Separator for lithium secondary battery and lithium secondary battery including same

Abstract

The present invention provides a separator for a lithium secondary battery, which comprises: a porous polymer substrate; and a porous coating layer disposed on at least one surface of the porous polymer substrate and including inorganic particles and a binder polymer, wherein the inorganic particles include surface-modified calcium carbonate (CaCO3), the surface-modified calcium carbonate includes a first surface-modified calcium carbonate, a second surface-modified calcium carbonate, or a combination thereof, the first surface-modified calcium carbonate includes: a first calcium carbonate; and a fatty acid-derived functional group chemically bonded to the surface of the first calcium carbonate, and the second surface-modified calcium carbonate includes: a second calcium carbonate; and an organosilane-derived functional group chemically bonded to the surface of the second calcium carbonate.

Description

Separator for lithium secondary battery and lithium secondary battery containing same

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

[0002] This application claims the benefit of priority to Korean Patent Application No. 10-2024-0072643, filed June 3, 2024, the entire contents of which are incorporated herein by reference.

[0003]

[0004] Lithium secondary batteries are widely used as power sources for portable electronic devices such as laptops, cell phones, digital cameras, and camcorders, as well as electric vehicles. As lithium secondary batteries become increasingly widespread, safety concerns are emerging. For example, as lithium secondary batteries advance to higher capacities and outputs, the likelihood of abnormal temperature increases during charging and discharging due to various causes increases. This can lead to thermal runaway, a phenomenon in which sparks explode at high temperatures. In thermal runaway, fires are difficult to extinguish. Safety issues are recognized as one of the most critical issues to be addressed in high-capacity, high-output lithium secondary batteries.

[0005]

[0006] The present invention provides a separator for a lithium secondary battery having a porous coating layer including surface-modified calcium carbonate having excellent dispersibility and wettability without including a dispersant or a wetting agent.

[0007] The present invention provides a separator for a lithium secondary battery capable of preventing or delaying heat transfer when a thermal runaway phenomenon occurs, including surface-modified calcium carbonate.

[0008] The present invention provides a separator for a lithium secondary battery having low surface roughness due to excellent dispersibility of surface-modified calcium carbonate.

[0009] The present invention provides a lithium secondary battery having excellent resistance characteristics by not including a dispersant or wetting agent in a porous coating layer.

[0010] According to one aspect of the present invention, a separator for a lithium secondary battery and a lithium secondary battery including the same according to the following embodiments are provided.

[0011] According to a first embodiment, a separator for a lithium secondary battery is provided, comprising: a porous polymer substrate; and a porous coating layer positioned on at least one surface of the porous polymer substrate and comprising inorganic particles and a binder polymer, wherein the inorganic particles comprise surface-modified calcium carbonate (CaCO3), wherein the surface-modified calcium carbonate comprises a first surface-modified calcium carbonate, a second surface-modified calcium carbonate, or a combination thereof, wherein the first surface-modified calcium carbonate comprises a first calcium carbonate; and a fatty acid-derived functional group chemically bonded to a surface of the first calcium carbonate, and wherein the second surface-modified calcium carbonate comprises a second calcium carbonate; and an organosilane-derived functional group chemically bonded to a surface of the second calcium carbonate.

[0012] According to a second embodiment, in the first embodiment, the surface-modified calcium carbonate may include surface-modified precipitated calcium carbonate.

[0013] According to a third embodiment, in any one of the first to second embodiments, the surface-modified calcium carbonate D 50 (Average particle size) may be within the range of 0.1 μm to 2.0 μm.

[0014] According to a fourth embodiment, in any one of the first to third embodiments, the surface-modified calcium carbonate may have an aspect ratio within a range of 1.0 to 1.5.

[0015] According to the fifth embodiment, in any one of the first to fourth embodiments, the fatty acid-derived functional group has a carbon number of C10 -C 24 It may be derived from fatty acids or their salts.

[0016] According to a sixth embodiment, in any one of the first to fifth embodiments, the organosilane-derived functional group is vinyltrimethoxysilane, vinyltriethoxysilane, vinyltris(β-methoxyethoxy)silane, β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, γ-(2-aminoethyl)aminopropyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropyltrimethyldiethoxysilane, γ-glycidoxypropyltriethoxysilane, γ-methacryloxypropylmethyldimethoxysilane, γ-methacryloxypropyltrimethoxysilane, γ-methacryloxypropylmethyldiethoxysilane, γ-methacryloxypropyltriethoxysilane, N-β(aminoethyl)γ-aminopropylmethyldimethoxysilane, N-β(aminoethyl)γ-aminopropyltrimethoxysilane, N-β(aminoethyl)γ-aminopropyltriethoxysilane,It may be derived from an organosilane such as 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, N-phenyl-γ-aminopropyltrimethoxysilane, γ-chloropropyltrimethoxysilane, γ-mercaptopropyltrimethoxysilane, bis-(3-[triethoxysilyl]-propyl)-tetrasulfide (TESPT), bis-(3-[triethoxysilyl]-propyl)-disulfide, or a combination thereof.

[0017] According to the seventh embodiment, in any one of the first to sixth embodiments, the inorganic particles are Pb(Zr,Ti)O3(PZT), Pb 1-x La x Zr 1-y Ti y O3(PLZT), Pb(Mg3Nb 2 / 3 )O3-PbTiO3(PMN-PT), hafnia (HfO2), SrTiO3, SnO2, CeO2, MgO, NiO, CaO, ZnO, ZrO2, Y2O3, Al2O3, TiO 2, SiC, AlO(OH), Al2O3·H2O, lithium phosphate (Li3PO4), lithium titanium phosphate (Li x Ti y (PO4)3, 0 <x<2, 0<y<3), 리튬알루미늄티타늄포스페이트(Li x Al y Ti z (PO4)3, 0 <x<2, 0<y<1, 0<z<3), 14Li2O-9Al2O3-38TiO2-39P2O 5　 (LiAlTiP) etc.x O y Series Glass (0) <x<4, 0<y<13), 리튬란탄티타네이트(Li x La y TiO3, 0 <x<2, 0<y<3), Li 3.25 Ge 0.25 P 0.75 Lithium germanium thiophosphate (Li) such as S4 x Ge y P z S w , 0 <x<4, 0<y<1, 0<z<1, 0<w<5), Li3N 등과 같은 리튬나이트라이드(Li x N y , 0 <x<4, 0<y<2), Li3PO4-Li2S-SiS 2　 SiS2 series glass (Li) such as x Si y S z , 0 <x<3, 0<y<2, 0<z<4), LiI-Li2S-P2S 5　 P2S5 series glass (Li) such as x P y S z , 0 <x<3, 0<y<3, 0<z<7) 또는 이들의 혼합물을 더 포함하는 것일 수 있다.

[0018] According to an eighth embodiment, in any one of the first to seventh embodiments, the binder polymer is polymethylmethacrylate, polybutylacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, polyethylene-co-vinyl acetate, polyethylene oxide, polyarylate, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethylpullulan, cyanoethylpolyvinylalcohol, cyanoethylcellulose, cyanoethylsucrose (cyanoethylsucrose), pullulan, carboxyl methyl cellulose, or two or more thereof.

[0019] According to the ninth embodiment, in any one of the first to eighth embodiments, when performing a turbiscan analysis on the surface-modified calcium carbonate, the hourly sedimentation rate (% / hr) may be -2.5 or more.

