Pouch type lithium secondary battery

Abstract

The present invention relates to a pouch-type lithium secondary battery. The pouch-type lithium secondary battery comprises an electrode assembly provided with a first electrode plate, a second electrode plate, and a separator interposed between the first electrode plate and the second electrode plate, wherein the separator comprises: a porous substrate; and a first layer and a second layer which are successively disposed on at least one surface of the porous substrate. The first layer comprises a crosslinked product of a binder and a crosslinking agent, and a filler, wherein the binder includes a (meth)acrylic binder including 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 crosslinking agent includes an aziridine-based crosslinking agent; the second layer includes an adhesive binder; and the adhesive binder includes a mixture of a fluorine-based adhesive binder having a hydroxyl group or a carboxylic acid group and a fluorine-based adhesive binder without a hydroxyl group and a carboxylic acid group.

Description

Pouch-type lithium secondary battery

[0001] This is about pouch-type lithium secondary batteries.

[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 an electrode assembly comprising a separator between a positive electrode and a negative electrode. The separator is impregnated in an 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.

[0006] In pouch-type lithium secondary batteries, the electrode assemblies are arranged in a stacked or wound configuration. Therefore, separators used in pouch-type lithium secondary batteries require high adhesion to the anode or cathode and high bending strength compared to separators used in cylindrical, prismatic, or coin-type lithium secondary batteries.

[0007]

[0008] One embodiment provides a pouch-type battery comprising a separator for a lithium secondary battery having a low thermal shrinkage rate in the electrolyte, low membrane resistance, high wet adhesion to the anode or cathode, and high bending strength.

[0009]

[0010] One embodiment is a pouch-type lithium secondary battery.

[0011] 1. The pouch-type lithium secondary battery comprises an electrode assembly having a first electrode plate, a second electrode plate, and a separator interposed between the first electrode plate and the second electrode plate, wherein the separator comprises a porous substrate; and a first layer and a second layer sequentially positioned on at least one surface of the porous substrate, and the first layer comprises a crosslinked material of a binder and a crosslinking agent; The binder comprises a filler and 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 hydroxyalkyl (meth)acrylate, and a third structural unit derived from (meth)acrylamidosulfonic acid or a salt thereof, the crosslinking agent comprises an aziridine-based crosslinking agent, the second layer comprises an adhesive binder, and the adhesive binder comprises a mixture of a fluorine-based adhesive binder having a hydroxyl group or a carboxylic acid group and a fluorine-based adhesive binder without a hydroxyl group or a carboxylic acid group.

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

[0013] A pouch-type lithium secondary battery according to 3.1 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.

[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, a pouch-type lithium secondary battery.

[0015] 5.1 to 4, wherein the filler comprises a filler having a size D50 of 0.1 to 0.3 μm, a pouch-type lithium secondary battery.

[0016] A pouch-type lithium secondary battery according to 6.1 to 5, wherein the filler is plate-shaped and boehmite.

[0017] 7.1 to 6, a pouch-type lithium secondary battery comprising the (meth)acrylic binder and the filler 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 pouch-type lithium 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 represented by the following chemical formula 8, a pouch-type lithium secondary battery:

[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 pouch-type lithium 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 pouch-type lithium 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 comprises 95 mol% or more with respect to 100 mol% of the (meth)acrylic binder.

[0050] A pouch-type lithium 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 first layer.

[0051] A pouch-type lithium secondary battery according to 13.1 to 12, wherein the fluorine-based adhesive binder having a carboxylic acid group or a hydroxyl group and the fluorine-based adhesive binder not having a carboxylic acid group and a hydroxyl group are included in the mixture in a weight ratio of 1:1 to 1:5.

[0052] A pouch-type lithium secondary battery according to 14.1 to 13, wherein the fluorine-based adhesive binder having a carboxylic acid group or a hydroxyl group is a polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP)-based binder having a carboxylic acid group or a hydroxyl group, and the fluorine-based adhesive binder having a carboxylic acid group and a hydroxyl group is a polyvinylidene fluoride-hexafluoropropylene-based binder not having a carboxylic acid group or a hydroxyl group.

[0053] A pouch-type lithium secondary battery according to 15.1 to 14, wherein the first layer has a thickness of 0.1 μm to 3 μm and the second layer has a thickness of 0.1 μm to 3 μm.

[0054]

[0055] A separator for a lithium secondary battery according to one embodiment has high wet adhesion and bending strength to the positive or negative electrode, making it suitable for a pouch type, and has low thermal shrinkage and membrane resistance in the electrolyte, so the pouch-type lithium secondary battery can have high reliability.

[0056]

[0057] FIG. 1 is a cross-sectional view schematically showing a pouch-type lithium secondary battery according to one embodiment.

[0058] FIG. 2 is a cross-sectional view showing a separator for a lithium secondary battery according to one embodiment.

[0059] Figure 3 is a schematic diagram of the measurement of the bending strength of the separation membrane.

[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. Or, 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 spherical, the above size may refer to the particle 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] A pouch-type lithium secondary battery according to one embodiment comprises an electrode assembly having a first electrode plate, a second electrode plate, and a separator interposed between the first electrode plate and the second electrode plate, wherein the separator comprises a porous substrate; and a first layer and a second layer sequentially positioned on at least one surface of the porous substrate, and the first layer comprises a crosslinked material of a binder and a crosslinking agent; The binder comprises a filler and 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, the crosslinking agent comprises an aziridine-based crosslinking agent, the second layer comprises an adhesive binder, and the adhesive binder comprises a mixture of a fluorine-based adhesive binder having a hydroxyl group or a carboxylic acid group and a fluorine-based adhesive binder without a hydroxyl group or a carboxylic acid group.

