Separator and lithium secondary battery including the same

Abstract

To provide a separator having excellent withstand voltage characteristics, heat resistance, adhesion, and permeability, and also to provide a lithium secondary battery having high capacity / high output characteristics, high stability, and a low defect rate at a low voltage, by including the separator.SOLUTION: A separator includes: 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 separator has a ratio of the breakdown voltage (kV) of the separator to the overall average thickness (μm) of the separator of 0.15 kV / μm or more, has a peak appearing in a range of 1,070-1,082 cm-1 in a spectrum by Fourier-transform infrared spectroscopy (FT-IR), 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, and has ΔGurley permeability of 100 sec / 100 cc or less.SELECTED DRAWING: None

Description

Technical Field

[0001] The present disclosure relates to a separator having significantly excellent withstand voltage characteristics and a lithium secondary battery including the same.

Background Art

[0002] In an electrochemical device, a separator is very important for improving the stability and performance (such as life and capacity) 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] Research on such separators for secondary batteries has been carried out in the direction of thinning the thickness for the high-capacity / high-output characteristics of electrochemical devices. However, with the trend of thinning such separators, a major problem has emerged that the breakdown voltage of the separator decreases and the withstand voltage characteristics deteriorate.

[0004] The breakdown voltage (BDV) means the voltage at which when a voltage is applied to an insulator, corona discharge occurs through the insulator, and that part becomes conductive and loses its insulating property. The higher the breakdown voltage, the better the withstand voltage characteristics are evaluated. The breakdown voltage depends greatly on the thickness of the insulator. As the thickness of the separator decreases, the breakdown voltage of the electrochemical device decreases, the stability of the battery deteriorates, and there is a risk of an increase in the low-voltage failure rate of the battery. Therefore, there is a need for a separator for a battery that has a thin thickness, a high breakdown voltage, high-capacity / high-output characteristics, and at the same time, high stability and a low low-voltage failure rate.

Summary of the Invention

Problems to be Solved by the Invention

[0005] According to one aspect of the present disclosure, a separator excellent in withstand voltage characteristics, heat resistance, adhesiveness, and permeability can be provided.

[0006] According to another aspect of the present disclosure, by including the separator, a lithium secondary battery having high capacity / high output characteristics, high stability, and a low low-voltage failure rate can be provided.

[0007] The separator of the present disclosure is widely applicable in the field of green technologies such as electric vehicles, battery charging stands, and other solar power generation and wind power generation using batteries. In addition, 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

[0008] The separator according to the present disclosure 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. The ratio of the breakdown voltage (kV) of the separator to the overall average thickness (μm) of the separator is 0.15 kV / μm or more. In the spectrum by Fourier transform infrared spectroscopy (FT-IR), it has a peak shown in the range of 1070 cm -1 ~1082 cm -1 . 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, and the Δ Gurley permeability calculated by the following calculation formula 1 is 100 sec / 100 cc or less. [Calculation formula 1] Δ Gurley permeability (sec / 100 cc) = P m - P s In the above calculation formula 1, P m is the gas permeability of the separator, and P s is the gas permeability of the porous substrate.

[0009] 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.

[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) larger than that of the first inorganic particles.

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

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

[0015] In one embodiment, the particulate 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 any one or more selected from the group consisting of ester-based polymers, amide-based polymers, imide-based polymers, acrylic-based polymers, acrylamide-based polymers, vinyl alcohol-based polymers, fluorine-based polymers, and vinyl pyrrolidone-based polymers.

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

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

[0020] In one embodiment, the packing density of the inorganic particle layer may be 1.2 g / m 2 .μm or more.

[0021] The present disclosure also provides a lithium secondary battery including the separator as described above.

Advantages of the Invention

[0022] The separator according to the present disclosure can have excellent withstand voltage characteristics, heat resistance, adhesiveness, and permeability.

[0023] In addition, by including the separator according to one embodiment, the present 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] 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.

[0025] 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.

[0026] In addition, 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 numerical ranges limited to different forms. 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.

[0027] Furthermore, throughout the specification, "comprising" a certain component means, unless otherwise stated to the contrary, not excluding other components, but may further include other components.

[0028] In this specification, unless otherwise defined, the average particle size of the inorganic particles and the particulate binder means the D50 value. D50 means the particle size of the inorganic particles and the particulate binder corresponding to 50% in terms of the volume-based integrated fraction. The average particle size can be derived from the results of the particle size distribution obtained by sampling a sample in accordance with the ISO 13320-1 standard and analyzing it using S3500 manufactured by MICROTRAC for the inorganic particles and the particulate binder to be measured.

