Separator and lithium secondary battery including the same

Abstract

To provide a separator having significantly improved heat resistance, and a lithium secondary battery including the same.SOLUTION: According to one aspect of the present disclosure, there is provided a separator including: a porous substrate; and an inorganic particle layer which is formed on at least one surface of the porous substrate and includes a binder and inorganic particles. The substrate has a ratio of the total thickness of the inorganic particle layer to the thickness of the porous substrate of 0.2 to 0.6, has a peak appearing in a range of 1,070-1,082 cm-1 in a spectrum by Fourier-transform infrared spectroscopy (FT-IR), and has heat shrinkage rates in a machine direction and in a transverse direction of 5% or less as measured after being left at 150°C for 60 minutes.SELECTED DRAWING: None

Description

Technical Field

[0001] The present disclosure relates to a separator with significantly improved heat resistance and a lithium secondary battery including the same.

Background Art

[0002] In an electrochemical device, the separator of a battery is very important for improving the stability, life, and performance of the battery. The main function of the separator is to provide a path for ion movement in the battery and prevent physical contact between the negative electrode and the positive electrode. By improving the characteristics of the separator, a battery with excellent performance can be manufactured.

[0003] In order to improve the characteristics of the separator used in a battery, a multilayer separator is formed by laminating polyolefin-based porous polymers, or a separator is developed in which a binder and inorganic particles are mixed with a porous polymer as a base material to form a coating layer. The coating layer mixed with a multilayer separator or a binder can improve various characteristics of the separator compared to a single-layer separator, but the thickness of the separator may increase, and the battery performance may rather decrease due to low permeability, decreased wettability, and decreased cohesiveness. In order to solve such problems, various characteristics of the separator are quite suitable for the battery separator, and since the thickness is also thin and mechanical and chemical stability are also satisfied, research is being conducted to manufacture a separator that can improve the battery performance.

Summary of the Invention

Problems to be Solved by the Invention

[0004] According to one aspect of the present disclosure, a separator excellent in heat resistance and adhesiveness can be provided.

[0005] According to another aspect of the present disclosure, a lithium secondary battery having excellent resistance characteristics and thermal safety can be provided.

[0006] The separator of the present disclosure is widely applicable in the field of green technologies, such as electric vehicles, battery charging stations, and solar and wind power generation that use other batteries. Further, the separator of the present disclosure can be used in eco-friendly electric vehicles, hybrid vehicles, etc. that suppress air pollution and greenhouse gas emissions and prevent climate change.

Means for Solving the Problems

[0007] The separator according to the present disclosure includes a porous substrate and an inorganic particle layer containing a binder and inorganic particles on at least one surface of the porous substrate, and the ratio of the total thickness of the inorganic particle layer to the thickness of the porous substrate is 0.2 to 0.6. In the spectrum obtained by Fourier transform infrared spectroscopy (FT-IR), it has a peak shown in the range of 1070 cm -1 ~1082 cm -1 and after being left at 150 °C for 60 minutes, the thermal shrinkage rates in the machine direction and width direction measured are 5% or less.

[0008] In one embodiment, the inorganic particles may include any one or two or more selected from the group consisting of metal hydroxides, metal oxides, metal nitrides, and metal carbides.

[0009] In one embodiment, the inorganic particles may have an average particle size (D50) of 0.01 μm to 0.65 μm.

[0010] In one embodiment, the inorganic particles may include first inorganic particles having an average particle size (D50) of 0.01 μm to 0.5 μm.

[0011] In one embodiment, the inorganic particles may further include second inorganic particles having an average particle size (D50) larger than that of the first inorganic particles.

[0012] In one embodiment, the second inorganic particles may be contained in an amount of 50% by weight or less based on the total weight of the first inorganic particles and the second inorganic particles.

[0013] In one embodiment, the thermal shrinkage rates in the machine direction and the width direction may be 3% or less.

[0014] In one embodiment, the thickness of the porous substrate may be 5 μm to 15 μm.

[0015] In one embodiment, the binder may include a polyacrylamide-based resin.

[0016] In one embodiment, the polyacrylamide-based resin may be a copolymer containing units derived from (meth)acrylamide-based monomers and units derived from comonomers.

[0017] In one embodiment, the polyacrylamide-based resin may include structural units derived from (meth)acrylamide-based monomers and structural units derived from (meth)acrylic monomers containing a hydroxy group.

[0018] In one embodiment, the polyacrylamide-based resin may have a weight average molecular weight of 100,000 g / mol to 2,000,000 g / mol.

[0019] In one embodiment, the binder may be contained in an amount of 0.1 part by weight to 20 parts by weight based on 100 parts by weight of the inorganic particles.

[0020] In one embodiment, the binder may further include any one or two or more additional binders selected from the group consisting of polyvinyl alcohol, polyvinylidene fluoride, carboxymethyl cellulose, styrene-butadiene rubber, polyacrylic acid, polyethylene glycol, polyacrylonitrile, polyvinylpyrrolidone, and copolymers thereof.

[0021] In one embodiment, the content of the additional binder may be 0.1 wt% to 30 wt% based on the total content of the binder.

[0022] The lithium secondary battery according to the present disclosure includes a separator as described above.

Advantages of the Invention

[0023] The separator according to the present disclosure can have excellent heat resistance and adhesiveness.

[0024] Further, by including a separator according to one embodiment, the present disclosure can provide a lithium secondary battery having excellent resistance characteristics and thermal safety.

Embodiments for Carrying Out the Invention

[0025] Hereinafter, the present disclosure will be described in detail. However, the embodiments described in this specification may be modified into various different forms, and the technology according to one embodiment is not limited to the embodiments described below. Also, the embodiments of one embodiment are provided to more fully explain the present disclosure to those having average knowledge in the technical field.

[0026] Also, the singular forms used in the specification and the appended claims are intended to include the plural forms as well, unless otherwise specifically stated in the context.

[0027] Also, the numerical ranges used in this specification include the lower limit value and the upper limit value, all values within that range, increments logically derived from the form and width of the defined range, all of the limited values among them, and all possible combinations of the upper and lower limits of the numerically limited ranges different from each other. In this specification, unless otherwise defined, values outside the numerical range that may occur due to experimental error or rounding of values are also included in the defined numerical range.

[0028] Furthermore, throughout the specification, unless otherwise indicated to the contrary, the term "comprising" a certain component means including, rather than excluding, other components, and may further include other components.

[0029] Hereinafter, in this specification, unless otherwise specifically defined, "(meth)acrylic" means acrylic and / or methacrylic.

