Diaphragm and lithium secondary battery comprising the same

Abstract

The present disclosure relates to a separator having a remarkably excellent voltage resistance property and a lithium secondary battery including the same. According to one aspect of the present disclosure, there is provided a separator including: a porous substrate; and an inorganic particle layer formed on at least one side of the porous substrate, containing a binder and inorganic particles, a ratio of an insulation breakdown voltage (kV) of the separator to an overall average thickness (µm) of the separator being 0.15 kV / µm or more, having a peak appearing in a range of 1070 cm ‑1 to 1082 cm ‑1 in a spectrum based on Fourier transform infrared spectroscopy (FT-IR), a thermal shrinkage rate in a machine direction and a width direction measured after being left at 150℃ for 60 minutes being 5% or less, and a Δ Gurley air permeability being 100 sec / 100cc or less.

Description

Technical Field

[0001] This disclosure relates to a separator with significantly superior voltage resistance characteristics and a lithium secondary battery including the separator. Background Technology

[0002] In electrochemical devices, the separator is crucial for improving the stability and performance (lifetime, capacity, etc.) of the battery. The main function of the separator is to provide a path for ion movement within the battery and prevent physical contact between the negative and positive electrodes. High-performance batteries can be manufactured by improving the properties of the separator.

[0003] To achieve high capacity / high output characteristics for electrochemical devices, research on separators for secondary batteries is moving towards thinning. However, with the trend towards thinner separators, the breakdown voltage of the separator decreases, thus the decline in voltage withstand characteristics has become a significant problem.

[0004] Breakdown voltage (BDV) is the voltage at which a spark discharge occurs through an insulator when a voltage is applied, causing that portion to become conductive and lose its insulating properties. A higher BDV indicates better voltage withstand characteristics. BDV is highly dependent on the thickness of the insulator. As the separator thickness decreases, the BDV of the electrochemical device decreases, potentially leading to reduced battery stability and increased low-voltage failure rate. Therefore, there is an urgent need for a battery separator that combines a thinner profile with a higher BDV, thereby achieving high capacity / high output characteristics while maintaining high stability and a low low-voltage failure rate. Summary of the Invention

[0005] Technical issues

[0006] According to one aspect of this disclosure, a diaphragm with excellent voltage resistance, heat resistance, adhesion and permeability can be provided.

[0007] According to another aspect of this disclosure, a lithium secondary battery including the separator can be provided, which has high capacity / high output characteristics, high stability and low voltage failure rate.

[0008] The separator disclosed herein can be widely used in green technology fields such as electric vehicles, battery charging stations, and other battery-powered solar and wind power generation. Furthermore, the separator disclosed herein can be used in eco-friendly electric vehicles and hybrid vehicles to prevent climate change by suppressing air pollution and greenhouse gas emissions.

[0009] Technical solution

[0010] The diaphragm according to this disclosure comprises: a porous substrate; and an inorganic particulate layer formed on at least one side of the porous substrate, comprising an adhesive and inorganic particles, wherein the ratio of the insulation breakdown voltage (kV) of the diaphragm to the overall average thickness (µm) of the diaphragm is 0.15kV / µm or higher, and has a light intensity at 1070 cm⁻¹ in a Fourier transform infrared spectroscopy (FT-IR) spectrum. -1 Up to 1082cm -1 The peaks appearing within the range, the thermal shrinkage rate in the mechanical and width directions measured after being placed at 150°C for 60 minutes is less than 5%, and the ΔGerley air permeability calculated by the following formula 1 is less than 100sec / 100cc.

[0011] [Equation 1]

[0012] ΔGree air permeability = P m -P s The unit for ΔGree air permeability is sec / 100cc.

[0013] In the above formula 1, P m For the air permeability of the diaphragm, P s The air permeability of porous substrates.

[0014] In one embodiment, the inorganic particles may include any one or more of the group consisting of metal hydroxides, metal oxides, metal nitrides and metal carbides.

[0015] In one embodiment, the average particle size (D50) of the inorganic particles can be from 0.01µm to 0.65µm.

[0016] In one embodiment, the inorganic particles may include first inorganic particles with an average particle size (D50) of 0.01 µm to 0.5 µm.

[0017] In one embodiment, the inorganic particles may further include second inorganic particles with an average particle size (D50) greater than that of the first inorganic particles.

[0018] In one embodiment, based on the total weight of the first inorganic particles and the second inorganic particles, the content of the second inorganic particles can be less than 50% by weight.

[0019] In one embodiment, the adhesive may include a particulate adhesive and a water-soluble adhesive.

[0020] In one embodiment, the glass transition temperature of the particulate adhesive can be from -60°C to 0°C.

