Separator for secondary battery and secondary battery comprising same

Abstract

The present invention relates to a separator for a secondary battery and a secondary battery comprising same. The separator for a secondary battery comprises a porous substrate and a coating layer positioned on at least one side of the porous substrate. The coating layer comprises: a cross-linked product of a binder and a cross-linking agent; and a filler. The binder comprises a (meth)acryl-based binder comprising: a first structural unit derived from (meth)acrylic acid, (meth)acrylate, or a salt thereof; a second structural unit derived from hydroxyalkyl (meth)acrylate; and a third structural unit derived from (meth)acrylamidosulfonic acid or a salt thereof. The cross-linking agent comprises an aziridine-based cross-linking agent. The filler comprises a filler mixture in which a first filler having a D50 size of 150-200 nm and a second filler having a D50 size of 50-100 nm are mixed in a weight ratio of 95: 5 to 75: 25 based on 100 parts by weight of the total amount.

Description

Separator for secondary batteries and secondary battery including the same

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

[0002]

[0003] Recently, accompanied by the rapid proliferation of battery-powered electronic devices such as mobile phones, laptop computers, and electric vehicles, the demand for high-energy-density, high-capacity rechargeable batteries is rapidly increasing. Accordingly, research and development to improve the performance of lithium-ion batteries is actively underway.

[0004] A lithium secondary battery is a battery comprising a positive electrode and a negative electrode containing an active material capable of lithium ion intercalation and deintercalation, 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.

[0005] A lithium secondary battery may include a separator between the positive and negative electrodes. The separator is impregnated in the electrolyte and bonded to the positive or negative electrode. Therefore, it may be desirable for the separator to have a low thermal shrinkage rate and low membrane resistance within the electrolyte. Meanwhile, it may be desirable to increase the coating density of the separator as the thickness of the separator becomes thinner.

[0006]

[0007] One embodiment provides a separator for a secondary battery having low dry thermal shrinkage rate, low thermal shrinkage rate in the electrolyte, and low membrane resistance, and high coating density.

[0008] Another embodiment provides a secondary battery comprising the above-mentioned separator for the secondary battery.

[0009]

[0010] One embodiment is a separator for a secondary battery.

[0011] 1. The separator for the secondary battery comprises a porous substrate and a coating layer located on at least one surface of the porous substrate, wherein the coating layer comprises a crosslink of a binder and a crosslinking agent; and a filler, wherein the binder comprises a (meth)acrylic-based binder comprising a first structural unit derived from (meth)acrylic acid, (meth)acrylate, or a salt thereof, a second structural unit derived from a hydroxyalkyl (meth)acrylate, and a third structural unit derived from (meth)acrylamidosulfonic acid or a salt thereof, wherein the crosslinking agent comprises an aziridine-based crosslinking agent, and the filler comprises a filler mixture in which a first filler having a size D50 of 150 to 200 nm and a second filler having a size D50 of 50 to 100 nm are mixed in a weight ratio of 95:5 to 75:25 based on a total of 100 parts by weight.

[0012] 2.1 A separator for a secondary battery, wherein the coating layer is formed from a composition for a coating layer comprising the (meth)acrylic binder, the aziridine-based crosslinking agent, and the filler mixture.

[0013] 3.1 or 2, wherein the aziridine-based crosslinking agent comprises one or more of N,N'-toluene-2,4-bis(1-aziridin-carboxamide), N,N'-(methylenedi-p-phenylene)bis(aziridin-1-carboxamide), triethylenemelamine, 1,1-isophthaloylbis(2-methylaziridine), tris(1-aziridinyl)phosphine oxide, N,N-hexamethylene-bis(aziridin-carboxamide), trimethylolpropane tris(2-methyl-1-aziridinpropionate), trimethylolpropane tris(beta-N-aziridinyl)propionate, and pentaerythritol tris(3-(1-aziridinyl)propionate, a separator for a secondary battery.

[0014] 4.1 to 3, wherein the crosslinking agent is included in an amount of 5 to 50 parts by weight per 100 parts by weight of the (meth)acrylic binder, for a separator for a secondary battery.

[0015] 5.1 to 4, wherein the first filler and the second filler are each cubic in shape, a separator for a secondary battery.

[0016] 6.1 to 5, wherein the first filler and the second filler are each boehmite, a separator for a secondary battery.

[0017] 7.1 to 6, a separator for a secondary battery, wherein the (meth)acrylic binder: filler mixture is included in a mass ratio of 1:10 to 1:50.

[0018] In 8.1 to 7, the first structural unit is represented by the following chemical formula 1, chemical formula 2, chemical formula 3, or a combination thereof:

[0019] [Chemical Formula 1]

[0020]

[0021] [Chemical Formula 2]

[0022]

[0023] [Chemical Formula 3]

[0024]

[0025] The above second structural unit is represented by the following chemical formula 4:

[0026] [Chemical Formula 4]

[0027]

[0028] The above-mentioned third structural unit is a separator for a secondary battery represented by the following chemical formulas 5, 6, 7, or a combination thereof:

[0029] [Chemical Formula 5]

[0030]

[0031] [Chemical Formula 6]

[0032]

[0033] [Chemical Formula 7]

[0034]

[0035] R 1 to R 14 Each independently hydrogen or a C1 to C10 alkyl group,

[0036] L 1 to L 4 Each is 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,

[0037] a, b, c, and d are each independently one of integers from 0 to 2,

[0038] M is an alkali metal.

[0039] 9.1 to 8, wherein the (meth)acrylic binder is a separator for a secondary battery represented by the following chemical formula 8:

[0040] [Chemical Formula 8]

[0041]

[0042] In the above chemical formula 8,

[0043] R 15 to R 20 Each independently contains hydrogen or a C1 to C10 alkyl group,

[0044] L 5 and L 6 Each is 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,

[0045] M is an alkali metal,

[0046] e and f are each independently one of integers from 0 to 2,

[0047] l, m, and n are the molar ratios of each unit, l + m + n = 1.

[0048] A separator for a secondary battery according to 10.1 to 9, wherein the first structural unit is included in an amount of 20 to 75 mol%, the second structural unit in an amount of 1 to 20 mol%, and the third structural unit in an amount of 20 to 75 mol%, with respect to 100 mol% of the (meth)acrylic binder.

[0049] A separator for a secondary battery according to 11.1 to 10, wherein the total sum of the first structural unit, the second structural unit, and the third structural unit is 95 mol% or more with respect to 100 mol% of the (meth)acrylic binder.

[0050] A separator for a secondary battery according to 12.1 to 11, wherein the aziridine-based crosslinking agent is included in an amount of 95% by weight or more of the total crosslinking agent in the composition for the coating layer.

[0051] 13.1 to 12, wherein the filler mixture comprises 95% by weight or more of the total filler in the composition for the coating layer, a separator for a secondary battery.

[0052] 14.1 to 13, wherein the coating layer has a thickness of 0.1 μm to 2 μm, a separator for a secondary battery.

[0053] Another embodiment is a secondary battery.

[0054] The above secondary battery includes a positive electrode, a negative electrode, and a separator for the secondary battery located between the positive electrode and the negative electrode.