[0030] In this specification, unless otherwise defined, the average particle diameter of inorganic particles means the D50 value. D50 means the particle diameter of inorganic particles corresponding to 50% in terms of the cumulative fraction on a volume basis. The average particle diameter can be derived from the results of the particle size distribution obtained by sampling a sample in accordance with the ISO 13320-1 standard for the inorganic particles to be measured and analyzing it using an S3500 manufactured by MICROTRAC.

[0031] In this specification, when a part such as a layer, film, region, or plate is said to be "on" or "above" another part, this includes not only the case where it is "immediately above" the other part but also the case where there are further other parts in between.

[0032] Terms such as first, second, etc. used in this specification can be used to describe various components, but the components should not be limited by the terms. The terms are used only for the purpose of distinguishing one component from another.

[0033] In this specification, "MD (machine direction)" means the longitudinal direction in a porous substrate and a separator manufactured in a long shape (longitudinal direction), and "TD (transverse direction)" means the direction perpendicular to MD in the plane direction of the porous substrate and the separator. In this disclosure, TD may also be referred to as the "transverse direction".

[0034] One embodiment provides a separator that can provide a battery with high heat resistance, adhesiveness, and excellent resistance characteristics. Specifically, the separator according to one embodiment includes a porous substrate and an inorganic particle layer formed on at least one surface of the porous substrate and containing a binder and inorganic particles, and the ratio of the total thickness of the inorganic particle layer to the thickness of the porous substrate is 0.2 to 0.6, and in the spectrum by Fourier transform infrared spectroscopy (FT-IR), there is a peak (hereinafter, the first peak) shown in the range of 1070 cm -1 ~1082 cm -1 . After standing at 150 °C for 60 minutes, the thermal shrinkage rates in the machine direction and the width direction measured are 5% or less. The separator according to one embodiment satisfies that the ratio of the thickness of the inorganic particle layer to the thickness of the porous substrate is 0.2 to 0.6, and the peak shown in the FT-IR spectrum is 1070 cm -1 ~1082 cm -1 . By satisfying this, it was first recognized and invented that it can have a significantly reduced high-temperature thermal shrinkage rate.

[0035] Also, the lithium secondary battery according to one embodiment includes a separator that simultaneously satisfies the first peak in a specific range shown in the FT-IR spectrum and the ratio of the thickness of the inorganic particle layer to the thickness of the porous substrate in a specific range, so that it can have both excellent resistance characteristics and thermal safety. Specifically, the lithium secondary battery according to one embodiment can be shown to have a significantly low discharge resistance after 600 cycles and can have improved charge-discharge performance.

[0036] The above effect is achieved by adjusting the ratio of the thickness of the inorganic particle layer to that of the porous substrate and the peaks shown in the FT-IR spectrum to specific ranges, and it is not an effect that is only affected by certain components of the separator or certain elements during the manufacturing process of the separator. As confirmed in one embodiment, the thickness of each layer of the separator, the average particle size of the inorganic particles, the combination of inorganic particles, the weight ratio of multiple inorganic particles, the type and content of the binder, and further the type and content of the binder used, the surface characteristics of the porous substrate, etc., can be realized by various means including various factors. As long as this can be achieved, the means are not particularly limited. For example, the first peak can be derived from the bond energy between atoms contained in the inorganic particles included in the inorganic particle layer, and the range of the first peak is not determined only by the characteristics of the inorganic particles themselves such as the average particle size and material, but can be determined by various factors such as the characteristics of the binder and the porous substrate in addition to the inorganic particles.

[0037] In one embodiment, the first peak is at 1070 cm -1 ~1082 cm -1 and is a peak having the maximum intensity in this range. Specifically, it may be a peak having the maximum intensity in the range of 1071 cm -1 ~1081 cm -1 or in the range of 1072 cm -1 ~1081 cm -1 .

[0038] In one embodiment, the separator may further have a second peak shown in the range of 1140 cm -1 ~1160 cm -1 on the FT-IR spectrum. The second peak is a peak having the maximum intensity in the above range. Specifically, it may be a peak having the maximum intensity in the range of 1145 cm -1 ~1155 cm -1 .

[0039] In one embodiment, the separator has, on the FT-IR spectrum, a range of 2910 cm -1 ~2930 cm -1It may further have a third peak shown in the range. The third peak is a peak having the maximum intensity in the above-mentioned range. Specifically, 2915 cm -1 ~2925 cm -1 range or a peak having the maximum intensity in the range of 2915 cm -1 ~2920 cm -1 range may be sufficient.

[0040] In one embodiment, the separator may further have a fourth peak shown in the range of 3090 cm -1 ~3100 cm -1 on the FT-IR spectrum. The fourth peak is a peak having the maximum intensity in the above-mentioned range. Specifically, a peak having the maximum intensity in the range of 3095 cm -1 ~3100 cm -1 range may be sufficient.

[0041] In one embodiment, the separator may further have a fifth peak shown in the range of 3270 cm -1 ~3300 cm -1 on the FT-IR spectrum. The fifth peak is a peak having the maximum intensity in the above-mentioned range. Specifically, a peak having the maximum intensity in the range of 3280 cm -1 ~3300 cm -1 range or a peak having the maximum intensity in the range of 3285 cm -1 ~3300 cm -1 range may be sufficient.

[0042] In one embodiment, the FT-IR spectrum of the separator may be measured using an FT-IR equipment equipped with an MCT (mercury cadmium telluride) detector. Specifically, in the range of 4000 cm -1 ~675 cm -1 , it may be scanned 5 to 200 times with a resolution of 4 cm -1 and measured in transmission mode.

[0043] In one embodiment, the inorganic particles are not limited as long as they are inorganic particles used in the technical field. As non-limiting examples, the inorganic particles may include any one or two or more selected from the group consisting of metal hydroxides, metal oxides, metal nitrides, and metal carbides. For example, the inorganic particles may include any one or two or more selected from the group consisting of magnesium oxide (MgO), magnesium hydroxide (Mg(OH)₂), alumina (Al₂O₃), boehmite (γ-AlO(OH)), aluminum hydroxide (Al(OH)₃), silica (SiO₂), silicon carbide (SiC), calcium oxide (CaO), titanium dioxide (TiO₂), strontium titanate (SrTiO₃), zinc oxide (ZnO), yttrium oxide (Y₂O₃), zirconium dioxide (ZrO₂), tin oxide (SnO₂), and cerium oxide (CeO₂). From the perspective of battery stability and the like, the inorganic particles are preferably any one or two or more metal hydroxide particles selected from the group consisting of boehmite, aluminum hydroxide (Al(OH)₃), and magnesium hydroxide (Mg(OH)₂).

[0044] In one embodiment, the form of the inorganic particles is not limited and may be spherical, elliptical, needle-shaped, plate-shaped, plate-like, etc.

