Separator and lithium secondary battery containing the same

Abstract

To provide a separator with excellent voltage resistance, heat resistance, adhesion, and permeability. [Solution] The separator comprises a porous substrate and an inorganic particle layer formed on at least one surface of the porous substrate, containing a binder and inorganic particles, wherein the ratio of the dielectric breakdown voltage (kV) of the separator to the overall average thickness (μm) of the separator is 0.15kV / μm or more, and the spectrum obtained by Fourier transform infrared spectroscopy (FT-IR) is 1070 cm⁻¹. -1 ~1082cm -1 A separator is provided which has a peak shown in the range, and after being left at 150°C for 60 minutes, the measured thermal shrinkage in the mechanical and width directions is 5% or less, and the ΔGurley transmittance is 100 sec / 100 cc or less.

Description

[Technical Field]

[0001] This disclosure relates to a separator having remarkably excellent voltage withstand characteristics and a lithium secondary battery including the same. [Background technology]

[0002] In electrochemical devices, separators are crucial for improving battery stability and performance (lifespan, capacity, etc.). The main function of a separator is to provide ion movement pathways within the battery and prevent physical contact between the negative and positive electrodes. Improving the properties of the separator allows for the manufacture of batteries with superior performance.

[0003] While research is being conducted to reduce the thickness of separators for secondary batteries in order to achieve high capacitance / high power characteristics of electrochemical elements, a major problem has emerged as this trend towards thinner separators is that the dielectric breakdown voltage of the separator decreases, and the withstand voltage characteristics deteriorate.

[0004] The breakdown voltage (BDV) refers to the voltage at which, when a voltage is applied to an insulator, corona discharge occurs through the insulator, causing that portion to become conductive and lose its insulating properties. A higher breakdown voltage indicates superior dielectric strength. The breakdown voltage is highly dependent on the thickness of the insulator; as the separator thickness decreases, the breakdown voltage of the electrochemical element decreases, potentially leading to reduced battery stability and an increased low-voltage failure rate. Therefore, there is a need for a separator that is thin, has a high breakdown voltage, and simultaneously possesses high capacity / high output characteristics, high stability, and a low low-voltage failure rate for batteries. [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] According to one aspect of this disclosure, a separator with excellent voltage resistance, heat resistance, adhesion, and permeability can be provided.

[0006] According to other aspects of this disclosure, the inclusion of the separator makes it possible to provide a lithium secondary battery having high capacity / high output characteristics, high stability, and a low low voltage failure rate.

[0007] The separators disclosed herein are widely applicable in green technology fields such as electric vehicles, battery charging stations, and other battery-powered solar and wind power generation. Furthermore, the separators disclosed herein can be used in eco-friendly electric vehicles, hybrid vehicles, and other vehicles that reduce air pollution and greenhouse gas emissions and prevent climate change. [Means for solving the problem]

[0008] The separator according to this disclosure comprises a porous substrate and an inorganic particle layer formed on at least one surface of the porous substrate, comprising a binder and inorganic particles, wherein the ratio of the dielectric breakdown voltage (kV) of the separator to the overall average thickness (μm) of the separator is 0.15kV / μm or greater, and the spectrum obtained by Fourier transform infrared spectroscopy (FT-IR) is 1070 cm⁻¹. -1 ~1082cm -1 The sample exhibits a peak within the specified range, and after being left at 150°C for 60 minutes, the measured thermal shrinkage in the mechanical and width directions is 5% or less, and the ΔGurley transmittance calculated using the following formula 1 is 100 sec / 100 cc or less. [Formula 1] ΔGurley transmittance (sec / 100cc)=P m -P s In the above calculation formula 1, P m This is the gas permeability of the separator, and P s This is the gas permeability of the porous substrate.

[0009] In one embodiment, the inorganic particles may include one or more selected from the group consisting of metal hydroxides, metal oxides, metal nitrides, and metal carbides.

[0010] In one embodiment, the inorganic particles may have an average particle size (D50) of 0.01 μm to 0.65 μm.

[0011] 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.

[0012] In one embodiment, the inorganic particles may further include second inorganic particles having an average particle size (D50) greater than that of the first inorganic particles.

[0013] In one embodiment, the second inorganic particles may be present in an amount of 50% by weight or less relative to the total weight of the first and second inorganic particles.

[0014] In one embodiment, the binder may include a particulate binder and a water-soluble binder.

[0015] In one embodiment, the particle-type binder may have a glass transition temperature of -60°C to 0°C.

[0016] In one embodiment, the water-soluble binder may have a glass transition temperature of 180°C to 220°C.

[0017] In one embodiment, the particulate binder and the water-soluble binder may each independently include one or more polymers selected from the group consisting of ester polymers, amide polymers, imide polymers, acrylic polymers, acrylamide polymers, vinyl alcohol polymers, fluorine polymers, and vinylpyrrolidone polymers.

[0018] In one embodiment, the binder may be present in an amount of 0.1 to 20 parts by weight per 100 parts by weight of inorganic particles.

[0019] In one embodiment, the weight ratio of the water-soluble binder to the particle-type binder may be 1:1 to 1:10.

[0020] In one embodiment, the packing density of the inorganic particle layer is 1.2 g / m³ 2 It may be 0 μm or larger.

[0021] Furthermore, this disclosure provides a lithium secondary battery including the separator described above. [Effects of the Invention]

[0022] The separator according to this disclosure can have excellent voltage resistance, heat resistance, adhesiveness, and permeability.

[0023] Furthermore, by including a separator according to one embodiment, this disclosure can provide a lithium secondary battery having high capacity / high output characteristics, high stability, and a low low voltage failure rate. [Modes for carrying out the invention]

[0024] The present disclosure will be described in detail below. However, the embodiments described herein may be modified into various different forms, and the technology of one embodiment is not limited to the embodiments described below. Furthermore, an embodiment of one embodiment is provided to further fully explain the present disclosure to a person of average skill in the art.

[0025] Furthermore, the singular form used in the specification and the attached claims may also include plural forms unless otherwise specified in the context.

[0026] Furthermore, the numerical ranges used herein include lower and upper limits, all values ​​within that range, increments logically derived from the form and width of the defined range, all limited values ​​among them, and all possible combinations of upper and lower limits of numerical ranges limited to different forms. Unless otherwise defined herein, values ​​outside the numerical range that may occur due to experimental error or rounding of values ​​are also included in the defined numerical range.

[0027] Furthermore, throughout the specification, "including" a component means, unless otherwise stated, that it may include other components rather than excluding them.

[0028] In this specification, unless otherwise defined, the average particle size of inorganic particles and particulate binders refers to the D50 value. D50 refers to the particle size of inorganic particles and particulate binders corresponding to 50% of the cumulative fraction by volume. The average particle size can be derived from the particle size distribution results obtained by sampling the inorganic particles and particulate binders to be measured in accordance with ISO 13320-1 and analyzing them using a MICROTRAC S3500.

[0029] In this specification, "MD (machine direction)" means the longitudinal direction in porous substrates and separators manufactured in a longitudinal shape, and "TD (transverse direction)" means the direction perpendicular to the MD in the planar direction of the porous substrate and separator. In this disclosure, TD may also be referred to as the "transverse direction".

