Separator for lithium secondary battery and lithium secondary battery comprising same

Abstract

The present invention relates to a separator for a lithium secondary battery and a lithium secondary battery comprising same, the separator for a lithium secondary battery comprising: a porous substrate; and a coating layer positioned on at least one surface of the porous substrate. The coating layer comprises: a crosslinked product of a binder, a crosslinking agent, and carboxyalkyl cellulose or a salt thereof; and a filler, wherein the binder includes a (meth)acrylic binder comprising a structural unit derived from (meth)acrylate or (meth)acrylic acid, a structural unit containing a cyano group, and a structural unit containing a sulfonate group, the crosslinking agent includes an aziridine-based crosslinking agent, and the filler is surface-modified and has a particle diameter D100 of 1.0 μm or smaller.

Description

Separator for lithium secondary battery and lithium secondary battery including same

[0001] The present invention relates to a separator for a lithium secondary battery and a lithium secondary battery including the same.

[0002] The recent rapid proliferation of battery-powered electronic devices, such as mobile phones, laptops, and electric vehicles, has led to a rapid increase in demand for high-energy density and high-capacity secondary batteries. Accordingly, active research and development is underway to improve the performance of lithium secondary batteries.

[0003] A lithium secondary battery is a battery that includes a positive electrode and a negative electrode that contain active materials capable of intercalating and deintercalating lithium ions, and an electrolyte, and produces electrical energy through oxidation and reduction reactions when lithium ions are intercalated and deintercalated from the positive electrode and the negative electrode.

[0004] Lithium secondary batteries may include a separator between the positive and negative electrodes. The separator is impregnated within the electrolyte. It may be desirable for the separator to maintain its original shape without undergoing thermal shrinkage within the electrolyte, ensuring battery safety.

[0005] One embodiment provides a separator for a lithium secondary battery having excellent heat resistance.

[0006] Another embodiment provides a separator for a lithium secondary battery that has both low dry shrinkage and low shrinkage in electrolyte solution, thereby enhancing the safety of the battery.

[0007] Another embodiment provides a lithium secondary battery including the separator for the lithium secondary battery.

[0008] According to one embodiment, a separator for a lithium secondary battery is provided.

[0009] The above-mentioned lithium secondary battery separator comprises a porous substrate and a coating layer positioned on at least one surface of the porous substrate, wherein the coating layer comprises a binder; a crosslinking agent; and a crosslinked product of carboxyalkyl cellulose or a salt thereof; and a filler, wherein the binder comprises a (meth)acrylic binder including a structural unit derived from (meth)acrylate or (meth)acrylic acid, a cyano group-containing structural unit, and a sulfonate group-containing structural unit, wherein the crosslinking agent comprises an aziridine-based crosslinking agent, and the filler is surface-modified and has a particle diameter D100 of 1.0 μm or less.

[0010] According to another embodiment, a lithium secondary battery is provided.

[0011] The above lithium secondary battery includes a positive electrode, a negative electrode, and a separator for the lithium secondary battery positioned between the positive electrode and the negative electrode.

[0012] A separator for a lithium secondary battery according to one embodiment has excellent heat resistance and low dry shrinkage rate and shrinkage rate in an electrolyte solution, thereby improving the safety of the battery.

[0013] Figure 1 is a cross-sectional view showing a separator for a lithium secondary battery according to one embodiment.

[0014] Figures 2 to 5 are cross-sectional views schematically showing a lithium secondary battery according to one embodiment.

[0015] Hereinafter, embodiments of the present invention will be described in detail. However, these are presented as examples and are not intended to limit the present invention. The present invention is defined solely by the scope of the claims set forth below.

[0016] Unless otherwise specified herein, when a part such as a layer, film, region, plate, etc. is said to be “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 is another part in between.

[0017] Unless otherwise specified herein, the singular may also include the plural. Furthermore, unless otherwise specified, "A or B" may mean "including A, including B, or including A and B."

[0018] As used herein, “combination thereof” may mean mixtures, laminates, composites, copolymers, alloys, blends, and reaction products of the components.

[0019] In this specification, 'particle diameter D100' means the particle diameter that means the size of the particle whose cumulative volume is 100 volume% in the particle size distribution. The particle size distribution can be measured by a method widely known to those skilled in the art. For example, the particle size distribution can be measured by a particle size analyzer, or can be measured by a transmission electron microscope photograph or a scanning electron microscope photograph. Alternatively, the D100 value can be obtained by measuring using a measuring device that utilizes dynamic light-scattering, performing data analysis to count the number of particles for each particle size range, and calculating from the counted number. Alternatively, the D100 value can be obtained by measuring using a laser diffraction method. When measuring by laser diffraction, more specifically, after the particles to be measured are dispersed in a dispersion medium, they are introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac MT 3000) and irradiated with ultrasonic waves of approximately 28 kHz at an output of 60 W, and then D100 based on 100% of the size distribution in the measuring device can be calculated.

[0020] In this specification, 'particle size D50' refers to the size of particles having a cumulative volume of 50% by volume in the particle size distribution. The particle size distribution can be obtained by referring to the method described in the 'particle size D100' above.

[0021] In this specification, ‘diameter D100’ may mean ‘size D100’.

[0022] In this specification, ‘particle diameter D50’ may mean ‘size D50’.

[0023] In this specification, '(meth)acrylic' means acrylic and / or methacrylic.

[0024] Unless otherwise defined below, "substitution" means that hydrogen in a compound is substituted with a C1 to C30 alkyl group, a C2 to C30 alkenyl group, a C2 to C30 alkynyl group, a C6 to C30 aryl group, a C7 to C30 alkylaryl group, a C1 to C30 alkoxy group, a C1 to C30 heteroalkyl group, a C3 to C30 heteroalkylaryl group, a C3 to C30 cycloalkyl group, a C3 to C15 cycloalkenyl group, a C6 to C30 cycloalkynyl group, a C2 to C30 heterocycloalkyl group, a halogen (F, Cl, Br or I), a hydroxy group (-OH), a nitro group (-NO2), a cyano group (-CN), an amino group (-NRR') (wherein R and R' are each independently hydrogen or a C1 to C6 alkyl group), a sulfobetaine group (-RR'N + (CH2) n SO3 - , n is a natural number from 1 to 10), carboxybetaine group (-RR'N + (CH2) n COO -, n is a natural number from 1 to 10) (wherein, R and R' are each independently a C1 to C20 alkyl group), azido 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 to C6 alkyl group, a C1 to C6 alkoxy group, or a C6 to C12 aryl group), carboxyl group (-COOH) or a salt thereof (-C(=O)OM, where M is an organic or inorganic cation), sulfonic acid group (-SO3H) or a salt thereof (-SO3M, where M is an organic or inorganic cation), phosphoric acid group (-PO3H2) or a salt thereof (-PO3MH or -PO3M2, where M is an organic or inorganic cation) and combinations thereof.

[0025] Hereinafter, a C1 to C3 alkyl group means a methyl group, an ethyl group, or a propyl group. A C1 to C10 alkylene group can be, for example, a C1 to C6 alkylene group, a C1 to C5 alkylene group, a C1 to C3 alkylene group, and can be, for example, a methylene group, an ethylene group, or a propylene group. A C3 to C20 cycloalkylene group can be, for example, a C3 to C10 cycloalkylene group, or a C5 to C10 cycloalkylene group, and can be, for example, a cyclohexylene group. A C6 to C20 arylene group can be, for example, a C6 to C10 arylene group, and can be, for example, a phenylene group. A C3 to C20 heterocyclic group can be, for example, a C3 to C10 heterocyclic group, and can be, for example, a pyridine group.

[0026] Hereinafter, “hetero” means containing one or more heteroatoms selected from N, O, S, Si, and P.

[0027] In the chemical formulas described herein, the * symbol indicates a part that is connected to the same or different atoms, groups, or structural units.

[0028] Unless otherwise specifically stated in the chemical formulas described herein, hydrogen may be considered to be bonded in the structure of the chemical formula.

[0029] Hereinafter, “alkali metal” refers to an element belonging to Group 1 of the periodic table, such as lithium, sodium, potassium, rubidium, cesium, or francium, which can exist in a cationic or neutral state.