[0075] According to one embodiment, the crosslinker may be a thermal crosslinker.

[0076] According to one embodiment, the first layer may be formed from a composition for the first layer comprising the (meth)acrylic binder, the aziridine-based crosslinking agent, and the filler.

[0077] According to one embodiment, the first layer may be a heat-resistant layer.

[0078] According to one embodiment, the second layer may be formed from a mixture of the fluorine-based adhesive binder.

[0079] According to one embodiment, the second layer may be an adhesive layer.

[0080] The first layer and the second layer can be formed by direct contact with each other.

[0081] The above separator may have a thermal shrinkage rate in the electrolyte of 10% or less in the MD (machine direction) and TD (transverse direction), for example, 5% or less. The aforementioned 'MD' and 'TD' are each in the same direction as the MD and TD of the porous substrate.

[0082] The above separator may have a membrane resistance of 0.85Ω or less, for example, 0.1 to 0.85Ω. Within this range, the resistance of the battery is low, which can increase the reliability of the battery.

[0083] The above separator may have a wet adhesion strength of 0.7 gf / mm or more, for example, 0.7 to 1.0 gf / mm. Within this range, when the separator is used in a pouch-type battery, the resistance to stacking and / or winding is low, which can increase the structural stability of the pouch-type battery.

[0084] The separator may have a bending strength of 400 N or more, for example, 400 to 500 N. Within this range, when the separator is used in a pouch-type battery, the resistance to stacking and / or winding is low, which can increase the structural stability of the pouch-type battery.

[0085] A separator having a first layer formed of a composition for a first 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 significantly higher thermal shrinkage rate in the electrolyte.

[0086] 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 first layer.

[0087] A separator having a first layer formed of a composition for a first 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 higher resistance.

[0088] According to one embodiment, the (met)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 (e.g., non-adhesive binder) in the composition.

[0089] A separator having a second layer that is not formed from a mixture of the above-mentioned fluorine-based adhesive binders or is formed from only one type of the above-mentioned fluorine-based adhesive binder mixture may have lower wet adhesion and dry adhesion with the electrode plate.

[0090] According to one embodiment, the mixture of the fluorine-based adhesive binder may be included in the second layer in an amount of 95% or more by weight, for example, 95 to 100% by weight, or 100% by weight.

[0091] FIG. 1 is a schematic cross-sectional view of a pouch-type lithium secondary battery according to one embodiment.

[0092] Referring to FIG. 1, a pouch-type secondary battery 100 may include an electrode assembly 110 and a pouch 130 that accommodates the electrode assembly 110.

[0093] The electrode assembly 100 may be formed by winding or stacking a laminate of a first electrode plate 112, a separator 116, and a second electrode plate 114 formed in a thin plate or film shape.

[0094] In the case where the electrode assembly 110 is a wound laminate, the winding axis may be parallel to the longitudinal direction of the sealing portion. Additionally, the electrode assembly may be a stack type rather than a wound type, and the shape of the electrode assembly is not limited in the present invention.

[0095] In addition, the electrode assembly 110 may be a Z-stack electrode assembly in which a positive plate and a negative plate are inserted on both sides of a separator folded into a Z-stack.

[0096] In addition, the electrode assembly 110 may be stored inside a sealing portion by stacking one or more electrode assemblies so that their long sides are adjacent to each other, and the number of electrode assemblies is not limited in the present invention.

[0097] The electrode assembly 110 is impregnated in the electrolyte 120 contained within the pouch 130.

[0098] Since the above pouch-type lithium secondary battery provides low membrane resistance, low thermal shrinkage rate in the electrolyte, high wet adhesion, and high bending strength through the separator, this will be explained in detail first.

[0099] Separator

[0100] The above separator comprises a porous substrate; and a first layer and a second layer sequentially located on at least one surface of the porous substrate.

[0101] <1st layer (=heat-resistant layer)>

[0102] 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.

[0103] According to one embodiment, the (mat)acrylic binder may be a non-adhesive binder.

[0104] The above (meth)acrylic binder can fix the filler onto the porous substrate and ensure that the first layer adheres well to the porous substrate and the second layer, 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 first layer to the porous substrate and the second layer, and increase the dispersibility of the filler within the first layer. Furthermore, the above (meth)acrylic binder can provide a separator with low membrane resistance in the first layer containing the filler described below.

[0105] 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.

[0106] The first structural unit is derived from (meth)acrylic acid, (meth)acrylate, or a salt thereof, and serves to fix the filler onto the porous substrate while providing adhesion so that the first layer adheres well to the porous substrate and electrode, and can contribute to improving the heat resistance and air permeability of the separator. In addition, the first structural unit can improve the dispersibility of the coating slurry by having a carboxyl functional group (-C(=O)O-) within the structural unit.

[0107] The above first structural unit may be represented by any one of the following chemical formulas 1 to 3:

[0108] [Chemical Formula 1]

[0109]

[0110] [Chemical Formula 2]

[0111]

[0112] [Chemical Formula 3]

[0113]

[0114] With respect to 100 mol% of the binder for the lithium 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 It may be included in mol%. When included within the above range, the separator may exhibit low membrane resistance, excellent adhesion to porous substrates and electrodes, as well as heat resistance, air permeability, and oxidation resistance.

[0115] According to one embodiment, the first structural unit may include a structural unit represented by Chemical Formula 2 and a structural unit represented by Chemical Formula 3, wherein the structural unit represented by Chemical Formula 2 and the structural unit represented by 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.