[0045] In one embodiment, the inorganic particles may have an average particle size (D50) of 0.01 μm or more, 0.05 μm or more, 0.1 μm or more, 0.65 μm or less, 0.5 μm or less, 0.4 μm or less, 0.3 μm or less, or a value between the above numerical values. For example, the D50 of the inorganic particles may be 0.01 μm to 0.65 μm, 0.01 μm to 0.5 μm, 0.05 μm to 0.4 μm, 0.1 μm to 0.3 μm, or 0.2 μm to 0.3 μm, but this can be changed as long as it does not deviate from the scope of the present disclosure.

[0046] In one embodiment, the inorganic particles may include first inorganic particles having an average particle size (D50) of 0.01 μm to 0.5 μm, and the D50 of the first inorganic particles may be 0.05 μm to 0.4 μm, 0.1 μm to 0.3 μm, or 0.2 μm to 0.3 μm.

[0047] In one embodiment, the inorganic particles may include the first inorganic particles and second inorganic particles having an average particle size (D50) larger than that of the first inorganic particles. Specifically, the inorganic particles may include the first inorganic particles and the second inorganic particles within a range where the average particle size (D50) satisfies the above range. The average particle size (D50) of the second inorganic particles may be 0.4 μm to 1.0 μm, 0.5 μm to 0.9 μm, 0.6 μm to 0.8 μm, or 0.7 μm to 0.8 μm.

[0048] In one embodiment, the second inorganic particles may be included in an amount of 50% by weight or less, 40% by weight or less, 35% by weight or less, 30% by weight or less, 1% by weight or more, 10% by weight or more, or a value between the numerical values, based on the total weight of the first inorganic particles and the second inorganic particles. For example, the content of the second inorganic particles may be 1% by weight to 50% by weight, 1% by weight to 45% by weight, 10% by weight to 40% by weight, or 30% by weight to 40% by weight, based on the total weight of the first inorganic particles and the second inorganic particles. For example, the weight ratio of the first inorganic particles: the second inorganic particles may be 50 to 99:1 to 50. For example, the weight ratio of the first inorganic particles: the second inorganic particles may be 60 to 99:1 to 40, 70 to 99:1 to 30. When the weight ratio within the above range is satisfied, a separator having better heat resistance can be provided.

[0049] The first inorganic particles and the second inorganic particles may be made of the same or different inorganic substances. When the first inorganic particles and the second inorganic particles are each composed of the same inorganic substance, they can be distinguished by different particle size distributions and different D 50 values.

[0050] The separator according to one embodiment can have excellent heat resistance. In one embodiment, after leaving the separator at 150°C for 60 minutes, the measured heat shrinkage rates in the machine direction and the width direction may be 5% or less, 4% or less, 3.5% or less, 3% or less, 2.5% or less, 2% or less, or 1.5% or less. For example, they may be 0.1 - 5% or 0.2 - 3.5%.

[0051] In one embodiment, the thickness of the porous base material is not necessarily limited to this, but can be 5 μm or more, 8 μm or more, 15 μm or less, 12 μm or less, or a value between these numerical values. For example, the average thickness of the porous base material can be 5 μm - 15 μm, 8 μm - 12 μm, or 9 μm - 12 μm. Here, the thickness of the porous base material means the average thickness, and means the average thickness of only the porous base material on which the inorganic particle layer is not provided on at least one surface. In one embodiment, the average thickness of the porous base material may be determined by the following method. After stacking 10 layers of only the porous base material on which the inorganic particle layer is not provided on at least one surface, the thickness is measured at 5 arbitrary points in the width direction (TD) using a thickness measuring instrument manufactured by Mitutoyo, and then divided by 5 to derive the average thickness of the 10 - layer porous base material, and also divided by 10 to derive the average thickness t2 of the porous base material. For example, in the case of obtaining the average thickness of the porous base material on which the inorganic particle layer is provided on at least one surface, the inorganic particle layer can be detached by making full use of all known methods in the technical field without limitation, and after being sufficiently dried, the average thickness of the porous base material from which the inorganic particle layer has been detached may be obtained.

[0052] In one embodiment, the inorganic particle layer may be coated on one or both surfaces of the porous base material. When the inorganic particle layer is coated on both surfaces of the porous base material, the thicknesses of the inorganic particle layers coated on one surface and the other surface may be the same as each other or different.

[0053] In one embodiment, the total thickness t1 of the inorganic particle layer is not necessarily limited thereto, but may be 0.5 μm or more, 1 μm or more, 1.5 μm or more, 9 μm or less, 6 μm or less, or a value between the above numerical values. For example, the total thickness of the inorganic particle layer may be 0.5 μm to 9 μm, 1 μm to 6 μm, 1.5 μm to 6 μm, or 2 μm to 6 μm. Here, the total thickness of the inorganic particle layer may be calculated and derived as a value obtained by subtracting the average thickness of the porous base material from the average thickness of the entire separator. Here, the average thickness of the entire separator means the average thickness of the entire separator including the porous base material and the inorganic particle layer provided on at least one surface of the porous base material. In one embodiment, the average thickness t of the entire separator may be determined by the following method. After stacking 10 separators, the thickness is measured at any 5 points in the TD direction using a thickness measuring instrument manufactured by Mitutoyo, and then divided by 5 to derive the average thickness of the 10 - layer separator, and further divided by 10 to derive the average thickness of the entire single separator. For example, the average thickness of the separator may be 5 μm to 25 μm or 6 μm to 20 μm.

[0054] In one embodiment of the present disclosure, the ratio t1 / t2 of the total thickness t1 of the inorganic particle layer to the thickness t2 of the porous base material may be 0.2 to 0.6. Within the above range, a thermal shrinkage rate of 5% or less, excellent heat resistance, excellent adhesive strength, and low discharge resistance of the battery after 600 cycles may be provided simultaneously.

[0055] In one embodiment, the porous base material may be a polyolefin - based porous base material such as polyethylene, polypropylene, or a copolymer thereof, but is not limited thereto, and all known porous base materials can be used as the porous base material of the separator for a lithium secondary battery. In one embodiment, the porous base material may be manufactured as a film or a sheet, but is not particularly limited.

[0056] In one embodiment, the porosity of the porous base material may be 20% to 60%, 30% to 60%, 40% to 50%, or 40% to 43%, but is not limited thereto.

[0057] In one embodiment, the inorganic particle layer may include a binder and inorganic particles, and may be a porous inorganic particle layer in which the inorganic particles are connected and fixed by the binder to form pores. In one embodiment, the inorganic particle layer is provided on at least one surface of the porous substrate, and may occupy an area fraction of 60% or more, 70% or more, 80% or more, or 90% or more with respect to the entire surface of the porous substrate. Preferably, the inorganic particle layer may be formed on 100% of the area of the porous substrate.

