Separation membrane for lithium secondary batteries and lithium secondary batteries containing the same

Abstract

This invention provides a separation membrane for lithium secondary batteries that enhances battery safety and lifespan due to its low dry shrinkage rate and low electrolyte shrinkage rate. [Solution] The present invention relates to a separation membrane for a lithium secondary battery and a lithium secondary battery containing the same, wherein the separation membrane for the lithium secondary battery comprises a porous substrate and a coating layer located on at least one surface of the porous substrate, the coating layer being formed from a composition comprising a mixture of a binder, a crosslinking agent, and a filler, the mixture of fillers comprising a filler having an amine group and a filler having a carboxylic acid group or a carboxylic acid salt.

Description

[Technical Field]

[0001] Reference to related applications This application is based on the priority claim of Korean Patent Application No. 10-2024-0195896, filed with the Korean Intellectual Property Office on December 24, 2024, and incorporates its full disclosure by reference herein.

[0002] Technical field This invention relates to a separator membrane for lithium secondary batteries and a lithium secondary battery containing the same. [Background technology]

[0003] Recently, with the rapid proliferation of electronic devices using batteries, such as mobile phones, laptops, and electric vehicles, the demand for high-energy-density, high-capacity rechargeable batteries has been rapidly increasing. Therefore, research and development to improve the performance of lithium-ion rechargeable batteries is being actively pursued.

[0004] A lithium-ion secondary battery is a battery that includes a positive electrode and a negative electrode containing an active material that allows for the insertion and deintercalation of lithium ions, and an electrolyte. It generates electrical energy through oxidation and reduction reactions that occur when lithium ions are inserted into and removed from the positive and negative electrodes.

[0005] Lithium secondary batteries may include a separator membrane between the positive and negative electrodes. The separator membrane is impregnated in the electrolyte. It is preferable for the separator membrane to maintain its initial shape without thermal shrinkage in the electrolyte to ensure the safety of the battery. [Overview of the project] [Problems that the invention aims to solve]

[0006] One embodiment provides a separation membrane for lithium secondary batteries that enhances battery safety and lifespan because both the dry shrinkage rate and the electrolyte shrinkage rate are low.

[0007] Another embodiment provides a lithium secondary battery including the aforementioned separator membrane for lithium secondary batteries. [Means for solving the problem]

[0008] One embodiment is a separation membrane for lithium secondary batteries.

[0009] The separation membrane for the lithium secondary battery comprises a porous substrate and a coating layer located on at least one surface of the porous substrate, wherein the coating layer is formed from a composition comprising a mixture of a binder, a crosslinking agent, and a filler, and the mixture of fillers comprises a filler having an amine group and a filler having a carboxylic acid group or a carboxylic acid salt.

[0010] Another embodiment provides a lithium secondary battery comprising the aforementioned separator membrane for lithium secondary batteries, a positive electrode, and a negative electrode. [Effects of the Invention]

[0011] A separation membrane for lithium secondary batteries according to one embodiment exhibits remarkably low dry shrinkage and electrolyte shrinkage rates, thereby improving the safety and lifespan of the battery. [Brief explanation of the drawing]

[0012] [Figure 1] This is a cross-sectional view showing a separation membrane for a lithium secondary battery according to one embodiment. [Figure 2] This is a schematic cross-sectional view showing a lithium secondary battery according to one embodiment. [Figure 3] This is a schematic cross-sectional view showing a lithium secondary battery according to one embodiment. [Figure 4] This is a schematic cross-sectional view showing a lithium secondary battery according to one embodiment. [Figure 5] This is a schematic cross-sectional view showing a lithium secondary battery according to one embodiment. [Modes for carrying out the invention]

[0013] Embodiments of the present invention will be described in detail below. However, these are presented as examples only and are not limited thereto, and the present invention is defined solely by the claims.

[0014] Unless otherwise specified in this specification, when a layer, film, region, plate, or other part is described as being "on top of" another part, this includes not only cases where it is "directly on top" of the other part, but also cases where there are other parts in between.

[0015] Unless otherwise specified in this specification, singular nouns may also include plural nouns. Unless otherwise specified, "A or B" may mean "including A, including B, or including both A and B."

[0016] In this specification, “these combinations” may mean mixtures, laminates, composites, copolymers, alloys, blends, and reaction products of the constituents.

[0017] In this specification, "particle size D100" refers to the particle size, meaning the diameter of the particle whose cumulative volume in the particle size distribution is 100% by volume. The particle size distribution can be measured by methods widely known to those skilled in the art. For example, the particle size distribution can be measured with a particle size analyzer, or with a transmission electron microscope or scanning electron microscope. Alternatively, it can be measured using a dynamic light-scattering device, and the D100 value can be calculated by counting the number of particles for each particle size range through data analysis. Alternatively, it can be measured using the laser diffraction method. When measuring using laser diffraction, more specifically, the particles to be measured are dispersed in a dispersion medium, then introduced into a commercially available laser diffraction particle size distribution analyzer (for example, Microtrac MT3000), and after irradiating with ultrasound at approximately 28 kHz at an output of 60 W, D100 can be calculated based on 100% of the particle size distribution of the analyzer.

[0018] In this specification, "particle size D50" refers to the particle size whose cumulative volume in the particle size distribution is 50% by volume. The particle size distribution is obtained by referring to the method described for "particle size D100".

[0019] In this specification, "(meth)acrylic" means acrylic and / or methacrylic.

[0020] Unless otherwise defined, "substitution" in a compound means that the hydrogen atom is replaced by a C1-C30 alkyl group, C2-C30 alkenyl group, C2-C30 alkynyl group, C6-C30 aryl group, C7-C30 alkylaryl group, C1-C30 alkoxy group, C1-C30 heteroalkyl group, C3-C30 heteroalkylaryl group, C3-C30 cycloalkyl group, C3-C15 cycloalkenyl group, C6-C30 cycloalkynyl group, C2-C30 heterocycloalkyl group, halogen (F, Cl, Br, or I), hydroxyl group (-OH), nitro group (-NO2), cyano group (-CN), amino group (-NRR') (where R and R' are independently hydrogen or a C1-C6 alkyl group), or sulfobetaine group (-RR'N + (CH2) n SO3 - (where n is a natural number from 1 to 10), carboxybetaine group (-RR'N + (CH2) n COO - (where n is a natural number from 1 to 10) (where R and R' are independently C1-C20 alkyl groups), azide group (-N3), amidino group (-C(=NH)NH2), hydrazino group (-NHNH2), hydrazono group (=N(NH2), carbamoyl group (-C(O)NH2), thiol group (-SH), acyl group (-C(=O)R, where R is hydrogen, a C1-C6 alkyl group, a C1-C6 alkoxy group, or a C6-C12 aryl group) This means that the molecule is substituted with a substituent selected from a carboxyl group (-COOH) or its salt (-C(=O)OM, where M is an organic or inorganic cation), a sulfonic acid group (-SO3H) or its salt (-SO3M, where M is an organic or inorganic cation), a phosphate group (-PO3H2) or its salt (-PO3MH or -PO3M2, where M is an organic or inorganic cation), and combinations thereof.

[0021] Hereinafter, C1-C3 alkyl groups refer to methyl, ethyl, or propyl groups. C1-C10 alkylene groups may be, for example, C1-C6 alkylene groups, C1-C5 alkylene groups, or C1-C3 alkylene groups, and may be, for example, methylene, ethylene, or propylene groups. C3-C20 cycloalkylene groups may be, for example, C3-C10 cycloalkylene groups or C5-C10 cycloalkylene groups, and may be, for example, cyclohexylene groups. C6-C20 allylene groups may be, for example, C6-C10 allylene groups, and may be, for example, phenylene groups. C3-C20 heterocyclic groups may be, for example, C3-C10 heterocyclic groups, and may be, for example, pyridine groups.

[0022] Hereinafter, "hetero" means containing one or more heteroatoms selected from N, O, S, Si, and P.

[0023] In addition, in chemical formulas, the asterisk (*) indicates a part that is linked to the same or different atoms, groups, or structural units.