[0116] According to another embodiment, the first structural unit may include only the structural unit represented by the chemical formula 2.

[0117] 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 first layer adheres well to the porous substrate and the second layer. In addition, the second structural unit can improve the dispersibility of the coating slurry by having a carboxyl functional group (-C(=O)O-) within the structural unit.

[0118] The above second structural unit can be represented by the following chemical formula 4:

[0119] [Chemical Formula 4]

[0120]

[0121] With respect to 100 mol% of the binder for the lithium 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 to the porous substrate of the first layer and the second layer.

[0122] 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.

[0123] 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.

[0124] 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.

[0125] 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. Additionally, if 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.

[0126] The above third structural unit may be represented by the following chemical formulas 5, 6, 7, or a combination thereof.

[0127] [Chemical Formula 5]

[0128]

[0129] [Chemical Formula 6]

[0130]

[0131] [Chemical Formula 7]

[0132]

[0133] 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.

[0134] 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.

[0135] For example, the above (meth)acrylamidoalkane sulfonic acid may be 2-(meth)acrylamido-2-methylpropane sulfonic acid.

[0136] 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.

[0137] The description of the above chemical formulas 1 to 7 is as follows.

[0138] 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.

[0139] 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-*.

[0140] 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.

[0141] 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.

[0142] A representative example of a binder for a lithium secondary battery according to one embodiment is as shown in Chemical Formula 8 below:

[0143] [Chemical Formula 8]

[0144]

[0145] The explanation for the above chemical formula 8 is as follows.

[0146] 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.

[0147] 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-*.

[0148] 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.

[0149] 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.

[0150] e and f can each independently be one of integers from 0 to 2. For example, e and f can both be 1.

[0151] 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.

[0152] 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.

[0153] 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.

[0154] The above (meth)acrylic 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.

[0155] 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.

[0156] The above (meth)acrylic binder can be manufactured by a solution polymerization method.

[0157] According to one embodiment, the (met)acrylic binder may be included in the coating layer of the separator in the form of a film.

[0158] The above crosslinking agent includes an aziridine-based crosslinking agent.

[0159] The above aziridine-based crosslinking agent can crosslink the above (meth)acrylic binder and at the same time facilitate the separator reaching the shrinkage rate range and membrane resistance range within the electrolyte.

[0160] 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.

[0161] 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.

[0162] 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.

[0163] 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 20 parts by weight, 5 to 15 parts by weight, or 5 to 10 parts by weight, based on 100 parts by weight of the (meth)acrylic binder. The heat resistance effect may be improved within the above range.

[0164] The above filler may have a size D50 of 0.4 μm or less. Within this range, it may be easy to achieve the shrinkage rate in the electrolyte when combined with the (meth)acrylic binder and the crosslinking agent. For example, the filler may have a size D50 of 0.35 μm or less, 0.3 μm or less, 0.1 to 0.3 μm, or 0.15 to 0.2 μm. Within this range, there may be an effect of improving heat resistance properties.

[0165] According to one embodiment, the filler having a size D50 of 0.4 μm or less may be included in an amount of 95% or more by weight of the total filler in the first layer, for example, 95 to 100% by weight, 98 to 100% by weight, or 100% by weight. Within this range, the effect of the separator membrane may be easily realized.

[0166] According to one embodiment, the filler may not be surface modified, but may be surface modified.

[0167] The above filler may be, for example, an inorganic filler, an organic filler, an organic-inorganic composite filler, or a combination thereof. The above inorganic filler may be a ceramic material capable of improving heat resistance. The above inorganic filler may include, for example, a metal oxide, a metal metal oxide, a metal fluoride, a metal hydroxide, or a combination thereof. The above 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 above organic filler may include an acrylic compound, an imide compound, an amide compound, or a combination thereof, but is not limited thereto. The above organic filler may have a core-shell structure, but is not limited thereto. For example, the above filler may preferably be boehmite.

[0168] The above filler may be spherical, plate-shaped, cubic, or amorphous. Preferably, the filler may be cubic, and the cubic shape may have a significantly lower shrinkage rate.

[0169] The above filler should be included in an appropriate amount with respect to the above binder, for example, the above (meth)acrylic binder. According to one embodiment, the (meth)acrylic binder:the above filler 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.

[0170] The above filler 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 first layer. When the above filler is included in the above range, it may exhibit excellent heat resistance, durability, oxidation resistance, and stability.

[0171] Each of the first layers may have a thickness of 0.01㎛ to 20㎛, and within the above range, may have a thickness of 0.01㎛ to 7㎛, or 0.1㎛ to 5㎛, or 1㎛ to 3㎛.

[0172] Layer 2 (=Adhesive Layer)

[0173] With the adhesive binder, the separator maintains heat resistance and adhesive strength, while improving battery stability and lifespan when subsequently used in a battery, and can also improve the resistance of the battery. In addition, the adhesive binder increases the bending strength of the separator, thereby lowering the resistance received by the separator when the electrode assembly including the separator is formed into a stacked or wound type within a pouch-type battery, which can increase the structural stability of the pouch-type battery.

[0174] The above adhesive binder is an organic binder and includes a mixture of a fluorine-based adhesive binder having a carboxylic acid group or a hydroxyl group and a fluorine-based adhesive binder not having a carboxylic acid group or a hydroxyl group.

[0175] According to one embodiment, a fluorine-based adhesive binder having a carboxylic acid group or a hydroxyl group and a fluorine-based adhesive binder not having a carboxylic acid group and a hydroxyl group may be included in the mixture in a weight ratio of 1:1 to 1:5. For example, the weight ratio may be 1:1, 1:1.5, 1:2, 1:2.5, 1:3, 1:3.5, 1:4, 1:4.5, or 1:5.