[0030] In this specification, the overall average thickness of the separator means the overall average thickness of a separator including a porous substrate and an inorganic particle layer provided on at least one surface of the porous substrate. In one embodiment, the overall average thickness (μm) of the separator can be determined by the following method. After stacking 10 separators, the thickness is measured at 5 arbitrary points in the TD direction using a thickness measuring instrument manufactured by Mitutoyo. Then, divide by 5 to derive the average thickness of the 10 - layer separator, and further divide by 10 to derive the overall average thickness of a single separator.

[0031] In this specification, the average thickness of the porous substrate means the average thickness of only the porous substrate on which the inorganic particle layer is not provided on at least one surface. In one embodiment, the average thickness (μm) of the porous substrate can be determined by the following method. After stacking only the porous substrates on which the inorganic particle layer is not provided on at least one surface 10 - fold, the thickness is measured at 5 arbitrary points in the TD direction using a thickness measuring instrument manufactured by Mitutoyo. Then, divide by 5 to derive the average thickness of the 10 - layer porous substrate, and further divide by 10 to derive the average thickness of the porous substrate. For example, when determining the average thickness of a porous substrate on which an inorganic particle layer is provided on at least one surface, the inorganic particle layer is detached using any method known in the art without limitation, dried sufficiently, and then the average thickness of the porous substrate from which the inorganic particle layer has been detached is determined.

[0032] In this specification, the packing density (g / (m 2 .μm)) of the inorganic particle layer means the weight of the inorganic particle layer loaded per unit area (m 2 ) and per unit height (μm) of the porous substrate. In one embodiment, the method for measuring the packing density of the inorganic particle layer can be by the following method. According to the above - mentioned method, after measuring the average thickness of the porous substrate and the overall average thickness of the separator on which the inorganic particle layer is provided on the porous substrate respectively, subtract the average thickness of the porous substrate from the overall average thickness of the separator to calculate the thickness T (μm) of the inorganic particle layer. For the separator in which the inorganic particle layer is provided on at least one surface of the porous substrate, a 10 mm×10 mm (0.01 m 2Area S(m²) 2 After cutting the material and measuring its weight, the weight of the porous substrate is subtracted to calculate the weight W (g) of the inorganic particle layer alone. The packing density of the inorganic particle layer is calculated as W / (T*S).

[0033] In this specification, the glass transition temperature (Tg) refers to the temperature range in which the glass transition occurs, and means a value measured using a dilatometer or differential scanning calorimeter (DSC).

[0034] In this specification, when a part such as a layer, film, region, or plate is said to be "on top of" or "on" another part, this includes not only the case where it is "immediately on top of" the other part, but also the case where there are other parts in between.

[0035] The terms "first," "second," etc., used herein may be used to describe various components, but the components should not be limited by the terms. The terms are used solely for the purpose of distinguishing one component from another.

[0036] This disclosure provides a separator capable of providing a battery with high voltage withstand characteristics, heat resistance, adhesion, and permeability, as well as high capacity / high power characteristics, high stability, and a low low voltage failure rate. Specifically, a separator according to one embodiment includes a porous substrate and an inorganic particle layer containing a binder and inorganic particles on at least one surface of the porous substrate, wherein the ratio of the dielectric breakdown voltage BDV (kV) of the separator to the overall average thickness t (μm) of the separator (hereinafter, BDV / t) is 0.15kV / μm or more, and the spectrum obtained by Fourier transform infrared spectroscopy (FT-IR) is 1070 cm⁻¹. -1 ~1082cm -1The peak shown within the range (hereinafter referred to as the first peak) indicates that, after being left at 150°C for 60 minutes, the measured thermal shrinkage rate in the mechanical direction and width direction is 5% or less, and the ΔGurley transmittance calculated by the following formula 1 is 100 sec / 100 cc or less.

[0037] [Formula 1] ΔGurley transmittance (sec / 100cc)=P m -P s

[0038] In the above calculation formula 1, P m This is the gas permeability of the separator, and P s This is the gas permeability of the porous substrate.

[0039] In one embodiment, the separator satisfies the following conditions: the ratio of the dielectric breakdown voltage (kV) of the separator to the overall average thickness (μm) of the separator is 0.15kV / μm or higher, 0.16kV / μm or higher, and 0.163kV / μm or higher, and the peak shown in the FT-IR spectrum is 1070 cm⁻¹. -1 ~1082cm -1 It was first recognized and invented that by satisfying the above conditions and having the thermal shrinkage rate and ΔGurley permeability within the aforementioned range, it is possible to simultaneously possess remarkably excellent dielectric strength, heat resistance, adhesion, and permeability even at thin thicknesses.

[0040] Furthermore, a lithium secondary battery according to one embodiment can have high capacity / high power characteristics, high stability, and a low low-voltage failure rate by including a separator that simultaneously satisfies a first peak in a specific range shown in the FT-IR spectrum, a specific range of BDV / t, thermal shrinkage coefficient, and ΔGurley transmittance value. In particular, a lithium secondary battery according to one embodiment can have improved power characteristics by including a separator with significantly improved voltage withstand characteristics at a thin thickness, resulting in not only a low discharge resistance measured initially, but also a significantly lower increase in discharge resistance after 300 cycles compared to the initial discharge resistance.

[0041] The aforementioned effect is due to the adjustment of the ratio of the dielectric breakdown voltage (kV) of the separator to the overall average thickness (μm) of the separator, the peaks shown in the FT-IR spectrum, the thermal shrinkage rate, and the ΔGurley transmittance to specific ranges, and is not an effect that is solely influenced by the components of the separator or a specific element in the separator manufacturing process. As confirmed in one embodiment, this can be achieved by various means involving various factors such as the average particle size of the inorganic particles, the combination of inorganic particles, the weight ratio of two or more types of inorganic particles, and the type and properties of the binder. The means are not particularly limited as long as this can be achieved. For example, the first peak may originate from the binding energy between the constituent factors of the inorganic particles contained in the inorganic particle layer, and the range of the first peak may not be determined solely by the properties of the inorganic particles themselves, such as the average particle size and material, but may also be determined by various factors other than the inorganic particles, such as the properties of the binder and the porous substrate.

[0042] In one embodiment, the dielectric breakdown voltage (BDV, kV) of the separator is measured in accordance with ASTM D 3755, and is the voltage (kV) when the leakage current value is 5 mA, measured under the condition that the separator is placed between the electrodes of a dielectric strength tester (Croma, model 19052) in a dry room (dew point temperature: -60°C) and the applied voltage is increased at 5 kV / 10 sec. This voltage is evaluated as the dielectric breakdown voltage (BDV).

[0043] In one embodiment, the BDV / t may be 0.15kV / μm or more, 0.155kV / μm or more, and its upper limit is not particularly limited, but for example, it may be 0.3kV / μm or less, 0.25kV / μm or less, or 0.2kV / μm or less. In a specific embodiment, the value of formula (1) may be 0.15~0.3kV / μm, 0.15~0.25kV / μm, 0.155~0.2kV / μm, or 0.156~0.164kV / μm, but is not limited thereto.

[0044] In one embodiment, the first peak is 1070 cm. -1 ~1082cm-1 This is the peak with the highest intensity within the range, specifically at 1071 cm. -1 ~1082cm -1 Range: 1072cm -1 ~1082cm -1 Range: 1075cm -1 ~1082cm -1 or 1075cm -1 ~1081cm -1 It may also be the peak with the maximum intensity within the range.

[0045] In one embodiment, the separator is located at 1140 cm⁻¹ on the FT-IR spectrum. -1 ~1160cm -1 It may further have a second peak indicated within the range of 1145 cm². The second peak is the peak having the maximum intensity within the range described above, specifically 1145 cm². -1 ~1155cm -1 It may also be the peak with the maximum intensity within the range.