[0055]

[0056] A separator for a secondary battery according to one embodiment has low dry thermal shrinkage rate, low thermal shrinkage rate in the electrolyte, and low membrane resistance, and has a high coating density, which can improve the capacity, safety, and lifespan of the battery.

[0057]

[0058] FIG. 1 is a cross-sectional view showing a separator for a secondary battery according to one embodiment.

[0059] FIGS. 2 to 5 are cross-sectional views schematically showing a secondary battery according to one embodiment.

[0060]

[0061] 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, and the present invention is defined only by the scope of the claims set forth below.

[0062] Unless otherwise specifically stated in this specification, when a part such as a layer, film, region, plate, etc. is described as being "on" another part, this includes not only cases where it is "immediately on" another part, but also cases where there is another part in between.

[0063] Unless otherwise specified in this specification, a singular form may also include a plural form. Additionally, unless otherwise specified, "A or B" may mean "including A, including B, or including A and B."

[0064] In this specification, "combination of these" may mean a mixture of components, a laminate, a composite, a copolymer, an alloy, a blend, and a reaction product, etc.

[0065] In this specification, 'size D50' refers to the average size of a particle whose cumulative volume is 50% by volume in the particle size distribution. The particle size distribution can be measured by methods widely known to those skilled in the art. For example, the particle size distribution may be measured using a particle size analyzer, or by using a transmission electron microscope (TEM) image or a scanning electron microscope (SEM) image. Alternatively, the D50 value may be obtained by measuring using a measuring device utilizing dynamic light scattering, performing data analysis to count the number of particles for each particle size range, and then calculating from this. Alternatively, it may be measured using a laser diffraction method. When measuring by laser diffraction, more specifically, after dispersing the particles to be measured 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 ultrasound of about 28 kHz at an output of 60 W, and then D50 can be calculated based on 50% of the particle size distribution in the measuring device.

[0066] If the above particle is a spherical particle, the above size may refer to the particle size or diameter.

[0067] In this specification, '(meth)acrylic' means acrylic and / or methacrylic.

[0068] Unless otherwise defined below, "substitution" means that a hydrogen in a compound is a C1 to C30 alkyl group, C2 to C30 alkenyl group, C2 to C30 alkynyl group, C6 to C30 aryl group, C7 to C30 alkylaryl group, C1 to C30 alkoxy group, C1 to C30 heteroalkyl group, C3 to C30 heteroalkylaryl group, C3 to C30 cycloalkyl group, C3 to C15 cycloalkenyl group, C6 to C30 cycloalkynyl group, C2 to C30 heterocycloalkyl group, halogen (F, Cl, Br, or I), hydroxyl group (-OH), nitro group (-NO2), cyano group (-CN), amino group (-NRR') (wherein R and R' are independently hydrogen or C1 to C6 alkyl groups), or 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) (where R and R' are independently C1 to C20 alkyl groups), 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 its salt (-C(=O)OM, where M is an organic or inorganic cation), sulfonic acid group (-SO3H) or its salt (-SO3M, where M is an organic or inorganic cation), phosphate group (-PO3H2) or its salt (-PO3MH or -PO3M2, where M is an organic or inorganic cation) and means being substituted with a substituent selected from a combination thereof.

[0069] In the following, C1 to C3 alkyl groups refer to methyl groups, ethyl groups, or propyl groups. C1 to C10 alkylene groups may be, for example, C1 to C6 alkylene groups, C1 to C5 alkylene groups, or C1 to C3 alkylene groups, and may be, for example, methylene groups, ethylene groups, or propylene groups. C3 to C20 cycloalkylene groups may be, for example, C3 to C10 cycloalkylene groups or C5 to C10 cycloalkylene groups, and may be, for example, cyclohexylene groups. C6 to C20 arylene groups may be, for example, C6 to C10 arylene groups, and may be, for example, phenylene groups. C3 to C20 heterocyclic groups may be, for example, C3 to C10 heterocyclic groups, and may be, for example, pyridine groups.

[0070] In the following, "hetero" means containing one or more heteroatoms selected from N, O, S, Si, and P.

[0071] In chemical formulas, the * symbol indicates a part connected to the same or different atoms, groups, or structural units. Unless specifically stated otherwise in the chemical formulas described herein, hydrogen may be considered to be bonded in the structure of the chemical formula.

[0072] In the following, "alkali metal" 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 positive or neutral state.

[0073] In this specification, when describing a numerical range, 'X to Y' means 'X or greater and Y or less (X ≤ and ≤ Y).'

[0074] Hereinafter, the separator for a secondary battery and the secondary battery including the same according to the present invention will be described in detail.

[0075] The following description applies only to lithium secondary batteries. However, the present invention can be applied to secondary batteries of different metal ions in addition to lithium secondary batteries.

[0076] The above-described separator for a secondary battery comprises a porous substrate and a coating layer located on at least one surface of the porous substrate, wherein the coating layer comprises a crosslink of a binder and a crosslinking agent; and a filler, wherein the binder comprises a (meth)acrylic-based binder comprising a first structural unit derived from (meth)acrylic acid, (meth)acrylate, or a salt thereof, a second structural unit derived from a hydroxyalkyl (meth)acrylate, and a third structural unit derived from (meth)acrylamidosulfonic acid or a salt thereof, wherein the crosslinking agent comprises an aziridine-based crosslinking agent, and the filler comprises a filler mixture in which a first filler having a size D50 of 150 to 200 nm and a second filler having a size D50 of 50 to 100 nm are mixed in a weight ratio of 95:5 to 75:25 based on a total of 100 parts by weight.

[0077] The above weight ratios may be 95:5, 94:6, 93:7, 92:8, 91:9, 90:10, 89:11, 88:12, 87:13, 86:14, 85:15, 84:16, 83:17, 82:18, 81:19, 80:20, 79:21, 78:22, 77:23, 76:24, 75:25.

[0078] The first filler above may have a size D50 of 150, 155, 160, 165, 170, 175, 180, 185, 190, 195, or 200 nm.

[0079] The above second filler may have a size D50 of 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, or 100 nm.

[0080] The above coating layer may be a heat-resistant layer.

[0081] The above crosslinker may be a thermal crosslinker.

[0082] The above coating layer may be formed from a composition for a coating layer comprising the above (meth)acrylic binder, the above aziridine-based crosslinking agent, and the above filler mixture.

[0083] The above separator may have low dry thermal shrinkage rate, thermal shrinkage rate in the electrolyte, and membrane resistance, and may have a high coating density.

[0084] The above separator may have a dry heat shrinkage rate of 3% or less in both the MD (machine direction) and TD (transverse direction).

[0085] The above separator may have a thermal shrinkage rate in the electrolyte of 15% or less for MD and TD, for example, 10% or less.

[0086] The aforementioned 'MD' and 'TD' are each oriented in the same direction as the MD and TD of the porous substrate.

[0087] The above separator may have a membrane resistance of 0.55Ω or less.

[0088] The above separator has a coating density of 1.2 g / cm³ 3 It could be more than that.