[0029] In this specification, "MD (machine direction)" means the longitudinal direction in a porous substrate and a separator manufactured in the longitudinal direction, and "TD (transverse direction)" means the direction perpendicular to the MD in the plane direction of the porous substrate and the separator. In the present disclosure, the 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 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 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 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 porous substrate, and further divided 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 of the methods known in the art without limitation, and after sufficient drying, 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, the average thickness of the porous substrate is subtracted from the overall average thickness of the separator to calculate the thickness T (μm) of the inorganic particle layer. The separator on which the inorganic particle layer is provided on at least one surface of the porous substrate is 10 mm × 10 mm (0.01 m 2) area S (m 2 ) After cutting and measuring the weight, subtract the weight of the porous substrate to calculate the weight W (g) of only the inorganic particle layer. The packing density of the inorganic particle layer is calculated by W / (T*S).

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

[0034] In this specification, when a part such as a layer, film, region, plate, etc. is "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.

[0035] 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.

[0036] The present disclosure provides a separator capable of providing a battery having high breakdown voltage characteristics, heat resistance, adhesiveness, and permeability, and having high capacity / high output characteristics, high stability, and a low low-voltage defect 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, and the ratio of the breakdown voltage BDV (kV) of the separator to the overall average thickness t (μm) of the separator (hereinafter, BDV / t) is 0.15 kV / μm or more, and in the spectrum by Fourier transform infrared spectroscopy (FT-IR), 1070 cm -1 ~1082 cm -1With the peak shown in the range (hereinafter referred to as the first peak), after leaving it at 150°C for 60 minutes, the thermal shrinkage rates in the machine direction and width direction measured are 5% or less, and the Δ Gurley permeability calculated by the following calculation formula 1 is 100 sec / 100 cc or less.

[0037] [Calculation formula 1] Δ Gurley permeability (sec / 100 cc) = P m - P s

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

[0039] The separator according to one embodiment satisfies that the ratio of the breakdown voltage (kV) of the separator to the overall average thickness (μm) of the separator is 0.15 kV / μm or more, 0.16 kV / μm or more, 0.163 kV / μm or more, and the peak shown in the FT-IR spectrum is 1070 cm -1 ~1082 cm -1 By satisfying this and having the thermal shrinkage rate and Δ Gurley permeability within the above range, it was first recognized and invented that it is possible to simultaneously have remarkably excellent withstand voltage characteristics, heat resistance, adhesiveness, and permeability even under a thin thickness.

[0040] 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, the BDV / t in a specific range, the thermal shrinkage rate, and the Δ Gurley permeability value, so that it can have all of high capacity / high output characteristics, high stability, and a low low-voltage failure rate. Specifically, the lithium secondary battery according to one embodiment includes a separator having remarkably improved withstand voltage characteristics under a thin thickness, so that not only the initial measured discharge resistance is low, but also the ratio of the increase in the discharge resistance after 300 cycles compared to the initial discharge resistance can be shown to be remarkably low, and it can have improved output characteristics.

[0041] The above effects are achieved by adjusting 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 Δ Gurley permeability to specific ranges, and are not effects influenced only by the components of the separator or certain elements during the manufacturing process of the separator. As confirmed in one embodiment, it can be realized by various means including various factors such as the average particle size of the inorganic particles, the combination of inorganic particles, the weight ratio of two or more inorganic particles, the type and physical properties of the binder, etc. As long as this can be achieved, the means are not particularly limited. For example, the first peak can be derived 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 is not determined only by the characteristics of the inorganic particles themselves such as the average particle size and the 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.

[0042] In one embodiment, the dielectric breakdown voltage (BDV, kV) of the separator is measured in accordance with ASTM D 3755. After placing the separator between the electrodes of a withstand voltage tester (model 19052, manufactured by Croma) under a dry room (dew point temperature: -60°C), the voltage (kV) is measured when the leakage current value measured under the condition of increasing the applied voltage at 5 kV / 10 sec is 5 mA. The voltage at this time is evaluated as the dielectric breakdown voltage (BDV).

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

[0044] In one embodiment, the first peak is 1070 cm -1 ~1082 cm-1 is a peak having the maximum intensity within the range of, specifically, 1071 cm -1 to 1082 cm -1 range, 1072 cm -1 to 1082 cm -1 range, 1075 cm -1 to 1082 cm -1 or 1075 cm -1 to 1081 cm -1 and may be a peak having the maximum intensity within the range thereof.

[0045] In one embodiment, the separator may further have a second peak shown in the range of 1140 cm -1 to 1160 cm -1 on the FT-IR spectrum. The second peak is a peak having the maximum intensity within the above-described range, specifically, a peak having the maximum intensity within the range of 1145 cm -1 to 1155 cm -1 and may be a peak having the maximum intensity within the range thereof.