[0020] According to a tenth embodiment, in any one of the first to ninth embodiments, the content of the fatty acid-derived functional group may be within a range of 0.5 parts by weight to 5 parts by weight based on 100 parts by weight of the first surface-modified calcium carbonate, and the content of the organosilane-derived functional group may be within a range of 0.5 parts by weight to 5 parts by weight based on 100 parts by weight of the second surface-modified calcium carbonate.

[0021] According to an eleventh embodiment, a lithium secondary battery is provided, characterized by including a positive electrode; a negative electrode; and a separator of any one of the first to tenth embodiments interposed between the positive electrode and the negative electrode.

[0022]

[0023] According to one embodiment of the present invention, a slurry for forming a porous coating layer including surface-modified calcium carbonate has excellent dispersibility and thus may not separately include a dispersant.

[0024] According to one embodiment of the present invention, a slurry for forming a porous coating layer including surface-modified calcium carbonate has excellent wettability and thus may not separately include a wetting agent.

[0025] A separator for a lithium secondary battery according to one embodiment of the present invention has excellent dispersibility and wettability by including surface-modified calcium carbonate, and thus can have excellent dispersibility and wettability even if the porous coating layer does not include a dispersant and a wetting agent.

[0026] A separator for a lithium secondary battery according to one embodiment of the present invention includes surface-modified calcium carbonate, and thus has excellent dispersibility and wettability, thereby preventing or slowing down heat transfer when a thermal runaway phenomenon occurs.

[0027] A separator for a lithium secondary battery according to one embodiment of the present invention includes surface-modified calcium carbonate, and thus has excellent dispersibility, and thus the surface roughness of the separator can be low.

[0028] A lithium secondary battery according to one embodiment of the present invention may have excellent resistance characteristics because the porous coating layer of the separator does not include a dispersant and a wetting agent.

[0029] A lithium secondary battery according to one embodiment of the present invention can prevent or slow down heat transfer between batteries when a thermal runaway phenomenon occurs.

[0030] The following drawings attached to this specification illustrate embodiments of the present invention, and serve to further understand the technical idea of ​​the present invention together with the contents of the invention described above, and therefore the present invention should not be interpreted as being limited to matters described in such drawings.

[0031] Figure 1 is a graph evaluating the dispersibility of the slurry of each example and comparative example.

[0032]

[0033] Terms or words used in this specification and claims should not be interpreted as limited to their usual or dictionary meanings, but should be interpreted as meanings and concepts that conform to the technical idea of ​​the present invention, based on the principle that the inventor can appropriately define the concept of the term to explain his or her own invention in the best way.

[0034] The terminology used herein is for the purpose of describing exemplary embodiments only and is not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly dictates otherwise.

[0035] Justice

[0036] Throughout this specification, when it is said that a part "includes" a component, this does not mean that it excludes other components, but rather that it may include other components, unless otherwise specifically stated.

[0037] Throughout this specification, the description of “A and / or B” means “A or B or both.”

[0038] Throughout this specification, D 50 (Average particle size) means the particle size at the 50% point of the cumulative particle number distribution according to particle size. That is, D 50 refers to the particle size at the 50% point of the cumulative distribution of particle numbers according to particle size. In addition, D 10 D means the particle size at the 10% point of the cumulative distribution of particle numbers according to particle size. 50 refers to the particle size at the 90% point of the cumulative distribution of particle numbers according to particle size.

[0039] The above particle size can be measured using the laser diffraction method. For example, after the powder to be measured is dispersed in a dispersion medium, it is introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac S3500) and the difference in diffraction pattern according to particle size is measured when the particles pass through the laser beam to calculate the particle size distribution. By calculating the particle diameters at points where the number of particles is 10%, 50%, and 90% of the cumulative distribution according to particle size in the measuring device, D is calculated, respectively. 10 , D 50 and D 90 can be measured. Alternatively, the particle size can be measured using a sedigraph.

[0040] The term "substantially" as used throughout this specification is used in the sense of, or close to, the numerical values ​​when manufacturing and material tolerances inherent in the meaning stated are presented, and is used to prevent unscrupulous infringers from unfairly exploiting disclosures that state exact or absolute values ​​to aid understanding of this specification.

[0041]

[0042] In terms of the safety characteristics of lithium secondary batteries, if the lithium secondary battery overheats and thermal runaway occurs or the separator is penetrated, there is a high risk of explosion and heat transfer between the cells of the lithium secondary battery.

[0043] Meanwhile, polyolefin-based porous polymer substrates, commonly used as separators in lithium secondary batteries, exhibit extreme thermal shrinkage behavior at temperatures above 100°C due to their material properties and manufacturing process characteristics, including stretching, which can cause short circuits between the positive and negative electrodes. To address this safety issue in lithium secondary batteries, ongoing efforts are being made to utilize heat-resistant nonwoven fabrics made from fibers that exhibit mild thermal shrinkage and have a higher melting point than polyolefins as separators.

[0044] Meanwhile, a separator has been proposed that includes a porous polymer substrate having a plurality of pores, wherein a slurry of an excessive amount of inorganic particles and a binder polymer is coated on at least one surface of the porous polymer substrate to form a porous coating layer. The inorganic particles contained in the porous coating layer generally have excellent heat resistance, and thus prevent or suppress short circuits between the positive and negative electrodes even when the lithium secondary battery is overheated. However, the inorganic particles have high surface energy, which reduces wettability in organic solvents, and the inorganic particles tend to clump together, resulting in poor dispersibility. In addition, in addition to the excellent heat resistance among the physical properties of the inorganic particles, there is a need for the development of inorganic particles that have excellent physical properties that can prevent or slow down heat transfer when a thermal runaway phenomenon occurs.

[0045] The present invention provides a separator for a lithium secondary battery having excellent dispersibility and wettability even when the porous coating layer including surface-modified calcium carbonate does not include a dispersant or a wetting agent.

[0046]

[0047] The present invention provides a separator for a lithium secondary battery according to one embodiment.

[0048] According to one embodiment of the present invention, a separator for a lithium secondary battery comprises: a porous polymer substrate; and a porous coating layer positioned on at least one surface of the porous polymer substrate and including inorganic particles and a binder polymer, wherein the inorganic particles include surface-modified calcium carbonate (CaCO3), wherein the surface-modified calcium carbonate includes first surface-modified calcium carbonate, second surface-modified calcium carbonate, or a combination thereof, wherein the first surface-modified calcium carbonate has a first calcium carbonate; and a fatty acid-derived functional group chemically bonded to a surface of the first calcium carbonate, and the second surface-modified calcium carbonate has a second calcium carbonate; and an organosilane-derived functional group chemically bonded to a surface of the second calcium carbonate.

[0049]

[0050] <Porous polymer substrate>

[0051] In one embodiment of the present invention, the porous polymer substrate refers to a substrate having a plurality of pores formed therein as a porous ion-conducting barrier that allows ions to pass while blocking electrical contact between the cathode and the anode. The pores are structured to be interconnected, allowing gas or liquid to pass from one side of the substrate to the other.

[0052] The material constituting the porous polymer substrate may be any organic or inorganic material having electrical insulation properties. In one embodiment, from the perspective of imparting a shutdown function to the substrate, a thermoplastic resin may be used as the constituent material of the substrate. Here, the shutdown function refers to a function in which, when the battery temperature increases, the thermoplastic resin melts and closes the pores of the porous substrate, thereby blocking the movement of ions and preventing thermal runaway of the battery. A thermoplastic resin having a melting point of less than about 200°C is suitable as the thermoplastic resin, and in one embodiment, a polyolefin may be used.