[0024] Hereinafter, "alkali metals" refers to elements belonging to Group 1 of the periodic table, such as lithium, sodium, potassium, rubidium, cesium, or francium, and may exist in a cationic or neutral state.

[0025] In this specification, when describing a numerical range, "X~Y" means "X or greater and Y or less (X ≤ and ≤ Y)."

[0026] According to one embodiment, the separation membrane for secondary batteries of the present invention exhibits remarkably low dry shrinkage rates and electrolyte shrinkage rates, thereby improving the safety and lifespan of the battery.

[0027] According to one embodiment, the dry thermal shrinkage rate of the separation membrane for lithium secondary batteries is 5% or less in both the mechanical direction and the width direction, and the thermal shrinkage rate in the electrolyte is 10% or less in both the mechanical direction and the width direction, for example, 5% or less.

[0028] The separation membrane comprises a porous substrate and a coating layer located on at least one surface of the porous substrate, wherein the coating layer is formed from a coating layer composition comprising a mixture of a binder, a crosslinking agent, and a filler, and the mixture of fillers comprises a filler having an amine group and a filler having a carboxylic acid group or a carboxylic acid salt.

[0029] Here, the carboxylic acid group is represented by -COOH, and the carboxylate salt is represented by -COO-M. + (M stands for alkali metal).

[0030] The coating layer may contain a crosslinked body of the coating layer composition.

[0031] The coating layer may include a crosslinked form of the amine group-containing filler and the carboxylic acid group or carboxylate salt-containing filler. The amine group-containing filler and the carboxylic acid group or carboxylate salt-containing filler can contribute to reducing the thermal shrinkage rate by being crosslinked during the process of forming the coating layer from the coating layer composition. Compared to the case where an amine group-containing binder and a carboxylic acid group-containing binder are crosslinked, the separation membrane can significantly reduce the thermal shrinkage rate by crosslinking the amine group-containing filler and the carboxylic acid group or carboxylate salt-containing filler.

[0032] According to one embodiment, the coating layer may include a crosslinked body of the binder and the crosslinking agent. The binder and the crosslinking agent are crosslinked during the process of forming the coating layer from the coating layer composition, thereby further reducing the thermal shrinkage rate.

[0033] According to one embodiment, the coating layer may include a crosslinked body of the binder and the filler having an amine group. The binder and the filler having an amine group are crosslinked during the process of forming the coating layer from the coating layer composition, thereby further reducing the thermal shrinkage rate.

[0034] According to one embodiment, the coating layer may include the binder, the filler having a carboxylic acid group or a carboxylic acid salt, and a crosslinked filler having an amine group. The binder, the filler having a carboxylic acid group or a carboxylic acid salt, and the filler having an amine group can be crosslinked during the process of forming the coating layer from the coating layer composition, thereby further reducing the thermal shrinkage rate.

[0035] The configuration of a separation membrane according to one embodiment will be described in detail below.

[0036] coating layer The aforementioned coating layer may be a heat-resistant coating layer.

[0037] binder The binder may consist of the first binder alone, or it may contain a mixture of the first binder and the second binder. The mixture of the first binder and the second binder may be present in the binder in an amount of 95% by weight or more, for example, 95-100% by weight, or 100% by weight.

[0038] The second binder is a binding binder. The second binder contains one or more of polyvinyl alcohol, polyacrylic acid, and poly(vinyl alcohol-co-acrylic acid). One or more of polyvinyl alcohol, polyacrylic acid, and poly(vinyl alcohol-co-acrylic acid) can enhance the adhesion between the first binder and the filler that is not surface modified.

[0039] According to one embodiment, the second binder may have a glass transition temperature of -20 to 30°C, for example, -20, -19, -18, -17, -16, -15, -14, -13, -12, -11, -10, -9, -8, -7, -6, -5, -4, -3, -2, -1, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20°C. Within this range, it may be advantageous to provide the low dry thermal shrinkage and low in-electrolyte thermal shrinkage. The glass transition temperature can be measured using a differential scanning calorimeter (DSC).

[0040] According to one embodiment, the second binder may have a weight-average molecular weight of 100,000 to 800,000 g / mol, for example, 100,000, 200,000, 300,000, 400,000, 500,000, 600,000, 700,000, 800,000 g / mol, or 200,000 to 500,000 g / mol. Within this range, it may be advantageous to provide the low dry thermal shrinkage and low in-electrolyte thermal shrinkage. The weight-average molecular weight is determined by gel permeation chromatography on a polystyrene basis.

[0041] The second binder may be included in amounts of 10 to 25 parts by weight, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, or 25 parts by weight per 100 parts by weight of the total of the first and second binders. Within this range, it may be advantageous to provide the low dry heat shrinkage and low in-electrolyte heat shrinkage.

[0042] The first binder is a non-adhesive binder with high heat resistance, which can contribute to reducing the thermal shrinkage rate of the separation membrane. The first binder may be a water-based heat-resistant binder.

[0043] The first binder may be included in amounts of 75 to 90 parts by weight, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, or 90 parts by weight per 100 parts by weight of the total of the first and second binders. Within this range, it may be advantageous to increase the substrate bonding strength and reduce the thermal shrinkage rate.

[0044] The first binder may be a (meth)acrylic binder.

[0045] The (meth)acrylic binder may include a first structural unit derived from (meth)acrylamide; and a second structural unit comprising at least one of the structural units derived from (meth)acrylic acid or (meth)acrylate or a salt thereof, and the structural unit derived from (meth)acrylamide sulfonic acid or a salt thereof.

[0046] The (meth)acrylic binder may be a binary copolymer having the first structural unit and structural units derived from (meth)acrylamide sulfonic acid or a salt thereof. The (meth)acrylic binder may be a ternary copolymer having the first structural unit, structural units derived from (meth)acrylic acid or (meth)acrylate or a salt thereof, and structural units derived from (meth)acrylamide sulfonic acid or a salt thereof.

[0047] The first structural unit may be present in an amount of 55 mol% to 95 mol% relative to 100 mol% of the (meth)acrylic binder, and the second structural unit may be present in an amount of 5 mol% to 45 mol% relative to 100 mol% of the (meth)acrylic binder. Within this range, the (meth)acrylic binder can be easily manufactured, and the effects of the coating layer described above can be easily provided.

[0048] In one embodiment, the first structural unit may be present in an amount of 75 mol% to 95 mol%, for example, 80 mol% to 95 mol%, or 80 mol% to 90 mol%, relative to 100 mol% of the (meth)acrylic binder.

[0049] Among the second structural units, the structural unit derived from the (meth)acrylic acid or (meth)acrylate or its salt is contained at 0 to 40 mol%, for example, more than 0 mol% and 40 mol% or less, 1 to 40 mol% or 1 to 10 mol% with respect to 100 mol% of the (meth)acrylic binder, and the structural unit derived from the (meth)acrylamidosulfonic acid or its salt can be contained at 0 to 10 mol%, for example, more than 0 mol% and 10 mol% or less, 1 to 10 mol% with respect to 100 mol% of the (meth)acrylic binder.

[0050] The structural unit derived from the (meth)acrylamide is contained at 80 mol% to 90 mol% with respect to 100 mol% of the (meth)acrylic binder, the structural unit derived from the (meth)acrylic acid or (meth)acrylate or its salt is contained at 0 to 40 mol%, for example, 1 to 10 mol% with respect to 100 mol% of the (meth)acrylic binder, and the structural unit derived from the (meth)acrylamidosulfonic acid or its salt can be contained at 0 to 10 mol%, for example, 1 to 10 mol% with respect to 100 mol% of the (meth)acrylic binder. When the content of each structural unit is within the above range, the heat resistance and adhesion of the separation membrane can be further improved.

[0051] The first structural unit derived from the (meth)acrylamide can be represented by the following Chemical Formula 1.

[0052]

Chemical formula

[0053] In the Chemical Formula 1, R 1 and R 2 are each independently hydrogen or a methyl group.