[0030] When describing a numerical range in this specification, 'X to Y' means 'X or more and Y or less (X ≤ and ≤ Y).

[0031] According to one embodiment, a separator for a lithium secondary battery comprises a porous substrate and a coating layer positioned on at least one surface of the porous substrate, wherein the coating layer comprises a binder; a crosslinking agent; and a crosslinked product of carboxyalkyl cellulose or a salt thereof; and a filler, wherein the binder comprises a (meth)acrylic binder including a structural unit derived from (meth)acrylate or (meth)acrylic acid, a cyano group-containing structural unit, and a sulfonate group-containing structural unit, wherein the crosslinking agent comprises an aziridine-based crosslinking agent, and the filler is surface-modified and has a particle diameter D100 of 1.0 μm or less.

[0032] According to one embodiment, the coating layer may be formed of a composition for a coating layer including the (meth)acrylic binder; the aziridine crosslinking agent; the carboxyalkyl cellulose or a salt thereof; and the filler.

[0033] According to one embodiment, the crosslinking agent may be a thermal crosslinking agent.

[0034] The above coating layer may include the (meth)acrylic binder, the crosslinking agent, and the crosslinked product of the carboxyalkyl cellulose or its salt; and the filler, thereby improving the heat resistance of the separator.

[0035] In this regard, the cross-linked material may have a storage modulus of 3500 Pa or more, for example, 3500 to 6500 Pa. In the above range, the heat resistance may be excellent when evaluated by hole size during hot tip penetration evaluation. The hole size evaluation during hot tip penetration evaluation is another method for evaluating the heat resistance of the separator, which is different from the dry shrinkage rate and the electrolyte shrinkage rate of the separator. If the dry shrinkage rate and the electrolyte shrinkage rate of the separator are each used to evaluate the degree of shrinkage in the longitudinal direction of the entire separator, the hot tip penetration evaluation is used to evaluate the heat resistance in the thickness direction of a local region of the separator.

[0036] The above separator for a lithium secondary battery can have significantly low dry shrinkage and shrinkage in an electrolyte solution.

[0037] According to one embodiment, the dry shrinkage of the separator for a lithium secondary battery may be 10% or less, for example, 7% or less, in each of the machine direction (MD) and the transverse direction (TD), and the shrinkage in the electrolyte may be 10% or less, for example, 5% or less, in each of the machine direction (MD) and the transverse direction (TD).

[0038] According to one embodiment, the separator for a lithium secondary battery is characterized by providing a remarkably low shrinkage rate within an electrolyte. The shrinkage rate within the electrolyte takes into account the application location of the separator within a lithium secondary battery. The separator may be immersed in the electrolyte. A separator with a low shrinkage rate within the electrolyte can enhance the stability of the battery by maintaining heat resistance without deteriorating the mechanical properties of a (meth)acrylic binder when the separator is immersed in the electrolyte.

[0039] A separator having a coating layer formed with a composition for a coating layer that includes the above (meth)acrylic binder but does not include an aziridine-based crosslinking agent as a crosslinking agent or contains a crosslinking agent other than an aziridine-based crosslinking agent may not easily achieve the heat resistance and shrinkage rate of the separator.

[0040] According to one embodiment, the aziridine-based crosslinking agent may be included in an amount of 95 wt% or more, for example, 98 to 100 wt%, or 100 wt%, of the total crosslinking agent in the composition for the coating layer.

[0041] A separator having a coating layer formed with a composition for a coating layer that includes the above-mentioned aziridine-based crosslinking agent and the above-mentioned filler, but does not include the above-mentioned (meth)acrylic-based binder or contains a binder other than the above-mentioned (meth)acrylic-based binder may not easily achieve the above-mentioned heat resistance and shrinkage ratio of the separator.

[0042] According to one embodiment, the (meth)acrylic binder may be included in an amount of 95 wt% or more, for example, 98 to 100 wt%, or 100 wt%, of the total binder in the composition for the coating layer.

[0043] A separator formed with a composition for a coating layer that does not include the above carboxyalkyl cellulose or its salt may not easily reach the above heat resistance and shrinkage rate of the separator.

[0044] coating layer

[0045] The above binder includes a (meth)acrylic binder including a structural unit derived from (meth)acrylate or (meth)acrylic acid, a cyano group-containing structural unit, and a sulfonate group-containing structural unit.

[0046] The above (meth)acrylic binder is a water-based heat-resistant binder that can fix the filler onto a porous substrate and provide adhesive strength so that the coating layer adheres well to the porous substrate and electrode, and can contribute to improving the heat resistance, air permeability, and oxidation resistance of the separator. In addition, the (meth)acrylic binder can increase the storage elastic modulus of the cross-linked product, thereby providing a separator with high heat resistance when evaluating the penetration of a hot tip of the separator.

[0047] In the structural unit derived from the above (meth)acrylate or (meth)acrylic acid, the (meth)acrylate may be a conjugate base of (meth)acrylic acid, a (meth)acrylic acid salt, or a derivative thereof. The structural unit derived from the above (meth)acrylate or (meth)acrylic acid may be represented by, for example, the following chemical formula 1, chemical formula 2, chemical formula 3, or a combination thereof:

[0048] [Chemical Formula 1]

[0049]

[0050] [Chemical Formula 2]

[0051]

[0052] [Chemical Formula 3]

[0053]

[0054] (In the above chemical formulas 1 to 3,

[0055] R 1 , R 2 , R 3 , R 4 , R 5 and R 6 are each independently hydrogen or methyl group,

[0056] In the above chemical formula 2,

[0057] M is an alkali metal).

[0058] The alkali metal may be, for example, lithium, sodium, potassium, rubidium or cesium.

[0059] The structural unit derived from the (meth)acrylate or (meth)acrylic acid may be included in the (meth)acrylic binder in an amount of 10 mol% to 70 mol%, for example, 20 mol% to 60 mol%, 30 mol% to 60 mol%, 40 mol% to 55 mol%, or 10 mol% to 50 mol%. When the structural unit derived from the (meth)acrylate or (meth)acrylic acid is included in the above range, a separator including the (meth)acrylic binder may exhibit excellent adhesive strength, heat resistance, air permeability, and oxidation resistance.

[0060] For example, the structural unit derived from the (meth)acrylate or (meth)acrylic acid may include a structural unit represented by the chemical formula 2 and a structural unit represented by the chemical formula 3, and in this case, the structural unit represented by the chemical formula 2 and the structural unit represented by the chemical formula 3 may be included in a molar ratio of 10:1 to 1:2, or 10:1 to 1:1, or 5:1 to 1:1.

[0061] The above cyano group-containing structural unit can be represented, for example, by the following chemical formula 4.

[0062] [Chemical Formula 4]

[0063]

[0064] (In the above chemical formula 4,

[0065] R 7 and R 8 are each independently hydrogen or a C1 to C3 alkyl group,

[0066] L 1 is -C(=O)-, -C(=O)O-, -OC(=O)-, -O- or -C(=O)NH-,

[0067] x is an integer from 0 to 2,

[0068] L 2is a substituted or unsubstituted C1 to C10 alkylene group, a substituted or unsubstituted C3 to C20 cycloalkylene group, a substituted or unsubstituted C6 to C20 arylene group, or a substituted or unsubstituted C3 to C20 heterocyclic group,

[0069] y is an integer from 0 to 2).

[0070] The above cyano group-containing structural unit may be a structural unit derived from, for example, (meth)acrylonitrile, alkene nitrile, cyanoalkyl(meth)acrylate or 2-(vinyloxy)alkane nitrile. Here, the alkene may be a C1 to C20 alkene, a C1 to C10 alkene or a C1 to C6 alkene, the alkyl may be a C1 to C20 alkyl, a C1 to C10 alkyl or a C1 to C6 alkyl, and further, the alkane may be a C1 to C20 alkane, a C1 to C10 alkane or a C1 to C6 alkane.