[0176] According to one embodiment, the fluorine-based adhesive binder having a carboxylic acid group or a hydroxyl group may be a polyvinylidene fluoride (PVDF)-based binder having a carboxylic acid group or a hydroxyl group.

[0177] According to one embodiment, the fluorine-based adhesive binder having a carboxylic acid group or a hydroxyl group may be a polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP)-based binder having a carboxylic acid group or a hydroxyl group.

[0178] The above polyvinylidene fluoride-based binder comprises, for example, a structural unit derived from vinylidene fluoride and a structural unit derived from a monomer having at least one carboxylic acid group or a hydroxyl group. The structural unit derived from the monomer having at least one carboxylic acid group or a hydroxyl group can provide improved wet adhesion, durability, and air permeability. The monomer having at least one carboxylic acid group or a hydroxyl group may be one or more selected from the group consisting of (meth)acrylic acid, itaconic acid or its derivatives, maleic acid or its derivatives, and hydroxyalkanes and allyl ethers.

[0179] The above polyvinylidene fluoride-based binder may further include structural units derived from vinylidene fluoride and copolymerizable monomers. The copolymerizable monomers may be one or more selected from the group consisting of trichloroethylene, chlorotrifluoroethylene, trifluoroethylene, hexafluoropropylene, ethylene tetrafluoride, and ethylene monomers.

[0180] According to one embodiment, the polyvinylidene fluoride-based binder is a copolymer of vinylidene fluoride, a monomer having a carboxylic acid group or a hydroxyl group, and hexafluoropropylene, and may include a structural unit derived from vinylidene fluoride, a structural unit derived from a monomer having a carboxylic acid group or a hydroxyl group, and a structural unit derived from hexafluoropropylene.

[0181] The polyvinylidene fluoride-based binder having the above-mentioned carboxylic acid group or hydroxyl group has a glass transition temperature (Tg) value of -70°C to -20°C, and the weight-average molecular weight can be 200,000 to 3,000,000 g / mol, 200,000 to 2,000,000 g / mol, or 300,000 to 1,500,000 g / mol. When within the above range, the separator can have excellent adhesion.

[0182] The glass transition temperature can be measured by thermomechanical analysis (TMA), and the weight-average molecular weight can be measured as a polystyrene equivalent value by gel permeation chromatography.

[0183] According to one embodiment, the polyvinylidene fluoride-based compound may comprise 80 mol% to 99 mol% of vinylidene fluoride repeating units, 0.5 mol% to 10 mol% of hexafluoropropylene repeating units, and 0.5 mol% to 10 mol% of repeating units derived from monomers having carboxylic acid groups or hydroxyl groups.

[0184] The above polyvinylidene fluoride-based binder may be in various forms, such as an alternating polymer in which the repeating units are alternately distributed, a randomly distributed polymer, or a graft polymer in which some repeating units are grafted. In addition, the above polyvinylidene fluoride-based binder may be a linear polymer, a branched polymer, or a mixture thereof.

[0185] In the above polyvinylidene fluoride-based binder, the vinylidene fluoride repeating unit may be included in an amount of 90 mol% to 99.5 mol%, 93 mol% to 99 mol%, or 95 mol% to 99 mol%, and the hexafluoropropylene repeating unit may be included in an amount greater than 0 mol%, 10 mol% or less, 0.5 mol% to 10 mol%, 1 mol% to 10 mol%, 1 mol% to 9 mol%, 2 mol% to 7 mol%, or 4 mol% to 6 mol%. Within the above ranges, the polyvinylidene fluoride-based compound can ensure chemical stability while exhibiting excellent solubility in low-boiling point solvents and can exhibit excellent adhesion. Accordingly, an adhesive layer can be formed using a low-boiling point solvent without a separate additional process, and a decrease in air permeability that may inevitably occur when using a high-boiling point solvent can be prevented. A low boiling point solvent may be, for example, a solvent having a boiling point of about 80°C or lower, and may be, for example, acetone, methyl ethyl ketone, ethyl isobutyl ketone, tetrahydrofuran, dimethylformaldehyde, cyclohexane, or a mixture thereof, but is not limited thereto.

[0186] The degree of crystallization of the polyvinylidene fluoride-based binder having the carboxylic acid group or hydroxyl group may be 40% to 65%, for example, 45% to 60%, or 50% to 55%. In this case, the binder may exhibit excellent adhesion. The degree of crystallization of the polyvinylidene fluoride-based binder may be considered higher than the degree of crystallization of the polyvinylidene fluoride-based binder described later. The degree of crystallization may be measured by the XRD (x-ray diffraction) method or spectroscopy, but is not limited thereto.

[0187] The melting point of the polyvinylidene fluoride-based binder having the above-mentioned carboxylic acid group or hydroxyl group can be 150°C or higher, for example, 150 to 200°C.

[0188] The above-mentioned fluorine-based binder that does not have carboxylic acid and hydroxyl groups can help improve the bending strength of the separation membrane.

[0189] The fluorine-based binder that does not have the above-mentioned carboxylic acid group and hydroxyl group may include repeating units derived from vinylidene fluoride and the copolymerizable monomer. Such copolymerizable monomer may be one or more selected from the group consisting of trichloroethylene, chlorotrifluoroethylene, trifluoroethylene, hexafluoropropylene, ethylene tetrafluoride, and ethylene monomer.