[0021] In one embodiment, the glass transition temperature of the water-soluble adhesive can be from 180°C to 220°C.

[0022] In one embodiment, the particulate adhesive and the water-soluble adhesive may each independently comprise any one or more polymers selected from the group consisting of ester polymers, amide polymers, imide polymers, acrylic polymers, acrylamide polymers, vinyl alcohol polymers, fluorinated polymers, and vinylpyrrolidone polymers.

[0023] In one embodiment, the content of the adhesive may be from 0.1 parts by weight to 20 parts by weight relative to 100 parts by weight of inorganic particles.

[0024] In one embodiment, the weight ratio of the water-soluble adhesive to the granular adhesive can be from 1:1 to 1:10.

[0025] In one embodiment, the packing density of the inorganic particle layer can be 1.2 g / m³. 2 • Above µm.

[0026] Furthermore, this disclosure provides a lithium secondary battery including the separator described above.

[0027] The effects of the invention

[0028] The diaphragm according to this disclosure can have excellent voltage resistance, heat resistance, adhesion and permeability.

[0029] Furthermore, this disclosure provides a lithium secondary battery that includes a separator according to one embodiment, thereby having high capacity / high output characteristics, high stability, and low voltage failure rate. Detailed Implementation

[0030] The present disclosure will now be described in detail. However, the embodiments described in this specification can be modified in many other ways, and the technology according to one embodiment is not limited to the embodiments described below. Moreover, one embodiment is provided to provide a more complete explanation of the present disclosure to those skilled in the art.

[0031] Furthermore, the singular form used in the specification and appended claims may be intended to also include the plural form, unless specifically indicated by the context.

[0032] Furthermore, the numerical ranges used in this specification include lower and upper limits, as well as all values ​​within that range, increments logically derived from the form and magnitude of the defined range, all values ​​with double limits, and all possible combinations of upper and lower limits of numerical ranges defined in other forms. Unless otherwise defined in this specification, values ​​outside the defined numerical range that may occur due to experimental errors or rounding are also included within the defined numerical range.

[0033] Furthermore, throughout the specification, unless otherwise stated, “include” a constituent element does not mean that other constituent elements are excluded, but rather that other constituent elements may also be included.

[0034] Unless otherwise defined in this specification, the average particle size of inorganic particles and granular adhesives refers to the D50 value. D50 refers to the particle size of the cumulative fraction of inorganic particles and granular adhesives on a volume basis equivalent to 50%. The average particle size can be derived from the particle size distribution results of the inorganic particles and granular adhesives to be measured, collected according to ISO 13320-1 standard and analyzed using a Microtrac S3500.

[0035] In this specification, "MD (machine direction)" refers to the longitudinal direction of the porous substrate and diaphragm manufactured in the longitudinal direction, and "TD (transverse direction)" refers to the direction orthogonal to MD in the surface direction of the porous substrate and diaphragm. In this disclosure, TD is also referred to as the "transverse direction".

[0036] In this specification, the overall average thickness of the separator refers to the overall average thickness of the separator comprising a porous substrate and an inorganic particulate layer disposed on at least one side of the porous substrate. In one embodiment, the overall average thickness (µm) of the separator can be obtained by the following method: After stacking 10 layers of separator, the thickness is measured at any 5 points on the TD using a Mitutoyo thickness gauge. The result is then divided by 5 to obtain the average thickness of the 10 separator layers, and then divided by 10 to obtain the overall average thickness of a single separator.

[0037] In this specification, the average thickness of the porous substrate refers to the average thickness of a porous substrate without an inorganic particle layer on at least one side. In one embodiment, the average thickness (µm) of the porous substrate can be obtained by the following method: After stacking 10 layers of a porous substrate without an inorganic particle layer on at least one side, the thickness is measured at any 5 points on a TD using a Mitutoyo thickness gauge. The result is then divided by 5 to derive the average thickness of the 10 porous substrate layers, and then divided by 10 to derive the average thickness of the porous substrate. If the average thickness of a porous substrate with an inorganic particle layer on at least one side is required, the average thickness of the porous substrate after the inorganic particle layer has been removed can be determined without limitation using any method known in the art and after thorough drying.

[0038] In this specification, the bulk density of the inorganic particle layer (g / (m³)) is... 2•µm) refers to the unit area (m²) of a porous substrate. 2 The weight of the inorganic particle layer per unit height (µm) is also considered. In one embodiment, the packing density of the inorganic particle layer can be measured by the following method: After measuring the average thickness of the porous substrate and the overall average thickness of the membrane with the inorganic particle layer on the porous substrate according to the above method, the thickness (T, µm) of the inorganic particle layer is calculated by subtracting the average thickness of the porous substrate from the overall average thickness of the membrane. The membrane with the inorganic particle layer on at least one side of the porous substrate is cut into 10mm × 10mm (0.01m) pieces. 2 Area (S, m) 2 The weight of the inorganic particle layer was measured, and then the weight of the porous substrate was subtracted to calculate the thickness (W, g) of the inorganic particle layer alone. The bulk density of the inorganic particle layer was calculated as W / (T*S).