[0071] The alkene nitrile may be, for example, cyanoallyl, 4-pentene nitrile, 3-pentene nitrile, 2-pentene nitrile, or 5-hexene nitrile. The cyanoalkyl (meth)acrylate may be, for example, cyanomethyl (meth)acrylate, cyanoethyl (meth)acrylate, cyanopropyl (meth)acrylate, or cyanooctyl (meth)acrylate. The 2-(vinyloxy)alkane nitrile may be, for example, 2-(vinyloxy)ethane nitrile or 2-(vinyloxy)propane nitrile.

[0072] The above cyano group-containing structural unit may be included in the (meth)acrylic binder in an amount of 30 mol% to 85 mol%, for example, 40 mol% to 85 mol%, 30 mol% to 70 mol%, 30 mol% to 60 mol%, 35 mol% to 60 mol%, or 35 mol% to 55 mol%. When the above cyano group-containing structural unit is included in the above range, the (meth)acrylic binder and the separator including the same can secure excellent oxidation resistance and exhibit adhesive strength, heat resistance, and air permeability.

[0073] The above sulfonate group-containing structural unit may be a structural unit containing a conjugate base of sulfonic acid, a sulfonate salt, a sulfonic acid, or a derivative thereof. For example, the sulfonate group-containing structural unit may be represented by the following chemical formula 5, chemical formula 6, chemical formula 7, or a combination thereof.

[0074] [Chemical Formula 5]

[0075]

[0076] [Chemical Formula 6]

[0077]

[0078] [Chemical Formula 7]

[0079]

[0080] (In the above chemical formulas 5 to 7,

[0081] R 9 , R 10 , R 11 , R 12 , R 13 and R 14 are each independently hydrogen or a C1 to C3 alkyl group,

[0082] L 3 , L 5 and L 7 are each independently -C(=O)-, -C(=O)O-, -OC(=O)-, -O- or -C(=O)NH-,

[0083] L 4, L 6 and L 8 are each independently a substituted or unsubstituted C1 to C10 alkylene group, a substituted or unsubstituted C3 to C20 cycloalkylene group, a substituted or unsubstituted C6 to C20 arylene group, or a substituted or unsubstituted C3 to C20 heterocyclic group,

[0084] a, b, c, d, e and f are each independently integers from 0 to 2,

[0085] In the above chemical formula 6,

[0086] M is an alkali metal).

[0087] For example, in the chemical formulas 5 to 7,

[0088] L 3 , L 5 and L 7 are each independently -C(=O)NH-,

[0089] L 4 , L 6 and L 8 are each independently a C1 to C10 alkylene group,

[0090] a, b, c, d, e and f can be integers greater than 1.

[0091] The above sulfonate group-containing structural unit may include only one of the structural unit represented by the above chemical formula 5, the structural unit represented by the above chemical formula 6, and the structural unit represented by the above chemical formula 7, or may include two or more types. For example, the sulfonate group-containing structural unit may include the structural unit represented by the above chemical formula 6, and for another example, the sulfonate group-containing structural unit may include the structural unit represented by the above chemical formula 6 and the structural unit represented by the above chemical formula 7.

[0092] The above sulfonate group-containing structural unit may be a structural unit derived from, for example, vinyl sulfonic acid, allyl sulfonic acid, styrene sulfonic acid, anethole sulfonic acid, (meth)acrylamidoalkane sulfonic acid, sulfoalkyl (meth)acrylate or a salt thereof.

[0093] Here, the alkane may be a C1 to C20 alkane, a C1 to C10 alkane or a C1 to C6 alkane, and the alkyl may be a C1 to C20 alkyl, a C1 to C10 alkyl or a C1 to C6 alkyl. The salt refers to a salt composed of the above-mentioned sulfonic acid and a suitable ion. The ion may be, for example, an alkali metal ion, in which case the salt may be a sulfonic acid alkali metal salt.

[0094] The above (meth)acrylamidoalkane sulfonic acid may be, for example, 2-(meth)acrylamido-2-methylpropane sulfonic acid, and the above sulfoalkyl (meth)acrylate may be, for example, 2-sulfoethyl (meth)acrylate, 3-sulfopropyl (meth)acrylate, etc.

[0095] The above sulfonate group-containing structural unit may be included in the (meth)acrylic binder in an amount of 0.1 mol% to 20 mol%, for example, 0.1 mol% to 10 mol%, 1 mol% to 20 mol%, or 1 mol% to 10 mol%. When the above sulfonate group-containing structural unit is included in the above range, the (meth)acrylic binder and the separator including the same may exhibit excellent adhesive strength, heat resistance, air permeability, and oxidation resistance.

[0096] As described above, the (meth)acrylic binder may include an alkali metal. The alkali metal may exist in a cation form, such as lithium, sodium, potassium, rubidium, or cesium. For example, the alkali metal may be combined with the (meth)acrylic binder and exist in the form of a salt. The alkali metal may assist in the synthesis of the (meth)acrylic binder in an aqueous solvent, enhance the adhesiveness of the coating layer, and improve the heat resistance, air permeability, and oxidation resistance of the separator.

[0097] The alkali metal may be included in an amount of 1 wt% to 40 wt% of the alkali metal and the (meth)acrylic binder, for example, 1 wt% to 30 wt%, or 1 wt% to 20 wt%, or 10 wt% to 20 wt%. For example, the (meth)acrylic binder and the alkali metal may be included in a weight ratio of 99:1 to 60:40, a weight ratio of 99:1 to 70:30, a weight ratio of 99:1 to 80:20, or a weight ratio of 90:10 to 80:20.

[0098] Additionally, the alkali metal may be included in an amount of 0.1 mol% to 1.0 mol% based on the total content of the alkali metal and the (meth)acrylic binder. When the alkali metal is included in the above range, the coating layer may have excellent adhesiveness, and a separator including the alkali metal may exhibit excellent heat resistance, air permeability, and oxidation resistance.

[0099] The above (meth)acrylic binder can be represented by, for example, the following chemical formula 8.

[0100] [Chemical Formula 8]

[0101]

[0102] In the above chemical formula 8,

[0103] R 15 , R 16 , R17 and R 18 are each independently hydrogen or methyl group,

[0104] R 19 , R 20 , R 21 and R 22 are each independently hydrogen or a C1 to C3 alkyl group,

[0105] L 1 and L 5 are each independently -C(=O)-, -C(=O)O-, -OC(=O)-, -O- or -C(=O)NH-,

[0106] L 2 and L 6 are each independently a substituted or unsubstituted C1 to C10 alkylene group, a substituted or unsubstituted C3 to C20 cycloalkylene group, a substituted or unsubstituted C6 to C20 arylene group, or a substituted or unsubstituted C3 to C20 heterocyclic group,

[0107] x, y, c and d are each independently integers from 0 to 2,

[0108] M is an alkali metal such as lithium, sodium, potassium, rubidium or cesium,

[0109] k, l, m and n represent the molar ratio of each structural unit.

[0110] For example, in the chemical formula 8, k+l+m+n=1. Also, for example, 0.1≤(k+l)≤0.5, 0.4≤m≤0.85, and 0.001≤n≤0.2, and for example, 0.1≤k≤0.5 and 0≤l≤0.25.

[0111] For example, in the chemical formula 8, x=y=0, and L 5 is -C(=O)NH-, and L 6 is a C1 to C10 alkylene group, and c=d=1.

[0112] In the above (meth)acrylic binder, an alkali metal (M +) may be 0.5 to 1.0 with respect to (k+n), for example, 0.6 to 0.9 or 0.7 to 0.9. When the degree of substitution of the alkali metal satisfies the above range, the (meth)acrylic binder and the separator including the same may exhibit excellent adhesive strength, heat resistance, and oxidation resistance.

[0113] The above (meth)acrylic heat-resistant binder can be in various forms, such as an alternating polymer in which the structural units are alternately distributed, a random polymer in which the structural units are randomly distributed, or a graft polymer in which some of the structural units are grafted.

[0114] The weight average molecular weight (Mw) of the (meth)acrylic binder may be 200,000 g / mol to 700,000 g / mol, for example 200,000 g / mol to 600,000 g / mol, for example 300,000 g / mol to 600,000 g / mol. When the weight average molecular weight of the (meth)acrylic binder satisfies the above range, the (meth)acrylic binder and the separator including the same may exhibit excellent adhesive strength, heat resistance, air permeability, and oxidation resistance. The weight average molecular weight may be a polystyrene-converted average molecular weight measured using gel permeation chromatography.