[0046] In one embodiment, the separator is located at 2910 cm⁻¹ on the FT-IR spectrum. -1 ~2930cm -1 It may further have a third peak indicated within the range of 2915 cm². The third peak is the peak having the maximum intensity within the range described above, specifically 2915 cm². -1 ~2925cm -1 Range or 2915cm -1 ~2920cm -1 It may also be the peak with the maximum intensity within the range.

[0047] In one embodiment, the separator is located at 3090 cm⁻¹ on the FT-IR spectrum. -1 ~3110cm -1 It may further have a fourth peak indicated within the range of 3095 cm². The fourth peak is the peak having the maximum intensity within the range described above, specifically 3095 cm². -1 ~3105cm -1 It may also be the peak with the maximum intensity within the range.

[0048] In one embodiment, the separator is located at 3280 cm⁻¹ on the FT-IR spectrum. -1 ~3320cm -1 It may further have a fifth peak indicated within the range of 3280 cm². The fifth peak is the peak having the maximum intensity within the range described above, specifically 3280 cm². -1 ~3310cm -1 Range or 3285cm -1 ~3300cm -1 It may also be the peak with the maximum intensity within the range.

[0049] In one embodiment, the FT-IR spectrum of the separator may be measured using an FT-IR setup equipped with an MCT (mercury cadmium telluride) detector, specifically at 4000 cm⁻¹. -1 ~675cm -1 Within the range of 4cm -1 You may also perform 5 to 200 scans at a resolution and measure in transmission mode.

[0050] A 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 thermal shrinkage rates in the mechanical direction and width direction may be 5% or less, preferably 4% or less, and more preferably 3.7% or less, 3.5% or less, 3.3% or less, 2% or less, 1.6% or less, 1.3% or less, 1.0% or less, 0.8% or less, or 0.6% or less. For example, they may be 0.5 to 3.5% or 0.5 to 2.0%.

[0051] A separator according to one embodiment can have excellent gas permeability. In one embodiment, the separator may have a ΔGurley permeability of 100 sec / 100 cc or less, calculated by the following formula 1, in the Gurley permeability measured in accordance with ASTM D726. Alternatively, the separator may have a ΔGurley permeability of 80 sec / 100 cc or less, 50 sec / 100 cc or less, 40 sec / 100 cc or less, or 35 sec / 100 cc or less, and the lower limit is not particularly limited, but as an example, it may be 5 sec / 100 cc or more, or 10 sec / 100 cc or more. In one specific embodiment, the ΔGurley transmittance of the separator may be 5-100 sec / 100 cc, 5-80 sec / 100 cc, 5-50 sec / 100 cc, 5-40 sec / 100 cc, 10-35 sec / 100 cc, or 25-35 sec / 100 cc.

[0052] [Formula 1] ΔGurley transmittance (sec / 100cc)=P m -P s

[0053] In the above calculation formula 1, P m This is the gas permeability of the separator, and P s This is the gas permeability of the porous substrate.

[0054] In one embodiment, the inorganic particles are not limited to any inorganic particles used in the art. As a non-limiting example, the inorganic particles may include one or more selected from the group consisting of metal hydroxides, metal oxides, metal nitrides, and metal carbides. For example, the inorganic particles may include one 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 oxide (ZrO2), tin oxide (SnO2), and cerium oxide (CeO2). From the viewpoint of battery stability and other factors, the inorganic particles may preferably be one or more metal hydroxide particles selected from the group consisting of boehmite, aluminum hydroxide (Al(OH)3), and magnesium hydroxide (Mg(OH)2).

[0055] In one embodiment, the morphology of the inorganic particles is not limited and may be spherical, elliptical, needle-shaped, plate-shaped, or plate-like in shape.

[0056] 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 numbers. 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, or 0.1 μm to 0.3 μm, and this is modifiable as long as it does not deviate from the scope of the present disclosure.

[0057] 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 0.35 μm, or 0.1 μm to 0.3 μm.

[0058] In one embodiment, the inorganic particles may include the first inorganic particles and second inorganic particles having an average particle size (D50) greater 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-mentioned 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.

[0059] In one embodiment, the second inorganic particles may be present 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, 20% by weight or more, or any value between the above numbers, relative to the total weight of the first and second inorganic particles. For example, the content of the second inorganic particles may be 1% to 50% by weight, 1% to 40% by weight, 5% to 40% by weight, 10% to 40% by weight, 20% to 40% by weight, or 20% to 30% by weight, relative to the total weight of the first and second inorganic particles.

[0060] According to another embodiment, the inorganic particles may include only first inorganic particles having an average particle size (D50) within the range described above.

[0061] That is, the inorganic particles may include 50 to 100% by weight of first inorganic particles having an average particle size (D50) within the above range and 0 to 50% by weight of second inorganic particles having an average particle size (D50) within the above range, relative to the total weight of the inorganic particles. Alternatively, the inorganic particles may include 65 to 100% by weight of the first inorganic particles and 0 to 35% by weight of the second inorganic particles, or 70 to 100% by weight of the first inorganic particles and 0 to 30% by weight of the second inorganic particles. When the composition ratio within the above range is satisfied, a separator with superior physical properties can be provided.

[0062] The first inorganic particles and the second inorganic particles may be composed of the same or different inorganic materials. If the first inorganic particles and the second inorganic particles are composed of the same inorganic material, they may have different particle size distributions and different D 50 They can be distinguished by their values.

[0063] The size of inorganic particles, or if first and second inorganic particles are used, these inorganic particles each have different sizes, and their respective particle size distributions and the resulting D 50 This can be defined by the value of . The different sizes of the first and second inorganic particles can be obtained by using first and second inorganic particles with separated size characteristics from the beginning when preparing the inorganic particle layer.

[0064] In one embodiment, the binder may include a particulate binder and a water-soluble binder. When a particulate binder and a water-soluble binder are used as the binder, better dielectric strength, heat resistance, adhesion, and permeability of the separator can be achieved.

[0065] In one embodiment, the specific shape of the particles in the particle binder is not particularly limited. For example, the particle binder may have spherical, elliptical, plate-like, or irregular particle shapes.

[0066] In one embodiment, the particle-type binder may have an average particle size (D50) of 10 nm or more, 100 nm or more, 150 nm or more, 1000 nm or less, 500 nm or less, 400 nm or less, or a value between the above values. In one embodiment, the particle-type binder may have an average particle size (D50) of 10 nm to 1000 nm, 100 nm to 500 nm, 150 nm to 400 nm, or 250 nm to 400 nm. When the average particle size is as described above, the binder can be uniformly dispersed together with the water-soluble binder in the aqueous slurry composition, enabling the separation of excellent voltage resistance, heat resistance, adhesion, and permeability.

[0067] In one embodiment, the particulate binder may have a glass transition temperature of -60°C to 0°C, -50°C to -10°C, -50°C to -20°C, or -45°C to -20°C. By including a particulate binder having a glass transition temperature within the above range, the separator according to one embodiment can simultaneously achieve excellent voltage resistance, heat resistance, adhesion, and permeability.

[0068] In one embodiment, the water-soluble binder may have a glass transition temperature of 180°C to 220°C, 190°C to 210°C, or 200°C to 210°C. By including water-soluble binders having glass transition temperatures in the respective ranges described above and the aforementioned particulate binders, the separator according to one embodiment can simultaneously achieve excellent voltage resistance, heat resistance, adhesion, and permeability. Furthermore, a battery to which such a separator is applied can have improved high capacity / high output characteristics, high stability, and a low low-voltage failure rate.

