 // thickness of the second coating layer: total of both sides 1um

D50 0.3㎛ boehmite (ACTILOX 200SM, Nabaltec) 14.3% by weight, polyacrylamide (Mw 400,000) 0.5% by weight, PVA (polyvinyl alcohol) (Daejeong Chemical, Mw 22,000) 0.2% by weight, DI water 85% by weight was mixed to prepare a coating solution 1 for forming the first coating layer.

Separately, 3.64% by weight of polyvinylidene fluoride, 1.2% by weight of acrylic resin, styrene-ethylhexyl acrylate copolymer (molar ratio of styrene and ethylhexyl acrylate = 8:2), 0.16% by weight of PVA (polyvinyl alcohol) , Deionized water (DI water) was mixed with 95% by weight to prepare a coating solution 2 for forming a second coating layer.

The coating solution 1 was coated on a cross section of a 5.5 μm thick polyethylene porous substrate (CZMZ, NW05535) to prepare a coating separator having a first coating layer having a basis weight ratio (unit weight of coating layer/unit weight of porous substrate) of 0.45.

The coating solution 2 was coated on both sides of the separator having the first coating layer by bar coating, and then dried under conditions of a temperature of 80° C. and a wind speed of 15 m/sec to form second coating layers (adhesive layers) each having a thickness of 0.5 μm. was coated to prepare a coating separator having a total thickness of 1 μm of the second coating layer (adhesive layer). Here, the total thickness of the second coating layer is the sum of the thicknesses of the second coating layers formed on both sides of the porous substrate.

Comparative Example 4

A separator was prepared in the same manner as in Example 1, except that the coating liquid 2 for forming the second coating layer was prepared by mixing 35 wt% of a polyvinylidene fluoride-based binder and 95 wt% of deionized water.

Reference example 1

A separator was prepared in the same manner as in Example 1, except that the second coating layer was not formed.

Evaluation Example 1: Evaluation of Thermal Shrinkage Rate Characteristics

The separators prepared in Example 1, Example 2, Comparative Examples 1 to 4, and Reference Example 1 were cut into a size of about 10 cm in width (MD) and about 10 cm in length (TD), respectively, and subjected to the following conditions 1 and 2 stored respectively.

<Condition 1>

Store for 1 hour in a chamber at 150°C.

<Condition 2>

An electrolyte solution was provided to the separator, and kept in a chamber at 150° C. for 10 minutes. As the electrolyte, 1M LiBF ₄ dissolved in propylene carbonate (PC) is used.

After storage according to the condition 1 or 2, the degree of shrinkage in the MD direction and the TD direction was measured, and the MD direction heat shrinkage rate and the TD direction heat shrinkage rate were calculated by the following equations 2 and 3, respectively, and the MD direction heat shrinkage rate and the TD direction heat shrinkage rate Among the heat shrinkage rates, the higher calculated value was calculated as the final value and listed in Table 1 below.

<Equation 2>

MD direction thermal contraction rate = (length reduced in MD direction after thermal contraction rate evaluation in electrolyte/length of separator in MD direction before evaluation)Х100

<Equation 3>

Thermal contraction rate in TD direction = (length reduced in TD direction after thermal contraction rate evaluation in electrolyte / length in TD direction of separator before evaluation) Х100

Heat shrinkage rate (Condition 1) Heat shrinkage rate (Condition 2) MD direction (%) TD direction (%) MD direction (%) TD direction (%) Example 1 2 2 8 8 Example 2 5 5 12 15 Comparative Example 1 20 15 ≥50 ≥50 Comparative Example 2 4 4 ≥30 ≥30 Comparative Example 3 ≥50 ≥50 ≥50 ≥50 Comparative Example 4 2 2 8 8 Reference example 1 2 2 8 8

Referring to Table 1, the separators of Examples 1 and 2 include a first coating layer using a cross-linkable acrylamide-based copolymer and an adhesive layer, and the separator uses an existing CMC as a binder rather than a cross-linking binder. Compared to Comparative Example 1 and Comparative Example 3 using polyacrylamide having no crosslinking reactivity, it can be seen that both the heat shrinkage in the MD direction and the heat shrinkage in the TD direction are significantly reduced. Through this, it was confirmed that the high-temperature heat resistance of the separator can be improved by coating the separator using the cross-linkable acrylamide-based copolymer.

As shown in Table 1, the separator of Comparative Example 2 had good thermal shrinkage characteristics in Condition 1, but poor thermal shrinkage characteristics in Condition 2.