[0054] The structural unit derived from the (meth)acrylic acid or (meth)acrylate can be represented by, for example, any one of the following Chemical Formula 2, Chemical Formula 3, Chemical Formula 4, and combinations thereof.

[0055] [ka]

[0056] [ka]

[0057] [ka]

[0058] In the aforementioned chemical formulas 2, 3, and 4, R 3 , R 4 , R 6 , R 7 , R 8 and R 9 Each of these is independently either a hydrogen atom or a methyl group, and R 5 is a substituted or unsubstituted C1-C20 alkyl group, and M is an alkali metal.

[0059] The alkali metal may be, for example, lithium, sodium, potassium, rubidium, or cesium.

[0060] The structural units derived from (meth)acrylate may also be derived from alkyl (meth)acrylates, perfluoroalkyl (meth)acrylates, and (meth)acrylates having functional groups in their side chains, for example, from alkyl (meth)acrylates. Furthermore, the number of carbon atoms in the alkyl group or perfluoroalkyl group bonded to the non-carbonyl oxygen atom of the alkyl (meth)acrylate or perfluoroalkyl (meth)acrylate may be specifically 1 to 20, more specifically 1 to 10, for example, 1 to 5.

[0061] Specific examples of alkyl (meth)acrylate esters having 1 to 5 carbon atoms in the alkyl or perfluoroalkyl group bonded to a non-carbonyl oxygen atom include alkyl acrylates such as methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate and t-butyl acrylate; 2-(perfluoroalkyl)ethyl acrylates such as 2-(perfluorobutyl)ethyl acrylate and 2-(perfluoropentyl)ethyl acrylate; alkyl methacrylates such as methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate and t-butyl methacrylate; and 2-(perfluoroalkyl)ethyl methacrylates such as 2-(perfluorobutyl)ethyl methacrylate and 2-(perfluoropentyl)ethyl methacrylate.

[0062] Other alkyl acrylates include: alkyl acrylates with 6 to 18 carbon atoms in the alkyl group bonded to a non-carbonyl oxygen atom, such as n-hexyl acrylate, 2-ethylhexyl acrylate, nonyl acrylate, lauryl acrylate, stearyl acrylate, cyclohexyl acrylate, and isobornyl acrylate; alkyl methacrylates with 6 to 18 carbon atoms in the alkyl group bonded to a non-carbonyl oxygen atom, such as n-hexyl methacrylate, 2-ethylhexyl methacrylate, octyl methacrylate, isodecyl methacrylate, lauryl methacrylate, silidecyl methacrylate, stearyl methacrylate, and cyclohexyl methacrylate; 2-(perfluorohexyl)ethyl acrylate, 2-(perfluorooctyl)ethyl acrylate, 2-(perfluorononyl)ethyl acrylate, 2-(perfluoro Examples include 2-(perfluoroalkyl)ethyl acrylate, 2-(perfluorododecyl)ethyl acrylate, 2-(perfluorotetradecyl)ethyl acrylate, and 2-(perfluorohexadecyl)ethyl acrylate, in which the perfluoroalkyl group bonded to a non-carbonyl oxygen atom has 6 to 18 carbon atoms; and 2-(perfluorohexyl)ethyl methacrylate, 2-(perfluorooctyl)ethyl methacrylate, 2-(perfluorononyl)ethyl methacrylate, 2-(perfluorodecyl)ethyl methacrylate, 2-(perfluorododecyl)ethyl methacrylate, 2-(perfluorotetradecyl)ethyl methacrylate, and 2-(perfluorohexadecyl)ethyl methacrylate, in which the perfluoroalkyl group bonded to a non-carbonyl oxygen atom has 6 to 18 carbon atoms.

[0063] The structural units derived from (meth)acrylic acid or (meth)acrylate or a salt thereof may each include, or together, the structural units represented by chemical formula 2, chemical formula 3, and chemical formula 4. If they are included together, the structural units represented by chemical formula 2, chemical formula 3, and chemical formula 4 may be present in a molar ratio of 10:1 to 1:1, preferably 6:1 to 1:1, and more preferably 3:1 to 1:1.

[0064] The structural unit derived from (meth)acrylamide sulfonic acid or a salt thereof may be a structural unit derived from (meth)acrylamide sulfonic acid or (meth)acrylamide sulfonate, and the (meth)acrylamide sulfonate may be a conjugate base of (meth)acrylamide sulfonic acid, a (meth)acrylamide sulfonate salt, or a derivative thereof. The structural unit derived from (meth)acrylamide sulfonic acid or (meth)acrylamide sulfonate may be represented, for example, by any one of the following chemical formulas 5, 6, 7, and combinations thereof.

[0065] [ka]

[0066] [ka]

[0067] [ka]

[0068] In the above chemical formulas 5 to 7, R 10 , R 11 , R 12 , R 13 , R 14 , R 15 These are, independently, hydrogen or a methyl group. L 1 , L2 , and L 3 Each of these is independently a substituted or unsubstituted C1-C10 alkylene group, a substituted or unsubstituted C3-C20 cycloalkylene group, a substituted or unsubstituted C6-C20 allylene group, or a substituted or unsubstituted C3-C20 heterocyclic group. a, b, and c are each independently integers between 0 and 2, and M is an alkali metal, which may be, for example, lithium, sodium, potassium, rubidium, or cesium.

[0069] As an example, in the above chemical formulas 5 to 7, L 1 , L 2 , and L 3 Each of these is independently a substituted or unsubstituted C1-C10 alkylene group, and a, b, and c can each be 1.

[0070] The structural units derived from (meth)acrylamide sulfonic acid or its salts may include, respectively, the structural units represented by chemical formula 5, the structural units represented by chemical formula 6, and the structural units represented by chemical formula 7, or may include two or more types together. For example, it may include the structural unit represented by chemical formula 6, or, as another example, it may include the structural units represented by chemical formula 7 and the structural units represented by chemical formula 7 together.

[0071] When the structural units represented by chemical formula 6 and chemical formula 7 are included together, the structural units represented by chemical formula 6 and chemical formula 7 may be included in a molar ratio of 10:1 to 1:2, preferably 5:1 to 1:1, and more preferably 3:1 to 1:1.

[0072] The sulfonate group within the structural unit derived from (meth)acrylamide sulfonic acid or a salt thereof may be, for example, a functional group derived from vinyl sulfonic acid, allyl sulfonic acid, styrene sulfonic acid, anethole sulfonic acid, acrylamide alkane sulfonic acid, sulfoalkyl (meth)acrylate, or salts thereof.

[0073] Here, the alkane may be a C1-C20 alkane, a C1-C10 alkane, or a C1-C6 alkane, and the alkyl may be a C1-C20 alkyl, a C1-C10 alkyl, or a C1-C6 alkyl. The salt means a salt composed of the aforementioned sulfonic acid and a suitable ion. The ion may be, for example, an alkali metal ion, in which case the salt may be an alkali metal sulfonic acid salt.

[0074] The acrylamide alkanesulfonic acid may be, for example, 2-acrylamido-2-methylpropanesulfonic acid, and the sulfoalkyl (meth)acrylate may be, for example, 2-sulfoethyl (meth)acrylate, 3-sulfopropyl (meth)acrylate, etc.

[0075] The (meth)acrylic binder mentioned above can be represented, for example, by the following chemical formula 8.

[0076] [ka]

[0077] In the above chemical formula 8, R 1 , R 2 , R 12 , R 13 , R 16 , R 17 These are, independently, hydrogen or a methyl group. R 18 is OR or O - M + R is hydrogen or a C1-C6 alkyl group, and M is an alkali metal. L 2 is a substituted or unsubstituted C1-C10 alkylene group, a substituted or unsubstituted C3-C20 cycloalkylene group, a substituted or unsubstituted C6-C20 allylene group, or a substituted or unsubstituted C3-C20 heterocyclic group, b is one integer from 0 to 2, M is an alkali metal, and l, m, and n represent the molar ratio of each unit.