[0069] In one embodiment, the water-soluble binder may have a polyethylene glycol weight-average molecular weight measured using gel permeation chromatography of 10,000 g / mol or more, 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 the above numbers. In one embodiment, the water-soluble binder may have a weight-average molecular weight of 10,000 to 2,000,000 g / mol, 100,000 to 2,000,000 g / mol, 200,000 to 1,000,000 g / mol, or 200,000 to 500,000 g / mol.

[0070] In one embodiment, the binder may include particulate binders and water-soluble binders, and a person of the ordinary skill in the art disclosed herein may appropriately select known binders according to the purpose and circumstances. That is, it is not limited as long as the inorganic particles formed on the surface of the porous substrate layer of the secondary battery separator are used as a binder for the inorganic particle layer in which pores are formed by the binder linking the inorganic particles together.

[0071] In one embodiment, the particulate binder and the water-soluble binder may include polymers, for example, each independently containing one or more selected from the group consisting of ester polymers, amide polymers, imide polymers, acrylic polymers, acrylamide polymers, vinyl alcohol polymers, fluorine polymers, and vinylpyrrolidone polymers. In one embodiment, the particulate binder may include an acrylic polymer, and the water-soluble binder may include an acrylamide polymer.

[0072] In one embodiment, the content of the total binder, including the particulate binder and the water-soluble binder, may be adjusted as appropriate within the scope of this disclosure, depending on the circumstances and purpose. For example, the binder content may be 0.1 to 20 parts by weight, 0.1 to 15 parts by weight, 1 to 10 parts by weight, or 2 to 8 parts by weight per 100 parts by weight of inorganic particles.

[0073] In one embodiment, the weight ratio of the water-soluble binder to the particle-type binder may be 1:1 to 1:10, 1:1 to 1:8, 1:3 to 1:7, or 1:4 to 1:6, but is not necessarily limited thereto.

[0074] In one embodiment, the packing density of the inorganic particle layer is 1.2 g / (m³). 2 .μm) or more, 1.3g / (m 2 .μm) or more, 2.5g / (m 2 .μm) or less, 2.0g / (m 2 .μm) or less, 1.8g / (m 2 The value may be less than or equal to .μm or between the above values, specifically 1.2 to 2.5 g / (m 2 .μm), 1.2~2.0g / (m 2 .μm) 1.2~1.8g / (m 2 .μm), 1.3~1.8g / (m 2 .μm), 1.2~1.5g / (m 2 .μm) or 1.2~1.4g / (m 2 It may also be (.μm), but is not limited to this.

[0075] In one embodiment, the inorganic particle layer may include a binder and inorganic particles, or it may be a porous inorganic particle layer in which inorganic particles are linked 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 of the entire surface of the porous substrate, preferably the inorganic particle layer is formed over 100% of the area of ​​the porous substrate.

[0076] In one embodiment, the inorganic particle layer may be coated on one or both sides of the porous substrate, and when the inorganic particle layer is coated on both sides of the porous substrate, the thickness of the inorganic particle layer coated on one side other than the other may be the same or different.

[0077] In one embodiment, a separator can simultaneously achieve excellent voltage resistance, heat resistance, adhesion, and permeability even when a thin inorganic particle layer is provided on at least one, preferably both, surfaces of a porous substrate. In one embodiment, the total thickness of the inorganic particle layer is not necessarily limited to this, 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 numbers. For example, the total thickness of the inorganic particle layer may be 0.5 μm to 9 μm, 1 μm to 6 μm, or 1.5 μm to 6 μm.

[0078] In one embodiment, the porous substrate may be a polyolefin-based porous substrate such as polyethylene, polypropylene, or a copolymer thereof, but is not limited thereto, and any porous substrate known as a porous substrate for lithium secondary battery separators may be used. In one embodiment, the porous substrate may be manufactured as a film or a sheet, but is not particularly limited.

[0079] In one embodiment, the porous substrate may have a porosity of 20-60% or 30-60%, but is not limited thereto.

[0080] In one embodiment, the porous substrate may have a Gurley transmittance of 10 sec / 100cc or more, 25 sec / 100cc or more, 500 sec / 100cc or less, 200 sec / 100cc or less, 150 sec / 100cc or less, or a value between the above numbers, and may be 10 to 500 sec / 100cc, 25 to 200 sec / 100cc, or 25 to 150 sec / 100cc, but is not limited thereto.

[0081] In one embodiment, the thickness of the porous substrate may be 1 μm or more, 3 μm or more, 5 μm or more, 100 μm or less, 50 μm or less, 30 μm or less, 20 μm or less, 15 μm or less, or a value between the above numbers, specifically 1 to 100 μm, 3 to 50 μm, 5 to 20 μm, or 5 to 15 μm for the realization of a high-capacity battery. Although not limited to these, the porous substrate may be manufactured by stretching.

[0082] The method for manufacturing the separator described herein will be explained below.

[0083] A method for manufacturing a separator that simultaneously satisfies the above-mentioned physical properties may include the steps of preparing a coating slurry containing a binder and inorganic particles, and applying the coating slurry to at least one surface of a porous substrate to form an inorganic particle layer.

[0084] Since the descriptions of each of the porous substrates, inorganic particle layers, inorganic particles, and binders are as described above, a detailed explanation will be omitted.

[0085] The method for preparing the coating slurry can be any of the common methods known in the art without limitation, and is not particularly limited. For example, the slurry may be produced by stirring to disperse the inorganic particles, or by using a ball mill to disperse the aggregated inorganic particles.

[0086] The coating slurry comprises inorganic particles, a binder, and a solvent, the solvent being not particularly limited, and a solvent that readily dissolves or disperses the binder may be selected. For example, one or more selected from water, lower alcohols such as ethanol, methanol, and propanol, dimethylformamide, acetone, tetrahydrofuran, diethyl ether, methylene chloride, DMF, N-methyl-2-pyrrolidone, hexane, and cyclohexane may be used.

[0087] In one embodiment, the solid content of the coating slurry is not particularly limited, but may be, for example, 10% to 50% by weight, 15% to 40% by weight, or 20% to 35% by weight.

[0088] In one embodiment, any conventional method known in the art can be applied to the porous substrate without limitation, and non-limiting examples include roll coating, spin coating, dip coating, bar coating, die coating, slit coating, inkjet printing, and combinations thereof. The applied slurry can be dried to form an inorganic particle layer. The drying may be performed by drying with hot air, hot air, low humidity air, vacuum drying, or irradiation by far-infrared rays or electron beams. The drying temperature is not particularly limited and may be adjusted as appropriate depending on 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.

[0089] This disclosure provides a lithium secondary battery including a separator according to one embodiment of the embodiments described above. By including such a separator, the lithium secondary battery can have high capacity / high output characteristics, high stability, and a low low-voltage failure rate. In particular, not only is the discharge resistance measured initially low, but the discharge resistance after 300 cycles can show a significantly lower increase compared to the initial discharge resistance, and can have improved output characteristics.

[0090] A lithium secondary battery according to one embodiment may include the above-mentioned separator between the positive electrode and the negative electrode. Here, the positive electrode and the negative electrode can be used without limitation as long as they are those that are normally used in lithium secondary batteries.

[0091] The components of the secondary battery described in this disclosure are explained further below.

[0092] [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.