[0190] The fluorine-based binder that does not have the above-mentioned carboxylic acid group and hydroxyl group may have various forms, such as alternating polymers, random polymers, or graft polymers. The fluorine-based binder that does not have the above-mentioned carboxylic acid group may be a linear polymer, a branched polymer, or a mixture thereof, and may be a polymer having more branched chains compared to the fluorine-based binder that has the above-mentioned carboxylic acid group.

[0191] The above-mentioned fluorine-based binder that does not have carboxylic acid groups and hydroxyl groups may include vinylidene fluoride repeating units and hexafluoropropylene repeating units.

[0192] According to one embodiment, the fluorine-based adhesive binder having carboxylic acid groups and hydroxyl groups may be a polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP)-based binder that does not have carboxylic acid groups and hydroxyl groups.

[0193] Vinylidene fluoride repeating units may be included in the binder in an amount of 90 mol% to 99.5 mol%, 93 mol% to 99 mol%, or 95 mol% to 99 mol%. When the vinylidene fluoride repeating units are included within the above range, the binder can secure excellent adhesion and electrolyte impregnation properties.

[0194] When the hexafluoropropylene repeating unit is included in the binder in an amount greater than 0 mol% and less than or equal to 10 mol%, or in an amount of 0.5 mol% to 10 mol%, 1 mol% to 9 mol%, 2 mol% to 8 mol%, 3 mol% to 7 mol%, or 4 mol% to 6 mol%, the binder can ensure chemical stability and exhibit excellent adhesion while showing excellent solubility in low-boiling point solvents. Accordingly, an adhesive layer can be formed using a low-boiling point solvent without a separate additional process, and a decrease in air permeability that may inevitably occur when using a high-boiling point solvent can be prevented.

[0195] The above-mentioned fluorine-based binder that does not have carboxylic acid groups and hydroxyl groups has a glass transition temperature (Tg) value of -70°C to 20°C and a weight-average molecular weight of 800,000 to 2,000,000 g / mol, and may be 800,000 to 1,900,000 g / mol. When having a weight-average molecular weight within the above range, an adhesive layer containing it may exhibit excellent wet adhesion and dry adhesion. The weight-average molecular weight may be the polystyrene-equivalent average molecular weight measured using gel permeation chromatography.

[0196] The degree of crystallization of the binder is 35% to 45%, for example, 35% to 40%. When the binder has a degree of crystallization within this range, the adhesive layer containing it exhibits excellent dry adhesion. The degree of crystallization of the binder can be said to be lower than the degree of crystallization of the fluorine-based binder having hydroxyl groups or carboxylic acid groups.

[0197] The melting point of the polyvinylidene fluoride-based binder that does not have the above-mentioned carboxylic acid group and hydroxyl group can be 150°C or higher, for example, 150 to 200°C.

[0198] Both of the above two binders can be manufactured by various known methods such as emulsion polymerization, suspension polymerization, bulk polymerization, solution polymerization, or bulk polymerization, and, for example, can be manufactured by emulsion polymerization.

[0199] Each of the above second layers may have a thickness of 0.01㎛ to 20㎛, and within the above range, may have a thickness of 0.01㎛ to 7㎛, or 0.1㎛ to 5㎛, or 0.1㎛ to 3㎛.

[0200] The ratio of the total thickness of the first layer and the second 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 this range, the separator may exhibit excellent air permeability, heat resistance, and adhesion.

[0201] <Porous Substrate>

[0202] 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.

[0203] 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 the olefin resin, or may include a copolymer of an olefin and a non-olefin monomer.

[0204] The porous substrate may have a thickness of 1 μm to 40 μm, and, for example, may have a thickness of 1 μm to 30 μm, 1 μm to 20 μm, or 5 μm to 15 μm.

[0205] A separator for a secondary battery according to one embodiment can be manufactured by applying a composition for forming a first layer to one or both sides of a porous substrate and drying it to form a first layer, and then applying a composition for a second layer and drying it to form a second layer. The drying can be performed using conventional methods known to those skilled in the art.

[0206] FIG. 2 is a cross-sectional view showing a separator for a lithium secondary battery according to one embodiment.

[0207] Referring to FIG. 2, a separator for a lithium secondary battery comprises a porous substrate 1 and a coating layer 2 located on both sides of the porous substrate 1. The coating layer 2 may include a heat-resistant layer 5 comprising a filler 3 and a crosslinked product 4 of a (meth)acrylic binder and a crosslinking agent; and an adhesive layer 7 located on the heat-resistant layer 5 and comprising an adhesive binder 6.

[0208] Referring again to FIG. 1, the first electrode plate 112 may include a first electrode tab 112a electrically connected to a first electrode active material portion coated with a first electrode active material and a first uncoated portion, which is an area where the first electrode active material is not coated. The first electrode tab 112a may serve as a passage for current flow between the first electrode plate 112 and a first current collector (not shown). In some examples, the first electrode tab 112a may be formed by cutting it to protrude to one side in advance when manufacturing the first electrode plate, and may protrude further to one side than the separator without separate cutting.

[0209] The second electrode plate 114 may include a second electrode tab 114a electrically connected to a second electrode active material portion coated with a second electrode active material and a second uncoated portion, which is an area not coated with the second electrode active material. The second electrode tab 114a may serve as a passage for current flow between the second electrode plate 114 and a second current collector (not shown). In some examples, the second electrode tab 114a may be formed by cutting it to protrude to the other side when manufacturing the second electrode plate, and may protrude further to the other side than the separator without separate cutting.