[0115] The glass transition temperature of the (meth)acrylic binder may be 200°C to 280°C, for example 210°C to 270°C, for example 210°C to 260°C. When the glass transition temperature of the (meth)acrylic binder satisfies the above range, the (meth)acrylic binder and the separator including the same may exhibit excellent adhesive strength, heat resistance, air permeability, and oxidation resistance. The glass transition temperature may be a value measured by differential scanning calorimetry.

[0116] According to one embodiment, the (meth)acrylic binder may be included in an amount of 20 to 70 wt%, for example, 20 to 65 wt%, 25 to 60 wt%, 20 to 60 wt%, 30 to 70 wt%, 30 to 60 wt%, or 40 to 60 wt%, of the total of the (meth)acrylic binder; the crosslinking agent; and the carboxyalkyl cellulose or its salt. In the above range, there may be an effect of improving heat resistance characteristics in the electrolyte.

[0117] The above (meth)acrylic binder can be manufactured by a solution polymerization method.

[0118] According to one embodiment, the (meth)acrylic binder may be included in the coating layer of the separator in the form of a film.

[0119] The above cross-linking agent includes an aziridine-based cross-linking agent.

[0120] The above aziridine-based crosslinking agent can crosslink the (meth)acrylic binder and the carboxyalkyl cellulose to facilitate the separator reaching the dry shrinkage rate and shrinkage rate in the electrolyte solution range and increasing the heat resistance of the coating layer.

[0121] The above aziridine cross-linking agent may be a bifunctional or higher aziridine cross-linking agent. Here, "bifunctional or higher" means that two or more aziridine groups are present in the molecule. According to one embodiment, the aziridine cross-linking agent may be a bifunctional or trifunctional aziridine cross-linking agent.

[0122] For example, the aziridine-based crosslinking agent may include at least one of N,N'-toluene-2,4-bis(1-aziridinecarboxamide), N,N'-(methylenedi-p-phenylene)bis(aziridine-1-carboxamide), triethylenemelamine, 1,1-isophthaloyl bis(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).

[0123] The above crosslinking agent, for example, the aziridine-based crosslinking agent, should be included in an appropriate amount with respect to the binder, for example, the (meth)acrylic-based binder and the carboxyalkyl cellulose or its salt.

[0124] According to one embodiment, the crosslinking agent may be included in an amount of 5 to 30 wt%, for example, 10 to 30 wt%, 10 to 20 wt%, of the total of the (meth)acrylic binder; the crosslinking agent; and the carboxyalkyl cellulose or its salt. Within this range, the effect of improving heat resistance within the electrolyte may be present.

[0125] The crosslinking agent, for example, the aziridine-based crosslinking agent, should be included in an appropriate amount relative to the binder, for example, the (meth)acrylic binder. For example, the crosslinking agent may be included in an amount of 5 to 60 wt%, for example, 10 to 60 wt%, or 20 to 60 wt%, relative to the (meth)acrylic binder. Within this range, the heat resistance effect may be improved.

[0126] The above carboxyalkyl cellulose or its salt has a cyclic structure within the molecule and can react with the crosslinking agent by having a carboxyl group within the molecule, thereby increasing the storage elastic modulus of the crosslinked product, thereby further reducing the dry shrinkage rate and shrinkage rate in an electrolyte solution, and can easily increase the heat resistance of the separator when evaluating penetration using a hot tip.

[0127] The above carboxyalkyl cellulose may be, for example, carboxymethyl cellulose.

[0128] The salt of the above carboxyalkyl cellulose may be a salt of carboxyalkyl cellulose, for example, a carboxyalkyl cellulose monovalent metal salt, for example, a carboxyalkyl cellulose sodium salt, etc.

[0129] The above carboxyalkyl cellulose or its salt should be included in an appropriate amount with respect to the binder, for example, the (meth)acrylic binder, and the crosslinking agent.

[0130] According to one embodiment, the carboxyalkyl cellulose or its salt may be included in an amount of 20 to 70 wt%, for example, 20 to 65 wt%, 25 to 60 wt%, 20 to 60 wt%, 30 to 70 wt%, 30 to 60 wt%, or 40 to 60 wt%, of the total of the (meth)acrylic binder; the crosslinking agent; and the carboxyalkyl cellulose or its salt. In the above range, there may be an effect of improving heat resistance characteristics in the electrolyte.

[0131] According to one embodiment, the sum total of the (meth)acrylic binder and the carboxyalkyl cellulose or salt thereof may be comprised in an amount of 70 to 95 wt%, for example, 85 to 90 wt%, of the sum total of the (meth)acrylic binder; the crosslinking agent; and the carboxyalkyl cellulose or salt thereof. Within this range, there may be an effect of improving heat resistance characteristics in the electrolyte.

[0132] The above filler is surface-modified and includes a filler having a particle size D100 of 1.0 μm or less. In the above range, when combined with the (meth)acrylic binder, the crosslinking agent, and the carboxyalkylsulfonyl ...

[0133] According to one embodiment, the filler may have a particle size D50 of 0.4 μm or less, for example, 0.35 μm or less, 0.3 μm or less, or 0.1 to 0.3 μm. Within this range, the heat resistance characteristics may be improved.

[0134] According to one embodiment, the filler having a particle size D100 of 1.0 μm or less may be included in an amount of 95 wt% or more, for example, 95 to 100 wt%, 98 to 100 wt%, or 100 wt%, of the total filler in the coating layer. Within the above range, the effect of the present separation membrane may be easily realized.

[0135] The above surface modification may include surface modification of the surface of the filler to have an amino group. Here, the 'amino group' is *N(R 1 )(R 2 )(Here, R 1 , R 2 may mean hydrogen or a substituted or unsubstituted C1 to C10 alkyl group), and preferably may mean a -NH2 group. Such surface modification may expand the particle size range of the filler required to provide the dry shrinkage rate and the shrinkage rate in the electrolyte solution compared to when the filler is not surface modified.

[0136] In one embodiment, the surface modification may comprise surface treating the non-surface-modified filler with an amino silane compound. The amino silane compound may comprise a silane compound having at least one nitrogen atom, for example, from 1 to 6 nitrogen atom(s).

[0137] In one specific example, the amino silane compound may include, but is not limited to, one or more compounds of the following formulae: 9, 10, and 11:

[0138] [Chemical Formula 9]

[0139]

[0140] [Chemical Formula 10]

[0141]

[0142] [Chemical Formula 11]

[0143]

[0144] In the above chemical formulas 9 to 11,

[0145] X 1 , X 2 and X 3 are each independently hydrogen, a hydroxyl group, a substituted or unsubstituted C1 to C20 alkyl group, a substituted or unsubstituted C6 to C20 aryl group, a substituted or unsubstituted C3 to C20 cycloalkyl group, a substituted or unsubstituted C7 to C20 arylalkyl group, a substituted or unsubstituted C1 to C20 alkoxy group, or a substituted or unsubstituted C6 to C20 aryloxy group,

[0146] X 1 , X 2 and X 3 At least one of them is a hydroxyl group, a substituted or unsubstituted C1 to C20 alkoxy group, or a substituted or unsubstituted C6 to C20 aryloxy group,

[0147] Y 1 , Y 2 , Y 2, Y 3 , Y 4 , Y 5 , Y 6 are each independently a divalent C1 to C20 aliphatic hydrocarbon group, a divalent C5 to C20 alicyclic hydrocarbon group, or a divalent C6 to C20 aromatic hydrocarbon group,

[0148] R 15 , R 16 , R 17 , R 18 . R 19 , R 20 , R 21 , R 22 , R 23 are each independently hydrogen, 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.