[0078] The alkali metal may be lithium, sodium, potassium, rubidium, or cesium, among others.

[0079] For example, in the above chemical formula 8, l + m + n = 1. Also, for example, 0.05 ≤ (l + n) ≤ 0.45 and 0.55 ≤ m ≤ 0.95, specifically 0 ≤ l ≤ 0.4 and 0 ≤ n ≤ 0.1, for example 0.8 ≤ m ≤ 0.9, 0 ≤ l ≤ 0.1 and 0 ≤ n ≤ 0.1, for example 0.8 ≤ m ≤ 0.9, 0.01 ≤ l ≤ 0.1 and 0.01 ≤ n ≤ 0.1.

[0080] As an example, in the above chemical formula 8, L 2 b is a substituted or unsubstituted C1-C10 alkylene group, and b can be 1.

[0081] In the (meth)acrylic binder mentioned above, alkali metal (M + The structural units substituted with (meth)acrylamidesulfonic acid may be present in an amount of 50 to 100 mol%, for example, 60 to 90 mol%, or 70 to 90 mol%, relative to 100 mol% of the total amount of (meth)acrylamidesulfonic acid structural units. When the above range is met, the (meth)acrylic binder and the separation membrane containing it can exhibit excellent adhesion, heat resistance, and oxidation resistance.

[0082] The (meth)acrylic binder may further contain other units in addition to the units described above. For example, the (meth)acrylic binder may further contain units derived from alkyl (meth)acrylates, units derived from dienes, units derived from styrenes, ester group-containing units, carbonate group-containing units, or combinations thereof.

[0083] The (meth)acrylic binder can take various forms, such as an alternating polymer in which the units are distributed alternately, a random polymer in which the units are distributed arbitrarily, or a graft polymer in which some structural units are grafted.

[0084] The weight-average molecular weight of the (meth)acrylic binder may be between 350,000 and 970,000, for example, between 450,000 and 970,000, or between 450,000 and 700,000. When the weight-average molecular weight of the (meth)acrylic binder satisfies the above range, the (meth)acrylic binder and the separation membrane containing it can exhibit excellent adhesion, heat resistance, and permeability. The weight-average molecular weight may be the average molecular weight on a polystyrene basis, measured using gel permeation chromatography.

[0085] The (meth)acrylic binder can be produced by a variety of known methods, such as emulsion polymerization, suspension polymerization, bulk polymerization, solution polymerization, or bulk polymerization.

[0086] The (meth)acrylic binder can be manufactured by solution polymerization.

[0087] Crosslinking agent The crosslinking agent comprises one or more aziridine-based crosslinking agents and carbodiimide-based crosslinking agents. Preferably, the aziridine-based crosslinking agent crosslinks the (meth)acrylic binder and at the same time facilitates the separation membrane reaching the range of dry shrinkage and electrolyte shrinkage.

[0088] The aziridine crosslinking agent may be a bifunctional or trifunctional aziridine crosslinking agent. Here, "bifunctional or trifunctional" means that there are two or more aziridine groups in the molecule. According to one embodiment, the aziridine crosslinking agent may be a bifunctional or trifunctional aziridine crosslinking agent.

[0089] For example, the aziridine crosslinking agent may contain one or more of the following: N,N'-toluene-2,4-bis(1-aziridinecarboxamide), N,N'-(methylenedi-p-phenylene)bis(aziridine-1-carboxamide), triethylenemelamine, 1,1-isophthaloylbis(2-methylaziridine), tris(1-aziridinyl)phosphine oxide, N,N-hexamethylene-bis(aziridinecarboxamide), trimethylolpropane tris(2-methyl-1-aziridinepropionate), trimethylolpropane tris(beta-N-aziridinyl)propionate, and pentaerythritol tris(3-(1-aziridinyl)propionate.

[0090] The crosslinking agent, for example, the aziridine crosslinking agent, must be included in an appropriate amount relative to the binder, for example, the (meth)acrylic binder. According to one embodiment, the aziridine crosslinking agent may be included in 5 to 50 parts by weight, for example, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50 parts by weight, 10 to 30 parts by weight, or 10 to 20 parts by weight, relative to 100 parts by weight of the first binder, i.e., the (meth)acrylic binder. Within the aforementioned range, an improvement in the shrinkage rate within the electrolyte solution may be possible.

[0091] Fillers containing amine groups The filler having the amine group has the amine group on its outermost surface. The thermal shrinkage rate can be reduced by crosslinking the amine group with the carboxylic acid group of the filler having the carboxylic acid group or carboxylic acid salt described below.

[0092] The filler having the amine group may include a filler whose surface has been modified to have the amine group.

[0093] The surface modification may include surface modification such that the surface of the filler has amine groups. Here, the "amine group" is *N(R 1 )(R 2 )(Here, R 1 , R 2 This can mean hydrogen or a substituted or unsubstituted C1-C10 alkyl group, preferably a -NH2 group. Such surface modification can broaden the particle size range of the filler required to provide the dry shrinkage rate and electrolyte shrinkage rate compared to when the unmodified filler is used.

[0094] According to one embodiment, the surface modification may include surface treatment of a filler that is not surface modified with an aminosilane compound. The aminosilane compound may include a silane compound having one or more nitrogen atoms, for example, one to six nitrogen atoms.

[0095] In one specific example, the aminosilane compound may include, but is not limited to, one or more compounds from the following chemical formulas 9, 10, and 11.

[0096] [ka]

[0097] [ka]

[0098] [ka]

[0099] In the aforementioned chemical formulas 9 to 11, X 1 , X 2 , X 3Each of these is independently a hydrogen atom, a hydroxyl group, a substituted or unsubstituted C1-C20 alkyl group, a substituted or unsubstituted C6-C20 aryl group, a substituted or unsubstituted C3-C20 cycloalkyl group, a substituted or unsubstituted C7-C20 arylalkyl group, a substituted or unsubstituted C1-C20 alkoxy group, or a substituted or unsubstituted C6-C20 aryloxy group. X 1 , X 2 , X 3 At least one of these is a hydroxyl group, a substituted or unsubstituted C1-C20 alkoxy group, or a substituted or unsubstituted C6-C20 aryloxy group. Y 1 , Y 2 , Y 2 , Y 3 , Y 4 , Y 5 , Y 6 These are, independently, a divalent C1-C20 aliphatic hydrocarbon group, a divalent C5-C20 alicyclic hydrocarbon group, or a divalent C6-C20 aromatic hydrocarbon group. R 15 , R 16 , R 17 , R 18 , R 19 , R 20 , R 21 , R 22 , R 23 Each of these is independently a hydrogen atom, a hydroxyl group, a substituted or unsubstituted monovalent aliphatic hydrocarbon group having 1 to 20 carbon atoms, a substituted or unsubstituted monovalent alicyclic hydrocarbon group having 3 to 20 carbon atoms, or a substituted or unsubstituted monovalent aromatic hydrocarbon group having 6 to 20 carbon atoms.

[0100] For example, the aminosilane compound may contain one or more of the following: 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropylmethyldimethoxysilane, 3-aminopropylmethyldiethoxysilane, aminoethylaminopropyltrimethoxysilane, aminoethylaminopropyltriethoxysilane, aminoethylaminopropylmethyldimethoxysilane, aminoethylaminopropylmethyldiethoxysilane, aminoethylaminomethyltriethoxysilane, aminoethylaminomethylmethyldiethoxysilane, diethylenetriaminopropyltrimethoxysilane, diethylenetriaminopropyltriethoxysilane, diethylenetriaminopropylmethyldimethoxysilane, diethylenetriaminopropylmethyldiethoxysilane, and diethylenetriaminomethylmethyldiethoxysilane.

[0101] According to one embodiment, the surface modification can be carried out by a conventional method using an aminosilane compound.