[0210] In some examples, the first electrode tab 112a may be located on the left side of the electrode assembly, and the second electrode tab 114a may be located on the right side of the electrode assembly, or on one side in the same direction. Here, the left and right sides are for convenience of explanation based on the secondary battery shown in FIG. 1, and their positions may change when the secondary battery rotates left and right or up and down.

[0211] The first electrode tab 112a and the second electrode tab 114a are each welded to the negative lead 152 and the positive lead 154 of the external terminal, respectively, and are electrically connected to the outside. A tab film 156 for insulation from the pouch 130 is attached to the negative lead 152 and the positive lead 154. The negative lead 152, the positive lead 154, and the tab film 156 form an integral tab film 150.

[0212] The sealing portion 132 of the pouch 130 is made of a heat-sealable material and has a structure in which a seal is achieved by bonding the heat-sealable layers together. Since heat-sealable materials generally have weak adhesion to metal, a thin film-type tab film 156 is attached to the tab and fused with the pouch 130.

[0213] The first electrode plate 112 of the electrode assembly 110 can act as a negative electrode, and the second electrode plate 114 can act as a positive electrode. Of course, the opposite is also possible.

[0214] anode

[0215] 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.

[0216] positive electrode active material

[0217] 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.

[0218] 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.

[0219] 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 Mn b Xc 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).

[0220] 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.

[0221] 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.

[0222] 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.

[0223] 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.

[0224] 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.

[0225] Al may be used as the current collector mentioned above, but is not limited thereto.

[0226] cathode

[0227] 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.

[0228] 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.

[0229] cathode active material

[0230] 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.

[0231] 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.

[0232] 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.

[0233] 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.

[0234] 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.

[0235] 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.

[0236] The above Si-based or Sn-based negative electrode active material can be used in combination with a carbon-based negative electrode active material.

[0237] 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.

[0238] 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.

[0239] 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.

[0240] 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.

[0241] 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.

[0242] 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.

[0243] 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.

[0244] Lithium secondary batteries may contain additional electrolyte.

[0245] electrolyte

[0246] The electrolyte for a lithium secondary battery may include a non-aqueous organic solvent and a lithium salt.

[0247] The above-mentioned non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can move.

[0248] 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.

[0249] 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.

[0250] Ester-based solvents such as methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methylpropionate, ethylpropionate, decanolide, mevalonolactone, valerolactone, and caprolactone may be used.

[0251] 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.

[0252] The above-mentioned non-aqueous organic solvent can be used alone or in a mixture of two or more types.

[0253] 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.

[0254] 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).

[0255] According to one embodiment, the non-aqueous organic solvent in the electrolyte may have an EC:PC:EP:PP ratio of 10:15:10 to 30:45 to 65 volume% based on a total volume of 100 volume%, for example, 10:15:10:65 volume%.

[0256] The above lithium salt may be included in the above electrolyte at a concentration of 0.1 to 2.0 M, for example 0.5 to 1.5 M, for example 1.0 to 1.7 M.

[0257] The above additive may include one or more of FEC (fluoroethylene carbonate), VEC (vinyl ethylene carbonate), and PS (propylene sulfone).

[0258] In one embodiment, with respect to 100 volume% of the non-aqueous organic solvent, the FEC may be included in an amount of 5 to 10 volume%, for example 7 volume%, the VEC in an amount of 0.1 to 5 volume%, for example 1 volume%, and the PS in an amount of 1 to 5 volume%, for example 3 volume%.

[0259]

[0260] 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.

[0261]

[0262] Preparation Example 1

[0263] 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, a (meth)acrylic binder was prepared, and about 10 mL of the reaction solution was taken to measure the non-volatile component (NV), which was 9.8 wt% (theoretical value 10 wt%). In addition, in the (meth)acrylic binder 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.

[0264] Preparation Example 2

[0265] 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 40:10:50. 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%).

[0266] Preparation Example 3

[0267] 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%).

[0268] Preparation Example 4

[0269] 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%).

[0270] Preparation Example 5

[0271] 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%).

[0272] Preparation Example 6

[0273] 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%).

[0274] Example 1

[0275] A methacrylic binder (10 wt%) prepared in Preparation Example 1 and boehmite (particle size D50: 150 nm, cubic type) as a filler were mixed in a mass ratio of 1:30 based on solid content of the methacrylic binder:filler, and after being added to a water solvent, a dispersion was prepared by milling and dispersing using a bead mill at 25°C for 30 minutes.

[0276] A composition for forming a first 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 was 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 methacrylic binder.

[0277] As a porous substrate, the composition for forming the first layer was coated to a thickness of 1.8 μm on both sides of a polyethylene-based film (thickness: 8 μm, SK, air permeability: 120 sec / 100 cc, puncture strength: 480 kgf) using a die coating method, and then dried and aged in an oven at 80°C for 16 hours to form the first layer.

[0278] As an adhesive binder, a polyvinylidene fluoride-hexafluoropropylene-based binder 75130 having carboxylic acid groups (weight-average molecular weight 1.3 million g / mol, molar ratio of polyvinylidene fluoride to hexafluoropropylene = 98:2, containing acrylic acid as a monomer, glass transition temperature -30°C, melting point: 154°C, degree of crystallinity 53%) was added to acetone at 8% by weight, and a first binder solution was prepared by stirring at 40°C for 3 hours using a stirrer. As an adhesive binder, a polyvinylidene fluoride-hexafluoropropylene-based binder LBG (weight-average molecular weight 1.3 million g / mol, molar ratio of polyvinylidene fluoride to hexafluoropropylene = 98:2, does not contain acrylic acid as a monomer, glass transition temperature -30°C, melting point: 151°C, degree of crystallinity 40%) was added to acetone at 8% by weight, and a second binder solution was prepared by stirring at 40°C for 3 hours using a stirrer. A composition for the second layer was prepared by mixing the first binder and the second binder in a weight ratio of 5:5 (1:1).