[0149] For example, the amino silane compound may include, but is not limited to, one or more of 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropylmethyldimethoxysilane, 3-aminopropylmethyldiethoxysilane, aminoethylaminopropyltrimethoxysilane, aminoethylaminopropyltriethoxysilane, aminoethylaminopropylmethyldimethoxysilane, aminoethylaminopropylmethyldiethoxysilane, aminoethylaminomethyltriethoxysilane, aminoethylaminomethylmethyldiethoxysilane, diethylenetriaminopropyltrimethoxysilane, diethylenetriaminopropyltriethoxysilane, diethylenetriaminopropylmethyldimethoxysilane, diethylenetriaminopropylmethyldiethoxysilane, diethylenetriaminomethylmethyldiethoxysilane.

[0150] According to one embodiment, the surface modification can be performed by a conventional method using an amino silane compound.

[0151] The filler may be, for example, an inorganic filler, an organic filler, an organic-inorganic composite filler, or a combination thereof. The inorganic filler may be a ceramic material capable of improving 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 a core-shell structure, but is not limited thereto. For example, the filler may be preferably boehmite.

[0152] The above filler may be spherical, plate-shaped, cubic, or amorphous. Preferably, the filler may be cubic, and the cubic filler may have a significantly lower shrinkage rate as described above.

[0153] The above filler should be included in an appropriate amount relative to the binder, for example, the (meth)acrylic binder. According to one embodiment, the (meth)acrylic binder: the filler may be included in a mass ratio of 1:10 to 1:50, for example, a mass ratio of 1:20 to 1:30. Within the above range, the heat resistance characteristics in the electrolyte may be improved.

[0154] The filler may be included in an amount of 50 wt% to 99 wt% of the total weight of the coating layer, for example, 70 wt% to 99 wt%, for example, 75 wt% to 99 wt%, for example, 80 wt% to 99 wt%, for example, 85 wt% to 99 wt%, for example, 90 wt% to 99 wt%, for example, 95 wt% to 99 wt%. When the filler is included in the above range, excellent heat resistance, durability, oxidation resistance, and stability may be exhibited.

[0155] The above coating layers may each have a thickness of 0.01 μm to 20 μm, and within the above range may have a thickness of 1 μm to 10 μm, or 1 μm to 5 μm, or 1 μm to 3 μm.

[0156] The ratio of the thickness of the coating layer to the thickness of the porous substrate may be 0.05 to 0.5, for example, 0.05 to 0.4, or 0.05 to 0.3, or 0.1 to 0.2. In the above range, the separator may exhibit excellent air permeability, heat resistance, and adhesive strength. Here, the 'thickness of the coating layer' means the thickness of one coating layer when the coating layer is formed on only one side of the porous substrate, and means the thickness of the entire two coating layers when the coating layers are formed on both sides of the porous substrate.

[0157] porous substrate

[0158] The porous substrate may be a substrate having a plurality of pores and typically used in electrochemical devices. The porous substrate may be, but is not limited to, a polymer selected from the group consisting of polyolefins such as polyethylene and 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, Teflon, and polytetrafluoroethylene, or a polymer film formed of a copolymer or mixture of two or more thereof.

[0159] The porous substrate may be, for example, a polyolefin-based substrate including polyolefin, and the polyolefin-based substrate may have an excellent shutdown function, thereby contributing to improved battery safety. The polyolefin-based substrate may be selected from, for example, a polyethylene single film, a polypropylene single film, a polyethylene / polypropylene bilayer film, a polypropylene / polyethylene / polypropylene triple film, and a polyethylene / polypropylene / polyethylene triple film. In addition, the polyolefin-based resin may include a non-olefin resin in addition to an olefin resin, or may include a copolymer of an olefin and a non-olefin monomer.

[0160] The porous substrate may 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.

[0161] A separator for a lithium secondary battery according to one embodiment may have excellent adhesive strength. Specifically, the separator for a lithium secondary battery may have an adhesive strength of 0.05 gf / mm or more, for example, 0.05 gf / mm to 0.1 gf / mm, for example, 0.05 gf / mm to 0.2 gf / mm. The adhesive strength may be measured by the following method:

[0162] A separator for a lithium secondary battery is placed between the positive and negative electrodes, and passed between rolls at a pressure of 250 kgf in an 80℃ chamber at a speed of 150 mm / sec to adhere the positive and negative electrodes and the separator. The separator adhered to the positive and negative electrodes is cut into a width of 25 mm and a length of 50 mm to produce a sample. A UTM is used as an adhesion measuring device. After separating the separator from the negative electrode plate by about 10 to 20 mm in the sample, the separator is fixed to the upper grip and the negative electrode plate to the lower grip with a gap of 20 mm between the grips, and then peeled by pulling in the 180° direction. The peeling speed is 20 mm / min, and the force required to peel 40 mm after the start of peeling is measured three times and the average value is obtained. The average value of the measured values ​​is calculated.

[0163] According to one embodiment, a separator for a lithium secondary battery may exhibit excellent air permeability, and may have an air permeability value of, for example, less than 200 sec / 100cc, for example, less than 190 sec / 100cc, or less than 180 sec / 100cc. That is, it may have an air permeability value of less than 40 sec / 100cc·1㎛ per unit thickness, for example, less than 30 sec / 100cc·1㎛ or less, or less than 25 sec / 100cc·1㎛. Here, the air permeability refers to the time (in seconds) it takes for 100cc of air to permeate the unit thickness of the separator. The air permeability per unit thickness can be obtained by measuring the air permeability for the entire thickness of the separator and then dividing it by the thickness. The air permeability can be measured by measuring the time (in seconds) it takes for 100cc of air to permeate using an air permeability measuring device (Asahi Seiko, EG01-55-1MR).

[0164] A secondary battery separator according to one embodiment can be formed by applying a composition for forming a coating layer to one or both sides of a porous substrate, drying the composition, and then curing the composition. The curing can be performed using a conventional method known to those skilled in the art.

[0165] Figure 1 is a cross-sectional view showing a separator for a lithium secondary battery according to one embodiment.

[0166] Referring to FIG. 1, a separator for a lithium secondary battery includes a porous substrate 1 and a coating layer 2 positioned on both sides of the porous substrate 1. The coating layer 2 includes a filler 3, a crosslinked product 4 of a (meth)acrylic binder and a crosslinking agent, and carboxyalkyl cellulose or a salt thereof (not shown).

[0167] Another embodiment provides a lithium secondary battery comprising a separator for a lithium secondary battery according to one embodiment; a positive electrode; and a negative electrode.

[0168] The separator for a lithium secondary battery refers to the content described above. The separator for a lithium secondary battery can be positioned between the positive electrode and the negative electrode.

[0169] 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 includes a positive electrode active material and may further include a binder and / or a conductive material. For example, the positive electrode may further include an additive that can function as a sacrificial positive electrode.

[0170] A compound capable of reversible intercalation and deintercalation of lithium (a lithiated intercalation compound) can be used as a cathode active material. Specifically, one or more of a composite oxide of lithium and a metal selected from cobalt, manganese, nickel, and combinations thereof can be used.

[0171] The above composite oxide may be a lithium transition metal composite oxide, and specific examples thereof include lithium nickel-based oxide, lithium cobalt-based oxide, lithium manganese-based oxide, lithium iron phosphate-based compound, cobalt-free nickel-manganese-based oxide, or a combination thereof.

[0172] As an example, a compound represented by any one of the following chemical formulas may be used: Lia 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 Mr 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 Ni 1-b-c Mr 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 Mr 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 Mr 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(0.90≤a≤1.8).

[0173] 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, a rare earth element, 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.

[0174] For example, the cathode active material may be a high-nickel cathode active material in which the nickel content 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, based on 100 mol% of metals excluding lithium in the lithium transition metal composite oxide. The high-nickel cathode active material can realize high capacity and thus can be applied to high-capacity, high-density lithium secondary batteries.

[0175] The content of the positive electrode active material may be 90 wt% to 99.5 wt% of 100 wt% of the positive electrode active material layer, and the contents of the binder and conductive material may be 0.5 wt% to 5 wt%, respectively, with respect to 100 wt% of the positive electrode active material layer.

[0176] The above binder serves to adhere the positive electrode active material particles well to each other and also to adhere the positive electrode active material well to the current collector. Representative examples of the binder include, but are not limited to, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, epoxy resin, (meth)acrylic resin, polyester resin, nylon, etc.