Evaluation Example 2: Electrode Thermal Shrinkage Rate in Electrolyte

Anodes were placed on both sides of the separators prepared in Examples 1-2, Comparative Examples 1 to 4, and Reference Example 1, and bonding was performed at about 80 ° C. for 1 hour at 300 kgf / cm to prepare a unit cell and an electrolyte solution. provided. As the electrolyte, 1M LiBF ₄ dissolved in propylene carbonate (PC) was used.

For the cathode, bubbles were removed from a mixture of LiCoO ₂ , polyvinylidene fluoride, and carbon black as a conductive material using a mixer to prepare a uniformly dispersed slurry for forming a cathode active material layer. N-methyl 2-pyrrolidone as a solvent was added to the mixture, and the mixing ratio of the composite cathode active material, polyvinylidene fluoride, and carbon black was 98:1:1 by weight. The slurry prepared according to the above process was coated on an aluminum foil using a doctor blade to form a thin electrode plate, dried at 135 ° C. for more than 3 hours, and then subjected to rolling and vacuum drying processes to prepare a positive electrode.

The unit cell prepared according to the above process was left at 150 ° C. for 1 hour, and then dismantled to measure the degree of shrinkage in the MD and TD directions described in Evaluation Example 1 for the heat shrinkage rate of the separator, and the following equations 4 and 5 Accordingly, the MD direction thermal contraction rate and the TD direction thermal shrinkage rate were calculated, respectively, and the larger value of the calculated value among the MD direction thermal shrinkage rate and the TD direction thermal shrinkage rate was calculated as the final value and listed in Table 2 below.

<Equation 4>

MD direction thermal contraction rate = (Decreased length in MD direction after evaluation of electrode thermal contraction rate in electrolyte / length of separator in MD direction before evaluation) Х100

<Equation 5>

TD direction thermal contraction rate = (length reduced in TD direction after evaluation of electrode thermal contraction rate in electrolyte / length of separator in TD direction before evaluation) Х100

Evaluation Example 3: Base material heat shrinkage rate in electrolyte solution

Aluminum foil was placed on both sides of the separators prepared in Examples 1-2, Comparative Examples 1 to 4, and Reference Example 1, and bonding was performed at about 80 ° C. and 300 kgf / cm for 1 hour to prepare a unit cell. . An electrolyte solution was provided to the unit cell. As the electrolyte, 1M LiBF4 dissolved in propylene carbonate (PC) was used.

The unit cell was left at 150 ° C. for 1 hour, then dismantled, and the degree of shrinkage in the MD and TD directions was measured according to the same method as in Evaluation Example 1 for the heat shrinkage rate of the separator, and the heat shrinkage in the MD direction was performed according to Equations 6 and 7 below. The shrinkage rate and the TD direction heat shrinkage rate were calculated, respectively, and the higher calculated value among the MD direction heat shrinkage rate and the TD direction heat shrinkage rate was calculated as the final value and shown in Table 2 below.

<Equation 6>

MD direction thermal contraction rate = (length reduced in MD direction after evaluation of thermal contraction rate of substrate in electrolyte / length of separator in MD direction before evaluation) Х100

<Equation 7>

Thermal contraction rate in TD direction = (length reduced in TD direction after evaluation of thermal contraction rate of substrate in electrolyte / length of separator in TD direction before evaluation) Х100

division Electrode thermal contraction rate in electrolyte Substrate heat shrinkage rate in electrolyte MD direction (%) TD direction (%) MD direction (%) TD direction (%) Example 1 2 2 9 9 Example 2 2 2 15 15 Comparative Example 1 10 10 ≥50 ≥50 Comparative Example 2 2 2 ≥50 ≥50 Comparative Example 3 15 15 ≥50 ≥50 Comparative Example 4 6 6 ≥50 ≥50 Reference example 1 ≥50 ≥50 ≥50 ≥50

Referring to Table 2, it can be seen that the separators of Examples 1 and 2 significantly decreased the electrode shrinkage rate and substrate heat shrinkage rate in the electrolyte solution compared to the separators of Comparative Example 1, Comparative Example 3, and Reference Example 1. Here, the separator of Reference Example 1 did not have a second coating layer (adhesive layer) compared to the separators of Examples 1 and 2, so it had no electrode adhesiveness and showed poor thermal shrinkage in the electrolyte.

As shown in Table 2, the separators of Comparative Example 2 and Comparative Example 4 had good thermal shrinkage of the electrode in the electrolyte, but poor thermal shrinkage of the electrolyte substrate.