[0089] A separator having a coating layer formed from 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 have a lower reliability of the battery due to an increased thermal shrinkage rate in the electrolyte. According to one embodiment, the aziridine-based crosslinking agent may be included in an amount of 95% or more by weight, for example, 98 to 100% by weight, or 100% by weight, of the total crosslinking agent in the composition for the coating layer.

[0090] A separator having a coating layer formed from a composition for a coating layer that includes the above-mentioned aziridine-based crosslinking agent but does not include the above-mentioned (meth)acrylic binder or contains a binder other than the above-mentioned (meth)acrylic binder may have a high thermal shrinkage rate, high membrane resistance, and high air permeability of the separator, which may cause problems with the capacity, lifespan, and safety of the battery. According to one embodiment, the above-mentioned (meth)acrylic binder may be included in an amount of 95% or more by weight, for example, 98 to 100% by weight, or 100% by weight, of the total binder in the composition.

[0091] The above filler comprises a filler mixture in which a first filler having a size D50 of 150 to 200 nm and a second filler having a size D50 of 50 to 100 nm are mixed in a weight ratio of 95:5 to 75:25. The weight ratio is based on 100 parts by weight of the total of the first filler and the second filler. If the first filler in the mixture is less than 75 parts by weight and the second filler is more than 25 parts by weight, there may be a problem in that the membrane resistance increases due to an excessive increase in air permeability. If the first filler in the mixture is more than 95 parts by weight and the second filler is less than 5 parts by weight, there may be a problem in that the coating density is low, making it difficult to secure heat resistance.

[0092] The above filler mixture may be included in an amount of 95% or more by weight, for example, 98 to 100% by weight, or 100% by weight, of the total filler in the separation membrane and composition.

[0093] Coating layer

[0094] The above binder comprises a (meth)acrylic binder comprising a first structural unit derived from (meth)acrylic acid, (meth)acrylate, or salts thereof, a second structural unit derived from hydroxyalkyl (meth)acrylate, and a third structural unit derived from (meth)acrylamidosulfonic acid or salts thereof.

[0095] The above (mat)acrylic binder may be a non-adhesive binder.

[0096] The above (meth)acrylic binder can fix the filler onto the porous substrate and ensure 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 above (meth)acrylic binder can facilitate the movement of lithium ions to lower membrane resistance and improve ion conductivity, increase the adhesion of the coating layer to the porous substrate and electrode, and improve the dispersibility of the filler within the coating layer. Furthermore, the above (meth)acrylic binder can provide a separator with low membrane resistance in a coating layer containing the filler described below.

[0097] With respect to 100 mol% of the above (meth)acrylic binder, the total sum of the above first structural unit, the above second structural unit, and the above third structural unit may be included in an amount of 95 mol% or more, for example, 95 to 100 mol%, for example, 100 mol%. Within this range, the implementation of the above-described separation membrane effect may be easy.

[0098] The first structural unit described above is derived from (meth)acrylic acid, (meth)acrylate, or a salt thereof, and serves to fix the filler onto the porous substrate while simultaneously providing adhesion to ensure the coating layer adheres well to the porous substrate and electrode, and can contribute to improving the heat resistance and air permeability of the separator. Additionally, the first structural unit can improve the dispersibility of the coating layer composition by having a carboxyl functional group (-C(=O)O-) within the structural unit.

[0099] The above first structural unit may be represented by any one of the following chemical formulas 1 to 3:

[0100] [Chemical Formula 1]

[0101]

[0102] [Chemical Formula 2]

[0103]

[0104] [Chemical Formula 3]

[0105]

[0106] With respect to 100 mol% of the binder for the secondary battery above, the first structural unit is 20 to 75 mol%, for example, 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, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75 mol%, 25 to 70 mol%, 30 to 65 mol%, 30 to 60 mol%, 40 to 65 mol%. It may be included. When included within the above range, the separator may exhibit low membrane resistance, excellent adhesion to porous substrates and electrodes, heat resistance, air permeability, and oxidation resistance.

[0107] The first structural unit 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.

[0108] The first structural unit may include only the structural unit represented by the above chemical formula 2 or the above chemical formula 3.

[0109] The second structural unit is derived from hydroxyalkyl (meth)acrylate and serves to fix the filler onto the porous substrate, while simultaneously providing adhesion so that the coating layer adheres well to the porous substrate and the electrode. In addition, the second structural unit can improve the dispersibility of the coating layer composition by having a carboxyl functional group (-C(=O)O-) within the structural unit.

[0110] The above second structural unit can be represented by the following chemical formula 4:

[0111] [Chemical Formula 4]

[0112]

[0113] With respect to 100 mol% of the binder for the secondary battery, the second structural unit may be included in an amount of 1 to 20 mol%, for example, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 mol%, 2 to 15 mol%, or 5 to 15 mol%. Within this range, it may be easy to increase the adhesion of the coating layer to the porous substrate and the electrode.

[0114] The second structural unit above may be a structural unit derived, for example, from hydroxyalkyl (meth)acrylate. Here, the alkyl may be a C1 to C20 alkyl, a C1 to C10 alkyl, or a C1 to C6 alkyl.

[0115] The above hydroxyalkyl (meth)acrylate may include, for example, one or more of hydroxymethyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, and 6-hydroxyhexyl (meth)acrylate.

[0116] The third structural unit derived from the above (meth)acrylamidosulfonic acid or its salt can lower the membrane resistance of the separator by increasing the possibility of lithium ion movement in the presence of the first structural unit and the second structural unit.

[0117] The above third structural unit includes a bulky functional group derived from (meth)acrylamidosulfonic acid or a salt thereof, thereby enhancing the heat resistance of the separator through the effect of increasing the glass transition temperature. When the above third structural unit includes a functional group derived from a salt of (meth)acrylamidosulfonic acid, metals (M) can move through the above third structural unit by means of a metal (M) substituted sulfonic acid functional group, which can exhibit the effect of lowering membrane resistance.

[0118] The above third structural unit may be represented by the following chemical formulas 5, 6, 7, or a combination thereof.

[0119] [Chemical Formula 5]

[0120]

[0121] [Chemical Formula 6]

[0122]

[0123] [Chemical Formula 7]

[0124]

[0125] The third structural unit may include only one of the structural unit represented by Chemical Formula 5, the structural unit represented by Chemical Formula 6, and the structural unit represented by Chemical Formula 7, or it may include two or more types. For example, the third structural unit may include the structural unit represented by Chemical Formula 6, and for another example, the third structural unit may include the structural unit represented by Chemical Formula 6 and the structural unit represented by Chemical Formula 7.

[0126] The third structural unit may be, for example, a structural unit derived from (meth)acrylamidoalkane sulfonic acid or a salt thereof. 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 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.

[0127] For example, the above (meth)acrylamidoalkane sulfonic acid may be 2-(meth)acrylamido-2-methylpropane sulfonic acid.

[0128] The above third structural unit may be included in the above (meth)acrylic binder in an amount of 20 to 75 mol%, for example, 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, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75 mol%, 25 to 70 mol%, 20 to 65 mol%, 30 to 65 mol%, 30 to 60 mol%. When the above third structural unit is included within the above range, the (meth)acrylic binder and the separator containing it can exhibit significantly low membrane resistance.