[0046] In one embodiment, the separator may further have a third peak shown in the range of 2910 cm -1 to 2930 cm -1 on the FT-IR spectrum. The third peak is a peak having the maximum intensity within the above-described range, specifically, a peak having the maximum intensity within the range of 2915 cm -1 to 2925 cm -1 range or 2915 cm -1 to 2920 cm -1 and may be a peak having the maximum intensity within the range thereof.

[0047] In one embodiment, the separator may further have a fourth peak shown in the range of 3090 cm -1 to 3110 cm -1 on the FT-IR spectrum. The fourth peak is a peak having the maximum intensity within the above-described range, specifically, a peak having the maximum intensity within the range of 3095 cm -1 to 3105 cm -1 and may be a peak having the maximum intensity within the range thereof.

[0048] In one embodiment, the separator may further have a fifth peak shown in the range of 3280 cm -1 to 3320 cm -1 on the FT-IR spectrum. The fifth peak is a peak having the maximum intensity within the above-mentioned range. Specifically, it may be a peak having the maximum intensity in the range of 3280 cm -1 to 3310 cm -1 or in the range of 3285 cm -1 to 3300 cm -1 .

[0049] 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 to 675 cm -1 , it may be scanned 5 to 200 times at a resolution of 4 cm -1 and measured in the transmission mode.

[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 thermal shrinkage rates in the machine direction and the width direction measured may be 5% or less, preferably 4% or less, 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, 0.6% or less. For example, it may be 0.5 to 3.5% or 0.5 to 2.0%.

[0051] The separator according to one embodiment can have excellent gas permeability. In one embodiment, in the Gurley permeability measured according to ASTM D726, the ΔGurley permeability calculated by the following calculation formula 1 may be 100 sec / 100 cc or less. 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, 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, 10 sec / 100 cc or more. In a specific embodiment, the ΔGurley permeability of the separator may be 5 to 100 sec / 100 cc, 5 to 80 sec / 100 cc, 5 to 50 sec / 100 cc, 5 to 40 sec / 100 cc, 10 to 35 sec / 100 cc, or 25 to 35 sec / 100 cc.

[0052] [Calculation formula 1] ΔGurley permeability (sec / 100 cc) = P m - P s

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

[0054] In one embodiment, the inorganic particles are not limited as long as they are inorganic particles used in the present 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).

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

[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 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, or 0.1 μm to 0.3 μm, but this can be changed 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 diameter (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 diameter (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 diameter (D50) satisfies the above range. The average particle diameter (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 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, 20% by weight or more, or a value between the numerical values with respect to 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 40% by weight, 5% by weight to 40% by weight, 10% by weight to 40% by weight, 20% by weight to 40% by weight, or 20% by weight to 30% by weight with respect to the total weight of the first inorganic particles and the second inorganic particles.

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

[0061] That is, the inorganic particles may include 50 to 100% by weight of the first inorganic particles having an average particle size (D50) within the above range and 0 to 50% by weight of the second inorganic particles having an average particle size (D50) within the above range with respect 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, and may also include 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 having more excellent physical properties can be provided.

[0062] The first inorganic particles and the second inorganic particles may be composed 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 have different particle size distributions and different D 50 values and can be distinguished thereby.

[0063] Regarding the size of the inorganic particles, or when the first inorganic particles and the second inorganic particles are used, these inorganic particles have different sizes and can be defined by their respective particle size distributions and the resulting D 50 values. The different sizes of the first inorganic particles and the second inorganic particles can be obtained by initially using the first inorganic particles and the second inorganic particles whose size characteristics are classified 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, more excellent breakdown voltage characteristics, heat resistance, adhesiveness, and permeability of the separator can be realized.

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

[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 numerical values. As 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 having the above average particle size, the binder can be uniformly dispersed with the water-soluble binder in the aqueous slurry composition, realizing excellent breakdown voltage characteristics, heat resistance, adhesiveness, and permeability of the separator.

[0067] In one embodiment, the particle-type 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 the particle-type binder having a glass transition temperature within the above range, the separator according to one embodiment can simultaneously realize excellent breakdown voltage characteristics, heat resistance, adhesiveness, 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 the water-soluble binder having a glass transition temperature within each of the above ranges and the above particle-type binder, the separator according to one embodiment can simultaneously realize excellent breakdown voltage characteristics, heat resistance, adhesiveness, and permeability. Further, a battery to which the separator as described above 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 equivalent 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 numerical values. As 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 a particulate binder and a water-soluble binder, and a person of ordinary skill in the art to which the technology disclosed in the present application pertains may appropriately select a known binder according to the intended situation. That is, there is no limitation as long as it is used as a binder for an inorganic particle layer in which inorganic particles formed on the surface of the porous base material layer of the secondary battery separator are connected to each other by the binder to form pores.