[0279] After coating one surface of the first layer formed above with the composition for the second layer prepared above using a direct low-moisture method at a speed of 80 m / min, 14 g / m at 60°C 3 A separator for a lithium secondary battery was manufactured by drying in the presence of an absolute amount of water vapor (average value) to form a second layer with a thickness of 0.7㎛ on both sides (total).

[0280] Examples 2 to 4

[0281] A separator for a lithium secondary battery was manufactured in the same manner as in Example 1, except that boehmite (cubic type) was used as a filler as shown in Table 1 below, but the D50 was changed, the type of acrylic binder was changed, or the weight ratio was changed.

[0282] Comparative Examples 1 to 8

[0283] A separator for a lithium secondary battery was manufactured in the same manner as in Example 1, except that boehmite (cubic type) was used as a filler as shown in Table 2 below in Example 1, but the D50 was changed, the type of acrylic binder was changed, the thickness of the coating layer was changed, or the type of adhesive binder was changed.

[0284] In Comparative Example 5, the epoxy crosslinking agent is ethylene glycol diglycidyl ether.

[0285] In Comparative Example 6, the carbodiimide (CDI)-based crosslinking agent used was CARBODILITE V-50 (Nisshinbo Chemical).

[0286] In Comparative Example 7, only the first binder was used as the adhesive binder.

[0287] In Comparative Example 8, only the second binder was used as the adhesive binder.

[0288] Thermal shrinkage rate in electrolyte (Unit: %)

[0289] (Manufacturing of the cathode)

[0290] As a negative electrode 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 slurry for a negative electrode active material layer. 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 negative electrode.

[0291] (Manufacturing of the anode)

[0292] 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 slurry for the positive active material layer. 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.

[0293] One of the above samples was placed between the anode and the cathode to create three sets of anode-sample-cathode stacks, which were then placed in a pouch. Electrolyte was injected to completely immerse the stacks in the electrolyte, and the pouch was sealed and left at 25°C for 12 hours. The electrolyte contained 1.3M LiPF6 as a lithium salt, EC (ethylene carbonate) / PC (propylene carbonate) / EP (ethyl propionate) / PP (propyl propionate) (10 / 15 / 10 / 65, volume%) as a non-aqueous organic solvent, and as additives, 7 volume% of FEC (fluoroethylene carbonate), 1 volume% of VEC (vinyl ethylene carbonate), and 3 volume% of PS (propylene sulfone) relative to a total of 100 volume% of the non-aqueous organic solvent.

[0294] Then, after leaving the sample in an oven at 150°C for 1 hour, the sample was removed and cooled, and the dimensions of the sample were measured to calculate the shrinkage rate. The thermal shrinkage rate can be calculated according to the following mathematical formula 1.

[0295] [Mathematical Formula 1]

[0296] Thermal shrinkage rate = (L0 - L1) / L0 x 100

[0297] (L0 is the initial length of the membrane, L1 is the length of the membrane after standing at 150°C for 1 hour).

[0298] Film resistance (unit: Ω)

[0299] The membrane resistance was evaluated using electrochemical impedance spectroscopy (EIS) resistance. The separator prepared in the examples and comparative examples was impregnated with the electrolyte, 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). The electrolyte used had the same composition as described above.

[0300] Anodic adhesion (Unit: gf / mm, wet adhesion)

[0301] After attaching the separator to the positive electrode (manufactured in the same manner as the above battery), insert it into a pouch, inject the electrolyte, and leave it for 12 hours, then apply a pressure of 10 to 20 kgf / cm² 2 , and then disassembled after pressing under conditions of a temperature of 70°C to 90°C and a time of 5 to 20 seconds. After removing the separator and the anode from the pouch, the anode and the separator were spread 180°, and the force required to detach the anode from the separator was measured using a tension meter (Tinius Olsen, HT400). The electrolyte used had the same composition as described above.

[0302] Bending strength (unit: N)

[0303] An anode and a cathode were manufactured in the same manner as above, and a separator was placed between the anode and the cathode to manufacture an electrode assembly. The adhesion strength of the manufactured electrode assembly was evaluated by measuring the 3-point bending strength. Adhesion strength is bending strength.

[0304] The flat-plate wound electrode assembly is a rectangular prism with dimensions of length (L) 40.5 mm, width (W) 75 mm, and thickness 5.1 mm.

[0305] Referring to FIG. 3, the electrode assembly comprises an anode (a), a cathode (b), and a separator (c) located between the anode and the cathode, which are wound into a flat jelly roll shape and then housed in a pouch (d). Subsequently, an organic electrolyte is injected into the pouch, and the structure is sealed.

[0306] The electrode assembly was horizontally mounted on two supports (e) such that the midpoint of the length of the electrode assembly was positioned in the exact center between the two supports of a 3-point bending analyzer (INSTRON, Single column 3344), and the strength when the electrode assembly was bent, i.e., the maximum strength, was measured by pressing the midpoint of the length of the electrode assembly vertically from the top with a jig (f) equipped with a load cell with a maximum load of 1 kN at a speed of 5 mm / min. The measured maximum strength was evaluated as the bending strength of the electrode assembly.