[0129] The description of the above chemical formulas 1 to 7 is as follows.

[0130] R 1 to R 14 Each can independently be hydrogen or a C1 to C10 alkyl group. For example, R 1 to R 7 and R 9 to R 14 can be a hydrogen or a methyl group, respectively; R8 It can be a methyl group.

[0131] L 1 to L 4 Each may independently be 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. For example, L 1 can be a methylene group or an ethylene group; L 2 to L 4 Each can be independently *-C(CH3)2-CH2-*.

[0132] a, b, c, and d can each independently be one of integers from 0 to 2. For example, a, b, c, and d can all be 1.

[0133] M may be an alkali metal, and the alkali metal may be lithium, sodium, potassium, rubidium, or cesium. For example, M may be lithium or sodium.

[0134] A representative example of the above (meth)acrylic binder is as shown in Chemical Formula 8 below:

[0135] [Chemical Formula 8]

[0136]

[0137] The explanation for the above chemical formula 8 is as follows.

[0138] R 15 to R 20 Each can independently be hydrogen or a C1 to C10 alkyl group. For example, R 15 to R 17 , R 19 and R 20 Each can be a hydrogen or a methyl group; R 18 It can be a methyl group.

[0139] L 5 and L 6Each may independently be 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. For example, L 5 can be a methylene group or an ethylene group; L 6 It can be *-C(CH3)2-CH2-*.

[0140] M may be an alkali metal, and the alkali metal may be lithium, sodium, potassium, rubidium, or cesium. For example, M may be lithium or sodium.

[0141] l, m and n are the molar ratios of each unit, where l + m + n = 1. For example, 0.20≤l≤0.75, 0.01≤m≤0.2, and 0.2≤n≤0.75, for example, 0.25≤l≤0.70, 0.01≤m≤0.15, and 0.25≤n≤0.75; or 0.3≤l≤0.65, 0.05≤m≤0.15, and 0.3≤n≤0.65.

[0142] e and f can each independently be one of integers from 0 to 2. For example, e and f can both be 1.

[0143] The above (meth)acrylic binder may include an alkali metal. The alkali metal may exist in a cation form and may be, for example, lithium, sodium, potassium, rubidium, or cesium. For example, the alkali metal may be combined with the above (meth)acrylic binder and exist in the form of a salt. The alkali metal can assist in the synthesis of the above (meth)acrylic binder in an aqueous solvent, improve the adhesion of the coating layer, and improve the heat resistance, air permeability, and oxidation resistance of the separator.

[0144] The alkali metal may be included in an amount of 1 to 40 weight% of the alkali metal and the (meth)acrylic binder, for example, 1 to 30 weight%, or 1 to 20 weight%, or 10 to 20 weight%. 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, for example, a weight ratio of 99:1 to 80:20, or for example, a weight ratio of 90:10 to 80:20.

[0145] The alkali metal may be included in an amount of 0.1 to 1.0 mol% relative to the total content of the alkali metal and the (meth)acrylic binder. When the alkali metal is included within this range, the coating layer may have excellent adhesion, and the separator containing it may exhibit excellent heat resistance, air permeability, and oxidation resistance.

[0146] The above (meth)acrylic heat-resistant binder may be in various forms, such as an alternating polymer in which the structural units are alternately distributed, a randomly distributed polymer, or a graft polymer in which some structural units are grafted.

[0147] The weight-average molecular weight of the above (meth)acrylic binder may be 100,000 to 1,000,000 g / mol, 100,000 to 500,000 g / mol, 100,000 to 150,000 g / mol, 130,000 to 200,000 g / mol, or 300,000 to 900,000 g / mol. When the weight-average molecular weight of the above (meth)acrylic binder satisfies the above range, excellent adhesion and low resistance can be exhibited. The above weight-average molecular weight may be the polystyrene-equivalent average molecular weight measured using gel permeation chromatography.

[0148] The above (meth)acrylic binder can be manufactured by a solution polymerization method.

[0149] According to one embodiment, the (met)acrylic binder may be included in the coating layer of the separator in the form of a film.

[0150] The above crosslinking agent includes an aziridine-based crosslinking agent.

[0151] The above aziridine-based crosslinking agent can crosslink the above (meth)acrylic binder to facilitate the separator reaching a thermal shrinkage rate range within the electrolyte. Additionally, the above aziridine-based crosslinking agent can crosslink the above (meth)acrylic binder to significantly lower the membrane resistance of the separator. Furthermore, the above aziridine-based crosslinking agent can crosslink the above (meth)acrylic binder to increase adhesion to the electrode.

[0152] The above aziridine-based crosslinking agent may be a difunctional or more aziridine-based crosslinking agent. Here, "difunctional or more" means that there are two or more aziridine groups in the molecule. According to one embodiment, the above aziridine-based crosslinking agent may be a difunctional or trifunctional aziridine-based crosslinking agent.

[0153] For example, the above aziridine-based crosslinking agent may include one or more of N,N'-toluene-2,4-bis(1-aziridine-carboxamide), N,N'-(methylenedi-p-phenylene)bis(aziridine-1-carboxamide), triethylenemelamine, 1,1-isophthaloylbis(2-methylaziridine), tris(1-aziridinyl)phosphine oxide, N,N-hexamethylene-bis(aziridine-carboxamide), trimethylolpropane tris(2-methyl-1-aziridinepropionate), trimethylolpropane tris(beta-N-aziridinyl)propionate, and pentaerythritol tris(3-(1-aziridinyl)propionate.

[0154] The above crosslinking agent, for example, the aziridine-based crosslinking agent, must be included in an appropriate amount with respect to the above binder, for example, the (meth)acrylic-based binder. According to one embodiment, the crosslinking agent may be included in an amount of 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, 5 to 30 parts by weight, 5 to 25 parts by weight, or 5 to 20 parts by weight, based on 100 parts by weight of the (meth)acrylic binder. Within this range, the thermal shrinkage rate and membrane resistance of the separator in the electrolyte may be significantly reduced.

[0155] The above filler includes a mixture of the first filler and the second filler.

[0156] The first filler and the second filler may each not be surface modified, but may be surface modified.

[0157] The first filler and the second filler may each be 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, for example, Al2O3, SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, GaO, ZnO, ZrO2, Y2O3, SrTiO3, BaTiO3, Mg(OH)2, boehmite, or a combination thereof, but is not limited thereto. The organic filler may include an acrylic compound, an imide compound, an amide compound, or a combination thereof, but is not limited thereto. The organic filler may have a core-shell structure, but is not limited thereto. For example, the first and second fillers may preferably be boehmite.

[0158] The first and second fillers may each be spherical, plate-shaped, cubic, or amorphous. Preferably, the fillers may be cubic, and the cubic shape may have a significantly lower thermal shrinkage rate.

[0159] The above filler mixture must be included in an appropriate amount with respect to the above binder, for example, the above (meth)acrylic binder.

[0160] The above (meth)acrylic binder: The above filler mixture may be included in a mass ratio of 1:10 to 1:50, for example, 1:10, 1:15, 1:20, 1:25, 1:30, 1:35, 1:40, 1:45, 1:50, 1:10 to 1:40, or 1:20 to 1:30. Within the above range, there may be an effect of improving heat resistance properties in the electrolyte.