[0058] In one embodiment, the binder may include a polyacrylamide-based resin. The polyacrylamide-based resin may be polyacrylamide or a copolymer containing the same. The copolymer may be a block copolymer or a random copolymer, but the copolymer described in one embodiment of the present disclosure is a polymer obtained by mixing and polymerizing two or more monomers together, and means a random copolymer.

[0059] In one embodiment, the polyacrylamide-based resin may be a copolymer containing units derived from (meth)acrylamide-based monomers and units derived from comonomers. Preferably, the polyacrylamide-based resin may include structural units derived from (meth)acrylamide-based monomers and structural units derived from (meth)acrylic monomers containing a hydroxy group.

[0060] By including the copolymer rather than a homopolymer derived from an acrylamide-based monomer, the separator according to one embodiment can further improve heat resistance and adhesiveness. Further, the lithium secondary battery can have more excellent resistance characteristics and thermal safety by including the separator.

[0061] The unit derived from the (meth)acrylamide-based monomer of the polyacrylamide-based resin can be represented as in the following Chemical Formula 1.

[0062] [Chemical formula]

[0063] In the above Chemical formula 1, R1 may be hydrogen or a C1-C6 alkyl group.

[0064] The unit derived from the (meth)acrylic monomer containing a hydroxy group of the polyacrylamide resin may be represented as in the following Chemical formula 2.

[0065] [Chemical formula]

[0066] In the above Chemical formula 2, R2 is hydrogen or a C1-C6 alkyl group. Further, L1 may be a C1-C6 linear or branched alkylene group.

[0067] In the polyacrylamide resin according to one embodiment, the (meth)acrylamide monomer may be contained in an amount of 65 to 98 mol%, 70 to 97 mol%, or 75 to 95 mol%. The (meth)acrylic monomer containing a hydroxy group may be contained in an amount of 2 to 35 mol%, 3 to 30 mol%, or 5 to 25 mol%. When the polyacrylamide resin is produced within the above content range, sufficient adhesive strength can be obtained, and a more remarkable effect can be obtained in terms of the high-temperature shrinkage rate.

[0068] In one embodiment, the polyacrylamide-based resin may have a polyethylene glycol equivalent weight average molecular weight measured by gel permeation chromatography of 100,000 g / mol or more, 200,000 g / mol or more, 2,000,000 g / mol or less, 1,000,000 g / mol or less, 500,000 g / mol or less, or a value between these numerical values. For example, the polyacrylamide-based resin may have a weight average molecular weight of 100,000 to 2,000,000 g / mol, 200,000 to 1,000,000 g / mol, or 200,000 to 500,000 g / mol. According to one embodiment, when the weight average molecular weight of the polyacrylamide-based resin satisfies the above range, the heat resistance and adhesiveness can be further improved.

[0069] In one embodiment, the content of the binder may be appropriately adjusted according to the situation and purpose within the scope of the present disclosure. For example, the content of the binder may be 0.1 part by weight to 20 parts by weight, 0.1 part by weight to 15 parts by weight, 1 part by weight to 10 parts by weight, or 1 part by weight to 5 parts by weight with respect to 100 parts by weight of the inorganic particles.

[0070] In one embodiment, the binder may further include any one or more additional binders selected from the group consisting of polyvinyl alcohol (PVA), polyvinylidene fluoride (PVDF), carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), polyacrylic acid (PAA), polyethylene glycol (PEG), polyacrylonitrile (PAN), polyvinylpyrrolidone (PVP), and copolymers thereof. The separator according to one embodiment can further improve heat resistance and adhesiveness by using the above-mentioned additional binder together with a polyacrylamide-based resin as a binder.

[0071] In one embodiment, the content of the additional binder may be 0.1 wt% or more, 0.5 wt% or more, 1 wt% or more, 5 wt% or more, 30 wt% or less, 20 wt% or less, 15 wt% or less, or a value between the above numerical values, based on the total content of the binder. For example, the content of the additional binder may be 0.1 - 30 wt%, 0.5 - 30 wt%, 1 - 20 wt%, or 5 - 15 wt%, but is not necessarily limited thereto.

[0072] In one embodiment, the degree of saponification of the additional binder when it is polyvinyl alcohol may be 80 mol% - 95 mol%, or 85 mol% - 90 mol%, but is not particularly limited thereto. The degree of saponification of polyvinyl alcohol (PVA) means the degree of saponification in which the ester groups in the polyester system are converted into alcohol groups. The degree of saponification may be a value measured by a known method such as JIS K6726.

[0073] In one embodiment, the weight average molecular weight of the additional binder may be 10,000 to 100,000 g / mol, or 30,000 to 70,000 g / mol, but is not particularly limited thereto.

[0074] Hereinafter, a method for manufacturing the separator of the present disclosure will be described.

[0075] A method for manufacturing a separator that simultaneously satisfies the above physical properties may include a first step of manufacturing a coating slurry containing a binder and inorganic particles, and a second step of applying the coating slurry to at least one surface of a porous substrate to form an inorganic particle layer.

[0076] The description of each of the above porous substrate, inorganic particle layer, inorganic particles, and binder is as described above, and specific descriptions are omitted.

[0077] In the first step, the method for manufacturing the coating slurry can be applied without limitation to all ordinary methods known in the art. Without particular limitation, by way of non-limiting example, inorganic particles may be dispersed by stirring to produce a slurry, or aggregated inorganic particles may be dispersed using a ball mill.

[0078] The coating slurry contains inorganic particles, a binder, and a solvent. The solvent is not particularly limited, and a solvent that is easy to dissolve or disperse the binder may be selected. For example, any one or more selected from water, ethanol, methanol, lower alcohols such as propanol, dimethylformamide, acetone, tetrahydrofuran, diethyl ether, methylene chloride, DMF, N-methyl-2-pyrrolidone, hexane, and cyclohexane may be used.

[0079] In one embodiment, the solid content of the coating slurry is not particularly limited, but can be, for example, 10% by weight to 50% by weight, 15% by weight to 40% by weight, 20% by weight to 35% by weight, but is not limited thereto.

[0080] In one embodiment, the coating slurry may include 50 to 99.9% by weight of inorganic particles and 0.1 to 50% by weight of a binder based on the total weight of the solid content. Specifically, it may include 60 to 98% by weight of inorganic particles and 2 to 40% by weight of a binder, and more specifically, 80 to 98% by weight of inorganic particles and 2 to 20% by weight of a binder, but is not limited thereto.