[0102] The filler having the amine group may be, for example, an inorganic filler, an organic filler, an inorganic-alloy composite filler, or a combination thereof. The inorganic filler may be a ceramic material that can improve heat resistance. The inorganic filler may include, for example, a metal oxide, a metalloid oxide, a metal fluoride, a metal hydroxide, or a combination thereof. The inorganic filler may include, but is not limited to, Al2O3, SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, GaO, ZnO, ZrO2, Y2O3, SrTiO3, BaTiO3, Mg(OH)2, boehmite, or a combination thereof. The organic filler may include, but is not limited to, an acrylic compound, an imide compound, an amide compound, or a combination thereof. The organic filler may have, but is not limited to, a core-shell structure. For example, the filler may be boehmite.

[0103] The filler having the amine group may be spherical, plate-shaped, cubic, or amorphous. For example, the filler may be plate-shaped.

[0104] The filler having the amine group must be present in an appropriate amount relative to the binder, for example, the sum of the first binder and the second binder.

[0105] According to one embodiment, the total mass ratio of the first binder and the second binder to the filler having the amine group is 1:10 to 1:50, for example, 1:10, 1:11, 1:12, 1:13, 1:14, 1:15, 1:16, 1:17, 1:18, 1:19, 1:20, 1:21, 1:22, 1:23, 1:24, 1:25, 1:26 It may be included in mass ratios of 1:27, 1:28, 1:29, 1:30, 1:31, 1:32, 1:33, 1:34, 1:35, 1:36, 1:37, 1:38, 1:39, 1:40, 1:41, 1:42, 1:43, 1:44, 1:45, 1:46, 1:47, 1:48, 1:49, 1:50, 1:10~1:30, and 1:20~1:30. Within the above ranges, an effect of improving shrinkage in the electrolyte may be observed.

[0106] The filler having the amine group may have a particle size D100 of 1.0 μm or less. Within this range, when combined with the (meth)acrylic binder and the crosslinking agent, it may be easy to achieve the dry shrinkage rate and the electrolyte shrinkage rate. For example, the filler having the amine group may have a particle size D100 of 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0 μm, 0.5 μm or less, or 0.3 to 0.5 μm.

[0107] The filler having the amine group may have a particle size D50 of 0.4 μm or less, for example, 0.3 μm or less, for example, 0.2 to 0.3 μm. Within this range, an effect of improving shrinkage in the electrolyte may be observed.

[0108] The amine group-containing filler may be present in the total amount of the coating layer in an amount of 50% to 99% by weight, for example, 70% to 99% by weight, for example, 75% to 99% by weight, for example, 80% to 99% by weight, for example, 85% to 99% by weight, for example, 90% to 99% by weight, for example, 95% to 99% by weight. When the filler is present in the above range, it can exhibit excellent heat resistance, durability, oxidation resistance, and stability.

[0109] Fillers having a carboxylic acid group or a carboxylic acid salt A filler having a carboxylic acid group or a carboxylic acid salt has a carboxylic acid group or a carboxylic acid salt on its outermost surface. The said filler having a carboxylic acid group or a carboxylic acid salt may include a filler whose surface has been modified to have a carboxylic acid group or a carboxylic acid salt.

[0110] The surface modification can be carried out by oxidizing a filler having a hydroxyl group in its molecule with an oxidizing agent. The oxidizing agent may include, but is not limited to, TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl radical).

[0111] The filler having a hydroxyl group in the molecule may include cellulose nanocrystals, cellulose nanofibers, and the like. For example, the filler may be cellulose nanocrystals.

[0112] Cellulose-based nanocrystals and cellulose-based nanofibers having the aforementioned carboxylic acid group or carboxylic acid salt may have a carboxylic acid group or carboxylic acid salt linked to the C6 position of the cellulose unit.

[0113] According to one embodiment, the filler having the carboxylic acid group or carboxylic acid salt may have a maximum width of 5 to 20 nm and a maximum length of 100 to 250 nm. Within this range, an effect of improving shrinkage in the electrolyte may be observed.

[0114] The filler having the carboxylic acid group or carboxylic acid salt must be included in an appropriate amount relative to the filler having the amine group. According to one embodiment, the filler having the carboxylic acid group or carboxylic acid salt may be included in an amount of 2 to 15 parts by weight per 100 parts by weight of the filler having the amine group, for example, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10, 10.5, 11, 11.5, 12, 12.5, 13, 13.5, 14, 14.5, or 15 parts by weight, ranging from 2.5 to 10 parts by weight. Within this range, an effect of improving shrinkage in the electrolyte may be observed.

[0115] The coating layer can be formed by coating at least one surface of a porous substrate, as described below, with the coating layer composition and curing it.

[0116] Each of the coating layers can have a thickness of 0.01 μm to 20 μm, and within that range, it can have a thickness of 0.1 μm to 10 μm, or 0.1 μm to 5 μm, or 0.1 μm to 3 μm.

[0117] The ratio of the thickness of the coating layer to the thickness of the porous substrate can be 0.05 to 0.5, for example, 0.05 to 0.4, or 0.05 to 0.3, or 0.1 to 0.2. Within this range, the separation film can exhibit excellent breathability, heat resistance, and adhesion. Here, "thickness of the coating layer" means the thickness of one coating layer if the coating layer is formed on only one surface of the porous substrate, or the total thickness of two coating layers if the coating layers are formed on both surfaces of the porous substrate.

[0118] porous substrate Porous substrates have numerous pores and are typically used as substrates for electrochemical devices. Porous substrates are not limited to these but may be polymer films formed from any one polymer selected from the group consisting of polyethylene, polyolefins such as polypropylene, polyesters such as polyethylene terephthalate and polybutylene terephthalate, polyacetal, polyamide, polyimide, polycarbonate, polyetheretherketone, polyaryletherketone, polyetherimide, polyamideimide, polybenzimidazole, polyethersulfone, polyphenylene oxide, cyclic olefin copolymer, polyphenylene sulfide, polyethylene naphthalate, glass fiber, and polytetrafluoroethylene (e.g., Teflon®), or from copolymers or mixtures of two or more of these polymers.

[0119] The porous substrate may, for example, be a polyolefin-based substrate containing polyolefin, and this polyolefin-based substrate has excellent shutdown function and can contribute to improving battery safety. The polyolefin-based substrate can be selected from, for example, a single polyethylene film, a single polypropylene film, a polyethylene / polypropylene bilayer film, a polypropylene / polyethylene / polypropylene triple layer film, and a polyethylene / polypropylene / polyethylene triple layer film. Furthermore, the polyolefin-based resin may contain a non-olefin resin in addition to the olefin resin, or a copolymer of an olefin and a non-olefin monomer.

[0120] The porous substrate can have a thickness of 1 μm to 40 μm, for example, 1 μm to 30 μm, 1 μm to 20 μm, or 5 μm to 15 μm.

[0121] A separation membrane for lithium secondary batteries according to one embodiment can exhibit excellent permeability, and can have permeability values ​​of, for example, less than 200 sec / 100 cc, for example, 190 sec / 100 cc or less, or 180 sec / 100 cc or less. That is, it can have permeability values ​​of less than 40 sec / 100 cc·1 μm per unit thickness, for example, 30 sec / 100 cc·1 μm or less, or 25 sec / 100 cc·1 μm or less. Here, permeability refers to the time (seconds) it takes for 100 cc of air to pass through a unit thickness of the separation membrane. Permeability per unit thickness can be determined by measuring the permeability for the total thickness of the separation membrane and then dividing by the thickness. Permeability can be measured using an permeability measuring device (Asahi Seiko Co., Ltd., EG01-55-1MR) to measure the time (seconds) it takes for 100 cc of air to pass through.

[0122] Figure 1 is a cross-sectional view showing a separation membrane for a lithium secondary battery according to one embodiment.

[0123] Referring to Figure 1, the separation membrane for lithium secondary batteries includes a porous substrate 1 and a coating layer 2 located on one surface of the porous substrate 1. The coating layer 2 includes a first binder 3, a second binder 4, a filler 5 having a carboxylic acid group, and a filler 6 having an amine group. Although not shown in Figure 1, the first binder 3 is crosslinked with a crosslinking agent.