[0093] (Positive electrode current collector) The positive electrode current collector may include stainless steel, nickel, aluminum, titanium, or alloys thereof. The positive electrode current collector may also include aluminum or stainless steel surface-treated with carbon, nickel, titanium, or silver. The positive electrode current collector may have a thickness of, for example, 10 μm to 50 μm, although this is not limited to the above.

[0094] (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 that can reversibly intercalate and deintercalate lithium ions.

[0095] According to exemplary embodiments, 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).

[0096] The positive electrode active material may further include coating elements or doping elements. For example, elements substantially identical or similar to the auxiliary elements described above may be used as coating elements or doping elements. For example, one or more of the above elements may be used as coating elements or doping elements.

[0097] The positive electrode active material may include nickel-cobalt-manganese (NCM) lithium oxide. In this case, an NCM lithium oxide with an increased nickel content may be used.

[0098] The Ni content in the NCM-based lithium oxide (for example, the mole fraction of nickel in the total number of moles of nickel, cobalt, and manganese) may be 0.6 or higher, 0.7 or higher, or 0.8 or higher. In some embodiments, the Ni content 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.

[0099] In some embodiments, the positive electrode active material may 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 (LFP)-based active material (e.g., LiFePO4).

[0100] (Method of manufacturing the positive electrode) For example, a positive electrode slurry may be produced by mixing the positive electrode active material in a solvent. After coating the positive electrode slurry onto a positive electrode current collector, the positive electrode active material layer may be produced by drying and rolling. The coating process may be carried out by methods such as gravure coating, slot die coating, simultaneous multilayer die coating, imprinting, doctor blade coating, dip coating, bar coating, and casting, and is not limited to these. The positive electrode active material layer may further contain a binder, and optionally further contain conductive materials, thickeners, and the like.

[0101] (Positive electrode solvent) Non-limiting examples of solvents used in the production of the positive electrode slurry include N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, N,N-dimethylaminopropylamine, ethylene oxide, and tetrahydrofuran.

[0102] (Positive electrode binder) The binder may include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer, polyacrylonitrile, polymethyl methacrylate, acrylonitrile butadiene rubber (NBR), polybutadiene rubber (BR), styrene-butadiene rubber (SBR), and the like. In one embodiment, a PVDF-based binder may be used as the positive electrode binder.

[0103] (Positive electrode conductive material) The conductive material may be added to enhance the conductivity and / or the mobility of lithium ions or electrons in the positive electrode active material layer. For example, the conductive material may include, but is not limited to, carbon-based conductive materials such as graphite, carbon black, acetylene black, Ketjenblack, graphene, carbon nanotubes, VGCF (vapor-grown carbon fiber), and carbon fibers, and / or metallic conductive materials such as tin, tin oxide, titanium oxide, LaSrCoO3, and LaSrMnO3.

[0104] (Positive electrode thickener / dispersant) If necessary, the cathode slurry may further contain a thickener and / or a dispersant. In one embodiment, the cathode slurry may contain a thickener such as carboxymethylcellulose (CMC).

[0105] [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.

[0106] (Negative electrode current collector) Non-limiting examples of negative electrode current collectors include copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, and polymer substrates coated with conductive metals. The negative electrode current collector is not limited to these, but may have a thickness of, for example, 10 μm to 50 μm.

[0107] (Negative electrode material) The negative electrode active material layer may include a negative electrode active material. The negative electrode active material may be a material capable of adsorbing and desorbing lithium ions. For example, the negative electrode active material may be a carbon-based material such as crystalline carbon, amorphous carbon, carbon composite, or carbon fiber, or a lithium metal, lithium alloy, silicon (Si)-containing material, or tin (Sn)-containing material.

[0108] Examples of amorphous carbon include hard carbon, soft carbon, coke, mesocarbon microbeads (MCMB), and mesophase pitch-based carbon fiber (MPCF).

[0109] Examples of the aforementioned crystalline carbon include graphite-based carbons such as natural graphite, artificial graphite, graphitized coke, graphitized MCMB, and graphitized MPCF.

[0110] The lithium metal may be pure lithium metal or lithium metal with a protective layer formed on it to suppress dendrite growth, etc. In one embodiment, a lithium metal-containing layer deposited or coated on a negative electrode current collector may be used as the negative electrode active material layer. In one embodiment, a lithium thin film layer may be used as the negative electrode active material layer.

[0111] Examples of elements contained in the aforementioned lithium alloy include aluminum, zinc, vizmus, cadmium, antimony, silicon, lead, tin, gallium, or indium.

[0112] The silicon-containing substance can provide increased capacity characteristics. The silicon-containing substance may include Si, SiO x (0 < x < 2), metal-doped SiO x (0 < x < 2), and may include silicon-carbon composites and the like. The metal may include lithium and / or magnesium, and metal-doped SiO x (0 < x < 2) may include metal silicates.

[0113] (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 thickener, etc.

[0114] 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.

[0115] (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, and the like.

[0116] (Negative electrode binder / conductive material / thickener) As the binder, conductive material, and thickener, the above-mentioned substances that can be used during the production of the positive electrode may be used.

[0117] In some embodiments, as the negative electrode binder, a styrene-butadiene rubber (SBR) - based binder, carboxymethyl cellulose (CMC), polyacrylic acid - based binder, poly(3,4 - ethylenedioxythiophene), PEDOT - based binder, etc. may be used.

[0118] [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.

[0119] [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.

[0120] (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 - where 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 - and the like can be mentioned.

[0121] The organic solvent may include organic compounds that have sufficient solubility in the lithium salt and additives and that do not react within the battery. The organic solvent may include, for example, at least one of carbonate solvents, ester solvents, ether solvents, ketone solvents, alcohol solvents, and aprotic solvents.Examples of the aforementioned organic solvents include 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), and dibutyl ether (dibutyl Other substances that may be used include ether, tetraethylene glycol dimethyl ether (TEGDME), diethylene glycol dimethyl ether (DEGDME), dimethoxyethane, tetrahydrofuran (THF), and 2-methyltetrahydrofuran, ethanol (ethyl alcohol), isopropyl alcohol, dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, sulfolane, gamma-butyrolactone, and propylene sulfite. These may be used individually or in combination of two or more.

[0122] (Additives) The non-aqueous electrolyte may further contain additives. These additives may include, for example, cyclic carbonate compounds, fluorine-substituted carbonate compounds, sultone compounds, cyclic sulfate compounds, cyclic sulfite compounds, phosphate compounds, and borate compounds. The cyclic carbonate compounds may include vinylene carbonate (VC), vinyl ethylene carbonate (VEC), etc. The fluorine-substituted carbonate compounds may be fluorine-substituted cyclic carbonate compounds. The fluorine-substituted cyclic carbonate compounds may include fluoroethylene carbonate (FEC), etc. The sultone compounds may include 1,3-propane sultone, 1,3-propene sultone, 1,4-butane sultone, etc. The cyclic sulfate compound may include 1,2-ethylene sulfate, 1,2-propylene sulfate, etc. The cyclic sulfite compound may include ethylene sulfite, butylene sulfite, etc. The phosphate compound may include lithium difluorobis-oxalato phosphate, lithium difluoro phosphate, etc. The borate compound may include lithium bis(oxalate) borate, etc.

[0123] The embodiments of this disclosure will be further described below with reference to specific experimental examples. The embodiments and comparative examples included in the experimental examples are illustrative of this disclosure and do not limit the scope of the appended claims. It will be obvious to those skilled in the art that various changes and modifications to the embodiments are possible within the scope of this disclosure and the technical concept, and it goes without saying that such variations and modifications fall within the scope of the appended claims.