[0307] Example 1 2 3 4 Binder AA 30 40 6 5 3 0 HEMA 10 10 5 10 AMS 60 50 30 6 0 Filler D 50 150 150 20 0 15 0 Weight Ratio 1:30 1:20 1:30 1:30 Type of Crosslinking Agent Aziridine Aziridine Aziridine Aziridine Parts by Weight 10 10 10 5 Heat Resistance Layer Thickness 1.8 1.9 2.1 1.7 Adhesive Binder PVDF Type 2 PVDF Type 2 PVDF Type 2 PVDF Type 2 Adhesive Layer Thickness 0.7 0.7 0.7 0.8 Electrolyte Shrinkage MD 3.8 3.9 4.9 4.3 TD 3.4 3.7 4.5 4.6 Wet Adhesion (gf / mm) 0.78 0.76 0.79 0.77 Film Resistance (Ω) 0.72 0.8 20.74 0.78 Bending Strength(N)480456402420

[0308]

[0309] Comparative Example 1 2345678 Binder AA074424040404040HEMA740581010101010AMPS262605050505050 Filler D50150150150150150150150150100 Weight Ratio 1:201:201:201:201:201:201:201:201:201 Crosslinking Agent Type Aziridine Aziridine Aziridine None Epoxy CDI Aziridine Aziridine Parts by Weight 101010010101010 Heat Resistant Layer Thickness 1.81.91.81.81.81.91.81.8 Adhesive Binder PVDF Type 2 PVDF Type 2 PVDF Type 2 PVDF Type 2 PVDF Type 2 PVDF Type 2 PVDF Type 1 PVDF Type 1 Adhesive Layer Thickness 0.7 0.8 0.8 0.7 0.8 0.8 0.7 Electrolyte Shrinkage MD 4 2 4 5 5 4 6 8 7 1 6 9 4.2 4.4 TD 4 8 5 3 6 1 6 2 6 9 7 2 3.9 4.1 Wet Adhesion (gf / mm) 0.7 8 0.7 6 0.7 4 0.7 8 0.7 6 0.7 9 0.5 4 0.6 1 Film Resistance (Ω) 0.9 4 0.9 2 1.0 4 0.9 2 0.8 9 0.9 1 0.8 9 0.8 8 Bending Strength (N) 4 9 2 4 3 8 4 0 2 4 6 2 4 1 4 4 3 2 2 6 4 2 3 4

[0310]

[0311] As shown in Table 1 above, the lithium secondary battery of the example includes a separator for a lithium secondary battery that has a low thermal shrinkage rate in the electrolyte, low membrane resistance, high wet adhesion to the positive or negative electrode, and high bending strength, which can increase the reliability of the battery.

[0312] As shown in Table 2 above, the lithium secondary battery of the comparative example had an inferior effect compared to the example.

[0313]

[0314] 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

The electrode assembly comprises a first electrode plate, a second electrode plate, and a separator interposed between the first electrode plate and the second electrode plate. The above separator comprises a porous substrate; and a first layer and a second layer sequentially located on at least one surface of the porous substrate, and The first 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, and the crosslinking agent comprises an aziridine-based crosslinking agent. A pouch-type lithium secondary battery, wherein the second layer comprises an adhesive binder, and the adhesive binder comprises a mixture of a fluorine-based adhesive binder having a hydroxyl group or a carboxylic acid group and a fluorine-based adhesive binder not having a hydroxyl group or a carboxylic acid group. A pouch-type lithium secondary battery according to claim 1, wherein the first layer is formed from a composition for the first layer comprising the (meth)acrylic binder, the aziridine-based crosslinking agent, and the filler. A pouch-type lithium 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. A pouch-type lithium secondary battery according to any one of claims 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. A pouch-type lithium secondary battery according to any one of claims 1 to 4, wherein the filler comprises a filler having a size D50 of 0.1 to 0.3 μm. A pouch-type lithium secondary battery according to any one of claims 1 to 5, wherein the filler is plate-shaped and boehmite. A pouch-type lithium secondary battery according to any one of claims 1 to 6, wherein the (meth)acrylic binder and the filler are included in a mass ratio of 1:10 to 1:

50. 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 pouch-type lithium 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. In any one of claims 1 to 8, the pouch-type lithium secondary battery wherein the (meth)acrylic binder is 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. A pouch-type lithium 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 in an amount of 1 to 20 mol%, and the third structural unit in an amount of 20 to 75 mol%. A pouch-type lithium secondary battery according to any one of claims 1 to 10, wherein, with respect to 100 mol% of the (meth)acrylic binder, the total sum of the first structural unit, the second structural unit, and the third structural unit comprises 95 mol% or more. A pouch-type lithium secondary battery according to any one of claims 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 first layer. A pouch-type lithium secondary battery according to any one of claims 1 to 12, wherein the fluorine-based adhesive binder having a carboxylic acid group or a hydroxyl group and the fluorine-based adhesive binder not having a carboxylic acid group and a hydroxyl group are included in the mixture in a weight ratio of 1:1 to 1:

5. A pouch-type lithium secondary battery according to any one of claims 1 to 13, wherein the fluorine-based adhesive binder having a carboxylic acid group or a hydroxyl group is a polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP)-based binder having a carboxylic acid group or a hydroxyl group, and the fluorine-based adhesive binder having a carboxylic acid group and a hydroxyl group is a polyvinylidene fluoride-hexafluoropropylene-based binder not having a carboxylic acid group or a hydroxyl group. A pouch-type lithium secondary battery according to any one of claims 1 to 14, wherein the first layer has a thickness of 0.1 μm to 3 μm and the second layer has a thickness of 0.1 μm to 3 μm.

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