[0124] Figure 1 shows a separation membrane in which the coating layer 2 is located on only one surface of the porous substrate 1. However, separation membranes in which the coating layer 2 is located on both sides of the porous substrate 1 may also be included within the scope of the present invention.

[0125] Lithium-ion battery Another embodiment provides a lithium secondary battery comprising a separator membrane for a lithium secondary battery according to one embodiment, a positive electrode, and a negative electrode.

[0126] The separator membrane for lithium secondary batteries is as described above. The separator membrane for lithium secondary batteries may be located between the positive and negative electrodes.

[0127] positive electrode A positive electrode for a lithium secondary battery may include a current collector and a positive electrode active material layer formed on the current collector. The positive electrode active material layer may include a positive electrode active material and further include a binder and / or a conductive material. As an example, the positive electrode may further include an additive that can act as a sacrificial positive electrode.

[0128] positive electrode active material As the positive electrode active material, a compound capable of reversible intercalation and deintercalation of lithium (lithium-intercalated intercalation compound) can be used. Specifically, one or more composite oxides of lithium with metals selected from cobalt, manganese, nickel, and combinations thereof can be used.

[0129] The aforementioned composite oxides may be lithium transition metal composite oxides, and specific examples include lithium nickel oxides, lithium cobalt oxides, lithium manganese oxides, lithium iron phosphate compounds, cobalt-free nickel-manganese oxides, or combinations thereof.

[0130] As an example, a compound represented by any one of the following chemical formulas can be used: Li a A 1-b X b O 2-c D c (0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.05);Li a Mn 2-b X b O 4-c D c (0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.05);Li a Ni 1-b-c Co b X c O 2-α D α (0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.5, 0<α<2);Li a Ni1-b-c Mn b X c O 2-α D α (0.90 ≦ a ≦ 1.8, 0 ≦ b ≦ 0.5, 0 ≦ c ≦ 0.5, 0 < α < 2); Li a Ni b Co c L 1 d G e O2(0.90 ≦ a ≦ 1.8, 0 ≦ b ≦ 0.9, 0 ≦ c ≦ 0.5, 0 ≦ d ≦ 0.5, 0 ≦ e ≦ 0.1); Li a NiG b O2(0.90 ≦ a ≦ 1.8, 0.001 ≦ b ≦ 0.1); Li a CoG b O2(0.90 ≦ a ≦ 1.8, 0.001 ≦ b ≦ 0.1); Li a Mn 1-b G b O2(0.90 ≦ a ≦ 1.8, 0.001 ≦ b ≦ 0.1); Li a Mn2G b O4(0.90 ≦ a ≦ 1.8, 0.001 ≦ b ≦ 0.1); Li a Mn 1-g G g PO4(0.90 ≦ a ≦ 1.8, 0 ≦ g ≦ 0.5); Li (3-f) Fe2(PO4)3(0 ≦ f ≦ 2); Li a FePO4(0.9 ≦ a ≦ 1.8).

[0131] In the above chemical formula, A is Ni, Co, Mn or a combination thereof; X is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, rare earth elements or a combination thereof; D is O, F, S, P or a combination thereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V or a combination thereof; L 1 is Mn, Al or a combination thereof.

[0132] As an example, the positive electrode active material may be a high-nickel positive electrode active material in which the nickel content relative to 100 mol% of the metal excluding lithium is 80 mol% or more, 85 mol% or more, 90 mol% or more, 91 mol% or more, or 94 mol% or more, and 99 mol% or less in a lithium transition metal composite oxide. High-nickel positive electrode active materials can achieve high capacity and can be applied to high-capacity, high-density lithium secondary batteries.

[0133] The content of the positive electrode active material is 90% to 99.5% by weight of 100% by weight of the positive electrode active material layer, and the content of the binder and conductive material may be 0.5% to 5% by weight, respectively, of 100% by weight of the positive electrode active material layer.

[0134] The binder plays a role in ensuring good adhesion between positive electrode active material particles and good adhesion of the positive electrode active material to the current collector. Typical examples of binders include, but are not limited to, polyvinyl alcohol, carboxymethylcellulose, hydroxypropylcellulose, diacetylcellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, (meth)acrylate styrene-butadiene rubber, epoxy resin, (meth)acrylic resin, polyester resin, nylon, etc.

[0135] The conductive material is used to impart conductivity to the electrodes, and any electronically conductive material that does not cause chemical changes in the battery can be used. Examples of conductive materials include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjenblack, carbon fibers, carbon nanofibers, and carbon nanotubes; metallic materials containing copper, nickel, aluminum, silver, etc., in the form of metal powder or metal fiber; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0136] Al can be used as the current collector, but is not limited to it.

[0137] negative electrode A negative electrode for a lithium secondary battery includes a current collector and a negative electrode active material layer located on the current collector. The negative electrode active material layer includes a negative electrode active material and may further include a binder and / or a conductive material.

[0138] For example, the negative electrode active material layer may contain 90% to 99% by weight of negative electrode active material, 0.5% to 5% by weight of binder, and 0% to 5% by weight of conductive material.

[0139] negative electrode active material The negative electrode active material includes materials capable of reversibly intercalating / deintercalating lithium ions, lithium metals, alloys of lithium metals, materials that can be doped and dedoped with lithium, or transition metal oxides.

[0140] The material capable of reversibly intercalating / deintercalating the lithium ions may include carbon-based negative electrode active materials, such as crystalline carbon, amorphous carbon, or a combination thereof. Examples of crystalline carbon include graphite such as amorphous, plate-like, flake-like, spherical, or fibrous natural or artificial graphite, while examples of amorphous carbon include soft carbon or hard carbon, mesophase pitch carbide, calcined coke, and the like.

[0141] As the lithium metal alloy, an alloy of lithium and a metal selected from Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn can be used.

[0142] As the material capable of being doped and undoped with lithium, a Si-based negative electrode active material or a Sn-based negative electrode active material can be used. The Si-based negative electrode active material can be silicon, a silicon-carbon composite, SiOx (0 < x < 2), a Si-Q alloy (where Q is selected from alkali metals, alkaline earth metals, group 13 elements, group 14 elements (excluding Si), group 15 elements, group 16 elements, transition metals, rare earth elements, and combinations thereof), or a combination of these. The Sn-based negative electrode active material can be Sn, SnO2, a Sn-based alloy, or a combination of these.

[0143] The silicon-carbon composite can be a composite of silicon and amorphous carbon. According to one embodiment, the silicon-carbon composite can be in a form in which silicon particles are coated with amorphous carbon on the surface of the silicon particles. For example, it may include secondary particles (cores) formed by granulating primary silicon particles and an amorphous carbon coating layer (shell) located on the surface of the secondary particles. The amorphous carbon may also be located between the primary silicon particles. For example, the primary silicon particles may be coated with amorphous carbon. The secondary particles may be dispersed in an amorphous carbon matrix.

[0144] The silicon-carbon composite can further include crystalline carbon. For example, the silicon-carbon composite may include a core containing crystalline carbon and silicon particles and an amorphous carbon coating layer located on the surface of the core.

[0145] The Si-based negative electrode active material or the Sn-based negative electrode active material can be used by mixing with a carbon-based negative electrode active material.

[0146] The binder serves to make the negative electrode active material particles adhere well to each other and also make the negative electrode active material adhere well to the current collector. As the binder, a non-aqueous binder, an aqueous binder, a dry binder, or a combination of these can be used.

[0147] Examples of the non-aqueous binder include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene propylene copolymer, polystyrene, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide-imide, polyimide, or combinations thereof.

[0148] The aqueous binder can be selected from styrene-butadiene rubber, (meth)acrylate styrene-butadiene rubber, (meth)acrylonitrile-butadiene rubber, (meth)acrylic rubber, butyl rubber, fluororubber, polyethylene oxide, polyvinylpyrrolidone, polyepichlorohydrin, polyphosphazene, poly(meth)acrylonitrile, ethylene propylene diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, (meth)acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, and combinations thereof.