[0161] The above filler mixture may be included 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, of the total amount of the coating layer. When the filler is included within the above range, it may exhibit excellent heat resistance, durability, oxidation resistance, and stability.

[0162] Each of the above coating layers may have a thickness of 0.01 μm to 20 μm, and within the above range, may have a thickness of 0.01 μm to 7 μm, or 0.1 μm to 5 μm, or 0.1 μm to 3 μm. For example, the thickness of the coating layer may be 0.1 to 2 μm.

[0163] The ratio of the thickness of the coating layer to the thickness of the porous substrate may be 0.01 to 0.7, for example, 0.01 to 0.5, or 0.01 to 0.4, or 0.01 to 0.3. Within the above range, the separator may exhibit excellent air permeability, heat resistance, and adhesion. Here, 'thickness of the coating layer' refers to the thickness of one coating layer when the coating layer is formed only on one side of the porous substrate, and refers to the total thickness of two coating layers when the coating layer is formed on both sides of the porous substrate.

[0164] <Porous Substrate>

[0165] The porous substrate may be a substrate having a number of pores and typically used in electrochemical devices. The porous substrate may be, but is not limited to, any one 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 membrane formed from two or more copolymers or mixtures of these.

[0166] The porous substrate may be a polyolefin-based substrate including, for example, a polyolefin, and the polyolefin-based substrate may contribute to improving the safety of the battery by having an excellent shutdown function. The polyolefin-based substrate may be selected from, for example, a polyethylene single membrane, a polypropylene single membrane, a polyethylene / polypropylene double membrane, a polypropylene / polyethylene / polypropylene triple membrane, and a polyethylene / polypropylene / polyethylene triple membrane. 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.

[0167] 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.

[0168] The porous substrate may have an air permeability of less than 200 sec / 100cc, for example, 190 sec / 100cc or less, or 180 sec / 100cc or less. Within the above range, it may be used in a separator.

[0169] The above-mentioned separator for a secondary battery may exhibit excellent air permeability and may have an air permeability value of, for example, less than 200 sec / 100cc, for example, 190 sec / 100cc or less, or 180 sec / 100cc or less. That is, it may have an air permeability value of less than 40 sec / 100cc·1㎛ per unit thickness, for example, 30 sec / 100cc·1㎛ or less, or 25 sec / 100cc·1㎛ or less.

[0170] Here, air permeability refers to the time (in seconds) required for 100cc of air to pass through a unit thickness of the separator. Air permeability per unit thickness can be obtained by measuring the air permeability over the entire thickness of the separator and then dividing by the thickness. Air permeability can be measured using an air permeability measuring device (Asahi Seiko, EG01-55-1MR) to measure the time (in seconds) required for 100cc of air to pass through.

[0171] A separator for a secondary battery can be formed by applying a composition for forming a coating layer to one or both sides of a porous substrate and then drying it. The drying can be performed using conventional methods known to those skilled in the art.

[0172] FIG. 1 is a cross-sectional view showing a separator for a secondary battery according to one embodiment.

[0173] Referring to FIG. 1, a separator for a secondary battery comprises a porous substrate 1 and a coating layer 2 located on each side of the porous substrate 1. The coating layer 2 may include a first filler 3; a second filler 5; and a crosslinked product 4 of a (meth)acrylic binder and a crosslinking agent.

[0174] secondary battery

[0175] Another embodiment provides a secondary battery comprising a separator for a secondary battery according to one embodiment; a positive electrode; and a negative electrode.

[0176] The separator for a secondary battery is described above. The separator for a secondary battery can be located between the positive electrode and the negative electrode.

[0177] anode

[0178] 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 may further include a binder and / or a conductive material. As an example, the positive electrode may further include an additive capable of acting as a sacrificial electrode.

[0179] positive electrode active material

[0180] As a positive electrode active material, a compound capable of reversible intercalation and deintercalation of lithium (a lithated intercalation compound) may be used. Specifically, one or more composite oxides of lithium and a metal selected from cobalt, manganese, nickel, and combinations thereof may be used.

[0181] The above composite oxide may be a lithium transition metal composite oxide, and specific examples include a lithium nickel-based oxide, a lithium cobalt-based oxide, a lithium manganese-based oxide, a lithium iron phosphate-based compound, a cobalt-free nickel-manganese-based oxide, or a combination thereof.

[0182] As an example, a compound represented by any one of the following chemical formulas may 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 Ni 1-b-c Mnb 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(0.90≤a≤1.8).

[0183] 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.

[0184] For example, the above-mentioned 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 in the lithium transition metal composite oxide 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. The high-nickel positive electrode active material can achieve high capacity and can be applied to high-capacity, high-density lithium secondary batteries.

[0185] The content of the above positive active material is 90% to 99.5% by weight of 100% by weight of the positive active material layer, and the content of the binder and the conductive material may each be 0.5% to 5% by weight with respect to 100% by weight of the positive active material layer.

[0186] The above binder serves to adhere the positive active material particles well to each other and also to adhere the positive active material well to the current collector. Representative 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)acrylated styrene-butadiene rubber, epoxy resin, (meth)acrylic resin, polyester resin, nylon, etc.

[0187] The above conductive material is used to impart conductivity to the electrode, and any electronically conductive material that does not cause chemical changes can be used in the battery being constructed. Examples of conductive materials include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, carbon nanofiber, carbon nanotube; metal-based materials in the form of metal powder or metal fibers containing copper, nickel, aluminum, silver, etc.; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0188] Al may be used as the current collector mentioned above, but is not limited thereto.

[0189] cathode

[0190] A negative electrode for a lithium secondary battery comprises a current collector and a negative electrode active material layer located on the current collector. The negative electrode active material layer comprises a negative electrode active material and may further comprise a binder and / or a conductive material.

[0191] For example, the negative electrode active material layer may comprise 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.

[0192] cathode active material

[0193] 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.

[0194] A material capable of reversibly intercalating / deintercalating the above lithium ions may be a carbon-based negative electrode active material, such as crystalline carbon, amorphous carbon, or a combination thereof. Examples of the crystalline carbon include graphite such as amorphous, plate-like, flake-like, spherical, or fibrous natural graphite or artificial graphite, and examples of the amorphous carbon include soft carbon or hard carbon, mesophase pitch carbide, calcined coke, etc.

[0195] 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 may be used.

[0196] As a material capable of doping and undoping the above 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.

[0197] 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, it may include a secondary particle (core) assembled from silicon primary particles and an amorphous carbon coating layer (shell) located on the surface of the secondary particle. The amorphous carbon may also be located between the silicon primary particles, so that, for example, the silicon primary particles may be coated with amorphous carbon. The secondary particles may be dispersed in an amorphous carbon matrix.

[0198] The silicon-carbon composite may further include crystalline carbon. For example, the silicon-carbon composite may include a core comprising crystalline carbon and silicon particles and an amorphous carbon coating layer located on the surface of the core.

[0199] The above Si-based or Sn-based negative electrode active material can be used in combination with a carbon-based negative electrode active material.