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

[0072] In one embodiment, the content of the total binder including the particulate binder and the water-soluble binder may be appropriately adjusted within the scope of the present disclosure according to the situation and purpose. For example, the content of the binder 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 based on 100 parts by weight of the inorganic particles.

[0073] In one embodiment, the weight ratio of the water-soluble binder to the particulate 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 / (m 2 .μm) or more, 1.3 g / (m 2 .μm) or more, 2.5 g / (m 2 .μm) or less, 2.0 g / (m 2 .μm) or less, 1.8 g / (m 2 .μm) or less, or a value between the above numerical values. Specifically, it may be 1.2 to 2.5 g / (m 2 .μm), 1.2 to 2.0 g / (m 2 .μm), 1.2 to 1.8 g / (m 2 .μm), 1.3 to 1.8 g / (m 2 .μm), 1.2 to 1.5 g / (m 2 .μm), or 1.2 to 1.4 g / (m 2 .μm), but is not limited thereto.

[0075] 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.

[0076] In one embodiment, the inorganic particle layer may be coated on one or both surfaces of the porous substrate. When the inorganic particle layers are coated on both surfaces of the porous substrate, the thicknesses of the inorganic particle layers coated on one surface different from the other surface may be the same as or different from each other.

[0077] The separator according to one embodiment can simultaneously achieve excellent withstand voltage characteristics, heat resistance, adhesiveness, and permeability even when a thin inorganic particle layer is provided on at least one surface, preferably both surfaces of the porous substrate. In one embodiment, the total thickness 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, 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 a separator of a lithium secondary battery may be used. In one embodiment, the porous substrate may be manufactured into a film or a sheet, but is not particularly limited.

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

[0080] In one embodiment, the Gurley permeability of the porous substrate may be 10 sec / 100 cc or more, 25 sec / 100 cc or more, 500 sec / 100 cc or less, 200 sec / 100 cc or less, 150 sec / 100 cc or less, or a value between the above numerical values, and may be 10 to 500 sec / 100 cc, 25 to 200 sec / 100 cc, or 25 to 150 sec / 100 cc, 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 numerical values, specifically, 1 to 100 μm, and for the realization of a high-capacity battery, it may specifically be 3 to 50 μm, 5 to 20 μm, or 5 to 15 μm. Although not limited, the porous substrate may be manufactured by stretching.

[0082] Hereinafter, the manufacturing method of the separator of the present disclosure will be described.

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

[0084] Since the descriptions of the respective porous substrates, inorganic particle layers, inorganic particles, and binders are as described above, specific descriptions are omitted.

[0085] The method for preparing the coating slurry can be applied without limitation to any ordinary method 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.

[0086] The coating slurry contains inorganic particles, a binder, and a solvent. The solvent is not particularly limited, and a solvent that easily dissolves or disperses the binder may be selected. For example, any 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, and may 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.

[0088] In one embodiment, as a method of applying the coating slurry onto a porous substrate, any ordinary method known in the art can be applied without limitation, and non-limiting examples include roll coating, spin coating, dip coating, bar coating, die coating, slit coating, inkjet printing, and methods combining these. The applied slurry can 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 and electron beams. Since the drying temperature is not particularly limited, it may be appropriately adjusted according to the experimental environment and purpose, and may be, for example, 30°C to 120°C, 30°C to 100°C, or 30°C to 60°C.

[0089] 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 both high-capacity / high-output characteristics, high stability, and a low low-voltage failure rate. Specifically, not only is the discharge resistance measured initially low, but the ratio of the increase in the discharge resistance after 300 cycles compared to the initial discharge resistance can be shown to be significantly low, and it can have improved output characteristics.

[0090] 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 usually used in lithium secondary batteries.

[0091] Hereinafter, the components of the secondary battery according to the present disclosure will be further described.

[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 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, and for example, may have a thickness of 10 μm to 50 μm.

[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 capable of reversibly intercalating and deintercalating lithium ions.

[0095] 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).

[0096] 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.

[0097] 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.

[0098] 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) may 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.

[0099] In some embodiments, the cathode 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-based (LFP) active material (for example, LiFePO4).

[0100] (Method for manufacturing the cathode) For example, the cathode active material may be mixed in a solvent to produce a cathode slurry. After coating the cathode slurry on a cathode current collector, it may be dried and rolled to produce a cathode 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 cathode active material layer may further include a binder, and optionally, may further include a conductive material, a thickener, etc.