[0124] First, we will explain the method for measuring the physical properties of separators and the method for evaluating the characteristics of secondary batteries.

[0125] [Glass transition temperature] The glass transition temperature was measured using a differential scanning calorimeter (DSC). The manufacturer was Mettler Toledo, and the model was DSC1.

[0126] The measurement method involved preparing 5-10 mg test specimens according to the DSC pan size, placing the specimens in a container, and compressing them with a crimper press. The prepared samples and reference samples were placed side by side, and the analysis was performed by selecting the temperature range, heating rate, and reactive gas.

[0127] The measurement conditions are as follows:

[0128] Temperature range: -100 to 250°C Reactive gas: N2 Heating / cooling rate: 10°C / min

[0129] [Average particle size] The average particle size was determined from the particle size distribution results obtained by sampling the target particles according to the ISO 13320-1 standard and analyzing them using a MICROTRAC S3500. This method was used to measure the average particle size of inorganic particles and particle-type binders.

[0130] [Molecular weight] Weight-average molecular weight was measured using a GPC (EcoSEC HLC-8320 GPC Reflective Index detector, Tosoh Corporation). The GPC column consisted of a TSKgel guard PWxl, two TSKgel GMPWxl columns, and a TSKgel G2500PWxl (7.8 × 300 mm) column linked together. The solvent used was a 0.1 M NaNO3 aqueous solution, and the standard substance used was PEG / PEO. The analysis was performed at 40°C and a flow rate of 1 mL / min.

[0131] 1) GPC (Gel permeation chromatograph) sample processing (1) Sample pretreatment: Use the provided sample as is. (2) Sample dissolution state: Completely dissolved (3) Filtration of sample solution: 0.45 μm nylon filter

[0132] 2) Conditions for GPC (Gel Permeation Chromatograph) analytical instruments (1) Analytical instrument: EcoSEC HLC-8320 GPC manufactured by Tosoh Corporation (2) Detector: RI-detector (3) Developing solvent: 0.1M NaNO3 (4) Column (maker, model no.): Tskgel guard PWxl+2 x TSKgel GMPWxl+TSKgel G2500PWxl (7.8×300mm) (5) Temperature: 40℃ (6)Flow rate: 1.0mL / min (7) Injection volume: 100μl, 10mg / mL (8) Standard material: PEG / PEO

[0133] [viscosity] Viscosity was measured at 25°C using a Brookfield viscometer (model RVDV2), spindle CPA-52Z, and rpm set to a torque of 60-70%.

[0134] [Porosity] The porosity of the porous substrate was calculated using the following mathematical formula after cutting a rectangular sample of A cm × B cm. Measurements were taken by cutting A and B in the range of 5 to 20 cm.

[0135] Porosity = {1 - (M ÷ ρ) ÷ (A × B × T)} × 100

[0136] Here, T = thickness of the separator (cm) M = weight of the sample (g) ρ = true density of porous substrate (g / cm³) 3 )

[0137] [Gurley transmittance] The Gurley permeability of the porous substrate was measured using a Toyoseiki Densometer in accordance with the ASTM D726 standard. The time it took for 100cc of air to pass through a 1 square inch area of ​​the porous substrate was recorded in seconds and compared.

[0138] [Pin Puncture Strength] The pin puncture strength of the separator was measured according to the ASTM D3763_02 standard, with three measurements taken for each sample and the average value calculated. Speed: 120mm / min Pin diameter: 1.0mm

[0139] [FT-IR spectral measurement] The separator was cut into 1cm x 1cm pieces to prepare the sample for measurement. Measurements were then performed using an FT-IR system equipped with an MCT (mercury cadmium telluride) detector (Thermo Scientific, Nicolet iN10 Infrared Microscope) under the following conditions. The average values ​​of the major peaks shown in the measured FT-IR spectra are shown in Table 2 below.

[0140] - Resolution: 4cm -1 -scans:16 -range: 4000~675cm -1 - Measurement points per sample: 15 points (10 μm intervals) * 15 points (10 μm intervals) mapping 3 positions

[0141] [Average thickness of separator and porous substrate (μm)] After stacking 10 separators, the thickness of each separator was measured at 5 arbitrary points in the width direction using a thickness measuring instrument manufactured by Mitutoyo Corporation. The sum of these measurements was then divided by 5 to obtain the average thickness of the 10 separators, and then divided again by 10 to obtain the overall average thickness of a single separator.

[0142] The average thickness of the porous substrate was calculated by stacking 10 layers of the porous substrate, measuring the thickness at 5 arbitrary points in the width direction using a thickness measuring instrument manufactured by Mitutoyo, summing the measurements, and then dividing by 5 to obtain the average thickness of the 10 layers of porous substrate. This was then divided by 10 to obtain the average thickness of the porous substrate. In the case where an inorganic particle layer had been formed, the inorganic particle layer was detached and thoroughly dried, and then the average thickness of the porous substrate from which the inorganic particle layer had detached was calculated using the method described above.

[0143] [BDV / t(kV / μm)] The dielectric breakdown voltage (BDV) was measured according to ASTM D 3755. The separator was placed between the electrodes of a dielectric strength tester (Croma, model 19052) in a dry room (dew point temperature: -60°C), and the voltage (kV) was evaluated as the voltage when the leakage current value was 5 mA, measured under the condition that the applied voltage was increased at 5 kV / 10 sec.

[0144] The overall average thickness t (μm) of the separator was calculated by stacking 10 separators as described above, measuring the thickness at 5 arbitrary points in the TD direction using a thickness measuring instrument manufactured by Mitutoyo, dividing by 5 to obtain the average thickness of the 10 separators, and then dividing by 10 to obtain the overall average thickness of a single separator.

[0145] Next, in order to compare the dielectric breakdown voltage secured for a given thickness, the value of BDV / t, which is the ratio of the measured dielectric breakdown voltage BDV to the overall average thickness t of the separator, was calculated.

[0146] [Packing density of inorganic particle layer (g / (m³)] 2 .μm))] Following the method described above, the average thickness of the porous substrate and the overall average thickness of the separator on which the inorganic particle layer is provided were measured. Then, the thickness T (μm) of the inorganic particle layer was calculated by subtracting the average thickness of the porous substrate from the overall average thickness of the separator. The separator on which the inorganic particle layer is provided was 10 mm × 10 mm (0.01 m 2 ) area S(m 2 After cutting the material into sections and measuring their weights, the weight of the porous substrate alone is subtracted to calculate the weight W (g) of the inorganic particle layer alone. The packing density of the inorganic particle layer is W / (T*S)(g / (m). 2 The calculation was performed using .μm.

[0147] [ΔGurley transmittance] The ΔGurley permeability was calculated using the following formula after measuring the Gurley permeability in seconds, which is the time it takes for 100cc of air to pass through a 1 square inch area of ​​a separator, using a Toyoseiki Densometer in accordance with the ASTM D726 standard.

[0148] ΔGurley transmittance (sec / 100cc)=P m -P s

[0149] The aforementioned P m This is the gas permeability of the separator, and P s This is the gas permeability of the porous substrate.