[0149] When an aqueous binder is used as the negative electrode binder, it may further contain a cellulosic compound that can impart viscosity. This cellulosic compound can be a mixture of one or more carboxymethylcellulose, hydroxypropylmethylcellulose, methylcellulose, or alkali metal salts thereof. The alkali metal can be Na, K, or Li.

[0150] The aforementioned dry inder is a polymer material that can be formed into fibers, and may be, for example, polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or a combination thereof.

[0151] The conductive material is used to impart conductivity to the electrodes, and any electronically conductive material that does not cause chemical changes in the battery can be used. Specific examples include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjenblack, carbon fibers, carbon nanofibers, and carbon nanotubes; metallic materials containing copper, nickel, aluminum, silver, etc., in the form of metal powder or metal fiber; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0152] As the negative electrode current collector, copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, and combinations thereof can be selected.

[0153] Lithium secondary batteries may also contain an electrolyte.

[0154] electrolyte The electrolyte for lithium secondary batteries may also contain a non-aqueous organic solvent and a lithium salt.

[0155] The aforementioned non-aqueous organic solvent acts as a medium through which ions involved in the electrochemical reaction of the battery can move.

[0156] The non-aqueous organic solvent may be a carbonate-based, ester-based, ether-based, ketone-based, or alcohol-based solvent, an aprotic solvent, or a combination thereof.

[0157] Examples of carbonate-based solvents that can be used include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC).

[0158] Suitable ester solvents include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, decanolide, mevalonolactone, valerolactone, and caprolactone.

[0159] As ether-based solvents, dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, tetrahydrofuran, etc. can be used. As ketone-based solvents, cyclohexanone, etc. can be used. As alcohol-based solvents, ethyl alcohol, isopropyl alcohol, etc. can be used, and as aprotic solvents, nitriles such as R-CN (where R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms, and may include a double bond, aromatic ring, or ether group); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane and 1,4-dioxolane; sulfolanes, etc. can be used.

[0160] The aforementioned non-aqueous organic solvents can be used alone or in combination of two or more.

[0161] Furthermore, when using carbonate-based solvents, cyclic carbonates and linear carbonates can be mixed, and these can be mixed in a volume ratio of 1:1 to 1:9.

[0162] The aforementioned lithium salts dissolve in organic solvents and act as a source of lithium ions within the battery, enabling the operation of basic lithium secondary batteries and promoting the movement of lithium ions between the positive and negative electrodes. Typical examples of lithium salts include LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiAlO2, LiAlCl4, LiPO2F2, LiCl, LiI, LiN(SO3C2F5)2, Li(FSO2)2N(lithium bis(fluorosulfonyl)imide (LiFSI), LiC4F9SO3, and LiN(C x F 2x+1SO2)(C y F 2y+1 SO2) (where x and y are integers from 1 to 20), may contain one or more selected from lithium trifluoromethanesulfonate, lithium tetrafluoroethanesulfonate, lithium difluorobis(oxalate)phosphate (LiDFOB), and lithium bis(oxalate)borate (LiBOB).

[0163] Lithium secondary batteries can be classified into cylindrical, prismatic, pouch-type, coin-type, etc., depending on their form. Figures 2 to 5 are schematic diagrams showing a lithium secondary battery according to one embodiment. Figure 2 shows a cylindrical type, Figure 3 shows a prismatic type, and Figures 4 and 5 show a pouch-type battery form. Referring to Figures 2 to 5, the lithium secondary battery 100 may include an electrode assembly 40 with a separator membrane 30 interposed between a positive electrode 10 and a negative electrode 20, and a case 50 in which the electrode assembly 40 is housed. The positive electrode 10, negative electrode 20, and separator membrane 30 may be impregnated with an electrolyte (not shown). The lithium secondary battery 100 may include a sealing member 60 that seals the case 50, as shown in Figure 2. Also, in Figure 3, the lithium secondary battery 100 may include a positive electrode lead tap 11 and a positive electrode terminal 12, and a negative electrode lead tap 21 and a negative electrode terminal 22. As shown in Figures 4 and 5, the lithium secondary battery 100 may also include electrode taps 70, namely a positive electrode tap 71 and a negative electrode tap 72, which serve as electrical pathways for guiding the current formed in the electrode assembly 40 to the outside.

[0164] A lithium secondary battery according to one embodiment of the present invention can be applied to automobiles, mobile phones, and / or various forms of electrical devices, but the present invention is not limited to these.

[0165] Examples and comparative examples of the present invention are described below. However, the following examples are merely illustrative of the present invention, and the present invention is not limited to the following examples.

[0166] Manufacturing Example 1 In a 10 L four-necked flask equipped with a stirrer, thermometer, and condenser, distilled water (6,361 g), acrylic acid (1.0 mol), acrylamide (8.5 mol), potassium persulfate (0.01 mol), 2-acrylamido-2-methylpropanesulfonic acid (0.5 mol), and 5N lithium hydroxide aqueous solution (1.05 equivalents relative to the total amount of 2-acrylamido-2-methylpropanesulfonic acid) were added. Then, the internal pressure was reduced to 10 mmHg using a diaphragm pump, and the internal pressure was returned to atmospheric pressure with nitrogen. This process was repeated three times.

[0167] The reaction mixture is allowed to proceed for 12 hours while controlling the temperature of the reaction solution to stabilize between 65°C and 70°C. After cooling to room temperature, the pH of the reaction solution is adjusted to 7-8 using a 25% aqueous ammonia solution.

[0168] The lithium salt poly(acrylate-co-acrylamide-co-2-acrylamide-2-methylpropanesulfonic acid) was produced using this method. Here, the molar ratio of structural units derived from acrylic acid, acrylamide, and 2-acrylamide-2-methylpropanesulfonic acid is 10:85:5. Approximately 10 mL of the reaction solution (reaction product) was taken, and the non-volatile components were measured, resulting in a concentration of 9.5% (theoretical value: 10%).

[0169] Manufacturing Example 2 In Example 1, the binder was prepared in the same manner as in Production Example 1, except that the molar ratio of structural units derived from acrylamide and structural units derived from 2-acrylamido-2-methylpropanesulfonic acid was 85:15.

[0170] Example 1 3-aminopropyltriethoxysilane equivalent to 1.5 wt% of the solid content of boehmite (particle size D100: 0.5 μm, particle size D50: 0.2 μm, plate-shaped) was added to dry toluene and refluxed at 80°C to produce boehmite (particle size D100: 0.5 μm, particle size D50: 0.2 μm) surface-modified with 3-aminopropyltriethoxysilane. The surface-modified boehmite has an amino group (-NH2) on its outermost surface.

[0171] Cellulose nanocrystals were added to water, followed by TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl radical), then an aqueous solution of NaClO (sodium hypochlorite) was added to adjust the pH to 10, and the mixture was stirred for 2 hours to produce cellulose nanocrystals containing carboxylic acid groups by TEMPO-catalyzed oxidation.

[0172] The acrylic binder produced in Production Example 1 (10% by weight in distilled water), polyacrylic acid (PAA, weight-average molecular weight: 300,000 g / mol, glass transition temperature: 5°C) as a binding binder (5% by weight in distilled water), boehmite having amino groups, and cellulose nanocrystals having carboxylic acid groups were mixed and added to an aqueous solvent. The mixture was then pulverized using a bead mill at 25°C for 30 minutes to disperse the mixture and produce a dispersion.

[0173] Trimethylolpropanetris (2-methyl-1-aziridinepropionate) (a trifunctional aziridine crosslinking agent) was added to the dispersion, and water was added to make a total solids content of 20% by weight to produce a coating layer forming composition.

[0174] In the aforementioned coating layer forming composition, the acrylic binder is included in an amount of 90 parts by weight and the binding binder in an amount of 100 parts by weight of the total of the acrylic binder and the binding binder.

[0175] In the aforementioned coating layer forming composition, the total of the acrylic binder and the binding binder is: boehmite having amino groups is included in a mass ratio of 1:20; the aziridine crosslinking agent is included in a mass ratio of 10 parts by weight per 100 parts by weight of the acrylic binder; and cellulose nanocrystals having carboxylic acid groups are included in a mass ratio of 2.5 parts by weight per 100 parts by weight of boehmite having amino groups.