Evaluation Example 4: Measurement of whether or not the first coating layer is detached

In a container, the separation membranes prepared according to Examples 1 to 4, Comparative Examples 1 to 4, and Reference Example 1 were cut into a size of about 5 cm in width (MD) and about 5 cm in length (TD), respectively, and soaked in deionized water. After shaking it and leaving it for 10 minutes, the presence or absence of detachment of the first coating layer was visually observed and evaluated. The evaluation results are shown in Table 3 below.

Evaluation Example 5: Electrode adhesive strength (wet adhesive strength)

An anode was placed on one side of the separator prepared in Example 1, Example 2, Comparative Examples 1 to 4, and Reference Example 1, and a polyethylene nonwoven fabric was placed on the other side of the separator, and about 80 ° C. for 1 hour at 300 kgf / cm Bonding was performed under the conditions to prepare a unit cell. An electrolyte solution was provided to the unit cell. As the electrolyte, 1M LiBF ₄ dissolved in propylene carbonate (PC) was used.

For the cathode, bubbles were removed from a mixture of LiCoO ₂ , polyvinylidene fluoride, and carbon black as a conductive material using a mixer to prepare a uniformly dispersed slurry for forming a cathode active material layer. N-methyl 2-pyrrolidone as a solvent was added to the mixture, and the mixing ratio of the composite cathode active material, polyvinylidene fluoride, and carbon black was 98:1:1 by weight. The slurry prepared according to the above process was coated on an aluminum foil using a doctor blade to form a thin electrode plate, dried at 135 ° C. for more than 3 hours, and then subjected to rolling and vacuum drying processes to prepare a positive electrode.

Subsequently, bonding was performed on the unit cell at about 80° C. and 300 kgf/cm for 1 hour. After dismantling, wet adhesion was evaluated through a peel test between the separator and the positive electrode, and the evaluation results are shown in Table 3 below.

division Whether or not the first coating layer is detached Electrode adhesion (wet adhesion) (gf/mm) Example 1 radish 0.45 Example 2 radish 0.45 Comparative Example 1 you 0.44 Comparative Example 2 you 0.20 Comparative Example 3 you not measurable Comparative Example 4 radish - Reference example 1 radish -

As shown in Table 3, the electrode adhesion of the separators of Examples 1 and 2 was greatly improved compared to the separators of Comparative Examples 2 and 3, and the separation of the first coating layer did not occur. In contrast, the separator of Comparative Example 2 had lower electrode adhesiveness compared to the separators of Examples 1 and 2, and the separator of Comparative Example 3 could not measure electrode adhesive strength. And, as shown in Table 3, in the separators of Comparative Examples 1 to 3, unlike the separators of Examples 1 to 4, a phenomenon in which the primary coating layer was easily detached was observed.

In the above, an embodiment has been described with reference to drawings and embodiments, but this is only exemplary, and those skilled in the art can understand that various modifications and equivalent other implementations are possible therefrom. will be. Therefore, the scope of protection of the present invention should be defined by the appended claims.

11: porous substrate 12: first coating layer
13: second coating layer
1: lithium battery 2: negative electrode
3: anode 4: separator
5: battery case 6: cap assembly
7: Pouch

Claims (18)