[0081] In the second step, as a method of applying the coating slurry, all ordinary methods known in the art can be applied without limitation. By way of non-limiting example, roll coating, spin coating, dip coating, bar coating, die coating, slit coating, inkjet printing, and methods combining these may be applied. The applied slurry may be dried and formed into an inorganic particle layer. The drying may be performed by drying with warm air, hot air, low-humidity air, vacuum drying, irradiation methods such as far-infrared rays or electron beams. The drying temperature is not particularly limited and may be appropriately adjusted according to the experimental environment and purpose. For example, it may be 30°C to 120°C, 30°C to 100°C, or 30°C to 60°C.

[0082] The present disclosure can provide a lithium secondary battery including a separator according to one of the above-described embodiments. By including the separator as described above, the lithium secondary battery can have a reduced electrical resistance, significantly excellent life characteristics, and excellent thermal stability at high temperatures.

[0083] A lithium secondary battery according to one embodiment may include the above-described separator between a positive electrode and a negative electrode. Here, the positive electrode and the negative electrode can be used without limitation as long as they are those normally used in lithium secondary batteries.

[0084] Hereinafter, the components of the secondary battery according to the present disclosure will be further described.

[0085] [Positive Electrode] The positive electrode may include a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector.

[0086] (Positive electrode current collector) The positive electrode current collector may include stainless steel, nickel, aluminum, titanium, or an alloy thereof. The positive electrode current collector may include carbon, nickel, titanium, aluminum surface-treated with silver, or stainless steel. The positive electrode current collector is not limited thereto. For example, the thickness may be 10 μm to 50 μm.

[0087] (Positive electrode material) The positive electrode active material layer may include a positive electrode active material. The positive electrode active material may include a compound capable of reversibly intercalating and deintercalating lithium ions.

[0088] According to an exemplary embodiment, any conventionally used positive electrode active material can be used without limitation. For example, the positive electrode active material may include a lithium-nickel metal oxide. The lithium-nickel metal oxide may further include at least one of cobalt (Co), manganese (Mn), and aluminum (Al).

[0089] The positive electrode active material may further include a coating element or a doping element. For example, an element substantially the same as or similar to the above-described auxiliary element may be used as the coating element or the doping element. For example, one or more of the above-described elements may be used alone or in combination as the coating element or the doping element.

[0090] The positive electrode active material may include a nickel-cobalt-manganese (NCM)-based lithium oxide. In this case, an NCM-based lithium oxide with an increased nickel content may be used.

[0091] Among the NCM-based lithium oxides, the content of Ni (for example, the molar fraction of nickel among the total moles of nickel, cobalt, and manganese) can be 0.6 or more, 0.7 or more, or 0.8 or more. In some embodiments, the content of Ni may be 0.8 to 0.95, 0.82 to 0.95, 0.83 to 0.95, 0.84 to 0.95, 0.85 to 0.95, or 0.88 to 0.95.

[0092] In some embodiments, the positive electrode active material may also include a lithium cobalt oxide-based active material, a lithium manganese oxide-based active material, a lithium nickel oxide-based active material, or a lithium iron phosphate-based (LFP) active material (for example, LiFePO4).

[0093] (Method for manufacturing the positive electrode) For example, the positive electrode active material may be mixed in a solvent to produce a positive electrode slurry. After coating the positive electrode slurry on a positive electrode current collector, it may be dried and rolled to produce a positive electrode active material layer. The coating process may be performed by methods such as gravure coating, slot die coating, simultaneous multilayer die coating, imprinting, doctor blade coating, dip coating, bar coating, casting, etc., and is not limited thereto. The positive electrode active material layer may further include a binder, and optionally, may further include a conductive material, a thickener, etc.

[0094] (Positive electrode solvent) Non-limiting examples of the solvent used for manufacturing the positive electrode slurry include N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, N,N-dimethylaminopropylamine, ethylene oxide, tetrahydrofuran, etc.

[0095] (Positive electrode binder) The binder may include polyvinylidene fluoride (PVDF), polyvinylidene fluoride - co - hexafluoropropylene, polyacrylonitrile, polymethylmethacrylate, acrylonitrile - butadiene rubber (NBR), polybutadiene rubber (BR), styrene - butadiene rubber (SBR), etc. In one embodiment, a PVDF - based binder may be used as the positive electrode binder.

[0096] (Positive electrode conductive material) The conductive material may be added to enhance the conductivity of the positive electrode active material layer and / or the mobility of lithium ions or electrons. For example, the conductive material may include carbon - based conductive materials such as graphite, carbon black, acetylene black, ketjen black, graphene, carbon nanotubes, VGCF (vapor - grown carbon fiber), carbon fiber, etc. and / or metal - based conductive materials including perovskite substances such as tin, tin oxide, titanium oxide, LaSrCoO3, LaSrMnO3, etc., but is not limited thereto.

[0097] (Positive electrode thickener / dispersant) If necessary, the positive electrode slurry may further include a thickener and / or a dispersant, etc. In one embodiment, the positive electrode slurry may include a thickener such as carboxymethyl cellulose (CMC).

[0098] [Negative electrode] The negative electrode may include a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector.

[0099] (Negative electrode current collector) Non-limiting examples of the negative electrode current collector include copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, and a polymer substrate coated with a conductive metal. The negative electrode current collector is not limited thereto, but for example, the thickness may be 10 μm to 50 μm.

[0100] (Negative electrode material) The negative electrode active material layer may include a negative electrode active material. As the negative electrode active material, a material capable of adsorbing and desorbing lithium ions may be used. For example, as the negative electrode active material, carbon-based materials such as crystalline carbon, amorphous carbon, carbon composites, and carbon fibers, lithium metal, lithium alloys, silicon (Si)-containing substances, or tin (Sn)-containing substances may be used.

[0101] Examples of the amorphous carbon include hard carbon, soft carbon, coke, mesocarbon microbeads (MCMB), and mesophase pitch-based carbon fibers (MPCF).

[0102] Examples of the crystalline carbon include graphite-based carbons such as natural graphite, artificial graphite, graphitized coke, graphitized MCMB, and graphitized MPCF.

[0103] Examples of the lithium metal include pure lithium metal or lithium metal with a protective layer formed for suppressing dendrite growth. In one embodiment, a lithium metal-containing layer vapor-deposited or coated on the negative electrode current collector may be used as the negative electrode active material layer. In one embodiment, a thin lithium film layer may be used as the negative electrode active material layer.

[0104] Examples of the elements included in the lithium alloy include aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium, or indium.

[0105] The silicon-containing material may provide even more increased capacity characteristics. The silicon-containing material may include Si, SiO x (0 < x < 2), metal-doped SiO x (0 < x < 2), and may include silicon-carbon composites, etc. The metal may include lithium and / or magnesium, and metal-doped SiO x (0 < x < 2) may include metal silicates.