[0053] In addition to polyolefin, it may further include at least one polymer resin such as polyethylene terephthalate, polybutylene terephthalate, polyacetal, polyamide, polycarbonate, polyimide, polyetheretherketone, polyethersulfone, polyphenylene oxide, polyphenylene sulfide, and polyethylene naphthalene. The porous polymer substrate may be, but is not limited to, a nonwoven fabric, a porous polymer film, or a laminate of two or more thereof.

[0054] In the present invention, the porous polymer substrate may be used with a thickness of about 3 µm to 12 µm or about 5 µm to 12 µm. Within the above numerical range, a sufficient conductive barrier function can be realized, and the resistance of the separator can be maintained at an appropriate value.

[0055] In one embodiment of the present invention, the weight average molecular weight of the polyolefin may be about 100,000 to 5 million. When the weight average molecular weight is in the range of about 100,000 to 5 million, not only sufficient mechanical properties can be secured, but also appropriate shutdown characteristics and molding characteristics can be maintained. In addition, the puncture strength of the porous polymer substrate may be about 300 gf or more from the viewpoint of improving the manufacturing yield. The puncture strength of the porous substrate refers to the maximum puncture load (gf) measured by performing a puncture test under the conditions of a needle tip radius of 0.5 mm and a puncture speed of 4 mm / sec using a Kato tech KES-G5 handy compression tester.

[0056] The porous polymer substrate may be any planar porous polymer substrate used in an electrochemical device, and according to one embodiment, an insulating thin film having high ion permeability and mechanical strength, a pore diameter of generally about 10 nm to 200 nm, and a thickness of generally about 5 ㎛ to 12 ㎛ may be used.

[0057]

[0058] Surface-modified calcium carbonate

[0059] The separator for a lithium secondary battery of the present invention comprises the porous polymer substrate and a porous coating layer positioned on at least one surface of the porous polymer substrate. In addition, the porous coating layer comprises inorganic particles and a binder polymer, and the inorganic particles comprise surface-modified calcium carbonate (CaCO3).

[0060] In one embodiment of the present invention, the inorganic particles included in the porous coating layer include surface-modified calcium carbonate. The surface-modified calcium carbonate includes a first surface-modified calcium carbonate, a second surface-modified calcium carbonate, or a combination thereof, wherein the first surface-modified calcium carbonate includes a first calcium carbonate having a fatty acid-derived functional group chemically bonded to its surface; and the second surface-modified calcium carbonate includes a second calcium carbonate having an organosilane-derived functional group chemically bonded to its surface.

[0061]

[0062] precipitated calcium carbonate

[0063] The first calcium carbonate and the second calcium carbonate may be the same in material or shape, or may be different from each other.

[0064] In one embodiment of the present invention, the surface-modified calcium carbonate may include surface-modified precipitated calcium carbonate. The first calcium carbonate and the second calcium carbonate may each independently include precipitated calcium carbonate.

[0065] In this specification, calcium carbonate can be distinguished into heavy calcium carbonate and light calcium carbonate.

[0066] The above ground calcium carbonate (GCC) is also called natural calcium carbonate. The above ground calcium carbonate is obtained from a mineral containing calcium carbonate, for example, selected from marble, chalk, limestone, and mixtures thereof, and can be manufactured through wet and / or dry processing such as mechanical crushing, screening, and / or fractionation. The above ground calcium carbonate has an irregular particle shape, and the particle size can be varied and have a wide distribution. For example, D of the above ground calcium carbonate 50 This may be about 2 μm to 10 μm, and the heavy calcium carbonate has a D lower than the lower limit even if it goes through a grinding process. 50 It can be difficult to have.

[0067] In one embodiment of the present invention, the precipitated calcium carbonate, also called precipitated calcium carbonate (PCC) or synthetic calcium carbonate, may be obtained by a chemical precipitation reaction. For example, the precipitated calcium carbonate may be obtained by subsequent precipitation resulting from the reaction of carbon dioxide and calcium hydroxide in an aqueous environment, or by the precipitation of calcium ions and carbonate ions, such as CaCl2 and Na2CO3, from a solution. According to one embodiment, the precipitated calcium carbonate may be produced by the lime soda process or the sorbay process, which is a byproduct of ammonia production.

[0068] In one embodiment of the present invention, the precipitated calcium carbonate may comprise calcite, aragonite, vaterite, or a combination thereof. The precipitated calcium carbonate may exist in the crystal form of calcite, aragonite, or vaterite, and each of these crystal forms may have many different polymorphs (relief walls). Calcite may have a trigonal structure with typical relief walls such as scalenohedral (S-PCC), rhombic hexahedral (R-PCC), hexagonal prisms, pinacoids, colloids (C-PCC), cubics, and prismatics (P-PCC). The aragonite may have an orthorhombic structure with typical relief walls in various combinations of twinned hexagonal prisms, thin elongated prisms, curved blades, sharp pyramids, chiseled crystals, branched trees, and coral- or worm-like forms. The above vaterite may belong to the hexagonal crystal system.

[0069] In one embodiment of the present invention, the hardened calcium carbonate has a BET specific surface area of ​​about 5 m 2 / g to 100 m 2 / g. The above BET specific surface area represents a value calculated from the nitrogen gas adsorption amount at liquid nitrogen temperature (77 K) using, for example, BELSORP-mino II of BEL Japan.

[0070] The above-mentioned precipitated calcium carbonate can be ground by a dry or wet grinding process. The grinding can be performed in a conventional grinding device, such as a ball mill, a rod mill, a vibrating mill, a roll mill, a centrifugal impact mill, a vertical bead mill, an attrition mill, a pin mill, a hammer mill, a crusher, a shredder, a de-clamper, a knife cutter, or one or more of the above-mentioned devices.

[0071]

[0072] In one embodiment of the present invention, D of the surface-modified calcium carbonate 50 The surface roughness of the porous coating layer manufactured therefrom may be maintained low by being used as an inorganic particle, and may be in the range of about 0.1 μm to 2.0 μm or about 0.2 μm to 1.8 μm. The D of the surface-modified calcium carbonate 50 By satisfying the above-described range, the dispersibility of the slurry for forming a porous coating layer including surface-modified calcium carbonate can be improved, the surface roughness of the porous coating layer formed from the slurry can be reduced, the mechanical properties can be improved, and the internal resistance of the lithium secondary battery manufactured therefrom can be lower.

[0073]

[0074] In one embodiment of the present invention, the surface-modified calcium carbonate may have an aspect ratio within the range of about 1.0 to 1.5, 1.0 to 1.3, or 1.0 to 1.2. Here, the aspect ratio is defined as the ratio of the length of the major axis to the minor axis of the surface-modified calcium carbonate, and the closer it is to 1, the closer it is to a sphere. The aspect ratio can be calculated, for example, using a particle shape analyzer (QICPIC-LIXELL, Sympatec GmbH). The closer the aspect ratio is to 1, the more uniformly the modified calcium carbonate can be distributed in the porous coating layer, and the lower the surface roughness of the porous coating layer, the better the adhesion of the porous coating layer.

[0075]

[0076] First surface-modified calcium carbonate and second surface-modified calcium carbonate

[0077] The first surface-modified calcium carbonate of the present invention is a first calcium carbonate having a fatty acid-derived functional group chemically bonded to the surface; and the second surface-modified calcium carbonate is a second calcium carbonate having an organosilane-derived functional group chemically bonded to the surface.