[0150] [Thermal shrinkage rate (%)] The separator was cut into a square shape with sides of 10 cm, and the transverse direction (TD) and machine direction (MD) were marked. The sample was placed in the center, and five sheets of paper were placed above and below the sample, and the four sides of the paper were wrapped with tape. The paper-wrapped sample was left in a 150°C hot air drying oven for 60 minutes. After that, the sample was removed, the separator was measured with a camera, and the thermal shrinkage rate in the machine direction (MD) and transverse direction (TD) was calculated using the following formula.

[0151] MD heat shrinkage rate (%) = (length of MD before heating - length of MD after heating) / length of MD before heating × 100 TD thermal shrinkage rate (%) = (TD length before heating - TD length after heating) / TD length before heating × 100

[0152] [Adhesive strength] Cut the separator to a size of 50mm wide x 50mm long and arrange it so that the inorganic particle layer is facing upwards. Place a sheet of black drawing paper (20mm wide x 150mm long x 0.25mm thick) with a dynamic friction coefficient of 0.15 on top and apply a predetermined pressure (200g / cm²) using a press device. 2After adding the substance, the black drawing paper is forcibly removed to the side and the amount of inorganic matter on the surface is checked. Based on the amount, the following grades are used to classify it as A / B / C / D / E / F.

[0153] A: Nothing to go with it. B: A small amount of inorganic matter comes off. C~F: These are levels where both binders and inorganic substances are present, with F indicating a more severe level of contamination.

[0154] [Battery resistance characteristics] Each battery manufactured according to 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 with a constant current at a rate of 0.5C at 25°C until the voltage reached 4.2V, and then charged with a constant voltage until the current reached 0.01C while maintaining 4.2V. Next, during discharge, the cycle of discharging at a constant current of 0.5C until the voltage reached 3.0V was repeated 300 times. Then, with a State of Charge (SOC) of 60%, the DC-IR (Direct Current Internal Resistance) was measured at the 1st and 300th cycles using the J-Pulse method, and the resistance increase rate was calculated using the following formula.

[0155] ΔR(%) = (R2 - R1) / R1 × 100

[0156] R1 is the resistance (DC-IR) at the first cycle, and R2 is the resistance (DC-IR) at the 300th cycle.

[0157] <Example 1> Manufacturing of coating slurries A coating slurry with a solid content of 25% by weight was prepared by adding 95% by weight of boehmite (γ-AlO(OH)) as inorganic particles with an average particle size (D50) of 0.3 μm, 4.2% by weight of polyacrylate (Tg: -45℃, D50: 250 nm, Sigma Aldrich Inc.) as a particulate binder, and 0.8% by weight of polyacrylamide (Mw: 230,000 g / mol, Tg: 200℃, Sigma Aldrich Inc.) as a water-soluble binder to water, and then stirring. Here, the polyacrylamide was added in the form of a dispersion with a solid content of 12% by weight and a viscosity of 2,000 mPas.

[0158] Manufacturing of separators A porous polyethylene film with an average thickness of 9 μm (porosity: 42%, Gurley transmittance: 118 sec. / 100cc, puncture strength: 440 gf) was used as the porous substrate. The prepared coating slurry was applied to both sides of the porous substrate and then dried to form an inorganic particle layer with an average thickness of 2.1 μm on each side of the porous substrate, thereby producing a separator.

[0159] Manufacturing of rechargeable batteries A homogeneous positive electrode slurry was prepared by adding 94% by weight of LiCoO2 as the positive electrode active material, 2.5% by weight of polyvinylidene fluoride as a bonding agent, and 3.5% by weight of carbon black as a conductive material to the solvent NMP (N-methyl-2-pyrrolidone), and stirring. The prepared slurry was coated onto a 30 μm thick aluminum foil, dried, and pressed to produce a positive electrode with a total thickness of 150 μm. A homogeneous negative electrode slurry was prepared by adding 95% by weight of artificial graphite as the negative electrode active material, 3% by weight of acrylic latex with a Tg of -52°C as a bonding agent, and 2% by weight of CMC (Carboxymethyl cellulose) as a thickening agent to the solvent water, and stirring. The manufactured slurry was coated onto a 20 μm thick copper foil, dried, and pressed to produce a negative electrode with a total thickness of 150 μm. After assembling a pouch-type battery by stacking the manufactured separator between the positive and negative electrodes, the assembled battery was heat-sealed in a hot press at 80°C and 1 MPa to fuse the positive electrode, negative electrode, and separator together. Subsequently, an electrolyte containing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a volume ratio of 3:5:2, with 1 M lithium hexafluorophosphate (LiPF6) dissolved in it was injected, and the battery was sealed to produce a secondary battery with a capacity of 2 Ah.

[0160] <Example 2> The separator and secondary battery were manufactured using the same method as in Example 1, except that boehmite with an average particle size (D50) of 0.27 μm was used as the inorganic particle during the production of the coating slurry.

[0161] <Example 3> The separator and secondary battery were manufactured using the same method as in Example 1, except that when preparing the coating slurry, a mixture of boehmite with average particle size (D50) of 0.3 μm and 0.7 μm, respectively, was used as inorganic particles in a weight ratio of 8:2.

[0162] <Example 4> The separator and secondary battery were manufactured using the same method as in Example 1, except that when preparing the coating slurry, a mixture of boehmite with average particle size (D50) of 0.3 μm and 0.7 μm, respectively, was used as inorganic particles in a weight ratio of 7:3.

[0163] <Example 5> The separator and secondary battery were manufactured using the same method as in Example 1, except that when preparing the coating slurry, a mixture of boehmite with average particle size (D50) of 0.3 μm and 0.7 μm, respectively, was used as inorganic particles in a weight ratio of 6:4.

[0164] <Comparative Example 1> Manufacturing of coating slurries A coating slurry with a solid content concentration of 25% by weight was prepared by adding 95% by weight of boehmite (γ-AlO(OH)) as inorganic particles with an average particle size (D50) of 1.3 μm and 5% by weight of polyacrylate (Mw: 120,000 g / mol, Tg: -45℃, D50: 250 nm, Sigma Aldrich Inc.) as a particulate binder to water, and then stirring.

[0165] Manufacturing of separators A porous polyethylene film with an average thickness of 9 μm (porosity: 42%, Gurley transmittance: 118 sec. / 100cc, puncture strength: 440 gf) was used as the porous substrate. The prepared coating slurry was applied to both sides of the porous substrate and then dried to form an inorganic particle layer with an average thickness of approximately 2.0 μm on each side of the porous substrate, thereby producing a separator.

[0166] Manufacturing of positive electrodes, negative electrodes, and batteries After manufacturing the positive electrode and negative electrode in the same manner as described in Example 1, a secondary battery was manufactured together with the manufactured separator.

[0167] <Comparative Example 2> Manufacturing of coating slurries A coating slurry with a solid content of 28% by weight was prepared by adding 95% by weight of boehmite (γ-AlO(OH)) as inorganic particles with an average particle size (D50) of 0.7 μm, 4.2% by weight of polyacrylate (Mw: 120,000 g / mol, Tg: -45°C, D50: 250 nm, Sigma Aldrich Inc.) and 0.8% by weight of polyacrylamide (Mw: 150,000 g / mol, Tg: 200°C, Sigma Aldrich Inc.) as binders to water, and then stirring. Here, the polyacrylamide was added in the form of a dispersion with a solid content of 12% by weight and a viscosity of 2,000 mPas.

[0168] Manufacturing of separators A porous polyethylene film with an average thickness of 9 μm (porosity: 42%, Gurley transmittance: 118 sec. / 100cc, puncture strength: 440 gf) was used as the porous substrate. The prepared coating slurry was applied to both sides of the porous substrate and then dried to form an inorganic particle layer with an average thickness of 2.0 μm on each side of the porous substrate, thereby producing a separator.