[0106] (Method for manufacturing the negative electrode) For example, the negative electrode active material may be mixed in a solvent to produce a negative electrode slurry. After coating / vapor-depositing the negative electrode slurry on a negative electrode current collector, it may be dried and rolled to produce a negative electrode active material layer. The coating process may be performed by methods such as gravure coating, slot die coating, simultaneous multilayer die coating, imprinting, doctor blade coating, dip coating, bar coating, casting, etc., and is not limited thereto. The negative electrode active material layer may further include a binder, and optionally, may further include a conductive material, a thickening agent, etc.

[0107] In some embodiments, the negative electrode may include a negative electrode active material layer in the form of lithium metal formed by a vapor deposition / coating process.

[0108] (Negative electrode solvent) Non-limiting examples of solvents that can be used during the production of the negative electrode slurry include water, pure water, deionized water, distilled water, ethanol, isopropanol, methanol, acetone, n-propanol, t-butanol, etc.

[0109] (Negative electrode binder / conductive material / thickening agent) As the binder, conductive material, and thickening agent, the above-mentioned substances that can be used during the production of the positive electrode may be used.

[0110] In some embodiments, as the negative electrode binder, a styrene-butadiene rubber (SBR)-based binder, carboxymethyl cellulose (CMC), a polyacrylic acid-based binder, a poly(3,4-ethylenedioxythiophene) (PEDOT)-based binder, etc. may be used.

[0111] [Electrode assembly] According to an exemplary embodiment, a positive electrode, a negative electrode, and a separator may be repeatedly arranged to form an electrode assembly. In some embodiments, the electrode assembly may be of a winding type, a stacking type, a z-folding type, or a stack-folding type.

[0112] [Electrolyte] The electrode assembly may be housed in a case together with an electrolyte to define a lithium secondary battery. According to an exemplary embodiment, a non-aqueous electrolyte may be used as the electrolyte.

[0113] (Lithium salt / Organic solvent) The non-aqueous electrolyte contains a lithium salt as an electrolyte and an organic solvent. The lithium salt is represented by, for example, Li + X - and the anion (X - ) of the lithium salt includes F - , Cl - , Br - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , PF6 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , CF3SO3 - , CF3CF2SO3- 、(CF3SO2)2N - 、(FSO2)2N - 、CF3CF2(CF3)2CO - 、(CF3SO2)2CH - 、(SF5)3C - 、(CF3SO2)3C - 、CF3(CF2)7SO3 - 、CF3CO2 - 、CH3CO2 - 、SCN - and (CF3CF2SO2)2N - etc. can be mentioned.

[0114] The organic solvent may include an organic compound that has sufficient solubility in the lithium salt and the additive and has no reactivity in the battery. As the organic solvent, for example, it may include at least one of carbonate solvents, ester solvents, ether solvents, ketone solvents, alcohol solvents, and aprotic solvents.As the organic solvent, for example, propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate, diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), methyl propyl carbonate, ethyl propyl carbonate, dipropyl carbonate, vinylene carbonate, methyl acetate (MA), ethyl acetate (EA), n-propyl acetate (n-PA), 1,1-dimethylethyl acetate (DMEA), methyl propionate (MP), ethyl propionate (EP), fluoroethyl acetate (FEA), difluoroethyl acetate (DFEA), trifluoroethyl acetate (TFEA), dibutyl ether, tetraethylene glycol dimethyl ether (TEGDME), diethylene glycol dimethyl ether (DEGDME), dimethoxyethane, tetrahydrofuran (THF) and 2-methyltetrahydrofuran, ethanol, isopropyl alcohol, dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, sulfolane, gamma-butyrolactone, and propylene sulfite may be used. These may be used alone or in combination of two or more.

[0115] (Additive) The non-aqueous electrolyte may further contain an additive. The additive may include, for example, a cyclic carbonate compound, a fluorine-substituted carbonate compound, a sultone compound, a cyclic sulfate compound, a cyclic sulfite compound, a phosphate compound, and a borate compound. The cyclic carbonate compound may include vinylene carbonate (VC), vinyl ethylene carbonate (VEC), and the like. The fluorine-substituted carbonate compound may be a fluorine-substituted cyclic carbonate compound. The fluorine-substituted cyclic carbonate compound may include fluoroethylene carbonate (FEC), and the like. The sultone compound may include 1,3-propane sultone, 1,3-propene sultone, 1,4-butane sultone, and the like. The cyclic sulfate compound may include 1,2-ethylene sulfate, 1,2-propylene sulfate, and the like. The cyclic sulfite compound may include ethylene sulfite, buthylene sulfite, and the like. The phosphate compound may include lithium difluoro bis-oxalato phosphate, lithium difluoro phosphate, and the like. The borate compound may include lithium bis(oxalate)borate, and the like.

[0116] Hereinafter, with reference to specific experimental examples, the embodiments of the present disclosure will be further described. The examples and comparative examples included in the experimental examples are illustrative of the present disclosure and do not limit the scope of the appended claims. It is obvious to those skilled in the art that various changes and modifications to the examples are possible within the scope of the present disclosure and the scope of the technical idea, and it goes without saying that such variations and modifications belong to the scope of the appended claims.

[0117] First, a method for measuring the physical properties of the separator and a method for evaluating the characteristics of the secondary battery will be described.

[0118] [Average particle size of inorganic particles] The average particle size was derived from the results of the particle size distribution analyzed using S3500 manufactured by MICROTRAC after sampling the particles to be measured in accordance with the ISO 13320-1 standard.

[0119] [Molecular weight] The measurement of the weight average molecular weight was performed using GPC (manufactured by Tosoh, EcoSEC HLC-8320 GPC Reflective Index detector). The GPC column was used by connecting TSKgel guard PWxl, two TSKgel GMPWxl, and TSKgel G2500PWxl (7.8×300 mm). The solvent used was 0.1M aqueous NaNO3 solution, and the standard substance used was polyethylene glycol / polyethylene oxide (PEG / PEO). The analysis was performed at 40°C with a flow rate of 1 mL / min.

[0120] 1) GPC (Gel permeation chromatography) sample treatment (1) Sample pretreatment: Use the provided sample as it is (2) Sample dissolution state: Completely dissolved (3) Sample solution filtration: 0.45μm nylon filter

[0121] 2) Conditions of GPC (Gel permeation chromatography) analyzer (1) Analyzer: EcoSEC HLC-8320 GPC manufactured by Tosoh Corporation (2) Detector: RI-detector (3) Developing solvent: 0.1M NaNO3 (4) Column (manufacturer, model no.): Tskgel guard PWxl + 2 x TSKgel GMPWxl + TSKgel G2500PWxl (7.8×300mm) (5) Temperature: 40°C (6) Flow rate: 1.0 mL / min (7) Injection volume: 100 μl, 10 mg / mL (8) Standard substance: PEG / PEO

[0122] [Porosity of the porous substrate] The porosity was calculated from the following mathematical formula after cutting a rectangular sample of A cm × B cm. Both A and B were cut and measured in the range of 5 to 20 cm respectively.