[0078] In general, calcium carbonate is an ionic compound and therefore has high surface energy. Accordingly, when calcium carbonate as an inorganic particle is dissolved in a solvent, for example, an organic solvent, to prepare a slurry for forming a porous coating layer, the calcium carbonates aggregate with each other, so the dispersibility of the slurry is low, and the surface roughness of the formed inorganic coating layer may be high, resulting in inferior mechanical properties. Accordingly, when the surface of calcium carbonate is chemically bonded with a fatty acid-derived functional group, which is an amphoteric substance, or with an organosilane-derived functional group, the first surface-modified calcium carbonate or the second surface-modified calcium carbonate may have superior dispersibility in the slurry compared to the first and second non-surface-modified calcium carbonates due to the hydrophobic portions of the fatty acid and organosilane.

[0079] In one embodiment of the present invention, the fatty acid-derived functional group has a carbon number of C 10 -C 24 Fatty acid, carbon number C 14 -C 20 Fatty acids, or those with carbon number C 16 -C 18 It may be derived from fatty acids or their salts, wherein the carbon number is C 10 -C 24 Fatty acid, carbon number C 14 -C 20 Fatty acids, or those with carbon number C 16 -C 18 Fatty acids or their salts are, for example, octadecanoic acid (C 18 H 36 O2), calcium octadecanoate, magnesium octadecanoate, zinc octadecanoate, hexadecanoic acid (C 16 H 32 O2), calcium hexadecanoate, magnesium hexadecanoate, zinc hexadecanoate, or a combination thereof.

[0080] In one embodiment of the present invention, a fatty acid is dehydrogenated (deprotonated) under alkaline conditions, and the dehydrogenated fatty acid reacts with calcium carbonate to obtain a first surface-modified calcium carbonate in which a fatty acid-derived functional group is chemically bonded to the surface of the first calcium carbonate.

[0081] In one embodiment of the present invention, the degree of modification by the fatty acid-derived functional group may be such that about 0.5 parts by weight to 5 parts by weight, or about 1 part by weight to 3 parts by weight, of the fatty acid is modified by reacting with calcium carbonate based on 100 parts by weight of the first calcium carbonate. For example, the content of the fatty acid-derived functional group may be within a range of about 0.5 parts by weight to 5 parts by weight, or about 1 part by weight to 3 parts by weight, based on 100 parts by weight of the first surface-modified calcium carbonate. When the content of the fatty acid satisfies the above-described range, the degree of dispersibility of the second surface-modified calcium carbonate in the slurry for forming a porous coating layer is high, so that additives such as a dispersant are unnecessary, and thus the resistance characteristics of the separation membrane can be excellent.

[0082]

[0083] In one embodiment of the present invention, the organosilane-derived functional group is vinyltrimethoxysilane, vinyltriethoxysilane, vinyltris(β-methoxyethoxy)silane, β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, γ-(2-aminoethyl)aminopropyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropyltrimethyldiethoxysilane, γ-glycidoxypropyltriethoxysilane, γ-Methacryloxypropylmethyldimethoxysilane, γ-Methacryloxypropyltrimethoxysilane, γ-Methacryloxypropylmethyldiethoxysilane, γ-Methacryloxypropyltriethoxysilane, N-β(aminoethyl)γ-aminopropylmethyldimethoxysilane, N-β(aminoethyl)γ-aminopropyltrimethoxysilane, N-β(aminoethyl)γ-aminopropyltrimethoxysilane, 3-aminopropyltrimethoxysilane,It may be derived from an organosilane such as 3-aminopropyltriethoxysilane, N-phenyl-γ-aminopropyltrimethoxysilane, γ-chloropropyltrimethoxysilane, γ-mercaptopropyltrimethoxysilane, bis-(3-[triethoxysilyl]-propyl)-tetrasulfide (TESPT), bis-(3-[triethoxysilyl]-propyl)-disulfide, or a combination thereof.

[0084] In one embodiment of the present invention, by mixing the second calcium carbonate and the organosilane together in distilled water, stirring, centrifuging, and drying (for example, at a temperature of 100°C), a second surface-modified calcium carbonate in which an organosilane-derived functional group is chemically bonded to the surface of the second calcium carbonate can be obtained.

[0085] In one embodiment of the present invention, the degree of modification by the organosilane-derived functional group may be such that about 0.5 parts by weight to 5 parts by weight, or about 1 part by weight to 3 parts by weight, of the organosilane is modified by reacting with calcium carbonate based on 100 parts by weight of the second surface-modified calcium carbonate. For example, the content of the organosilane-derived functional group may be within a range of about 0.5 parts by weight to 5 parts by weight, or about 1 part by weight to 3 parts by weight, based on 100 parts by weight of the second surface-modified calcium carbonate. When the content of the organosilane satisfies the above-described range, the degree of dispersion of the second surface-modified calcium carbonate in the slurry for forming a porous coating layer is high, so that additives such as a dispersant are unnecessary, and thus the resistance characteristics of the separator may be excellent. In addition, when the content of the organosilane satisfies the above-described range, the surface of the second calcium carbonate may be sufficiently modified, and thus the wettability of the manufactured separator may be excellent.

[0086] In one embodiment of the present invention, when surface-modified calcium carbonate is used as an inorganic particle, since the slurry for forming a porous coating layer including the same has excellent dispersibility due to a fatty acid-derived functional group or an organosilane-derived functional group, the porous coating layer may substantially not include a separate dispersant. For example, the porous coating layer may include less than about 5 wt%, less than about 4 wt%, less than about 3 wt%, less than about 2 wt%, or less than about 1 wt% of the dispersant based on 100 wt% of the porous coating layer. In this case, the dispersant may include ethylhydroxy ethyl cellulose (EHEC), methyl cellulose (MC), carboxymethyl cellulose sodium salt (CMC-Na), hydroxyalkyl methyl cellulose, or two or more thereof.

[0087] In one embodiment of the present invention, when surface-modified calcium carbonate is used as the inorganic particle, the hydrophobicity of the calcium carbonate surface-modified by the fatty acid-derived functional group or the organosilane-derived functional group increases, so that the wettability of the separator manufactured therefrom is excellent, and therefore the porous coating layer may substantially not include a wetting agent. For example, the porous coating layer may include less than about 5 wt%, less than about 4 wt%, less than about 3 wt%, less than about 2 wt%, or less than about 1 wt% of the wetting agent based on 100 wt% of the porous coating layer.

[0088]

[0089] Meanwhile, in one embodiment of the present invention, when performing a turbiscan analysis on the surface-modified calcium carbonate, the hourly sedimentation rate (% / hr) may be -2.5 or more.

[0090] In one embodiment of the present invention, the turbiscan analysis may be performed by placing a slurry containing surface-modified calcium carbonate in a vial or the like and then irradiating the vial with light in a wavelength range of 750 nm to 1200 nm, preferably a light source in a wavelength range of 790 nm to 900 nm, for example, 880 nm, in a direction parallel to the ground.

[0091] In one embodiment of the present invention, the turbiscan analysis may be performed at a temperature range of 10°C to 40°C, or 20°C to 30°C, for example, at a temperature of 25°C.

[0092] In one embodiment of the present invention, the turbiscan analysis may include a step of irradiating a light source on a slurry containing surface-modified calcium carbonate or inorganic particles, measuring forward scattering (FS) or back scattering (BS), and then measuring the ratio (%) of back scattering over time, and creating a graph by plotting the ratio (%) of back scattering over time, or deriving a derivative thereof.