[0200] The above binder serves to effectively bond the negative electrode active material particles to each other and also to effectively bond the negative electrode active material to the current collector. As the binder, a non-aqueous binder, an aqueous binder, a dry binder, or a combination thereof may be used.

[0201] Examples of the above-mentioned non-aqueous binders include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene propylene copolymer, polystyrene, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide imide, polyimide, or combinations thereof.

[0202] The above-mentioned water-based binder may be selected from styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, (meth)acrylonitrile-butadiene rubber, (meth)acrylic rubber, butyl rubber, fluororubber, polyethylene oxide, polyvinylpyrrolidone, polyepichlorohydrin, polyphosphazene, poly(meth)acrylonitrile, ethylenepropylenediene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, (meth)acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, and combinations thereof.

[0203] When a water-based binder is used as the above-mentioned cathode binder, a cellulose-based compound capable of imparting viscosity may be further included. As this cellulose-based compound, one or more types such as carboxymethyl cellulose, hydroxypropylmethyl cellulose, methyl cellulose, or alkali metal salts thereof may be mixed and used. Na, K, or Li may be used as the alkali metal.

[0204] The above dry binder is a polymer material capable of fiberization, and may be, for example, polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or a combination thereof.

[0205] The above conductive material is used to impart conductivity to the electrode, and any electronically conductive material that does not cause chemical changes can be used in the battery being constructed. Specific examples include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjenblack, carbon fiber, carbon nanofiber, carbon nanotube; metal-based materials in the form of metal powder or metal fibers including copper, nickel, aluminum, silver, etc.; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0206] As the above-mentioned cathode current collector, a material selected from copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, and combinations thereof may be used.

[0207] Lithium secondary batteries may contain additional electrolyte.

[0208] electrolyte

[0209] The electrolyte for a lithium secondary battery may include a non-aqueous organic solvent and a lithium salt.

[0210] The above-mentioned non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can move.

[0211] The above-mentioned non-aqueous organic solvent may be a carbonate-based, ester-based, ether-based, ketone-based, or alcohol-based solvent, a non-protic solvent, or a combination thereof.

[0212] The above carbonate-based solvents may include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), methyl ethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), etc.

[0213] Ester-based solvents such as methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methylpropionate, ethylpropionate, decanolide, mevalonolactone, valerolactone, and caprolactone may be used.

[0214] As ether-based solvents, dibutyl ether, tetraglame, diglame, dimethoxyethane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, tetrahydrofuran, etc. may be used. Additionally, as ketone-based solvents, cyclohexanone, etc. may be used. As alcohol-based solvents, ethyl alcohol, isopropyl alcohol, etc. may be used, and as aprotic solvents, nitriles such as R-CN (where R is a straight-chain, 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, 1,4-dioxolane; sulfolanes, etc. may be used.

[0215] The above-mentioned non-aqueous organic solvent can be used alone or in a mixture of two or more types.

[0216] In addition, when using a carbonate-based solvent, a mixture of cyclic carbonates and chain carbonates can be used, and the cyclic carbonates and chain carbonates can be mixed in a volume ratio of 1:1 to 1:9.

[0217] The above lithium salt is a substance that dissolves in an organic solvent and acts as a source of lithium ions within the battery, enabling the basic operation of a lithium secondary battery and facilitating the movement of lithium ions between the anode and cathode. 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+1It may include one or more selected from SO2)(x and y are integers from 1 to 20), lithium trifluoromethane sulfonate, lithium tetrafluoroethane sulfonate, lithium difluorobis(oxalate)phosphate (LiDFOB), and lithium bis(oxalate)borate (LiBOB).

[0218] Lithium secondary batteries can be classified into cylindrical, prismatic, pouch, coin, etc., depending on their shape. FIGS. 2 to 5 are schematic diagrams illustrating a lithium secondary battery according to one embodiment. FIG. 2 may be a cylindrical battery, FIG. 3 a prismatic battery, and FIGS. 4 and 5 a pouch battery. Referring to FIGS. 2 to 5, the lithium secondary battery (100) may include an electrode assembly (40) having a separator (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), 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 in FIG. 2. In addition, in FIG. 3, the lithium secondary battery (100) may include a positive lead tab (11) and a positive terminal (12), a negative lead tab (21) and a negative terminal (22). As shown in FIG. 4 and FIG. 5, the lithium secondary battery (100) may include electrode tabs (70), namely a positive tab (71) and a negative tab (72), which serve as electrical passages for inducing current formed in the electrode assembly (40) to the outside.

[0219] A lithium secondary battery according to one embodiment of the present invention may be applied to automobiles, mobile phones, and / or various types of electric devices, etc., but the present invention is not limited thereto.

[0220]

[0221] Examples and comparative examples of the present invention are described below. However, the following examples are merely one example of the present invention, and the present invention is not limited to the following examples.

[0222]

[0223] Preparation Example 1

[0224] In a 3L four-neck separable flask equipped with a stirrer, thermometer, and condenser, 1249.72 g of distilled water, 20% aqueous lithium hydroxide solution (203.69 g), acrylic acid (AA, 0.3 mol), 2-hydroxyethyl methacrylate (HEMA, 0.10 mol), 2-acrylamido-2-methylpropanesulfonic acid (AMPS, 0.6 mol), and ammonium persulfate (0.001 mol) were added. Subsequently, the internal pressure was reduced to 10 mmHg using a diaphragm pump, and the internal pressure was returned to atmospheric pressure using nitrogen, a process repeated three times. The reaction was carried out for 12 hours while controlling the heating so that the temperature of the reaction mixture stabilized between 65°C and 70°C. After cooling to room temperature, about 10 mL of the reaction solution was taken and the non-volatile component (NV) was measured, which was 9.8 wt% (theoretical value: 10 wt%). In addition, in the poly(acrylic acid-co-2-hydroxyethyl methacrylate-co-2-acrylamido-2-methylpropanesulfonic acid) lithium salt obtained here, the molar ratio of the first structural unit derived from the lithium acrylate salt, the second structural unit derived from 2-hydroxyethyl methacrylate, and the third structural unit derived from the lithium 2-acrylamido-2-methylpropanesulfonic acid salt is 30:10:60.

[0225] Preparation Example 2

[0226] Poly(lithium acrylate-co-2-hydroxyethyl methacrylate-co-2-acrylamido-2-methylpropanesulfonate lithium salt) was prepared by changing the content of each monomer in Preparation Example 1. The molar ratio of lithium acrylate, 2-hydroxyethyl methacrylate, and 2-acrylamido-2-methylpropanesulfonate lithium salt was 65:5:30. About 10 mL of the reaction solution (reaction product) was taken and the non-volatile component was measured, and the result was 9.0 wt% (theoretical value: 10 wt%).

[0227] Preparation Example 3

[0228] Poly(lithium acrylate-co-2-hydroxyethyl methacrylate-co-2-acrylamido-2-methylpropanesulfonate lithium salt) was prepared by changing the content of each monomer in Preparation Example 1. The molar ratio of lithium acrylate, 2-hydroxyethyl methacrylate, and 2-acrylamido-2-methylpropanesulfonate lithium salt was 40:5:55. About 10 mL of the reaction solution (reaction product) was taken and the non-volatile component was measured, and the result was 9.0 wt% (theoretical value: 10 wt%).