[0101] (Cathode solvent) Non-limiting examples of the solvent used for manufacturing the cathode slurry include N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, N,N-dimethylaminopropylamine, ethylene oxide, tetrahydrofuran, etc.

[0102] (Cathode 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 cathode binder.

[0103] (Cathode conductive material) The conductive material may be added to enhance the conductivity of the cathode 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.

[0104] (Cathode thickener / dispersant) Optionally, the cathode slurry may further include a thickener and / or a dispersant, etc. In one embodiment, the cathode slurry may include a thickener such as carboxymethyl cellulose (CMC).

[0105] [Anode] The anode may include an anode current collector and an anode active material layer disposed on at least one surface of the anode current collector.

[0106] (Anode 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 polymer substrates coated with conductive metals. The negative electrode current collector is not limited thereto, but for example, it may have a thickness of 10 μm to 50 μm.

[0107] (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.

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

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

[0110] 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 lithium thin film layer may be used as the negative electrode active material layer.

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

[0112] The silicon-containing material can provide 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.

[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 thickening agent, 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 in the production of the negative electrode slurry include water, pure water, deionized water, distilled water, ethanol, isopropanol, methanol, acetone, n-propanol, t-butanol, etc.

[0116] (Negative electrode binder / conductive material / thickening agent) As the binder, conductive material, and thickening agent, the above-mentioned substances that can be used in 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), a polyacrylic acid-based binder, a 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 - 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.

[0121] The organic solvent may include an organic compound having sufficient solubility in the lithium salt and the additive and having 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.

[0122] (Additive) The non-aqueous electrolyte can further contain an additive. The additive can 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.

[0123] 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.

[0124] 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.

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

[0126] The measurement method was as follows: A test piece of 5 - 10 mg was prepared according to the pan size of the DSC, placed in a container, and pressed with a crimper press. The prepared sample and the reference sample were placed, and the analysis was carried out by selecting the temperature range, heating rate, and reactive gas.

[0127] The measurement conditions were as follows.

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

[0129] [Average particle size] 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 according to the ISO 13320 - 1 standard. This method was used to measure the average particle size of inorganic particles and particulate binders.

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

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

[0132] 2) Conditions of GPC (Gel permeation chromatograph) analysis equipment (1) Analysis equipment: Manufactured by Tosoh Corporation, EcoSEC HLC-8320 GPC (2) Detector: RI-detector (3) Developing solvent: 0.1 M NaNO3 (4) Column (maker, model no.): Tskgel guard PWxl + 2 x TSKgel GMPWxl + TSKgel G2500PWxl (7.8×300 mm) (5) Temperature: 40°C (6) Flow rate: 1.0 mL / min (7) Injection volume: 100 μl, 10 mg / mL (8) Standard substance: PEG / PEO

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

[0134] [Porosity] The porosity of the porous substrate was calculated from the following mathematical formula by cutting a rectangular sample of A cm × B cm. A and B were cut and measured in the range of 5 - 20 cm respectively.

[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 the porous substrate (g / cm 3 )

[0137] [Gurley Permeability] The Gurley permeability of the porous substrate was measured using a Densometer manufactured by Toyoseiki, in accordance with ASTM D726 standard. The time taken for 100 cc of air to pass through an area of 1 square inch of the porous substrate was recorded in seconds and compared.

[0138] [Pin Puncture Strength] The method for measuring the Pin Puncture Strength of the separator was carried out in accordance with ASTM D3763_02 standard. Each sample was measured 3 times and the average value was obtained. Speed: 120 mm / min Diameter of the pin: 1.0 mm

[0139] [FT-IR Spectrum Measurement] The separator was cut into 1 cm × 1 cm sizes to prepare measurement samples, and measurements were performed under the following conditions using an FT-IR instrument (Nicolet iN10 Infrared Microscope manufactured by Thermo Scientific) equipped with an MCT (mercury cadmium telluride) detector. The average values of the main peaks shown in the measured FT-IR spectra are shown in Table 2 below.

[0140] -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

[0141] [Average thickness (μm) of separator and porous substrate] After stacking 10 separators, the thicknesses were measured at 5 arbitrary points in the width direction using a thickness gauge manufactured by Mitutoyo, and the sum was calculated. Then, the sum was divided by 5 to derive the average thickness of the 10-layer separator, and further divided by 10 to derive the overall average thickness of a single separator.