[0093] In one embodiment of the present invention, the sedimentation velocity can be derived from the average slope of the graph of the backscattering ratio (%) over time, or from the derivative of the graph.

[0094]

[0095] <Inorganic particles>

[0096] In one embodiment of the present invention, the inorganic particles are not particularly limited as long as they are electrochemically stable. The inorganic particles that can be used in the present invention can be used within the operating voltage range of the applied electrochemical device (e.g., Li / Li). + There are no particular limitations as long as no oxidation and / or reduction reaction occurs at a reference voltage of 0 to 5 V. When inorganic particles with a high dielectric constant are used as inorganic particles, the degree of dissociation of electrolyte salts, such as lithium salts, in the liquid electrolyte can be increased, thereby improving the ionic conductivity of the electrolyte.

[0097] In one embodiment of the present invention, the inorganic particles may be included in an amount of about 70 parts by weight to 90 parts by weight, or about 80 parts by weight to 85 parts by weight, based on 100 parts by weight of the inorganic coating layer.

[0098] For the reasons described above, the inorganic particles may include high-k inorganic particles having a dielectric constant of about 5 or more, or 10 or more.

[0099] In addition, the average particle diameter of the inorganic particles is not particularly limited, but may be about 0.1 μm to 2.0 μm or about 0.2 μm to 1.8 μm for forming a coating layer of uniform thickness and having an appropriate porosity. Within the above thickness range, appropriate dispersibility can be maintained, and the thickness of the formed inorganic coating layer can be maintained at an appropriate value.

[0100] In one embodiment of the present invention, the inorganic particles are surface-modified calcium carbonate, Pb(Zr,Ti)O3(PZT), Pb 1-x La x Zr 1-y Ti y O3(PLZT), PB(Mg3Nb 2 / 3 )O3-PbTiO3(PMN-PT), hafnia (HfO2), SrTiO3, SnO2, CeO2, MgO, NiO, CaO, ZnO, ZrO2, Y2O3, Al2O3, TiO 2, SiC, AlO(OH), Al2O3·H2O, lithium phosphate (Li3PO4), lithium titanium phosphate (Li x Ti y (PO4)3, 0 <x<2, 0<y<3), 리튬알루미늄티타늄포스페이트(Li x Al y Ti z (PO4)3, 0 <x<2, 0<y<1, 0<z<3), 14Li2O-9Al2O3-38TiO2-39P2O 5　 (LiAlTiP) etc. x O y Series Glass (0) <x<4, 0<y<13), 리튬란탄티타네이트(Li x La y TiO3, 0 <x<2, 0<y<3), Li 3.25 Ge 0.25 P 0.75 Lithium germanium thiophosphate (Li) such as S4 x Ge y P z S w, 0 <x<4, 0<y<1, 0<z<1, 0<w<5), Li3N 등과 같은 리튬나이트라이드(Li x N y , 0 <x<4, 0<y<2), Li3PO4-Li2S-SiS 2　 SiS2 series glass (Li) such as x Si y S z , 0 <x<3, 0<y<2, 0<z<4), LiI-Li2S-P2S 5　 P2S5 series glass (Li) such as x P y S z , 0 <x<3, 0<y<3, 0<z<7) 또는 이들의 혼합물을 더 포함하는 것일 수 있다.

[0101] In one embodiment of the present invention, the surface-modified calcium carbonate may be included in the inorganic particles in an amount of about 50 parts by weight or more, about 60 parts by weight or more, about 70 parts by weight or more, or about 80 parts by weight or more, based on 100 parts by weight of the inorganic particles. By satisfying the above-described range of the amount of the surface-modified calcium carbonate, the manufactured separator for a lithium secondary battery can more efficiently prevent or delay heat transfer when a thermal runaway phenomenon occurs.

[0102]

[0103] Binder polymer

[0104] In one embodiment of the present invention, the porous coating layer has a glass transition temperature (T g ) may include a binder polymer having a temperature of -200 to 200°C. The binder polymer can improve mechanical properties such as flexibility and elasticity of the porous separator that is ultimately formed, and faithfully performs the role of a binder that connects and stably fixes inorganic particles, thereby contributing to preventing deterioration of the mechanical properties of the separator.

[0105] In addition, the binder polymer does not necessarily need to have ion-conducting ability, but if a polymer having ion-conducting ability is used, the performance of the electrochemical device can be further improved. Therefore, the binder polymer may have a high dielectric constant as much as possible. In fact, since the degree of salt dissociation in the electrolyte depends on the dielectric constant of the electrolyte solvent, the higher the dielectric constant of the binder polymer, the better the degree of salt dissociation in the electrolyte. The dielectric constant of the binder polymer can be used in the range of about 1.0 to 100 (measurement frequency = 1 kHz), and in one embodiment, it can be 10 or more.

[0106] In one embodiment of the present invention, the binder polymer can exhibit a high degree of swelling by being gelled when impregnated with a liquid electrolyte. The solubility index of the binder polymer, i.e., the Hildebrand solubility parameter, is about 15 MPa. 1 / 2 Up to 45 MPa 1 / 2 or about 15 MPa 1 / 2 Up to 25 MPa 1 / 2 and about 30 MPa 1 / 2 Up to 45 MPa 1 / 2 It may be a range. In one embodiment of the present invention, when hydrophilic polymers having a large number of polar groups are used rather than hydrophobic polymers such as polyolefins, the above-described solubility index range can be satisfied.

[0107] In one embodiment of the present invention, the inorganic particles are filled and in contact with each other and are bound to each other by the binder polymer, thereby forming an interstitial volume between the inorganic particles, and the interstitial volume between the inorganic particles may be an empty space to form pores. The binder polymer may attach the inorganic particles to each other so that the particles can maintain a state in which they are bound to each other, for example, the binder polymer may connect and fix the inorganic particles. In addition, the pores of the separator are pores formed by the interstitial volume between the inorganic particles being an empty space, and this may be a space defined by the inorganic particles substantially meeting each other in a closed packed or densely packed structure by the inorganic particles.

[0108] In one embodiment of the present invention, any binder polymer commonly used in the relevant technical field can be used without limitation. The above binder polymers include, for example, polymethylmethacrylate, polybutylacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, polyethylene-co-vinyl acetate, polyethylene oxide, polyarylate, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethylpullulan, cyanoethylpolyvinylalcohol, cyanoethylcellulose, cyanoethylsucrose, pullulan, carboxyl methyl Cellulose (carboxyl methyl cellulose), or two or more of these.

[0109] The above binder polymer may be a particulate binder or a soluble binder. The particulate binder is a binder polymer that does not dissolve in a solvent. The binder polymer is a soluble binder, meaning that it dissolves in a solvent. In this case, the solvent may be an aqueous solvent or an organic solvent.

[0110] In one embodiment of the present invention, the binder polymer may be included in an amount of about 10 parts by weight to 30 parts by weight, or about 15 parts by weight to 20 parts by weight, relative to 100 parts by weight of the inorganic coating layer.