[0229] Preparation Example 4

[0230] An acrylic copolymer was prepared using the same method as in Preparation Example 1, except that 2-hydroxyethyl methacrylate and 2-acrylamido-2-methylpropanesulfonic acid were used, and acrylic acid was not used. The molar ratio of 2-hydroxyethyl methacrylate to lithium salt of 2-acrylamido-2-methylpropanesulfonic acid was 74:26. ​​The non-volatile component of the reaction solution was 9.0 wt% (theoretical value: 10 wt%).

[0231] Preparation Example 5

[0232] An acrylic copolymer was prepared using the same method as in Preparation Example 1, except that acrylic acid and 2-acrylamido-2-methylpropanesulfonic acid were used, and 2-hydroxyethyl methacrylate was not used. The molar ratio of acrylic acid to lithium 2-acrylamido-2-methylpropanesulfonic acid was 74:26. ​​The non-volatile component of the reaction solution was 9.0 wt% (theoretical value: 10 wt%).

[0233] Preparation Example 6

[0234] An acrylic copolymer was prepared in the same manner as in Preparation Example 1, except that acrylic acid and 2-hydroxyethyl methacrylate were used, and 2-acrylamido-2-methylpropanesulfonic acid was not used. The molar ratio of lithium acrylate to 2-hydroxyethyl methacrylate was 42:58. The non-volatile component of the reaction solution was 9.0 wt% (theoretical value: 10 wt%).

[0235] Example 1

[0236] A mixture was prepared of 90 parts by weight of boehmite (size D50: 150 nm, KC large injection KB-01S, cubic type) as the first filler and 10 parts by weight of boehmite (size D50: 50 nm, KC large injection, cubic type) as the second filler.

[0237] A methacrylic binder (10 wt%) prepared in Preparation Example 1 and the filler mixture prepared above were mixed in a mass ratio of methacrylic binder:filler mixture = 1:20 based on solid content, added to a water solvent, and then milled and dispersed using a bead mill at 25°C for 30 minutes to prepare a dispersion.

[0238] A composition for forming a coating layer was prepared by adding trimethylolpropane tris(2-methyl-1-aziridinepropionate) (a trifunctional aziridine crosslinking agent) as an aziridine crosslinking agent to the above dispersion, and adding water so that the total solid content is 20% by weight. At this time, the aziridine crosslinking agent is included in an amount of 10 parts by weight per 100 parts by weight of the acrylic binder.

[0239] A separator for a lithium secondary battery was manufactured by forming a coating layer by applying the above-mentioned composition for forming a coating layer to a thickness of 1 μm to only one side of a polyethylene-based film (thickness: 5.5 μm, CZMZ, air permeability: 110 sec / 100 cc, puncture strength: 340 kgf) as a porous substrate using a die coating method, and then drying and aging it in an oven at 70°C for 16 hours to form a coating layer.

[0240]

[0241] Examples 2 to 6

[0242] A separator for a lithium secondary battery was prepared in the same manner as in Example 1, except that the type of methacrylic binder and / or the type of filler in Example 1 was changed as shown in Table 1 below.

[0243]

[0244] Comparative Examples 1 to 8

[0245] A separator for a lithium secondary battery was prepared in the same manner as in Example 1, except that the type of methacrylic binder, and / or the type of filler, and / or the coating loading amount of the adhesive binder, and / or the type of adhesive binder were changed as shown in Table 2 below.

[0246] In Comparative Example 5, the epoxy crosslinking agent is ethylene glycol diglycidyl ether.

[0247] In Comparative Example 6, the carbodiimide (CDI)-based crosslinking agent used was CARBODILITE V-50 (Nisshinbo Chemical).

[0248]

[0249] Dry heat shrinkage rate (Unit: %)

[0250] A sample is prepared by cutting the separator for a lithium secondary battery of the example and comparative example into a size of 8 cm × 8 cm. A square measuring 5 cm × 5 cm is drawn on the surface of the sample, placed between paper or alumina powder, and left in an oven at 150°C for 1 hour. After removing the sample, the dimensions of the side of the drawn square are measured to calculate the shrinkage rate in the mechanical direction (MD) and the perpendicular direction (TD), respectively. The thermal shrinkage rate is calculated according to the following mathematical formula 1.

[0251] [Mathematical Formula 1]

[0252] Thermal shrinkage rate = (L0 - L1) / L0 x 100

[0253] (L0 is the initial length of the membrane, L1 is the length of the membrane after standing at 150°C for 1 hour).

[0254] Thermal shrinkage rate in electrolyte (Unit: %)

[0255] (Manufacturing of the cathode)

[0256] As a cathode active material, 97 wt% of graphite particles with an average particle size of 25 μm, 1.5 wt% of styrene-butadiene rubber (SBR) binder, and 1.5 wt% of carboxymethylcellulose (CMC) were mixed, added to distilled water, and stirred for 60 minutes using a mechanical stirrer to prepare a cathode active material slurry. The slurry was applied onto a copper current collector with a thickness of 10 μm using a doctor blade, dried in a hot air dryer at 100°C for 0.5 hours, dried once more under vacuum at 120°C for 4 hours, and then rolled to produce a cathode.

[0257] (Manufacturing of the anode)

[0258] 97 wt% of LiCoO2 as the positive active material, 1.5 wt% of carbon black powder as the conductive material, and 1.5 wt% of polyvinylidene fluoride (PVdF) were mixed and added to an N-methyl-2-pyrrolidone solvent, and then stirred for 30 minutes using a mechanical stirrer to prepare a positive active material slurry. The slurry was applied onto a 20 μm thick aluminum current collector using a doctor blade, dried in a hot air dryer at 100°C for 0.5 hours, dried once more under vacuum at 120°C for 4 hours, and then rolled to produce a positive electrode.

[0259] One sheet of the above sample was placed between the anode and the cathode to create three sets of anode-sample-cathode stacks, which were then placed in a pouch. 3 g of electrolyte (ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate dissolved in 1.5 M LiPF6 (volume ratio of 30:50:20 based on total volume 100)) was injected to completely immerse the stacks in the electrolyte, and the pouch was sealed and left at 25°C for 12 hours. Then, after leaving the pouch in an oven at 150°C for 1 hour, the sample was removed, cooled, and the dimensions of the sample were measured to calculate the shrinkage rate. The shrinkage rate can be calculated according to the above mathematical formula 1.

[0260] Film resistance (unit: Ω)

[0261] The membrane resistance was evaluated using electrochemical impedance spectroscopy (EIS) resistance. The separator prepared in the example and comparative example was impregnated with an electrolyte solution (2 / 1 / 7 volume ratio) of ethylene carbonate dissolved in 1.5M LiPF6, ethylmethyl carbonate, and dimethyl carbonate, fitted onto an aluminum foil electrode with a lead tab, and sealed in an aluminum pack to prepare a test cell. The resistance (Ω) of the test cell was measured at 20°C using the AC impedance method (measurement frequency 100 kHz).