[0039] In this specification, glass-transition temperature (Tg) refers to the temperature range in which the glass transition occurs, and is a value measured using a dilatometer or differential scanning calorimeter (DSC).

[0040] When this specification describes layers, films, regions, plates, etc., as being located "above" or "on" other parts, this includes not only cases where they are "directly" located "on" other parts, but also cases where there are other parts in between.

[0041] The terms "first," "second," etc., used in this specification may be used to describe various constituent elements, but the constituent elements are not limited by these terms. The terms are used only to distinguish one constituent element from another.

[0042] This disclosure provides a separator capable of providing batteries with high voltage resistance, heat resistance, adhesion, and permeability, high capacity / high output characteristics, high stability, and low low-voltage defect rate. Specifically, according to one embodiment, the separator includes: a porous substrate; and an inorganic particulate layer located on at least one side of the porous substrate, comprising an adhesive and inorganic particles, wherein the ratio of the separator's insulation breakdown voltage (BDV, kV) to the overall average thickness (t, µm) of the separator (hereinafter referred to as BDV / t) is 0.15 kV / µm or higher, and has a spectral density at 1070 cm⁻¹ in a Fourier transform infrared spectroscopy (FT-IR) spectrum. -1 Up to 1082cm -1The peak appearing within the range (hereinafter referred to as the first peak), after being placed at 150°C for 60 minutes, has a thermal shrinkage rate of less than 5% in the mechanical and width directions, and the ΔGerley air permeability calculated by the following formula 1 is less than 100sec / 100cc.

[0043] [Equation 1]

[0044] ΔGree air permeability (sec / 100cc) = P m -P s

[0045] In the above formula 1, P m For the air permeability of the diaphragm, P s The air permeability of porous substrates.

[0046] According to one embodiment, the diaphragm satisfies the following conditions: the ratio of the diaphragm's insulation breakdown voltage (kV) to its overall average thickness (µm) is 0.15 kV / µm or higher, 0.16 kV / µm or higher, or 0.163 kV / µm or higher, while simultaneously satisfying a peak at 1070 cm⁻¹ in the FT-IR spectrum. -1 Up to 1082cm -1 Furthermore, since the heat shrinkage rate and ΔGerley permeability are within the above range, it was invented that can simultaneously possess significantly excellent voltage resistance, heat resistance, adhesion and permeability even at a thin thickness.

[0047] Furthermore, the lithium secondary battery according to one embodiment includes a separator that simultaneously satisfies a first peak within a specific range in the FT-IR spectrum and specific ranges of BDV / t, thermal shrinkage rate, and ΔGerley permeability value, thus simultaneously possessing high capacity / high output characteristics, high stability, and low voltage defect rate. Specifically, the lithium secondary battery according to one embodiment includes a separator with significantly improved voltage withstand characteristics at a thin thickness, thus not only resulting in low initial discharge resistance but also a significantly low increase in discharge resistance after 300 cycles compared to the initial discharge resistance, thereby achieving improved output characteristics.

[0048] The effect is caused by adjusting the ratio of the membrane's insulation breakdown voltage (kV) to its overall average thickness (µm), the peaks appearing in the FT-IR spectrum, the thermal shrinkage rate, and the ΔGreley permeability to specific ranges, and is not solely influenced by the membrane's constituent elements or a specific element in the membrane's manufacturing process. As confirmed in one embodiment, it can be achieved through various schemes including 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, and the type and properties of the adhesive. There are no particular limitations on the scheme as long as it can be achieved. For example, the first peak can originate from the interatomic bonding energy of the inorganic particles contained in the inorganic particle layer, and the range of the first peak is not solely determined by the characteristics of the inorganic particles themselves, such as the average particle size and material, but can also be determined by various factors besides the inorganic particles, such as the characteristics of the adhesive or porous substrate.

[0049] In one embodiment, the insulation breakdown voltage (BDV, kV) of the diaphragm is measured according to ASTM D 3755. It is the voltage (kV) measured when the leakage current is 5 mA, after the diaphragm is positioned between the electrodes of a withstand voltage tester (Croma Model 19052) in a dry chamber (dew point temperature: -60°C) and a voltage is applied at a 5 kV / 10 sec ramp-up. This voltage is designated as the insulation breakdown voltage (BDV).