[0111]

[0112] <Method for manufacturing a separator for lithium secondary batteries>

[0113] In one embodiment of the present invention, the separator for the lithium secondary battery can be manufactured by preparing a slurry for forming a porous coating layer by mixing the aforementioned binder polymer and inorganic particles including surface-modified calcium carbonate into a solvent for forming a porous coating layer, applying the slurry onto a porous polymer substrate, and drying the same. In this case, the surface-modified calcium carbonate is first surface-modified calcium carbonate, second surface-modified calcium carbonate, or a combination thereof, and the method for producing the first surface-modified calcium carbonate and the method for producing the second surface-modified calcium carbonate are replaced with those described above.

[0114] In one embodiment of the present invention, the solvent for forming the porous coating layer is an organic solvent, and is not particularly limited as long as it can uniformly disperse the inorganic particles and binder polymer.

[0115] In one embodiment of the invention, the solvent for forming the coating layer is a cyclic aliphatic hydrocarbon such as cyclopentane, cyclohexane; an aromatic hydrocarbon such as toluene, xylene, ethylbenzene; a ketone such as acetone, ethyl methyl ketone, diisopropyl ketone, cyclohexanone, methylcyclohexane, ethylcyclohexane; a chlorinated aliphatic hydrocarbon such as methylene chloride, chloroform, carbon tetrachloride; an ester such as ethyl acetate, butyl acetate, γ-butyrolactone, ε-caprolactone; an acylonitrile such as acetonitrile, propionitrile; an ether such as tetrahydrofuran, ethylene glycol diethyl ether; an alcohol such as methanol, ethanol, isopropanol, ethylene glycol, ethylene glycol monomethyl ether; an ether such as N-methylpyrrolidone, N,N-dimethylformamide, etc. Amides may be mentioned, and the solvent may include acetone in consideration of the advantage in the drying process.

[0116] In one embodiment of the present invention, the solvent for forming the porous coating layer may be used alone, or a mixed solvent of two or more thereof may be used. Among these, by using a solvent with a low boiling point and high volatility, the solvent can be removed in a short time and at a low temperature. For example, acetone, toluene, cyclohexanone, cyclopentane, tetrahydrofuran, cyclohexane, xylene, or N-methylpyrrolidone, or a mixed solvent thereof, may be used.

[0117] At this time, the coating method can be used without limitation as a conventional coating method known in the art, and for example, various methods such as dip coating, die coating, roll coating, comma coating, microgravure coating, doctor blade coating, reverse roll coating, Mayer Bar coating, direct metering coating, or a mixed method thereof can be used.

[0118]

[0119] Lithium secondary battery

[0120] The present invention provides a lithium secondary battery.

[0121] The above lithium secondary battery includes a positive electrode; a negative electrode; a separator interposed between the positive electrode and the negative electrode; and an electrolyte.

[0122] In one embodiment of the present invention, the positive electrode can be manufactured by coating a composition for forming a positive electrode including a positive electrode active material, a binder, a conductive agent, a solvent, etc. on a positive electrode current collector.

[0123] The above-mentioned cathode active material may be a conventional cathode active material that can be used in the cathode of a conventional electrochemical device. For example, the above-mentioned cathode active material may be lithium manganese oxide, lithium cobalt oxide, lithium nickel oxide, lithium iron oxide, or a lithium composite oxide comprising these.

[0124] At this time, the positive electrode active material may be included in an amount of about 80 to 99 parts by weight, for example, about 85 to 98 parts by weight, based on the total weight of the solid content of the composition for forming the positive electrode. When the content of the positive electrode active material satisfies the above-described range, excellent capacity characteristics may be exhibited.

[0125] The positive electrode current collector is not particularly limited as long as it is conductive and does not cause chemical changes in the battery. For example, the positive electrode current collector may be made of stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc.

[0126] The above binder is a component that assists in the bonding of the positive electrode active material and the conductive material and the bonding to the current collector, and can typically be added in an amount of about 1 wt% to 30 wt% based on the total solid weight of the composition for forming the positive electrode. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol (PVA), carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluororubber, various copolymers, etc.

[0127] The above-mentioned conductive agent can typically be added in an amount of about 1 wt% to 30 wt% based on the total solid weight of the composition for forming the anode.

[0128] The conductive material is not particularly limited as long as it is conductive and does not cause a chemical change in the battery, and examples thereof include: graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fibers or metal fibers; metal powders such as fluorinated carbon, aluminum, and nickel powders; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives. Examples of commercially available conductive agents include acetylene blacks (Chevron Chemical Company, Denka Singapore Private Limited, Gulf Oil Company), Ketjenblack, EC series (Armak Company), Vulcan XC-72 (Cabot Company), and Super P (Timcal).

[0129] In addition, the positive electrode active material layer may optionally further include a dispersant as needed.

[0130] The above dispersant can be used without any special restrictions as long as it is used as a dispersant of the anode, and for example, an aqueous dispersant or an organic dispersant can be selectively used as needed. For example, the dispersant may be a cellulose compound, a polyalkylene oxide, a polyvinyl alcohol, a polyvinyl pyrrolidone, a polyvinyl acetal, a polyvinyl ether, a polyvinyl sulfonic acid, a polyvinyl chloride (PVC), a polyvinylidene fluoride, a chitosan, a starch, an amylose, a polyacrylamide, a poly-N-isopropylacrylamide, a poly-N,N-dimethylacrylamide, a polyethyleneimine, a polyoxyethylene, a poly(2-methoxyethoxyethylene), a poly(acrylamide-co-diallyldimethylammonium chloride), an acrylonitrile / butadiene / styrene (ABS) polymer, an acrylonitrile / styrene / acrylate ester (ASA) polymer, a mixture of an acrylonitrile / styrene / acrylate ester (ASA) polymer and propylene carbonate, Examples thereof include styrene / acrylonitrile (SAN) copolymer, methyl methacrylate / acrylonitrile / butadiene / styrene (MABS) polymer, styrene butadiene rubber, nitrile butadiene rubber, and fluoroelastomer, and any one or a mixture of two or more thereof may be used. Hydrogenated nitrile butadiene rubber (H-NBR) may be used. When the positive electrode active material layer further includes a dispersant, the dispersibility of the components of the positive electrode active material layer, particularly the conductive material, may be increased, but is not limited thereto.

[0131] In addition, the solvent may be a solvent generally used in the relevant technical field, such as dimethylsulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, and one of these may be used alone or as a mixture of two or more. The amount of the solvent used is sufficient to dissolve or disperse the positive electrode active material, conductive material, and binder in consideration of the coating thickness and manufacturing yield of the slurry, and to have a viscosity that can exhibit excellent thickness uniformity when applied thereafter for manufacturing the positive electrode.

[0132]

[0133] The negative electrode according to the present invention can be manufactured by coating a negative electrode forming composition including the above-described negative electrode active material, binder, conductive agent, solvent, etc. on a negative electrode current collector. In addition, the negative electrode forming composition may optionally further include a dispersant as needed.