[0262] Coating density (unit: g / cm³) 3 )

[0263] The thickness (a) and weight (b) of the porous substrate are measured before coating with the composition for the coating layer. After coating with the composition for the coating layer and drying in an oven at 70°C for 16 hours, the total thickness (c) and weight (d) are measured to calculate the coating thickness and weight. The coating density is calculated by dividing the coating weight by the thickness.

[0264] Coating thickness (e) = c - a

[0265] Coating weight (f) = d - b

[0266] Coating density = f / e

[0267] Example 1 23456 Binder AA 303030306540 ​​HEMA 1010101055 AMPS 606060603055 Filler Weight Ratio* 90:10 80:20 95:5 75:25 90:10 90:10 Weight Ratio** 1:201:201:201:201:201:20 Crosslinking Agent Type Aziridine Aziridine Aziridine Aziridine Aziridine Parts of Weight 101010101010 Dry Shrinkage MD 1.8 2.2 2.3 2.5 32.5 TD 2.5 2.3 2.5 32.5 Electrolyte Shrinkage MD 336655 TD 447766 Membrane Resistance 0.5 30.5 30.5 40.5 30.5 30.5 4 Coating Density 1.31.31.27 1.31.31.3

[0268] Comparative Example 1 2345678 Binder AA074424040404040HEMA740581010101010AMPS262605050505050 Filler Weight Ratio* 90:1090:1090:1090:1090:1090:1090:1098:270:30 Weight Ratio** 1:201:201:201:201:201:201:201:201:20 Crosslinking Agent Type Aziridine Aziridine Aziridine None Epoxy CDI Aziridine Aziridine Weight Parts 101010010101010 Dry Shrinkage Rate MD 15151521.81.845TD 15151522245 Electrolyte Shrinkage rate MD4545455245451215TD4545455845451515 Film resistance 0.750.750.750.530.530.530.550.59 Coating density 1.31.31.31.31.31.31.11

[0269]

[0270] In Tables 1 and 2 above,

[0271] Weight ratio*: Weight ratio of 1st pillar : 2nd pillar

[0272] Weight Ratio**: Weight ratio of (matte)acrylic binder to filler mixture.

[0273]

[0274] As shown in Table 1 above, the separator for a lithium secondary battery of the example has low dry thermal shrinkage rate, low thermal shrinkage rate in the electrolyte, and low membrane resistance, and has a high coating density, which can improve the capacity, safety, and lifespan of the battery.

[0275] However, as shown in Table 2 above, the separator of the comparative example did not provide an improved effect compared to the separator of the example.

[0276]

[0277] Although preferred embodiments of the present invention have been described above, the present invention is not limited thereto and can be implemented with various modifications within the scope of the claims, the detailed description of the invention, and the attached drawings, and it is obvious that such modifications also fall within the scope of the present invention.

Claims

1. A porous substrate and a coating layer located on at least one surface of the porous substrate, and The above coating layer comprises a binder and a crosslinked product of a crosslinking agent; and a filler, The above binder comprises a (meth)acrylic binder comprising a first structural unit derived from (meth)acrylic acid, (meth)acrylate, or a salt thereof, a second structural unit derived from a hydroxyalkyl (meth)acrylate, and a third structural unit derived from (meth)acrylamidosulfonic acid or a salt thereof, and The above crosslinking agent includes an aziridine-based crosslinking agent, and A separator for a secondary battery, comprising a filler mixture in which a first filler having a size D50 of 150 to 200 nm and a second filler having a size D50 of 50 to 100 nm are mixed in a weight ratio of 95:5 to 75:25 based on a total of 100 parts by weight.

2. A separator for a secondary battery according to claim 1, wherein the coating layer is formed from a composition for a coating layer comprising the (meth)acrylic binder, the aziridine-based crosslinking agent, and the filler mixture.

3. A separator for a secondary battery according to claim 1 or 2, wherein the aziridine-based crosslinking agent comprises one or more of N,N'-toluene-2,4-bis(1-aziridine-carboxamide), N,N'-(methylenedi-p-phenylene)bis(aziridine-1-carboxamide), triethylenemelamine, 1,1-isophthaloylbis(2-methylaziridine), tris(1-aziridinyl)phosphine oxide, N,N-hexamethylene-bis(aziridine-carboxamide), trimethylolpropane tris(2-methyl-1-aziridinepropionate), trimethylolpropane tris(beta-N-aziridinyl)propionate, and pentaerythritol tris(3-(1-aziridinyl)propionate.

4. A separator for a secondary battery, wherein, in any one of claims 1 to 3, the crosslinking agent is included in an amount of 5 to 50 parts by weight per 100 parts by weight of the (meth)acrylic binder.

5. A separator for a secondary battery, wherein, in any one of claims 1 to 4, the first filler and the second filler are each cubic in shape.

6. A separator for a secondary battery, wherein, in any one of claims 1 to 5, the first filler and the second filler are each boehmite.

7. A separator for a secondary battery, wherein, in any one of claims 1 to 6, the (meth)acrylic binder: the filler mixture is included in a mass ratio of 1:10 to 1:

50.

8. In any one of claims 1 to 7, the first structural unit 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] The above second structural unit is represented by the following chemical formula 4: [Chemical Formula 4] The above-mentioned third structural unit is a separator for a secondary battery represented by the following chemical formulas 5, 6, 7, or a combination thereof: [Chemical Formula 5] [Chemical Formula 6] [Chemical Formula 7] R 1 to R 14 Each independently hydrogen or a C1 to C10 alkyl group, L 1 to L 4 Each is 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, and d are each independently one of integers from 0 to 2, M is an alkali metal.

9. In any one of claims 1 to 8, the (meth)acrylic binder is a separator for a secondary battery represented by the following chemical formula 8: [Chemical Formula 8] In the above chemical formula 8, R 15 to R 20 Each independently contains hydrogen or a C1 to C10 alkyl group, L 5 and L 6 Each is 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, M is an alkali metal, e and f are each independently one of integers from 0 to 2, l, m, and n are the molar ratios of each unit, l + m + n = 1.

10. A separator for a secondary battery according to any one of claims 1 to 9, wherein, with respect to 100 mol% of the (meth)acrylic binder, the first structural unit is included in an amount of 20 to 75 mol%, the second structural unit is included in an amount of 1 to 20 mol%, and the third structural unit is included in an amount of 20 to 75 mol%.

11. A separator for a secondary battery, wherein, in any one of claims 1 to 10, the total sum of the first structural unit, the second structural unit, and the third structural unit comprises 95 mol% or more with respect to 100 mol% of the (meth)acrylic binder.

12. A separator for a secondary battery according to any one of claims 1 to 11, wherein the aziridine-based crosslinking agent comprises 95% by weight or more of the total crosslinking agent in the composition for the coating layer.

13. A separator for a secondary battery according to any one of claims 1 to 12, wherein the filler mixture comprises 95% by weight or more of the total filler in the composition for the coating layer.

14. A separator for a secondary battery, wherein, in any one of claims 1 to 13, the coating layer has a thickness of 0.1 μm to 2 μm.

15. A secondary battery comprising an anode, a cathode, and a separator for a secondary battery according to any one of claims 1 to 14 located between the anode and the cathode.

Images