[0050] In one embodiment, the BDV / t can be above 0.15 kV / µm or above 0.155 kV / µm, and its upper limit is not particularly limited, but for example, it can be below 0.3 kV / µm, below 0.25 kV / µm, or below 0.2 kV / µm. In a specific embodiment, the value of the above formula (1) can be 0.15 to 0.3 kV / µm, 0.15 to 0.25 kV / µm, 0.155 to 0.2 kV / µm, or 0.156 to 0.164 kV / µm, but is not limited to these values.

[0051] In one embodiment, the first peak is at 1070 cm⁻¹. -1 Up to 1082cm -1 The peak with the highest intensity within the range, specifically, can be at 1071 cm⁻¹. -1 Up to 1082cm -1 Range, 1072cm -1 Up to 1082cm -1 Range, 1075cm -1 Up to 1082cm -1 The range or 1075cm -1 Up to 1081cm -1 The peak with the highest intensity within the range.

[0052] In one embodiment, the diaphragm may also have an FT-IR spectrum at 1140 cm⁻¹ -1 Up to 1160cm -1 The second peak appears within the aforementioned range. Specifically, this second peak, as the peak with the highest intensity within the aforementioned range, can be at 1145 cm⁻¹. -1 Up to 1155cm -1 The peak with the highest intensity within the range.

[0053] In one embodiment, the diaphragm may also have an FT-IR spectrum at 2910 cm⁻¹ -1 Up to 2930cm -1 The third peak appears within the aforementioned range. Specifically, this third peak, considered to have the highest intensity within that range, can be at 2915 cm⁻¹. -1 Up to 2925cm -1 The range or 2915cm -1 Up to 2920cm -1 The peak with the highest intensity within the range.

[0054] In one embodiment, the diaphragm may also have an FT-IR spectrum at 3090 cm⁻¹ -1 Up to 3110cm -1 The fourth peak appears within the aforementioned range. Specifically, this fourth peak, considered to have the highest intensity within this range, can be at 3095 cm⁻¹. -1 Up to 3105cm -1 The peak with the highest intensity within the range.

[0055] In one embodiment, the diaphragm may also have an FT-IR spectrum at 3280 cm⁻¹ -1 Up to 3320cm -1 The fifth peak appears within the range. Specifically, this fifth peak, as the peak with the highest intensity within the aforementioned range, can be at 3280 cm⁻¹. -1 Up to 3310cm -1 The range or 3285cm -1 Up to 3300cm -1 The peak with the highest intensity within the range.

[0056] In one embodiment, the FT-IR spectrum of the diaphragm can be measured using an FT-IR device equipped with a mercury cadmium telluride (MCT) detector, specifically at 4000 cm⁻¹. -1 Up to 675cm -1 Within a range of 4cm -1The resolution is measured by scanning 5 to 200 times in transmission mode.

[0057] According to one embodiment, the diaphragm may have excellent heat resistance. In one embodiment, the thermal shrinkage rate in the mechanical and width directions, measured after the diaphragm is placed at 150°C for 60 minutes, may be less than 5%, preferably less than 4%, more preferably less than 3.7%, less than 3.5%, less than 3.3%, less than 2%, less than 1.6%, less than 1.3%, less than 1.0%, less than 0.8%, or less than 0.6%. For example, it may be from 0.5% to 3.5% or from 0.5% to 2.0%.

[0058] According to one embodiment, the diaphragm may have excellent air permeability. In one embodiment, the ΔGurley permeability of the diaphragm, measured by ASTM D726, calculated using the following formula 1, may be less than 100 sec / 100 cc. Alternatively, the ΔGurley permeability of the diaphragm may be less than 80 sec / 100 cc, less than 50 sec / 100 cc, less than 40 sec / 100 cc, or less than 35 sec / 100 cc, with no particular limitation on the lower limit, but as an example, it may be greater than 5 sec / 100 cc or greater than 10 sec / 100 cc. In a specific embodiment, the ΔGurley permeability of the diaphragm 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.

[0059] [Equation 1]

[0060] ΔGree air permeability (sec / 100cc) = P m -P s

[0061] In the above formula 1, P m For the air permeability of the diaphragm, P s The air permeability of porous substrates.

[0062] In one embodiment, the inorganic particles are not limited to any inorganic particles used in this technical field. As a non-limiting example, the inorganic particles may include any 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 any one or more selected from the group consisting of magnesium oxide (MgO), magnesium hydroxide (Mg(OH)2), aluminum oxide (Al2O3), boehmite (γ-AlO(OH)), aluminum hydroxide (Al(OH)3), silicon dioxide (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 perspective of battery stability, the inorganic particles are preferably any one or more metal hydroxide particles selected from the group consisting of boehmite, aluminum hydroxide (Al(OH)3) and magnesium hydroxide (Mg(OH)2).