[0177] The conductive material is used to provide conductivity to the electrode, and any material that does not cause chemical changes and is electronically conductive can be used in the battery. Examples of the conductive material include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, carbon nanofiber, and carbon nanotube; metal-based 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.

[0178] Al may be used as the above current collector, but is not limited thereto.

[0179] A negative electrode for a lithium secondary battery includes a current collector and a negative electrode active material layer positioned 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.

[0180] For example, the negative electrode active material layer may include 90 to 99 wt% of the negative electrode active material, 0.5 to 5 wt% of the binder, and 0 to 5 wt% of the conductive material.

[0181] The negative electrode active material includes a material capable of reversibly intercalating / deintercalating lithium ions, lithium metal, an alloy of lithium metal, a material capable of doping and dedoping lithium, or a transition metal oxide.

[0182] The material capable of reversibly intercalating / deintercalating the lithium ions may include a carbon-based negative electrode active material, for example, crystalline carbon, amorphous carbon, or a combination thereof. Examples of the crystalline carbon include graphite such as natural graphite or artificial graphite in an amorphous, plate-like, flake-like, spherical, or fibrous form, and examples of the amorphous carbon include soft carbon or hard carbon, mesophase pitch carbide, calcined coke, and the like.

[0183] As the above 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.

[0184] As the material capable of doping and dedoping the lithium, a Si-based negative electrode active material or a Sn-based negative electrode active material may be used. The Si-based negative electrode active material may be silicon, a silicon-carbon composite, SiOx (0 < x < 2), a Si-Q alloy (wherein 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 thereof. The Sn-based negative electrode active material may be Sn, SnO2, a Sn-based alloy, or a combination thereof.

[0185] The silicon-carbon composite may be a composite of silicon and amorphous carbon. According to one embodiment, the silicon-carbon composite may be in the form of silicon particles and amorphous carbon coated on the surface of the silicon particles. For example, the composite may include secondary particles (cores) in which silicon primary particles are assembled and an amorphous carbon coating layer (shell) positioned on the surface of the secondary particles. The amorphous carbon may also be positioned between the silicon primary particles, such that, for example, the silicon primary particles may be coated with amorphous carbon. The secondary particles may be dispersed and present in an amorphous carbon matrix.

[0186] The silicon-carbon composite may further comprise crystalline carbon. For example, the silicon-carbon composite may comprise a core comprising crystalline carbon and silicon particles and an amorphous carbon coating layer positioned on the surface of the core.

[0187] The above Si-based negative electrode active material or Sn-based negative electrode active material can be used in a mixture with a carbon-based negative electrode active material.

[0188] The above binder serves to adhere the negative electrode active material particles well to each other and also to adhere the negative electrode active material well to the current collector. The binder may be a non-aqueous binder, an aqueous binder, a dry binder, or a combination thereof.

[0189] Examples of the non-aqueous binder include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene propylene copolymer, polystyrene, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, or combinations thereof.

[0190] The above-mentioned aqueous binder may be selected from styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, (meth)acrylonitrile-butadiene rubber, (meth)acrylic rubber, butyl rubber, fluoroelastomer, polyethylene oxide, polyvinylpyrrolidone, polyepichlorohydrin, polyphosphazene, poly(meth)acrylonitrile, ethylene propylene diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, (meth)acrylic resin, phenol resin, epoxy resin, polyvinyl alcohol, and combinations thereof.

[0191] When using an aqueous binder as the above-mentioned negative electrode binder, a cellulose-based compound capable of imparting viscosity may be further included. The cellulose-based compound may be a mixture of one or more of carboxymethyl cellulose, hydroxypropylmethyl cellulose, methyl cellulose, or an alkali metal salt thereof. The alkali metal may be Na, K, or Li.

[0192] The above dry binder is a polymeric material capable of being fiberized, and may be, for example, polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or a combination thereof.

[0193] The conductive material is used to provide conductivity to the electrode, and any material that does not cause chemical changes and is electronically conductive can be used in the battery. Specific examples include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fibers, carbon nanofibers, and carbon nanotubes; metal-based materials in the form of metal powder or metal fibers, including copper, nickel, aluminum, and silver; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0194] The negative electrode current collector may be selected from copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, and a combination thereof.

[0195] Lithium secondary batteries may further contain electrolyte.

[0196] An electrolyte for a lithium secondary battery may include a non-aqueous organic solvent and a lithium salt.

[0197] The above non-aqueous organic solvent acts as a medium through which ions involved in the electrochemical reaction of the battery can move.

[0198] The above 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.

[0199] Examples of the above carbonate solvents that can be used include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), methylethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC).

[0200] Ester solvents that can be used include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, decanolide, mevalonolactone, valerolactone, and caprolactone.

[0201] Examples of ether solvents that can be used include dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, and tetrahydrofuran. In addition, examples of ketone solvents that can be used include cyclohexanone. Examples of alcohol solvents that can be used include ethyl alcohol and isopropyl alcohol, and examples of aprotic solvents that can be used include 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, an aromatic ring, or an ether group); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane and 1,4-dioxolane; and sulfolanes.

[0202] The above non-aqueous organic solvents can be used alone or in combination of two or more.

[0203] In addition, when using a carbonate solvent, a cyclic carbonate and a chain carbonate can be mixed and used, and the cyclic carbonate and the chain carbonate can be mixed in a volume ratio of 1:1 to 1:9.

[0204] The above lithium salt is a substance that dissolves in an organic solvent and acts as a source of lithium ions in the battery, enabling the basic operation of a lithium secondary battery and promoting the movement of lithium ions between the positive and negative electrodes. Representative 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, LiN(C x F 2x+1 SO2)(C y F 2y+1 SO2) (x and y are integers from 1 to 20), lithium trifluoromethanesulfonate, lithium tetrafluoroethanesulfonate, lithium difluorobis(oxalato)phosphate (LiDFOB), lithium bis(oxalato)borate (LiBOB).

[0205] Lithium secondary batteries can be classified into cylindrical, square, pouch, coin, etc. types according to their shapes. FIGS. 2 to 5 are schematic diagrams illustrating lithium secondary batteries according to one embodiment. FIG. 2 can be said to be a cylindrical battery type, FIG. 3 a square battery type, and FIGS. 4 and 5 a pouch-type battery type. Referring to FIGS. 2 to 5, a lithium secondary battery (100) may include an electrode assembly (40) having a separator (30) interposed between a positive electrode (10) and an negative electrode (20), and a case (50) in which the electrode assembly (40) is built. The positive electrode (10), the negative electrode (20), and the separator (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 FIG. 1. In addition, in FIG. 3, the lithium secondary battery (100) may include a positive lead tab (11), a positive terminal (12), a negative lead tab (21), and a negative terminal (22). As in FIGS. 4 and 5, the lithium secondary battery (100) may include electrode tabs (70), i.e., a positive tab (71) and a negative tab (72), which serve as electrical paths for inducing current formed in the electrode assembly (40) to the outside.

[0206] A lithium secondary battery according to one embodiment of the present invention can be applied to automobiles, mobile phones, and / or various types of electrical devices, but the present invention is not limited thereto.

[0207]

[0208] Hereinafter, examples and comparative examples of the present invention will be described. However, the following examples are merely examples of the present invention, and the present invention is not limited to the following examples.

[0209]

[0210] Manufacturing Example 1

[0211] In a 3 L four-necked flask equipped with a stirrer, thermometer and condenser, distilled water (968 g), acrylic acid (AA) (0.39 mol), ammonium persulfate (0.65 g, 2.85 mmol), 2-acrylamido-2-methylpropanesulfonic acid (AMPS) (0.02 mol) and 20% aqueous lithium hydroxide solution (0.8 equivalents based on the total amount of acrylic acid and 2-acrylamido-2-methylpropanesulfonic acid) are added, and then the internal pressure is reduced to 10 mmHg using a diaphragm pump, and the operation of returning the internal pressure to atmospheric pressure with nitrogen is repeated three times, and then acrylonitrile (AN) (0.59 mol) is added.