[0142] The average thickness of the porous substrate was obtained by stacking 10 porous substrates only, measuring the thicknesses at 5 arbitrary points in the width direction using a thickness gauge manufactured by Mitutoyo, calculating the sum, and then dividing the sum by 5 to derive the average thickness of the 10-layer porous substrate, and further dividing by 10 to derive the average thickness of the porous substrate. In the case after forming the inorganic particle layer, after detaching the inorganic particle layer and sufficiently drying it, the average thickness of the porous substrate from which the inorganic particle layer had been detached was derived by the above method.

[0143] [BDV / t (kV / μm)] The breakdown voltage (BDV) was measured in accordance with ASTM D 3755. After placing the separator between the electrodes of a withstand voltage tester (model 19052, manufactured by Croma) under a dry room (dew point temperature: -60°C), the voltage (kV) was evaluated when the leakage current value measured under the condition of increasing the applied voltage at 5 kV / 10 sec reached 5 mA.

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

[0145] Next, in order to compare the breakdown voltage secured with respect to the thickness, the value of BDV / t, which is the ratio of the measured breakdown voltage BDV to the overall average thickness t of the separator, was determined.

[0146] [Packing density of inorganic particle layer (g / (m 2 .μm))] After measuring the average thickness of the porous substrate and the overall average thickness of the separator provided with the inorganic particle layer on the porous substrate according to the above method, 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 provided with the inorganic particle layer on the porous substrate was cut into an area S (m 2 ) of 10 mm × 10 mm (0.01 m 2 ), and the weight was measured. After subtracting the weight of only the porous substrate, the weight W (g) of only the inorganic particle layer was calculated. The packing density of the inorganic particle layer was calculated as W / (T*S) (g / (m 2 .μm)).

[0147] [Δ Gurley permeability] The Δ Gurley permeability was calculated using the following formula after measuring the Gurley permeability, which was measured in seconds as the time it took for 100 cc of air to pass through an area of 1 square inch of the separator using a Densometer manufactured by Toyoseiki, in accordance with ASTM D726 standard.

[0148] Δ Gurley permeability (sec / 100cc) = P m - P s

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

[0150] [Thermal shrinkage rate (%)] The separator was cut into a square shape with a side length of 10 cm, and the transverse direction (TD) and machine direction (MD) were marked. The sample was placed in the middle, and 5 sheets of paper were placed on top and bottom of the sample, and the four sides of the paper were wrapped with tape. The paper-wrapped sample was left in a hot air drying oven at 150 °C for 60 minutes. Then, the sample was taken out, and the separator was measured with a camera. Using the following formula, the thermal shrinkage rate in the machine direction (MD) and the thermal shrinkage rate in the transverse direction (TD) were calculated.

[0151] 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

[0152] [Adhesive force] The separator was cut into a size of 50 mm in width × 50 mm in length and arranged so that the inorganic particle layer was on top. A black drawing paper (width 20 mm × length 150 mm × thickness 0.25 mm) with a coefficient of kinetic friction of 0.15 was placed on it, and a predetermined pressure (200 g / cm 2After adding ), the black drawing paper is forcibly taken out horizontally to check the degree of the inorganic substances attached to the surface. According to the degree of attachment, refer to the following grades and distinguish from A / B / C / D / E / F.

[0153] A: Nothing comes out B: A small amount of inorganic substances come out C~F: Both the binder and the inorganic substances come out at a certain level, and the degree gets worse as it goes to F

[0154] [Resistance characteristics of the battery] Each battery manufactured by the examples and comparative examples was charged at 4.2V with CC-CV (Constant current-constant voltage) using a charge / discharge cycle device and then discharged. Specifically, each battery was charged at a constant current at 25°C with a current of 0.5C rate 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 300 times. Then, the DC-IR (Direct Current Internal Resistance) of the first cycle and the 300th cycle was measured by the J-Pulse method at an SOC (State of charge) of 60%, and the resistance increase rate was calculated by the following formula.

[0155] ΔR(%)=(R2-R1) / R1×100

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

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

[0158] Manufacture of Separator As a porous substrate, a polyethylene porous film with an average thickness of 9 μm (porosity: 42%, Gurley permeability: 118 sec. / 100 cc, puncture strength: 440 gf) was used. After applying the manufactured coating slurry to both sides of the porous substrate, it was dried to form an inorganic particle layer with an average thickness of 2.1 μm on each side of the porous substrate, and a separator was manufactured.

[0159] Manufacture of Secondary Battery As a positive electrode active material, 94 wt% of LiCoO2, 2.5 wt% of polyvinylidene fluoride as a binder, and 3.5 wt% of carbon black as a conductive material were added to NMP (N-methyl-2-pyrrolidone) as a 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 a negative electrode active material, 95 wt% of artificial graphite, 3 wt% of an acrylic latex with a Tg of -52 °C as a binder, and 2 wt% of CMC (carboxymethyl cellulose) as a thickener were added to water as a 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 by stacking 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 heat press 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.