porous substrates; And disposed on one or both sides of the porous substrate,
A water-based cross-linking reactive acrylamide-based copolymer and the water-based cross-linking reactive
A binder containing at least one selected from crosslinked products of acrylamide-based copolymers; And inorganic particles; containing a first coating layer comprising,
A second coating layer including a fluorine-based polymer and a (meth)acrylic resin on the first coating layer,
The water-based crosslinkable acrylamide-based copolymer contains two or more crosslinkable crosslinkable reactive groups. The method of claim 1, wherein the fluorine-based polymer is polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride, hexafluoropropylene, tetrafluoroethylene, chlorotetrafluoroethylene and perfluoromethyl vinyl ether Separation membrane that is a copolymer of two or more monomers selected from the group consisting of, or a combination thereof. The separator according to claim 1, wherein the thickness of the first coating layer is 25% or less of the total thickness of the separator. The separator according to claim 1, wherein the mixing weight ratio of the fluorine-based polymer and the (meth)acrylic resin in the second coating layer is 1:1 to 5:1. The method of claim 1, wherein the (meth)acrylic resin includes polymethylmethacrylate, polybutylacrylate, (meth)acrylic copolymer or a combination thereof,
The (meth)acrylic copolymer includes (i) a repeating unit derived from (meth)acrylate, and (ii) a repeating unit derived from a monomer containing a polymerizable unsaturated group. The separator of claim 1 , wherein the second coating layer further includes an adhesive binder, and the adhesive binder includes polyvinyl alcohol. The method of claim 1, wherein the crosslinking reactive group in the composition for forming the first coating layer for the separation membrane comprises at least one first functional group selected from a carboxyl group, an amine group, and an isocyanate group; and
A separator comprising at least one second functional group selected from a hydroxyl group, an epoxy group, and an oxazoline group. The separation membrane according to claim 7, wherein the equivalent ratio of the first functional group and the second functional group is in the range of 30:70 to 70:30. The method of claim 1, wherein the acrylamide-based copolymer includes an (N-substituted) amide-based monomer,
The (N-substituted) amide-based monomer is (meth)acrylamide, N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, N,N-dipropyl(meth)acrylamide , N, N-diisopropyl (meth) acrylamide, N, N-di (n-butyl) (meth) acrylamide, N, N-di (t-butyl) (meth) acrylamide, etc. -Dialkyl(meth)acrylamide, N-ethyl(meth)acrylamide, N-isopropyl(meth)acrylamide, N-butyl(meth)acrylamide, Nn-butyl(meth)acrylamide, N-methylol (meth)acrylamide, N-ethylol (meth)acrylamide, N-methylolpropane (meth)acrylamide, N-methoxymethyl (meth)acrylamide, N-methoxyethyl (meth)acrylamide, N -Contains at least one selected from the group consisting of butoxymethyl (meth)acrylamide and N-acryloylmorpholine, and the content of the (N-substituted) amide-based monomer is the acrylamide-based copolymer Separation membrane in the range of 30 to 90 mol% based on the total mole of the constituent monomer components. The method of claim 1, wherein the acrylamide-based copolymer,
(N-substituted) amide-based monomers; and
A carboxyl group-containing monomer, an alkyl (meth)acrylate monomer, a hydroxyl group-containing monomer, an isocyanate group-containing monomer, an oxazoline group-containing monomer, a polyfunctional (meth)acrylate-based monomer, an acid anhydride group-containing monomer, a sulfonic acid group-containing monomer, A phosphoric acid group-containing monomer, a succinimide-based monomer, a maleimide-based monomer, an itaconimide-based monomer, a cyano-containing monomer, an aminoalkyl (meth)acrylate monomer, an alkoxyalkyl (meth)acrylate monomer, an acrylic monomer containing an epoxy group, Acrylic acid ester monomers having heterocycles, halogen atoms, silicon atoms, etc., acryloylmorpholine, (meth)acrylic acid esters having alicyclic hydrocarbon groups, (meth)acrylic acid esters having aromatic hydrocarbon groups, and terpene compound derivatives obtained from alcohols One or two or more acrylic monomers selected from the group consisting of (meth)acrylic acid esters;
The molar ratio of the (N-substituted) amide-based monomer and the acrylic monomer ranges from 1:99 to 99:1. The separator according to claim 1, wherein the acrylamide-based copolymer is a water-based cross-linking reactive polyacrylamide-acrylic acid-hydroxyethyl acryl-based copolymer. The separator according to claim 1, wherein the content of the acrylamide-based copolymer is 10 to 100% by weight based on the total weight of the binder. The method of claim 1, wherein the inorganic particles are boehmite , alumina, aluminum oxyhydroxide (AlOOH), zirconia, yttria, ceria, magnesia, titania, silica, aluminum carbide, titanium carbide, tungsten carbide, boron nitride , aluminum nitride. A separation membrane comprising at least one selected from the group consisting of calcium carbonate, barium sulfate, aluminum hydroxide, and magnesium hydroxide. The separator according to claim 1, wherein the separator has a heat shrinkage rate of 15% or less after storage at 150°C for 1 hour, and a heat shrinkage rate of the separator impregnated with electrolyte is 10% or less after storage at 150°C for 1 hour. The separator according to claim 1, wherein the separator has an adhesive force of 0.4 gf/mm or more to an electrode. Water-based cross-linking reactive acrylamide based on one or both sides of a porous substrate
binders including copolymers; inorganic particles; And water; forming a first coating layer on the porous substrate by coating a composition for a first coating containing and drying it; and
Forming a second coating layer by coating and drying a composition for forming a second coating layer containing a fluorine-based polymer, a (meth)acrylic resin, and water on top of the first coating layer; wherein any one of claims 1 to 15 A method of manufacturing a separator comprising the step of obtaining a separator. The method of claim 16, wherein the mixing weight ratio of the fluorine-based polymer and the (meth)acrylic resin is 1:1 to 5:1. anode; cathode; and a separator according to any one of claims 1 to 15 interposed therebetween.

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