[0212] The reaction is carried out for 18 hours while the temperature of the reaction solution is controlled to be stable between 65°C and 70°C, and after adding ammonium persulfate (0.22 g, 0.95 mmol) for the second time, the temperature is increased to 80°C and the reaction is carried out for another 4 hours. After cooling to room temperature, the pH of the reaction solution is adjusted to 7 to 8 using a 25% ammonia aqueous solution.

[0213] Poly(acrylic acid-co-acrylic acid lithium salt-co-acrylonitrile-co-2-acrylamido-2-methylpropanesulfonic acid) sodium salt was prepared in this manner. The molar ratio of acrylic acid + acrylic acid lithium salt, acrylonitrile, and 2-acrylamido-2-methylpropanesulfonic acid was 39:59:2. About 10 mL of the reaction solution (including the reaction product) was taken, and the non-volatile component was measured, and it was 9.0 wt% (theoretical value: 10 wt%).

[0214] Manufacturing Example 2

[0215] In a 10 L four-necked flask equipped with a stirrer, thermometer and condenser, distilled water (6361 g), acrylic acid (1.0 mol), acrylamide (8.5 mol), potassium persulfate (2.7 g, 0.01 mol), 2-acrylamido-2-methylpropanesulfonic acid (0.5 mol) and 5N lithium hydroxide aqueous solution (1.05 equivalents based on the total amount of 2-acrylamido-2-methylpropanesulfonic acid) are added, and then the internal pressure is reduced to 10 mmHg using a diaphragm pump, and the operation of returning the internal pressure to atmospheric pressure with nitrogen is repeated three times.

[0216] The reaction is carried out for 12 hours while the temperature of the reaction solution is controlled to stabilize between 65°C and 70°C. After cooling to room temperature, the pH of the reaction solution is adjusted to 7 to 8 using a 25% ammonia aqueous solution.

[0217] Poly(acrylic acid-co-acrylic acid lithium salt-co-acrylamide-co-2-acrylamido-2-methylpropanesulfonic acid lithium salt) was prepared in this manner. The molar ratio of acrylic acid + acrylic acid lithium salt, acrylamide, and 2-acrylamido-2-methylpropanesulfonic acid lithium salt was 10:85:5. About 10 mL of the reaction solution (reaction product) was taken, and the nonvolatile component was measured, and it was 9.5 wt% (theoretical value: 10 wt%).

[0218] Example 1

[0219] 3-Aminopropyltrimethoxysilane corresponding to 0.05 mmol per solid content of boehmite (particle size D100: 0.5 ㎛, particle size D50: 0.2 ㎛, cubic shape) was added to dry toluene and refluxed at 80°C to produce boehmite (particle size D100: 0.5 ㎛, particle size D50: 0.2 ㎛) surface-modified with 3-aminopropyltrimethoxysilane. The surface-modified boehmite has an amino group (-NH2) on its outer surface.

[0220] The acrylic binder (10 wt% in distilled water) manufactured in Manufacturing Example 1 and the surface-modified boehmite (particle size D100: 0.5 ㎛, particle size D50: 0.2 ㎛, cubic type) manufactured as a filler were mixed at a mass ratio of acrylic binder:filler = 1:30 based on solid content, and then added to a water solvent, milled and dispersed using a bead mill at 25°C for 30 minutes to prepare a dispersion.

[0221] To the above dispersion, trimethylolpropane tris(2-methyl-1-aziridinepropionate) (a trifunctional aziridine crosslinking agent) and carboxymethylcellulose (CMC) were added as an aziridine crosslinking agent, and water was added so that the total solid content became 20 wt%, thereby preparing a composition for forming a coating layer. At this time, the acrylic binder: carboxymethylcellulose: and aziridine crosslinking agent were included in a ratio of 45 parts by weight: 45 parts by weight: 10 parts by weight out of a total of 100 parts by weight.

[0222] The composition for forming the coating layer was coated on one side of a polyethylene film (thickness: 8 ㎛, SK Corporation, air permeability: 120 sec / 100 cc, puncture strength: 480 kgf) as a porous substrate to a thickness of 2 ㎛ by die coating, and then dried and aged in an oven at 80°C for 16 hours to manufacture a separator for a lithium secondary battery.

[0223] Examples 2 to 4

[0224] A separator was manufactured in the same manner as in Example 1, except that the components of the composition for the coating layer were changed as in Table 1 below.

[0225] Comparative Examples 1 to 5

[0226] A separator was manufactured in the same manner as in Example 1, except that the components of the composition for the coating layer were changed as in Table 1 below.

[0227] PVA is a homopolymer of polyvinyl alcohol.

[0228] Comparative Examples 6 and 7

[0229] A separator was manufactured in the same manner as in Example 1, except that the components of the composition for the coating layer were changed as in Table 1 below.

[0230] Dry shrinkage (unit: %)

[0231] The lithium secondary battery separator of the examples and comparative examples is cut into a size of 8 cm × 8 cm to prepare a sample. A 5 cm × 5 cm square is drawn on the surface of the sample, sandwiched between paper or alumina powder, and left in an oven at 150°C for 1 hour. Then, the sample is taken out, the dimensions of the sides of the drawn square are measured, and the shrinkage ratio in the mechanical direction (MD) and the vertical direction (TD) is calculated. The shrinkage ratio is calculated according to the following mathematical equation 1.

[0232] [Mathematical Formula 1]

[0233] Shrinkage = (L0 - L1) / L0 x 100

[0234] (L0 is the initial length of the membrane, L1 is the length of the membrane after leaving it at 150℃ for 1 hour)

[0235] Shrinkage in electrolyte (unit: %)

[0236] A sample is prepared by cutting the separator for a lithium secondary battery of the examples and comparative examples into a size of 8 cm × 8 cm. A square of size 5 cm × 5 cm is drawn on the surface of the sample.

[0237] A cathode slurry was prepared by mixing 97 wt% LiCoNiAl as a cathode active material, 1.5 wt% carbon nanotubes as a conductive material, and 1.5 wt% polyvinylidene fluoride as a binder, and adding water. The prepared cathode slurry was applied to aluminum foil, dried, and rolled to prepare a cathode.

[0238] A slurry of negative active material was prepared by mixing 97.4 wt% of negative active material, 1.0 wt% of carboxymethyl cellulose, 1.5 wt% of styrene-butadiene rubber as a binder, and 0.1 wt% of carbon nanotubes as a conductive material. A silicon-based negative active material was used as the negative active material. The prepared negative electrode slurry was applied to copper foil, dried, and rolled to prepare a negative electrode.

[0239] One sheet of the sample was placed between the positive and negative electrodes, and three sets of positive electrode-sample-negative electrode laminates were made, which were then placed in a pouch. 2 g of electrolyte (ethylene carbonate containing 1.5 M LiPF6, ethyl methyl carbonate, and dimethyl carbonate (volume ratio of 30:50:20)) was injected to completely saturate the laminate with the electrolyte, sealed, and left at 25°C for 12 hours. Then, after leaving it in an oven at 150°C for 1 hour, the sample was taken out, and the dimensions of the sides of the drawn rectangle were measured to calculate the shrinkage ratio in the mechanical direction (MD) and the vertical direction (transverse direction, TD). The shrinkage ratio can be calculated according to the above mathematical equation 1.

[0240] Hole size when penetrated by hot tip (unit: mm)

[0241] For the membranes of the examples and comparative examples, the longest diameter of the hole created when a soldering iron (with a spherical tip, the diameter of the tip is 2 mm) was pressed for 2 seconds from the coating layer of the membrane to penetrate 3 mm was measured. A smaller longest diameter of the hole indicates better heat resistance of the membrane.

[0242] Shear storage modulus of cross-linked material (unit: Pa)

[0243] In the examples and comparative examples, the remaining 15 g, excluding the filler, was poured into a 55 mm diameter container and crosslinked in an 80°C oven for 16 hours to produce a crosslinked film. The crosslinked film thus produced was precipitated in distilled water (DI water) for 24 hours to cause swelling. For measurement, it was punched to a diameter of 25 mm and stored in DI water until measurement. The produced crosslinked film was placed between the parallel plate spindles of a rheometer, and the plate spacing was adjusted to be amplitude sweep mode + normal force 0.2 to 0.3 N at room temperature (23 to 25°C) to measure the shear modulus (G), and the storage modulus (G') value was calculated from this.