[0160] <Example 2> When producing the coating slurry, a separator and a secondary battery were produced in the same manner as in Example 1, except that boehmite with an average particle size (D50) of 0.27 μm was used as the inorganic particles.

[0161] <Example 3> When producing the coating slurry, a separator and a secondary battery were produced in the same manner as in Example 1, except that a mixture of boehmite with average particle sizes (D50) of 0.3 μm and 0.7 μm in a weight ratio of 8:2 was used as the inorganic particles.

[0162] <Example 4> A separator and a secondary battery were manufactured in the same manner as in Example 1, except that when manufacturing the coating slurry, boehmite having an average particle size (D50) of 0.3 μm and 0.7 μm as inorganic particles was used, which were mixed at a weight ratio of 7:3.

[0163] <Example 5> A separator and a secondary battery were manufactured in the same manner as in Example 1, except that when manufacturing the coating slurry, boehmite having an average particle size (D50) of 0.3 μm and 0.7 μm as inorganic particles was used, which were mixed at a weight ratio of 6:4.

[0164] <Comparative Example 1> Manufacture of Coating Slurry To 95% by weight of boehmite (γ-AlO(OH)) having an average particle size (D50) of 1.3 μm as inorganic particles and 5% by weight of polyacrylate (Mw: 120,000 g / mol, Tg: -45 °C, D50: 250 nm, Sigma Aldrich Inc.) as a particulate binder with respect to the total weight of the solid content, water was added and then stirred to manufacture a coating slurry having a solid content concentration of 25% by weight.

[0165] Manufacture of Separator A polyethylene porous film having an average thickness of 9 μm (porosity: 42%, Gurley permeability: 118 sec. / 100 cc, puncture strength: 440 gf) was used as the porous substrate. After applying the manufactured coating slurry to both sides of the porous substrate, it was dried to form an inorganic particle layer with an average thickness of about 2.0 μm on each side of the porous substrate, thereby manufacturing a separator.

[0166] Manufacture of Positive Electrode, Negative Electrode and Battery After manufacturing the positive electrode and the 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> Manufacture of Coating Slurry Based on the total weight of the solid content, 95% by weight of boehmite (γ-AlO(OH)) with an average particle size (D50) of 0.7 μm as inorganic particles, 4.2% by weight of polyacrylate (Mw: 120,000 g / mol, Tg: -45°C, D50: 250 nm, Sigma Aldrich Inc.) as a binder, and 0.8% by weight of polyacrylamide (Mw: 150,000 g / mol, Tg: 200°C, Sigma Aldrich Inc.) were added to water, and then stirred to produce a coating slurry with a solid content concentration of 28% by weight. Here, 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] Manufacture of Separator A polyethylene porous film with an average thickness of 9 μm (porosity: 42%, Gurley permeability: 118 sec. / 100 cc, puncture strength: 440 gf) was used as the porous substrate. After applying the manufactured coating slurry to both sides of the porous substrate, it was dried to form an inorganic particle layer with an average thickness of 2.0 μm on each side of the porous substrate, and a separator was manufactured.

[0169] Manufacture of Positive Electrode, Negative Electrode and Battery After manufacturing the positive electrode and the 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> Manufacture of Coating Slurry Based on the total weight of the solid content, 90% by weight of inorganic particles obtained by mixing boehmite (γ-AlO(OH)) with average particle sizes (D50) of 0.3 μm and 0.7 μm respectively in a weight ratio of 8:2, and 10% by weight of polyacrylate (Mw: 120,000 g / mol, Tg: -45°C, D50: 250 nm, Sigma Aldrich Inc.) as a binder were added to water, and then stirred to produce a coating slurry with a solid content concentration of 25% by weight.

[0171] Manufacture of Separator A polyethylene porous film with an average thickness of 9 μm (porosity: 42%, Gurley permeability: 118 sec. / 100 cc, puncture strength: 440 gf) was used as the porous substrate. After applying the manufactured coating slurry to both sides of the porous substrate, it was dried to form an inorganic particle layer with an average thickness of 2.0 μm on each side of the porous substrate, and a separator was manufactured.

[0172] Manufacture of the positive electrode, negative electrode, and battery 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> Manufacture of the coating slurry 93% by weight of inorganic particles obtained by mixing boehmite (γ-AlO(OH)) with average particle diameters (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 °C, Sigma Aldrich Inc.) as a binder were added to water, and then stirred to manufacture a coating slurry with a solid content concentration of 25% by weight.