[0063] In one embodiment, the shape of the inorganic particles is not limited and can be spherical, elliptical, needle-shaped, plate-shaped, plate-like, etc.

[0064] In one embodiment, the average particle size (D50) of the inorganic particles can be 0.01µm or more, 0.05µm or more, 0.1µm or more, less than 0.65µm, less than 0.5µm, less than 0.4µm, less than 0.3µm, or a value between the above values. For example, the D50 of the inorganic particles can be 0.01µm to 0.65µm, 0.01µm to 0.5µm, 0.05µm to 0.4µm, or 0.1µm to 0.3µm, but may be varied as long as it does not depart from the scope of this disclosure.

[0065] In one embodiment, the inorganic particles may include a first inorganic particle with an average particle size (D50) of 0.01µm to 0.5µm, wherein the D50 of the first inorganic particle may be 0.05µm to 0.4µm, 0.1µm to 0.35µm, or 0.1µm to 0.3µm.

[0066] In one embodiment, the inorganic particles may include the first inorganic particles and a second inorganic particle with an average particle size (D50) larger than that of the first inorganic particle. Specifically, the inorganic particles may include both the first and second inorganic particles within the range described above for their average particle size (D50). The average particle size (D50) of the second inorganic particle may be 0.4µm to 1.0µm, 0.5µm to 0.9µm, 0.6µm to 0.8µm, or 0.7µm to 0.8µm.

[0067] In one embodiment, based on the total weight of the first and second inorganic particles, the content of the second inorganic particles can be less than 50% by weight, less than 40% by weight, less than 35% by weight, less than 30% by weight, more than 1% by weight, more than 10% by weight, more than 20% by weight, or values ​​between the above. For example, based on the total weight of the first and second inorganic particles, the content of the second inorganic particles can be from 1% to 50% by weight, from 1% to 40% by weight, from 5% to 40% by weight, from 10% to 40% by weight, from 20% to 40% by weight, or from 20% to 30% by weight.

[0068] According to another embodiment, the inorganic particles may consist only of first inorganic particles having an average particle size (D50) within the range described above.

[0069] That is, based on the total weight of the inorganic particles, the inorganic particles may comprise 50 to 100% by weight of first inorganic particles having an average particle size (D50) within the aforementioned range and 0 to 50% by weight of second inorganic particles having an average particle size (D50) within the aforementioned range. Alternatively, the inorganic particles may comprise 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 ratios within the aforementioned ranges are satisfied, a membrane with superior physical properties can be provided.

[0070] The first and second inorganic particles mentioned above can be composed of the same or different inorganic materials. When the first and second inorganic particles are composed of the same inorganic material, they can be distinguished by their different particle size distributions, i.e., different D50 values.

[0071] The size of the inorganic particles, or when using first and second inorganic particles, these inorganic particles each have different sizes, and can be defined by their respective particle size distributions and corresponding D50 values. The different sizes of the first and second inorganic particles can be achieved by using first and second inorganic particles with mutually distinct size characteristics from the outset when preparing the inorganic particle layer.

[0072] In one embodiment, the adhesive may include a particulate adhesive and a water-soluble adhesive. When using a particulate adhesive and a water-soluble adhesive as the adhesive, the voltage resistance, heat resistance, adhesion, and permeability of the diaphragm can be improved.

[0073] In one embodiment, the specific shape of the particles in the granular adhesive is not particularly limited. For example, the granular adhesive may have spherical, elliptical, plate-like, or irregularly shaped particles.

[0074] In one embodiment, the average particle size (D50) of the particulate adhesive can be 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 values ​​between these values. As an example, the average particle size (D50) of the particulate adhesive can be 10 nm to 1000 nm, 100 nm to 500 nm, 150 nm to 400 nm, or 250 nm to 400 nm. With the aforementioned average particle size, the adhesive can be uniformly dispersed together with the water-soluble adhesive in the aqueous slurry composition, thus achieving excellent voltage resistance, heat resistance, adhesion, and permeability of the diaphragm.

[0075] In one embodiment, the glass transition temperature of the particulate adhesive can be -60°C to 0°C, -50°C to -10°C, -50°C to -20°C, or -45°C to -20°C. Because the particulate adhesive contains a glass transition temperature within the aforementioned range, the diaphragm according to one embodiment can simultaneously achieve excellent voltage resistance, heat resistance, adhesion, and permeability.