[0134] As the negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium can be used. The negative electrode active material may be, for example, a silicon-based negative electrode active material exhibiting high capacity characteristics, a carbon-based negative electrode active material, or Li x Fe2O3(0≤x≤1), Li x WO2(0≤x≤1), Sn x Me 1-x Me' y O z(Me: Mn, Fe, Pb, Ge; Me': Al, B, P, Si, elements of group 1, 2, and 3 of the periodic table, halogens; 0 <x≤1; 1≤y≤3; 1≤z≤8) 등의 금속 복합 산화물; 리튬 금속; 리튬 합금; 주석계 합금; SnO, SnO2, PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4, 및 Bi2O6등의 금속 산화물; 폴리아세틸렌 등의 도전성 고분자; Li-Co-Ni 계 재료; 티타늄 산화물; 리튬 티타늄 산화물, 또는 이들 중 2이상일 수 있다. 상기 규소계 음극 활물질은 음극 활물질은 Si, SiOx(0.1<x<5), Si-금속 합금, Mg와 같은 금속이 도핑 또는 화학 결합된 실리콘 산화물 입자(SiOx, 0.1<x<5) 및 Si와 SiOx(0.1<x<5)의 합금으로부터 선택되는 하나 이상을 포함할 수 있다. 상기 탄소계 음극 활물질은 천연 흑연, 인조 흑연, 비정질 하드카본(hard carbon), 저결정질 소프트카본(soft carbon), 카본 블랙, 아세틸렌 블랙, 케첸 블랙, 수퍼 P, 그래핀 (graphene), 및 섬유상 탄소로부터 선택되는 하나 이상을 포함할 수 있다.

[0135] The negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloy, etc. can be used. In addition, the negative electrode current collector can typically have a thickness of about 3 ㎛ to 500 ㎛, and like the positive electrode current collector, fine unevenness can be formed on the surface of the current collector to strengthen the bonding strength of the negative electrode active material. For example, it can be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, a non-woven fabric, etc.

[0136] The conductive material, binder, solvent or dispersant included in the above-described composition for forming the cathode may be applied without any special limitation as long as it is generally usable in a composition for forming an electrode. For example, the conductive material, binder, solvent or dispersant described in the above-described composition for forming the anode may be applied.

[0137]

[0138] In the present invention, the electrolyte is A + B - As a salt with the same structure as A + is Li + , Na + , K + B containing an ion composed of an alkali metal cation or a combination thereof; - is PF6 - , BF4 - , Cl - , Br - , I - , ClO4 - , AsF6 - , CH3CO2 - , CF3SO3 - , N(CF3SO2)2 - , C(CF2SO2)3 - A salt containing an anion such as or a combination thereof is dissolved or dissociated in an organic solvent including propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, tetrahydrofuran, N-methyl-2-pyrrolidone (NMP), ethyl methyl carbonate (EMC), γ-butyrolactone, ester compounds, and mixtures of one or more selected from these, but is not limited thereto.

[0139]

[0140] Meanwhile, in one embodiment of the present invention, the organic solvent includes an ester compound, and according to one embodiment, the ester compound is about 30 wt% or more, about 50 wt% or more, about 60 wt% or more, or about 65 wt% or more, based on 100 wt% of the organic solvent.

[0141] In one embodiment of the present invention, the ester compound includes at least one selected from isobutyl propionate, isoamyl propionate, isobutyl butyrate, isopropyl propionate, methylpropionate, ethylpropionate, propylpropionate, butylpropionate, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl butyrate, ethyl butyrate, propyl butyrate, and butyl butyrate.

[0142] In one embodiment of the present invention, an electrolyte additive may be used as needed for the purpose of improving battery life characteristics, suppressing battery capacity decrease, and improving battery discharge capacity. Examples of the electrolyte additive include, but are not limited to, haloalkylene carbonate compounds such as vinylene carbonate (VC), fluoroethylene carbonate (FEC), and difluoroethylene carbonate (DFEC), pyridine, triethylphosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, and aluminum trichloride, and one or a mixture of two or more thereof may be used, but the present invention is not limited thereto. The above electrolyte additive may be contained, for example, in an amount of about 0.1 wt% or more and 15 wt% or less based on the total weight of the electrolyte.

[0143]

[0144] Hereinafter, the present invention will be described in more detail through examples, but the following examples are intended to illustrate the present invention, and the scope of the present invention is not limited to these examples.

[0145] <Example 1>

[0146] Preparation of first surface-modified calcium carbonate

[0147] 10 g of light calcium carbonate nanoparticles were added to 200 mL of distilled water, followed by addition of sodium hydroxide, followed by heating and stirring at 90°C, and 0.15 g of a saponified octadecanoic acid mixture as sodium octadecanoate was added thereto, followed by dehydration using a filter press and drying at 80°C using a box dryer to obtain the first surface-modified calcium carbonate. At this time, the octadecanoic acid-derived functional group was 1.48 parts by weight based on 100 parts by weight of calcium carbonate.

[0148] As inorganic particles, the first surface-modified calcium carbonate and acrylic binder were added to water at a weight ratio of 80:20 and stirred to prepare a slurry for forming a porous coating layer. The prepared slurry was applied to both sides of a 9 ㎛ thick polyethylene porous substrate and then dried to prepare a separator having an inorganic coating layer formed on each side with a thickness of 1.5 ㎛.

[0149]

[0150] <Example 2>

[0151] Preparation of second surface-modified calcium carbonate

[0152] 10 g of precipitated calcium carbonate nanoparticles were added to 200 mL of distilled water, 0.2 g of 3-aminopropyltrimethoxysilane was added, and the mixture was stirred at 25°C for 20 minutes. The mixture was centrifuged at 3000 rpm for 20 minutes using a centrifuge to separate the supernatant, which was then washed several times. A condensation reaction was performed between the OH group of precipitated calcium carbonate and the silanol (Si-OH) group of 3-aminopropyltrimethoxysilane in an oven at 100°C for 12 hours to obtain second surface-modified calcium carbonate mixed with functional groups derived from 3-aminopropyltrimethoxysilane. At this time, the functional groups derived from 3-aminopropyltrimethoxysilane were 1.96 parts by weight based on 100 parts by weight of calcium carbonate.

[0153] As inorganic particles, the second surface-modified calcium carbonate and acrylic binder were added to water at a weight ratio of 80:20 and stirred to prepare a slurry for forming a porous coating layer. The prepared slurry was applied to both sides of a 9 ㎛ thick polyethylene porous substrate and then dried to prepare a separator having an inorganic coating layer formed on each side with a thickness of 1.5 ㎛.

[0154]

[0155] <Comparative Example 1>

[0156] A membrane was manufactured in the same manner as in Example 1, except that alumina (Al2O3) was used instead of the first surface-modified calcium carbonate as the inorganic particle.

[0157]

[0158] <Comparative Example 2>

[0159] A membrane was manufactured in the same manner as in Example 1, except that unmodified calcium carbonate was used as the inorganic particle.

[0160]

[0161] <Experimental Example>

[0162] <Experimental Example 1: Flame Retardancy Evaluation>

[0163] To evaluate the flame retardancy properties of the membranes of each example and comparative example, combustion experiments using a flame torch were conducted. For example, each membrane was cut to a size of 13 mm × 125 mm, ignited, and the self-extinguishing time (the time it takes for the sample to extinguish spontaneously after ignition) was measured to evaluate flame retardancy. This process was repeated three times, and the average values ​​of the three tests are shown in Table 1 below.

[0164] Self-digestion time comparison Example 110.7 Example 11.87 Example 22.22

[0165] According to Table 1 above, the membranes of Examples 1 and 2 had a substantially shorter self-extinguishing time (the time when the sample naturally extinguishes after ignition) than the membrane of Comparative Example 1, confirming excellent flame retardancy.

[0166]

[0167] <Experimental Example 2: Dispersibility Evaluation>

[0168] To evaluate the dispersibility of the slurries for forming porous coating layers of each example and comparative example, dispersion stability was analyzed using TURBISCAN LAB equipment. Each slurry was placed in a 30 mL vial to a height of 55 mm, and the backscattering value (%) and the sedimentation rate over time (% / hr) were measured at 2-minute intervals for a total of 700 minutes, and the results are shown in Fig. 1. At this time, the measurement temperature was 25°C, and the wavelength of the light source used was 880 nm.