[0123] Porosity of the PE film = {1 - (M ÷ ρ) ÷ (A × B × T)} × 100

[0124] Here, T = thickness of the separator (cm) M = weight of the sample (g) ρ = true density of the PE film (g / cm 3 )

[0125] [Gurley permeability of the porous substrate] The Gurley permeability of the porous substrate was measured in accordance with ASTM D726 standard using a Densometer manufactured by Toyoseiki Co., Ltd. The time taken for 100 cc of air to pass through an area of 1 square inch of the porous substrate was recorded and compared in seconds.

[0126] [Tensile strength] The tensile strength of the porous substrate was measured in accordance with ASTM D882.

[0127] [Measurement of FT-IR Spectrum] The separator was cut into 1 cm × 1 cm size to prepare a measurement sample, and measurement was carried out under the following conditions using an FT-IR equipment (Nicolet iN10 Infrared Microscope manufactured by Thermo Scientific) equipped with an MCT (mercury cadmium telluride) detector. The average value of the main peaks shown in the measured FT-IR spectrum is shown in Table 3 below.

[0128] -resolution: 4 cm -1 -scans: 16 -range: 4000~675 cm -1 -Measurement points per sample: 15 point (10 μm interval) * 15 point (10 μm interval) mapping 3 positions

[0129] [Average Thickness (μm) of Separator and Porous Substrate] After stacking 10 separators, the thickness was measured at 5 arbitrary points in the width direction using a thickness measuring instrument manufactured by Mitutoyo, and the values were added together and then divided by 5 to derive the average thickness of the 10-layer separator, and then divided by 10 to derive the overall average thickness of a single separator.

[0130] The average thickness of the porous substrate was obtained by stacking only 10 porous substrates, measuring the thickness at 5 arbitrary points in the width direction using a thickness measuring instrument manufactured by Mitutoyo, adding the values together and then dividing by 5 to derive the average thickness of the 10-layer porous substrate, and then dividing by 10 to derive the average thickness of the porous substrate. In the case after forming the inorganic particle layer, after peeling off the inorganic particle layer and drying it sufficiently, the average thickness of the porous substrate from which the inorganic particle layer was peeled off was derived by the above method.

[0131] The total thickness of the inorganic particle layer was calculated and derived as the value obtained by subtracting the average thickness of the porous substrate from the overall average thickness of the separator obtained by the above method.

[0132] [Thermal Shrinkage Rate (%)] Cut the separator into a square shape with a side length of 10 cm, and label the transverse direction (TD) and the machine direction (MD). Place the sample in the center, put 5 sheets of paper on top and bottom of the sample, and wrap the four sides of the paper with tape. Leave the sample wrapped in paper in a hot air drying oven at 150 °C for 60 minutes. Then, take out the sample, measure the separator with a camera, and calculate the thermal shrinkage rate in the machine direction (MD) and the thermal shrinkage rate in the transverse direction (TD) using the following formula.

[0133] MD thermal shrinkage rate (%) = (Length of MD before heating - Length of MD after heating) / Length of MD before heating × 100 TD thermal shrinkage rate (%) = (Length of TD before heating - Length of TD after heating) / Length of TD before heating × 100

[0134] [Adhesive strength] Cut the separator into a size of 50 mm in width × 50 mm in length, and arrange it so that the inorganic particle layer is on top. Place a black drawing paper (width 20 mm × length 150 mm × thickness 0.25 mm) with a coefficient of kinetic friction of 0.15 on it, apply a predetermined pressure (200 g / cm 2 ), then forcefully pull out the black drawing paper horizontally and check the degree of the inorganic matter attached to the surface. Depending on the degree of attachment, refer to the following grades (A / B / C / D / E / F) for discrimination.

[0135] A: Nothing comes off B: A small amount of inorganic matter comes off C~F: Both the binder and the inorganic matter come off, and the degree gets worse as it goes to F

[0136] [Resistance characteristics of the battery] Each battery manufactured in the examples and comparative examples was charged at 4.2V CC-CV (Constant current-constant voltage) using a charge / discharge cycle device and then discharged. Specifically, each battery was charged at a constant current of 0.5C rate at 25°C until the voltage reached 4.2V, and then charged at a constant voltage while maintaining 4.2V until the current reached 0.01C. Next, during discharge, the cycle of discharging at a constant current of 0.5C until the voltage reached 3.0V was repeated 600 times. When the state of charge (SOC) at the 600th charge / discharge cycle was 60%, the DC-IR (Direct Current Internal Resistance) during discharge was measured by the J-Pulse method to derive the resistance value.

[0137] Here, based on the resistance value of Example 1, the resistance values of each battery manufactured according to the examples and comparative examples were relatively evaluated.

[0138] <Example 1> Manufacture of separator With respect to the total weight of the solid content, as inorganic particles, 96.5% by weight of boehmite (γ-AlOOH) with an average particle size (D50) of 0.2 μm and as a binder, 3.0% by weight of a polyacrylamide-based resin (Mw = 200,000 g / mol, 90 mol% of acrylamide and 10 mol% of 2-hydroxyethyl methacrylate) and 0.5% by weight of polyvinyl alcohol (saponification degree 85 mol%, Mw: 45,000 g / mol) were added to water, and then stirred to produce a coating slurry with a solid content concentration of 28% by weight.

[0139] As the porous substrate, a polyethylene porous film (A1) with an average thickness of 9 μm was used. The manufactured coating slurry was applied only at 2.9 g / m 2 on both sides of the porous substrate, and then dried to manufacture a separator with an inorganic particle layer formed on both sides of the porous substrate.

[0140] Manufacture of secondary battery As the positive electrode active material, 94% by weight of LiCoO2, 2.5% by weight of polyvinylidene fluoride as the binder, and 3.5% by weight of carbon black as the conductive material were added to NMP (N-methyl-2-pyrrolidone) as the solvent, and stirred to produce a uniform positive electrode slurry. The produced slurry was coated, dried, and crimped onto an aluminum foil with a thickness of 30 μm to produce a positive electrode with a total thickness of 150 μm. As the negative electrode active material, 95% by weight of artificial graphite, 3% by weight of an acrylic latex with a Tg of -52 °C as the binder, and 2% by weight of CMC (carboxymethyl cellulose) as the thickener were added to water as the solvent, and stirred to produce a uniform negative electrode slurry. The produced slurry was coated, dried, and crimped onto a copper foil with a thickness of 20 μm to produce a negative electrode with a total thickness of 150 μm. After assembling a pouch-type battery in a manner of laminating the produced separator between the positive electrode and the negative electrode, in order to fuse the positive electrode, the negative electrode, and the separator to each other, the assembled battery was heat-sealed with a hot press machine at 80 °C and 1 MPa. Then, an electrolyte in which 1 M of lithium hexafluorophosphate (LiPF6) was dissolved was injected into a solution containing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a volume ratio of 3:5:2, and then sealed to produce a secondary battery with a capacity of 2 Ah.