[0076] In one embodiment, the glass transition temperature of the water-soluble adhesive can be between 180°C and 220°C, between 190°C and 210°C, or between 200°C and 210°C. Because it includes both a water-soluble adhesive with a glass transition temperature within the aforementioned range and the aforementioned particulate adhesive, the separator according to one embodiment can simultaneously achieve excellent voltage resistance, heat resistance, adhesion, and permeability. Furthermore, batteries using the separator described above can simultaneously exhibit further improved high capacity / high output characteristics, high stability, and low low-voltage defect rate.

[0077] In one embodiment, for the water-soluble adhesive, the weight-average molecular weight of polyethylene glycol, measured using gel permeation chromatography, can be 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. As another embodiment, the weight-average molecular weight of the water-soluble adhesive can be 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.

[0078] In one embodiment, the adhesive may include particulate adhesives and water-soluble adhesives, and adhesives known to those skilled in the art as disclosed in this application may be appropriately selected depending on the purpose and circumstances. That is, any adhesive used as an inorganic particulate layer in which inorganic particles formed on the surface of a porous substrate layer of a secondary battery separator are interconnected by an adhesive to form pores is not limited.

[0079] In one embodiment, the particulate adhesive and the water-soluble adhesive may comprise polymers, for example, each independently comprising one or more selected from the group consisting of ester polymers, amide polymers, imide polymers, acrylic polymers, acrylamide polymers, vinyl alcohol polymers, fluoropolymers, and vinylpyrrolidone polymers. In one embodiment, the particulate adhesive may comprise an acrylic polymer, and the water-soluble adhesive may comprise an acrylamide polymer.

[0080] In one embodiment, the total content of the adhesive, including the granular adhesive and the water-soluble adhesive, may be appropriately adjusted within the scope of this disclosure, depending on the circumstances and purpose. For example, the content of the adhesive 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 relative to 100 parts by weight of inorganic particles.

[0081] In one embodiment, the weight ratio of the water-soluble adhesive to the granular adhesive can 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 to these ratios.

[0082] In one embodiment, the packing density of the inorganic particle layer can be 1.2 g / (m³). 2 ·µm) or more, 1.3g / (m 2 ·µm and above, 2.5g / (m 2 Less than µm, 2.0 g / (m 2Less than µm, 1.8 g / (m 2 Values ​​below (µm) or between the above values, specifically, can 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 not limited to this.

[0083] In one embodiment, the inorganic particle layer may comprise an adhesive and inorganic particles, and may be a porous inorganic particle layer in which the inorganic particles are connected and fixed by the adhesive to form pores. In one embodiment, the inorganic particle layer is disposed on at least one side of the porous substrate, and with the entire surface of the porous substrate as a reference, the area fraction may be more than 60%, more than 70%, more than 80%, or more than 90%. Preferably, the inorganic particle layer may be formed on 100% of the area of ​​the porous substrate.

[0084] In one embodiment, the inorganic particle layer may be coated on one or both sides of the porous substrate. 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 and the other side may be the same or different.

[0085] According to one embodiment, even if a thin inorganic particle layer is disposed on at least one side of a porous substrate, preferably both sides, the diaphragm can simultaneously achieve excellent voltage resistance, heat resistance, adhesion, and permeability. In one embodiment, the total thickness of the inorganic particle layer is not necessarily limited to this, but can be 0.5µm or more, 1µm or more, 1.5µm or more, 9µm or less, 6µm or less, or values ​​between the above values. For example, the total thickness of the inorganic particle layer can be 0.5µm to 9µm, 1µm to 6µm, or 1.5µm to 6µm.

[0086] In one embodiment, the porous substrate may be a polyolefin-based porous substrate such as polyethylene, polypropylene, or copolymers thereof, but is not limited thereto; any porous substrate known as a porous substrate for separators in lithium secondary batteries may be used. In one embodiment, the porous substrate may be manufactured into a film or sheet, but there are no particular limitations.

[0087] In one embodiment, the porosity of the porous substrate may be 20 to 60% or 30 to 60%, but is not limited thereto.

[0088] In one embodiment, the Gare air permeability of the porous substrate can be 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 values. It can be 10 to 500 sec / 100cc, 25 to 200 sec / 100cc, or 25 to 150 sec / 100cc, but is not limited to these values.

[0089] In one embodiment, the thickness of the porous substrate can be 1µm or more, 3µm or more, 5µm or more, less than 100µm, less than 50µm, less than 30µm, less than 20µm, less than 15µm, or a value between the above values, and can be from 1 to 100µm. Specifically, for the purpose of achieving a high-capacity battery, it can be from 3 to 50µm, 5 to 20µm, or 5 to 15µm. While not limited, the porous substrate can be formed by stretching.