[0169] According to FIG. 1, the slurry including the first surface-modified calcium carbonate of Example 1 had a sedimentation rate of -1.88 (% / hr) and the lowest backscattering value (%) was 45.11% compared to the initial value, and the slurry including the second surface-modified calcium carbonate of Example 2 had a sedimentation rate of -2.37 (% / hr) and the lowest backscattering value (%) was 36.24% compared to the initial value. On the other hand, the slurry including alumina of Comparative Example 1 had a sedimentation rate of -2.73 (% / hr) and the lowest backscattering value (%) was 36.76%. At this time, the sedimentation rate was derived by measuring the average slope between 0 and 700 minutes.

[0170] In conclusion, the slurries including the surface-modified calcium carbonate of Examples 1 and 2 had lower absolute values ​​of settling rates per hour than the slurry including alumina of Comparative Example 1, and thus settled more slowly. Through this, it was confirmed that the slurry including the surface-modified calcium carbonate had superior dispersibility compared to alumina.

[0171] Meanwhile, the slurry containing non-surface-modified calcium carbonate of Comparative Example 2 had sedimentation so rapidly during measurement that dispersion stability could not be evaluated using a turbiscan.

[0172] Through the results of Examples 1 and 2 and Comparative Examples 1 and 2, it was found that the separator using calcium carbonate surface-modified as an inorganic particle in the coating layer had significantly superior flame retardancy compared to the separator that did not use such a particle, and the dispersibility of the slurry for the coating layer was also significantly superior.

[0173]

[0174] Although the present disclosure has been described above with reference to embodiments thereof, it will be understood by those skilled in the art or having ordinary knowledge in the art that various modifications and changes to the various embodiments of the present disclosure may be made without departing from the technical scope of the various embodiments of the present disclosure as set forth in the claims below. Accordingly, the technical scope of the various embodiments of the present disclosure should not be limited to the contents described in the detailed description of the specification, but should be defined by the claims.

Claims

1. Porous polymer substrate; and A porous coating layer positioned on at least one surface of the porous polymer substrate and including inorganic particles and a binder polymer, The above inorganic particles include surface-modified calcium carbonate (CaCO3), The above surface-modified calcium carbonate comprises first surface-modified calcium carbonate, second surface-modified calcium carbonate or a combination thereof, The first surface-modified calcium carbonate comprises: first calcium carbonate; and a fatty acid-derived functional group chemically bonded to the surface of the first calcium carbonate; A separator for a lithium secondary battery, wherein the second surface-modified calcium carbonate comprises a second calcium carbonate; and an organosilane-derived functional group chemically bonded to the surface of the second calcium carbonate.

2. In claim 1, The above surface-modified calcium carbonate is a separator for a lithium secondary battery comprising surface-modified hard calcium carbonate.

3. In claim 1, D of the above surface-modified calcium carbonate 50 A separator for a lithium secondary battery having an average particle size of 0.1 μm to 2.0 μm.

4. In claim 1, The above surface-modified calcium carbonate is a separator for a lithium secondary battery having an aspect ratio in the range of 1.0 to 1.

5.

5. In claim 1, The above fatty acid-derived functional group has a carbon number of C 10 -C 24 A separator for a lithium secondary battery derived from fatty acids or their salts.

6. In claim 1, The above organosilane-derived functional group is vinyltrimethoxysilane, vinyltriethoxysilane, vinyltris(β-methoxyethoxy)silane, β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, γ-(2-aminoethyl)aminopropyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropyltrimethyldiethoxysilane, γ-glycidoxypropyltriethoxysilane, γ-Methacryloxypropylmethyldimethoxysilane, γ-Methacryloxypropyltrimethoxysilane, γ-Methacryloxypropylmethyldiethoxysilane, γ-Methacryloxypropyltriethoxysilane, N-β(aminoethyl)γ-aminopropylmethyldimethoxysilane, N-β(aminoethyl)γ-aminopropyltrimethoxysilane, N-β(aminoethyl)γ-aminopropyltrimethoxysilane, 3-aminopropyltrimethoxysilane,A separator for a lithium secondary battery derived from an organosilane such as 3-aminopropyltriethoxysilane, N-phenyl-γ-aminopropyltrimethoxysilane, γ-chloropropyltrimethoxysilane, γ-mercaptopropyltrimethoxysilane, bis-(3-[triethoxysilyl]-propyl)-tetrasulfide (TESPT), bis-(3-[triethoxysilyl]-propyl)-disulfide, or a combination thereof.

7. In claim 1, The above inorganic particles are Pb(Zr,Ti)O3(PZT), Pb 1-x La x Zr 1-y Ti y O3(PLZT), Pb(Mg3Nb 2 / 3 )O3-PbTiO3(PMN-PT), hafnia (HfO2), SrTiO3, SnO2, CeO2, MgO, NiO, CaO, ZnO, ZrO2, Y2O3, Al2O3, TiO 2, SiC, AlO(OH), Al2O3·H2O, lithium phosphate (Li3PO4), lithium titanium phosphate (Li x Ti y (PO4)3, 0 <x<2, 0<y<3), 리튬알루미늄티타늄포스페이트(Li x Al y Ti z (PO4)3, 0 <x<2, 0<y<1, 0<z<3), 14Li2O-9Al2O3-38TiO2-39P2O 5　 (LiAlTiP) etc. x O y Series Glass (0) <x<4, 0<y<13), 리튬란탄티타네이트(Li x La y TiO3, 0 <x<2, 0<y<3), Li 3.25 Ge 0.25 P 0.75 Lithium germanium thiophosphate (Li) such as S4 x Ge y P z S w , 0 <x<4, 0<y<1, 0<z<1, 0<w<5), Li3N 등과 같은 리튬나이트라이드(Li x N y , 0 <x<4, 0<y<2), Li3PO4-Li2S-SiS 2　 SiS2 series glass (Li) such as x Si y S z , 0 <x<3, 0<y<2, 0<z<4), LiI-Li2S-P2S 5　 P2S5 series glass (Li) such as x P y S z , 0<x<3, 0<y<3, 0<z<7) 또는 이들의 혼합물을 더 포함하는 리튬 이차전지용 분리막.

8. In claim 1, The above binder polymer is polymethylmethacrylate, polybutylacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, polyethylene-co-vinyl acetate, polyethylene oxide, polyarylate, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethylpullulan, cyanoethylpolyvinylalcohol, cyanoethylcellulose, cyanoethylsucrose, pullulan, carboxyl methyl cellulose (carboxyl methyl cellulose), or a separator for a lithium secondary battery comprising two or more of these.

9. In claim 1, A separator for a lithium secondary battery having a sedimentation rate per hour (% / hr) of -2.5 or more when performing a turbiscan analysis on the above surface-modified calcium carbonate.

10. In claim 1, The content of the fatty acid-derived functional group is within the range of 0.5 parts by weight to 5 parts by weight based on 100 parts by weight of the first surface-modified calcium carbonate, A lithium secondary battery separator having a content of the organic silane-derived functional group in a range of 0.5 parts by weight to 5 parts by weight based on 100 parts by weight of the second surface-modified calcium carbonate.

11. A lithium secondary battery comprising a positive electrode; a negative electrode; and a separator according to any one of claims 1 to 10 interposed between the positive electrode and the negative electrode.

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