[0244]

[0245] FillerBinder / FillerCoating LayerD50D100ModifiedBinder1Binder2CrosslinkerBinder1 / Binder2 / CrosslinkerStorage Elasticity of Crosslinked MaterialExample 10.20.5Amine1 / 30Preparation Example 1CMCAziridine45 / 45 / 104215Example 20.20.5Amine1 / 20Preparation Example 1CMCAziridine45 / 45 / 104215Example 30.20.5Amine1 / 20Preparation Example 1CMCAziridine25 / 60 / 156152Example 40.20.5Amine1 / 25Preparation Example 1CMCAziridine60 / 25 / 153845Comparative Example 10.20.5X1 / 20Preparation Example 1CMCAziridine45 / 45 / 104215Comparative Example 20.20. 5X1 / 20 Manufacturing Example 1X Aziridine 90 / 0 / 10 2964 Comparative Example 30.20.5X1 / 20 Manufacturing Example 1XX 100 / 0 / 0 1985 Comparative Example 40.20.5X1 / 20 PVA X Aziridine 90 / 0 / 10 Not measurable Comparative Example 50.20.5X1 / 20 PVAC MC Aziridine 45 / 45 / 10 1254 Comparative Example 60.20.5X1 / 20 Manufacturing Example 2 CMC Aziridine 45 / 45 / 10 4215 Comparative Example 70.71.5 Amine 1 / 20 Manufacturing Example 2 CMC Aziridine 45 / 45 / 10 4215

[0246] Dry shrinkage rate, shrinkage rate in electrolyte, pore size, MDTDMDTD, Example 1, 56, 434.01, Example 2, 45, 233.95, Example 3, 54, 873.90, Example 4, 67, 784.12, Comparative Example 1, 10, 11, 24, 275.88, Comparative Example 2, 12, 124, 1395.95, Comparative Example 3, 15, 16, 52, 586.53, Comparative Example 4, 18, 20, 51, 556.78, Comparative Example 5, 16, 155, 1556.61, Comparative Example 6, 10, 92, 42, 75.85, Comparative Example 7, 16, 14, 46, 516.39

[0247]

[0248] As shown in Tables 1 and 2 above, the separator for a lithium secondary battery of the example has excellent heat resistance, and both the dry shrinkage rate and the shrinkage rate in the electrolyte of the separator are low, and the pore size is small, so it can be seen that the heat resistance is excellent.

[0249]

[0250] Although the preferred embodiments of the present invention have been described above, the present invention is not limited thereto, and various modifications can be made within the scope of the patent claims, the detailed description of the invention, and the attached drawings, and it is obvious that this also falls within the scope of the present invention.

Claims

1. Comprising a porous substrate and a coating layer positioned on at least one surface of the porous substrate, The above coating layer comprises a binder; a crosslinking agent; and a crosslinked product of carboxyalkyl cellulose or its salt; and a filler. The above binder comprises a (meth)acrylic binder including a structural unit derived from (meth)acrylate or (meth)acrylic acid, a cyano group-containing structural unit, and a sulfonate group-containing structural unit, The above cross-linking agent includes an aziridine-based cross-linking agent, A separator for a lithium secondary battery, wherein the above filler is surface-modified and has a particle size D100 of 1.0㎛ or less.

2. A separator for a lithium secondary battery, wherein the coating layer is formed from a composition comprising the (meth)acrylic binder, the crosslinking agent, the carboxyalkyl cellulose or its salt, and the filler.

3. A separator for a lithium secondary battery, wherein the carboxyalkyl cellulose or salt thereof in claim 1 or 2 comprises carboxymethyl cellulose or a salt thereof.

4. A separator for a lithium secondary battery, wherein the carboxyalkyl cellulose or its salt is included in any one of the first to third clauses, in an amount of 20 to 70 wt% of the total of the (meth)acrylic binder; the crosslinking agent; and the carboxyalkyl cellulose or its salt.

5. A separator for a lithium secondary battery according to any one of claims 1 to 4, wherein the aziridine-based crosslinking agent comprises at least one of N,N'-toluene-2,4-bis(1-aziridinecarboxamide), N,N'-(methylenedi-p-phenylene)bis(aziridine-1-carboxamide), triethylenemelamine, 1,1-isophthaloyl bis(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).

6. A separator for a lithium secondary battery, wherein the filler comprises a filler having a particle diameter D50 of 0.4 ㎛ or less in any one of paragraphs 1 to 5.

7. A separator for a lithium secondary battery, wherein the filler is spherical, plate-shaped, cubic, or amorphous in any one of claims 1 to 6.

8. A separator for a lithium secondary battery, wherein the (meth)acrylic binder and the filler are included in a mass ratio of 1:10 to 1:50 in any one of paragraphs 1 to 7.

9. A separator for a lithium secondary battery according to any one of claims 1 to 8, wherein the (meth)acrylic binder; the crosslinking agent; and the carboxyalkyl cellulose or its salt are included in a total amount of 20 to 70 wt%, the crosslinking agent is included in a total amount of 5 to 30 wt%, and the carboxyalkyl cellulose or its salt is included in a total amount of 20 to 65 wt%.

10. A separator for a lithium secondary battery, wherein the total of the (meth)acrylic binder; the crosslinking agent; and the carboxyalkyl cellulose or salt thereof in any one of paragraphs 1 to 9 comprises 70 to 95 wt% of the total of the (meth)acrylic binder and the carboxyalkyl cellulose or salt thereof.

11. In any one of claims 1 to 10, the structural unit derived from (meth)acrylate or (meth)acrylic acid is represented by the following chemical formula 1, chemical formula 2, chemical formula 3, or a combination thereof: [Chemical Formula 1] [Chemical Formula 2] [Chemical Formula 3] (In the above chemical formulas 1 to 3, R 1 , R 2 , R 3 , R 4 , R 5 and R 6 are each independently hydrogen or methyl group, In the above chemical formula 2, M is an alkali metal), The above cyano group-containing structural unit is represented by the following chemical formula 4, [Chemical Formula 4] (In the above chemical formula 4, R 7 and R 8 are each independently hydrogen or a C1 to C3 alkyl group, L 1 is -C(=O)-, -C(=O)O-, -OC(=O)-, -O- or -C(=O)NH-, x is an integer from 0 to 2, L 2 is a substituted or unsubstituted C1 to C10 alkylene group, a substituted or unsubstituted C3 to C20 cycloalkylene group, a substituted or unsubstituted C6 to C20 arylene group, or a substituted or unsubstituted C3 to C20 heterocyclic group, y is an integer from 0 to 2), The above sulfonate group-containing structural unit is a separator for a lithium secondary battery, represented by the following chemical formula 5, chemical formula 6, chemical formula 7, or a combination thereof: [Chemical Formula 5] [Chemical Formula 6] [Chemical Formula 7] (In the above chemical formulas 5 to 7, R 9 , R 10 , R 11 , R 12 , R 13 and R 14 are each independently hydrogen or a C1 to C3 alkyl group, L 3 , L 5 and L 7 are each independently -C(=O)-, -C(=O)O-, -OC(=O)-, -O- or -C(=O)NH-, L 4 , L 6 and L 8 are each independently a substituted or unsubstituted C1 to C10 alkylene group, a substituted or unsubstituted C3 to C20 cycloalkylene group, a substituted or unsubstituted C6 to C20 arylene group, or a substituted or unsubstituted C3 to C20 heterocyclic group, a, b, c, d, e and f are each independently integers from 0 to 2, In the above chemical formula 6, M is an alkali metal).

12. A separator for a lithium secondary battery, wherein the filler is surface-modified to have an amino group according to any one of claims 1 to 11.

13. A separator for a lithium secondary battery, according to any one of claims 1 to 12, wherein the filler comprises boehmite surface-modified with an amino silane compound.

14. A separator for a lithium secondary battery according to any one of claims 1 to 13, wherein the crosslinked material has a storage elastic modulus of 3500 Pa or more at 23 to 25°C.

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

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