[0090] The method for manufacturing the diaphragm disclosed herein will be described below.

[0091] A method for manufacturing a diaphragm that simultaneously satisfies the above-mentioned physical properties may include: a step of preparing a coating slurry comprising an adhesive and inorganic particles; and a step of coating the coating slurry onto at least one side of a porous substrate to form an inorganic particle layer.

[0092] The descriptions of the porous substrates, inorganic particle layers, inorganic particles, and adhesives are the same as those described above, so specific details are omitted.

[0093] For the method of preparing the coating slurry, all conventional methods known in the art can be used without limitation. Although not particularly limited, according to non-limiting examples, the slurry can be prepared by stirring to disperse inorganic particles, or by using a ball mill to disperse aggregated inorganic particles.

[0094] The coating slurry comprises inorganic particles, a binder, and a solvent. The solvent is not particularly limited and can be selected from those that easily dissolve or disperse the binder. For example, it can be any one or more selected from water, ethanol, methanol, propanol and other lower alcohols, dimethylformamide, acetone, tetrahydrofuran, diethyl ether, methylene chloride, DMF, N-methyl-2-pyrrolidone, hexane, and cyclohexane.

[0095] 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, but is not limited thereto.

[0096] In one embodiment, as a method for coating the slurry onto a porous substrate, all conventional methods known in the art can be used without limitation; however, by non-limiting example, methods such as roller coating, spin coating, dip coating, bar coating, die coating, slot coating, inkjet printing, and combinations thereof can be employed. The coated slurry, upon drying, forms an inorganic particulate layer. The drying can be performed by methods such as warm air drying, hot air drying, low-humidity air drying, vacuum drying, far-infrared irradiation, or electron beam irradiation. The drying temperature is not particularly limited and can therefore be appropriately adjusted according to the experimental environment or purpose, for example, from 30°C to 120°C, 30°C to 100°C, or 30°C to 60°C.

[0097] This disclosure provides a lithium secondary battery including a separator according to one embodiment of the foregoing embodiments. The lithium secondary battery includes the separator as described above, and therefore can simultaneously possess high capacity / high output characteristics, high stability, and low voltage failure rate. Specifically, not only is the initially measured discharge resistance low, but the increase in discharge resistance after 300 cycles can also be significantly lower compared to the initial discharge resistance, thus resulting in improved output characteristics.

[0098] According to one embodiment, a lithium secondary battery may include the aforementioned separator between the positive and negative electrodes. Here, the positive and negative electrodes can be used without limitation, as long as they are commonly used in lithium secondary batteries.

[0099] The following provides a further explanation of the constituent elements of the secondary battery according to this disclosure.

[0100] [positive electrode]

[0101] The positive electrode may include a positive current collector and a layer of positive active material disposed on at least one side of the positive current collector.

[0102] (Positive current collector)

[0103] The positive electrode current collector may contain stainless steel, nickel, aluminum, titanium, or alloys thereof. It may also contain aluminum or stainless steel surface-treated with carbon, nickel, titanium, or silver. The thickness of the positive electrode current collector may be, for example, from 10 µm to 50 µm, but is not limited thereto.

[0104] (Cathode material)

[0105] The positive electrode active material layer may contain a positive electrode active material. The positive electrode active material may include compounds capable of reversibly inserting and deintercalating lithium ions.

[0106] According to the exemplary embodiments, any conventionally used positive electrode active material can be used without limitation; for example, the positive electrode active material may comprise a lithium-nickel metal oxide. The lithium-nickel metal oxide may also comprise at least one of cobalt (Co), manganese (Mn), and aluminum (Al).

[0107] The positive electrode active material may also contain coating elements or doping elements. For example, elements that are substantially the same as or similar to the auxiliary elements described above can be used as coating elements or doping elements. For example, one or more of the above elements can be used as coating elements or doping elements.

[0108] The positive electrode active material may contain nickel-cobalt-manganese (NCM)-based lithium oxide. In this case, NCM-based lithium oxide with increased nickel content can be used.

[0109] The Ni content in the NCM-based lithium oxide (e.g., the mole fraction of nickel in the total moles of nickel, cobalt, and manganese) can be 0.6 or more, 0.7 or more, or 0.8 or more. In some embodiments, the Ni content can 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.

[0110] In some embodiments, the positive electrode active material may also include lithium cobalt oxide-based active material, lithium manganese oxide-based active material, lithium nickel oxide-based active material, or lithium iron phosphate (LFP)-based active material (e.g., LiFePO4).