[0169] Manufacturing of positive electrodes, negative electrodes, and batteries After manufacturing the positive electrode and negative electrode in the same manner as described in Example 1, a secondary battery was manufactured together with the manufactured separator.

[0170] <Comparative Example 3> Manufacturing of coating slurries A coating slurry with a solid content of 25% by weight was prepared by adding 90% by weight of inorganic particles, consisting of boehmite (γ-AlO(OH)) with average particle size (D50) of 0.3 μm and 0.7 μm, respectively, in an 8:2 weight ratio relative to the total weight of solids, and 10% by weight of polyacrylate (Mw: 120,000 g / mol, Tg: -45℃, D50: 250 nm, Sigma Aldrich Inc.) as a binder to water, and then stirring.

[0171] Manufacturing of separators A porous polyethylene film with an average thickness of 9 μm (porosity: 42%, Gurley transmittance: 118 sec. / 100cc, puncture strength: 440 gf) was used as the porous substrate. The prepared coating slurry was applied to both sides of the porous substrate and then dried to form an inorganic particle layer with an average thickness of 2.0 μm on each side of the porous substrate, thereby producing a separator.

[0172] Manufacturing of positive electrodes, negative electrodes, and batteries After manufacturing the positive electrode and negative electrode in the same manner as described in Example 1, a secondary battery was manufactured together with the manufactured separator.

[0173] <Comparative Example 4> Manufacturing of coating slurries A coating slurry with a solid content of 25% by weight was prepared by adding 93% by weight of inorganic particles, which consisted of boehmite (γ-AlO(OH)) with average particle size (D50) of 0.3 μm and 0.7 μm, respectively, in a weight ratio of 8:2, and 7% by weight of polyacrylamide (Mw: 150,000 g / mol, Tg: 200℃, Sigma Aldrich Inc.) as a binder, to water and stirring.

[0174] Manufacturing of separators A porous polyethylene film with an average thickness of 9 μm (porosity: 42%, Gurley transmittance: 118 sec. / 100cc, puncture strength: 440 gf) was used as the porous substrate. The prepared coating slurry was applied to both sides of the porous substrate and then dried to form an inorganic particle layer with an average thickness of 2.0 μm on each side of the porous substrate, thereby producing a separator.

[0175] Manufacturing of positive electrodes, negative electrodes, and batteries After manufacturing the positive electrode and negative electrode in the same manner as described in Example 1, a secondary battery was manufactured together with the manufactured separator.

[0176] <Comparative Example 5> Manufacturing of coating slurries A coating slurry with a solid content of 25% by weight was prepared by adding 95% by weight of inorganic particles, which consisted of boehmite (γ-AlO(OH)) with average particle size (D50) of 0.3 μm and 0.7 μm, respectively, in a weight ratio of 8:2 relative to the total weight of solids, and 4.2% by weight of polyacrylate (Mw: 120,000 g / mol, Tg: -45℃, D50: 250 nm, Sigma Aldrich Inc.) and 0.8% by weight of polyethylene oxide (Mv: 200,000 g / mol, Tg: 65℃, Sigma Aldrich Inc.) as binders to water, and then stirring.

[0177] Manufacturing of separators A porous polyethylene film with an average thickness of 9 μm (porosity: 42%, Gurley transmittance: 118 sec. / 100cc, puncture strength: 440 gf) was used as the porous substrate. The prepared coating slurry was applied to both sides of the porous substrate and then dried to form an inorganic particle layer with an average thickness of 2.0 μm on each side of the porous substrate, thereby producing a separator.

[0178] Manufacturing of positive electrodes, negative electrodes, and batteries After manufacturing the positive electrode and negative electrode in the same manner as described in Example 1, a secondary battery was manufactured together with the manufactured separator.

[0179] The physical properties of the separators manufactured in the above examples and comparative examples, and the performance (resistive characteristics) of the secondary batteries were measured and are shown in Table 1 below. Furthermore, the results of the FT-IR spectral measurements of the separators manufactured in the above examples and comparative examples are shown in Table 2 below.

[0180] [Table 1]

[0181] [Table 2]

[0182] As can be seen from Tables 1 and 2 above, the BDV / t value is 0.15 or higher, and the FT-IR spectrum is 1070-1082 cm⁻¹. -1 The separator of the example, which has a peak shown in the range, a ΔGurley transmittance of 100 sec / 100 cc or less, and a thermal shrinkage rate of 5% or less, exhibited excellent voltage resistance even at thin thicknesses, high packing density of the inorganic particle layer, low ΔGurley transmittance and thermal shrinkage rate at high temperatures (150°C), and excellent adhesive strength. Furthermore, the initial discharge resistance and discharge resistance after 300 cycles of the battery to which it was applied were low.

[0183] On the other hand, the separators of Comparative Examples 1 to 5, which did not satisfy at least one of the following: the BDV / t value, the presence of a peak shown at a specific position in the FT-IR spectrum, the ΔGurley transmittance value, and the thermal shrinkage coefficient value, showed a significant decrease in one or more of the voltage withstand characteristics, heat resistance, adhesion, and permeability, and the discharge resistance of the batteries to which they were applied was higher initially and after 300 cycles compared to the examples.

[0184] The above is merely an example of applying the principles of this disclosure, and other configurations may be included without departing from the scope of this disclosure.

Claims

1. Porous substrate and Formed on at least one surface of the porous substrate, it includes an inorganic particle layer containing a binder and inorganic particles, The ratio of the dielectric breakdown voltage (kV) of the separator to the overall average thickness (μm) of the separator is 0.15 kV / μm or higher, and the spectrum obtained by Fourier transform infrared spectroscopy (FT-IR) is 1070 cm⁻¹. －１ ~1082cm －１ A separator having a peak shown within the range, with a thermal shrinkage rate of 5% or less in the mechanical direction and width direction measured after being left at 150°C for 60 minutes, and a ΔGurley transmittance of 100 sec / 100 cc or less calculated by the following formula 1. [Formula 1] ΔGrail transmittance (sec / 100cc) = P ｍ -P ｓ In the above calculation formula 1, P ｍ This is the gas permeability of the separator, and P ｓ This is the gas permeability of the porous substrate.

2. The separator according to claim 1, wherein the inorganic particles include one or more 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) greater 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 relative to the total weight of the first inorganic particles and the second inorganic particles.

7. The separator according to claim 1, wherein the binder comprises a particle-type binder and a water-soluble binder.

8. The separator according to claim 7, wherein the particle-type binder has a glass transition temperature of -60°C to 0°C.

9. The separator according to claim 7, wherein the water-soluble binder has a glass transition temperature of 180°C to 220°C.

10. The separator according to claim 7, wherein the particulate binder and the water-soluble binder each independently contain one or more selected from the group consisting of ester polymers, amide polymers, imide polymers, acrylic polymers, acrylamide polymers, vinyl alcohol polymers, fluorine polymers, and vinylpyrrolidone polymers.

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

12. The separator according to claim 7, wherein the weight ratio of the water-soluble binder to the particle-type binder is 1:1 to 1:

10.

13. The packing density of the inorganic particle layer is 1.2 g / m³. ２ The separator according to claim 1, wherein the particle size is 1 μm or larger.

14. A lithium secondary battery comprising a separator according to any one of claims 1 to 13.

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