[0174] Manufacture of the separator A polyethylene porous film with an average thickness of 9 μm (porosity: 42%, Gurley permeability: 118 sec. / 100 cc, puncture strength: 440 gf) was used as the porous substrate. After applying the manufactured coating slurry to both sides of the porous substrate, it was dried to form an inorganic particle layer with an average thickness of 2.0 μm on each side of the porous substrate, and a separator was manufactured.

[0175] Manufacture of the positive electrode, negative electrode, and battery 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> Manufacture of the coating slurry 95% by weight of inorganic particles obtained by mixing boehmite (γ-AlO(OH)) with average particle sizes (D50) of 0.3 μm and 0.7 μm, respectively, at a weight ratio of 8:2 based on the total weight of the solid content, 4.2% by weight of polyacrylate (Mw: 120,000 g / mol, Tg: -45°C, D50: 250 nm, Sigma Aldrich Inc.) as a binder, and 0.8% by weight of polyethylene oxide (Mv: 200,000 g / mol, Tg: 65°C, Sigma Aldrich Inc.) were added to water and then stirred to produce a coating slurry with a solid content concentration of 25% by weight.

[0177] Manufacture of Separator A polyethylene porous film with an average thickness of 9 μm (porosity: 42%, Gurley permeability: 118 sec. / 100 cc, puncture strength: 440 gf) was used as the porous substrate. After applying the produced coating slurry to both sides of the porous substrate, it was dried to form an inorganic particle layer with an average thickness of 2.0 μm on each side of the porous substrate, thereby manufacturing a separator.

[0178] Manufacture of Positive Electrode, Negative Electrode, and Battery After manufacturing the positive electrode and the negative electrode in the same manner as described in Example 1, a secondary battery was manufactured together with the produced separator.

[0179] The physical properties of the separators manufactured in the above Examples and Comparative Examples, and the performance (resistance characteristics) of the secondary batteries were measured and shown in Table 1 below. Also, the results of FT-IR spectrum 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 Table 1 and Table 2 above, the BDV / t value is 0.15 or more, and the separator of the example having a peak shown in the range of 1070 to 1082 cm -1 in the FT-IR spectrum, with a Δ Gurley permeability of 100 sec / 100 cc or less and a heat shrinkage rate of 5% or less, has excellent withstand voltage characteristics even at a thin thickness, a high packing density of the inorganic particle layer, a low Δ Gurley permeability and a low heat shrinkage rate at a high temperature (150 °C), and also has excellent adhesion. Further, the initial discharge resistance and the discharge resistance after 300 cycles of the battery to which this was applied were low.

[0183] On the other hand, the separators of Comparative Examples 1 to 5 that do not satisfy at least any one of the BDV / t value, the presence of a peak shown at a specific position in the FT-IR spectrum, the Δ Gurley permeability value, and the heat shrinkage rate value to be achieved in the present disclosure have a significant decrease in any one of the withstand voltage characteristics, heat resistance, adhesiveness, and permeability, and the initial and 300-cycle discharge resistances of the battery to which this was applied were higher than those of the examples.

[0184] The content described above is merely an exemplification of applying the principle 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, and an inorganic particle layer formed on at least one surface of the porous substrate and 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 more, and in the spectrum by Fourier transform infrared spectroscopy (FT-IR), there is a peak shown in the range of 1070 cm －１ to 1082 cm －１ . After leaving it standing at 150°C for 60 minutes, the thermal shrinkage rates in the machine direction and the width direction measured are 5% or less, and the Δ Gurley permeability calculated by the following calculation formula 1 is 100 sec / 100 cc or less. Separator. [Calculation formula 1] Δ Gurley transparency (sec / 100 cc) = P ｍ -P ｓ In the calculation formula 1, P ｍ is the gas permeability of the separator, and P ｓ is the gas permeability of the porous substrate.

2. The separator according to claim 1, wherein the inorganic particles include any one or two 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) 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. The separator according to claim 1, wherein the binder includes a particulate binder and a water-soluble binder.

8. The separator according to claim 7, wherein the particulate 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 include any one or more selected from the group consisting of ester-based polymers, amide-based polymers, imide-based polymers, acrylic-based polymers, acrylamide-based polymers, vinyl alcohol-based polymers, fluorine-based polymers, and vinyl pyrrolidone-based polymers.

11. The separator according to claim 1, wherein the binder is 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.

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

10.

13. The packing density of the inorganic particle layer is 1.2 g / m ２ .μm or more, and the separator according to claim 1.

14. A lithium secondary battery including the separator according to any one of claims 1 to 13.

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