[0141] <Examples 2 to 5> In the production of the separator of Example 1, except that the average particle size of the inorganic particles, the type of the porous substrate, and the coating amount of the coating slurry were changed as shown in Table 1 below, the separator and the secondary battery were produced in the same manner as in Example 1. The first inorganic particle and the second inorganic particle are each boehmite (γ-AlOOH).

[0142] <Example 6> In the production of the separator of Example 1, except that polyvinyl alcohol was not used as a binder and only 3.5% by weight of a polyacrylamide-based resin was used, and a porous substrate pretreated by the following method was used, the separator and the secondary battery were produced in the same manner as in Example 1. The pretreated porous substrate was produced by subjecting both sides of a polyethylene porous film (A1) with an average thickness of 9 μm to corona discharge treatment. Here, the corona discharge treatment was carried out at a power density of 2 W / mm and a speed of 3 to 20 mpm (meter per minute).

[0143] <Example 7> In the production of the separator of Example 1, except that polyacrylamide with a weight average molecular weight of 200,000 g / mol was used instead of the polyacrylamide-based resin used, the separator and the secondary battery were produced in the same manner as in Example 1.

[0144] <Comparative Examples 1 to 4> In the production of the separator of Example 1, except that the average particle size of the inorganic particles, the type of the porous substrate, and the coating amount of the coating slurry were changed as shown in Table 1 below, the separator and the secondary battery were produced in the same manner as in Example 1. The first inorganic particle and the second inorganic particle are each boehmite (γ-AlOOH).

[0145]

Table 1

[0146] The physical properties of the separators produced in the above Examples and Comparative Examples and the resistance characteristics of the secondary batteries were measured and shown in Table 2 below. Also, the results of FT-IR spectrum measurement of the separators produced in the above Examples and Comparative Examples are shown in Table 3 below.

[0147]

Table 2

[0148] [Table 3]

[0149] As can be seen from Table 2 and Table 3 above, the ratio of the total thickness of the inorganic particle layer to the thickness of the porous substrate is 0.2 to 0.6, and in the FT-IR spectrum, the separator of the example having a peak shown in the range of 1070 to 1082 cm -1 had a heat shrinkage rate of 5% or less, excellent heat resistance, no peeling in the adhesion test, and excellent adhesion. Also, the discharge resistance of the battery to which this was applied after 600 cycles was 5% or less lower than the value of Example 1 which was the reference.

[0150] On the other hand, since the separator of Comparative Example 1 did not have a peak shown in the range of 1070 to 1082 cm in the FT-IR spectrum, its heat resistance was significantly reduced, and the discharge resistance of the battery to which this was applied after 600 cycles was significantly higher than that of the example. -1

[0151] The separators of Comparative Example 2 and Comparative Example 3 had a peak shown in the range of 1070 to 1082 cm in the FT-IR spectrum, but since they did not satisfy the ratio of the total thickness of the inorganic particle layer to the thickness of the porous substrate, their heat resistance was significantly reduced, and the discharge resistance of the battery to which this was applied after 600 cycles was significantly higher than that of the example. -1

[0152] The separator of Comparative Example 4 could not have a peak shown in the range of 1070 to 1082 cm in the FT-IR spectrum, and since it did not satisfy the ratio of the total thickness of the inorganic particle layer to the thickness of the porous substrate, its heat resistance was significantly reduced, and the discharge resistance of the battery to which this was applied after 600 cycles was significantly higher than that of the example. -1

[0153] ​​​The content described above is merely an exemplification of applying the principles of the present disclosure, and other configurations can be further included without departing from the scope of the present disclosure.

Claims

1. A porous substrate; an inorganic particle layer containing a binder and inorganic particles on at least one surface of the porous substrate; the ratio of the total thickness of the inorganic particle layer to the thickness of the porous substrate is 0.2 to 0.6; In the Fourier transform infrared spectroscopy (FT-IR) spectrum, －１ ~1082cm －１ having a peak in the range A separator having a thermal shrinkage rate of 5% or less in both the machine direction and the width direction measured after being left at 150° C. for 60 minutes.

2. The separator according to claim 1 , wherein the inorganic particles include at least one selected from the group consisting of metal hydroxides, metal oxides, metal nitrides, and metal carbides.

3. The separator according to claim 1, wherein the inorganic particles have an average particle size (D50) of 0.01 μm to 0.65 μm.

4. The separator according to claim 1, wherein the inorganic particles include first inorganic particles having an average particle size (D50) of 0.01 μm to 0.5 μm.

5. The separator according to claim 4 , wherein the inorganic particles further include second inorganic particles having an average particle size (D50) larger than that of the first inorganic particles.

6. The separator according to claim 5 , wherein the second inorganic particles are contained in an amount of 50% by weight or less based on the total weight of the first inorganic particles and the second inorganic particles.

7. 2. The separator according to claim 1, wherein the heat shrinkage in the machine direction and the cross direction is 3% or less.

8. The separator according to claim 1, wherein the porous substrate has a thickness of 5 μm to 15 μm.

9. The separator according to claim 1 , wherein the binder comprises a polyacrylamide resin.

10. The separator according to claim 9 , wherein the polyacrylamide resin is a copolymer containing a unit derived from a (meth)acrylamide monomer and a unit derived from a comonomer.

11. The separator according to claim 10 , wherein the polyacrylamide resin contains a structural unit derived from a (meth)acrylamide monomer and a structural unit derived from a (meth)acrylic monomer containing a hydroxy group.

12. The separator according to claim 9, wherein the polyacrylamide resin has a weight average molecular weight of 100,000 g / mol to 2,000,000 g / mol.

13. 2. The separator according to claim 1, wherein the binder is contained in an amount of 0.1 to 20 parts by weight based on 100 parts by weight of the inorganic particles.

14. 10. The separator according to claim 9, wherein the binder further comprises one or more additional binders selected from the group consisting of polyvinyl alcohol, polyvinylidene fluoride, carboxymethyl cellulose, styrene butadiene rubber, polyacrylic acid, polyethylene glycol, polyacrylonitrile, polyvinylpyrrolidone, and copolymers thereof.

15. The separator according to claim 14, wherein the content of the additional binder is 0.1% by weight to 30% by weight based on the total content of the binder.

16. A lithium secondary battery comprising the separator according to any one of claims 1 to 15.

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