[0176] A polyethylene film (thickness: 5.5 μm, manufactured by CZMZ, permeability: 90 sec / 100 cc, puncture strength: 370 gf) was used as a porous substrate. The aforementioned coating layer-forming composition was coated to a thickness of 0.9 μm on both sides using a die-coating method, and then dried and aged in an oven at 80°C for 16 hours to produce a separation membrane for lithium secondary batteries.

[0177] Examples 2 to 4 In Example 1, the separation membrane was manufactured using the same method as in Example 1, except that the composition of the coating layer was changed as shown in Table 1 below.

[0178] Comparative Examples 1 to 5 In Example 1, the separation membrane was manufactured using the same method as in Example 1, except that the composition of the coating layer was changed as shown in Table 1 below.

[0179] The following physical properties were evaluated for the separation membranes produced in the examples and comparative examples.

[0180] Dry shrinkage rate (in %) The lithium secondary battery separation membranes of the examples and comparative examples are cut to a size of 10 cm x 10 cm to prepare the samples. After leaving the samples in an oven at 150°C for 1 hour, the dimensions of the sides of the rectangle of the sample are measured and the shrinkage rates in the mechanical direction (MD) and perpendicular direction (TD) are calculated. The shrinkage rates are calculated according to Formula 1 below. Contraction rate = (L0 - L1) / L0 × 100 [Formula 1] (L0 is the initial length of the separation membrane, and L1 is the length of the separation membrane after being left at 150°C for 1 hour.)

[0181] Electrolyte shrinkage rate (unit: %) Prepare samples by cutting out 5cm x 5cm pieces of the lithium secondary battery separator membranes from the examples and comparative examples. Draw a 5cm x 5cm rectangle on the surface of the sample.

[0182] A cathode slurry was prepared by mixing 97% by weight of lithium cobalt nickel aluminum oxide (LiCoNiAl) as the cathode active material, 1.5% by weight of carbon nanotubes, and 1.5% by weight of polyvinylidene fluoride as conductive materials, and adding N-methyl-2-pyrrolidone. The prepared cathode slurry was coated onto aluminum foil, dried, and rolled to produce the cathode.

[0183] A negative electrode slurry was prepared by mixing 97.4% by weight of artificial graphite, 1.0% by weight of carboxymethylcellulose, 1.5% by weight of styrene-butadiene rubber as the negative electrode active material, and 0.1% by weight of carbon nanotubes as a conductive material, and adding distilled water. The prepared negative electrode slurry was applied to copper foil, dried, and rolled to produce the negative electrode.

[0184] Three sets of positive-sample-negative electrode laminates were fabricated by positioning one sample between the positive and negative electrodes, and then placed in pouches. Two g of electrolyte (ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate in a 30:50:20 volume ratio with 1.5 M LiPF6 dissolved in it) was injected to completely impregnate the laminates in the electrolyte, and after sealing, they were left at 25°C for 12 hours. After that, they were left in an oven at 150°C for 1 hour, and then the samples were removed, the dimensions of the sides of the drawn rectangles were measured, and the shrinkage rates in the mechanical direction (MD) and perpendicular direction (TD) were calculated. The shrinkage rates can be calculated according to Equation 1 above.

[0185] [Table 1]

[0186] As is clear from Table 1 above, the separation membrane for lithium secondary batteries in the examples exhibits remarkably low dry shrinkage and electrolyte shrinkage rates, which can improve the safety and lifespan of the battery.

[0187] On the other hand, the separation membrane of the comparative example had a significantly higher in-electrolyte shrinkage rate or a higher dry shrinkage rate compared to the example.

[0188] Although preferred embodiments of the present invention have been described above, the present invention is not limited thereto and can be implemented in various ways within the scope of the claims, the detailed description of the invention, and the accompanying drawings, and these also naturally fall within the scope of the present invention.

Claims

1. The invention comprises a porous substrate and a coating layer located on at least one surface of the porous substrate. The coating layer is formed from a composition comprising a mixture of a binder, a crosslinking agent, and a filler. The aforementioned filler mixture comprises a filler having an amine group and a filler having a carboxylic acid group or a carboxylic acid salt, and is a separation membrane for lithium secondary batteries.

2. The separation membrane for lithium secondary batteries according to claim 1, wherein the crosslinking agent comprises an aziridine-based crosslinking agent.

3. The separation membrane for lithium secondary batteries according to claim 1, wherein the filler having the amine group is a filler modified with aminosilane.

4. The separation membrane for lithium secondary batteries according to claim 3, wherein the aminosilane comprises one or more of the following: 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropylmethyldimethoxysilane, 3-aminopropylmethyldiethoxysilane, aminoethylaminopropyltrimethoxysilane, aminoethylaminopropylmethyldimethoxysilane, aminoethylaminopropylmethyldiethoxysilane, aminoethylaminomethyltriethoxysilane, aminoethylaminomethylmethyldiethoxysilane, diethylenetriaminopropyltrimethoxysilane, diethylenetriaminopropyltriethoxysilane, diethylenetriaminopropylmethyldimethoxysilane, diethylenetriaminopropylmethyldiethoxysilane, and diethylenetriaminomethylmethyldiethoxysilane.

5. The separation membrane for lithium secondary batteries according to claim 1, wherein the filler having the amine group has a particle size D100 of 1.0 μm or less.

6. The separator membrane for lithium secondary batteries according to claim 1, wherein the filler having a carboxylic acid group or a carboxylic acid salt comprises one or more cellulose nanocrystals having a carboxylic acid group or a carboxylic acid salt, and cellulose nanofibers having a carboxylic acid group or a carboxylic acid salt.

7. The separator membrane for lithium secondary batteries according to claim 1, wherein the filler having the carboxylic acid group or carboxylic acid salt has a maximum width of 5 to 20 nm and a maximum length of 100 to 250 nm.

8. The separation membrane for lithium secondary batteries according to claim 6, wherein the cellulose nanocrystal having the carboxylic acid group or carboxylic acid salt, and the cellulose nanofiber having the carboxylic acid group or carboxylic acid salt, have a carboxylic acid group or carboxylic acid salt linked to the C6 position of the cellulose unit.

9. The separation membrane for lithium secondary batteries according to claim 1, wherein the filler having the carboxylic acid group or carboxylic acid salt is included in an amount of 2 to 15 parts by weight per 100 parts by weight of the filler having the amine group.

10. The binder includes a first binder and a second binder, The total of the first binder and the second binder: The filler having the amine group is contained in a mass ratio of 1:10 to 1:50, as described in claim 1, for a lithium secondary battery separation membrane.

11. The binder includes a first binder and a second binder, The separation membrane for lithium secondary batteries according to claim 2, wherein the aziridine crosslinking agent is contained in an amount of 5 to 50 parts by weight relative to the content of the first binder.

12. The binder includes a first binder and a second binder, The first binder is a (meth)acrylic binder, The separation membrane for lithium secondary batteries according to claim 1, wherein the (meth)acrylic binder comprises a first structural unit derived from (meth)acrylamide; and a second structural unit comprising at least one of a structural unit derived from (meth)acrylic acid or (meth)acrylate or a salt thereof, and a structural unit derived from (meth)acrylamide sulfonic acid or a salt thereof.

13. The binder includes a first binder and a second binder, The first binder is a (meth)acrylic binder, The separation membrane for lithium secondary batteries according to claim 1, wherein the second binder comprises one or more of polyvinyl alcohol, polyacrylic acid, and poly(vinyl alcohol-co-acrylic acid).

14. The separation membrane for a lithium secondary battery according to claim 1, wherein the coating layer comprises a crosslinked material of a filler having an amine group and a filler having a carboxylic acid group or a carboxylic acid salt.

15. A lithium secondary battery comprising a separator membrane for lithium secondary batteries according to any one of claims 1 to 14, a positive electrode, and a negative electrode.

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