[0111] (The manufacturing method of the positive electrode)

[0112] For example, a positive electrode slurry can be prepared by mixing the positive electrode active material in a solvent. The positive electrode active material layer can be manufactured by coating the positive electrode slurry onto a positive electrode current collector, followed by drying and calendering. The coating process can be performed using gravure coating, slot die coating, multilayer simultaneous die coating, embossing, doctor blade coating, dip coating, bar coating, casting, etc., and is not limited to these methods. The positive electrode active material layer may also contain a binder, and optionally may contain conductive materials, thickeners, etc.

[0113] (Positive electrode solvent)

[0114] Non-limiting examples of solvents used to prepare the positive electrode slurry include N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, N,N-dimethylaminopropylamine, ethylene oxide, tetrahydrofuran, etc.

[0115] (Positive electrode adhesive)

[0116] The adhesive may include polyvinylidene fluoride (PVDF), poly(vinylidene fluoride-co-hexafluoropropylene) copolymer, polyacrylonitrile, polymethyl methacrylate, nitrile rubber (NBR), polybutadiene rubber (BR), styrene-butadiene rubber (SBR), etc. In one embodiment, a PVDF series adhesive can be used as the positive electrode adhesive.

[0117] (Positive conductive material)

[0118] The conductive material may be added to improve the conductivity of the positive electrode active material layer and / or the mobility of lithium ions or electrons. For example, the conductive material may include carbon-based conductive materials such as graphite, carbon black, acetylene black, Ketjen black, graphene, carbon nanotubes, vapor-grown carbon fiber (VGCF), and carbon fiber, and / or metal-based conductive materials such as perovskite materials such as tin, tin oxide, titanium oxide, LaSrCoO3, and LaSrMnO3, but is not limited thereto.

[0119] (Positive electrode thickener / dispersant)

[0120] Depending on the requirements, the positive electrode slurry may also contain thickeners and / or dispersants. As an example, the positive electrode slurry may contain a thickener such as carboxymethyl cellulose (CMC).

[0121] [negative electrode]

[0122] The negative electrode may include a negative electrode current collector and a negative electrode active material layer disposed on at least one side of the negative electrode current collector.

[0123] (Negative electrode current collector)

[0124] 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 thickness of the negative electrode current collector can be, for example, from 10 µm to 50 µm, but is not limited thereto.

[0125] (Anode material)

[0126] The negative electrode active material layer may contain a negative electrode active material. A material capable of adsorbing and desorbing lithium ions can be used as the negative electrode active material. For example, carbon-based materials such as crystalline carbon, amorphous carbon, carbon composite materials, carbon fibers, etc.; lithium metal; lithium alloys; silicon (Si)-containing substances or tin (Sn)-containing substances, etc. can be used as the negative electrode active material.

[0127] Examples of the amorphous carbon may include hard carbon, soft carbon, coke, mesocarbon microbead (MCMB), mesophase pitch-based carbon fiber (MPCF), etc.

[0128] Examples of the crystalline carbon may include graphite-based carbons such as natural graphite, artificial graphite, graphitized coke, graphitized MCMB, graphitized MPCF, etc.

[0129] The lithium metal may include pure lithium metal or lithium metal formed with a protective layer for inhibiting dendrite growth, etc. In one embodiment, a lithium metal-containing layer deposited or coated on the negative electrode current collector can be used as the negative electrode active material layer. In one embodiment, a lithium thin film layer can also be used as the negative electrode active material layer.

[0130] Elements included in the lithium alloy may include aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium, or indium, etc.

[0131] The silicon-containing substance can provide further enhanced capacity characteristics. The silicon-containing substance may include silicon (Si), SiO x (0 < x < 2), metal-doped SiO x (0 < x < 2), silicon-carbon composites, etc. The metal may include lithium and / or magnesium, and metal-doped SiO x (0 < x < 2) may include metal silicates.

[0132] (Method for manufacturing the negative electrode)

[0133] For example, a negative electrode slurry can be prepared by mixing the negative electrode active material in a solvent. The negative electrode active material layer can be manufactured by coating / depositing the negative electrode slurry on the negative electrode current collector and then drying and calendering. The coating process can be carried out by processes such as gravure coating, slot die coating, multi-layer simultaneous 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 contain an adhesive, and may optionally contain a conductive material, a thickener, etc.

[0134] In some embodiments, the negative electrode may also include a negative electrode active material layer in the form of lithium metal formed by a deposition / coating process.

[0135] (Negative electrode solvent)

[0136] Non-limiting examples of solvents that can be used in preparing the negative electrode slurry include water, pure water, deionized water, distilled water, ethanol, isopropanol, methanol, acetone, n-propanol, tert-butanol, etc.

[0137] (Negative electrode adhesive / conductive material / thickener)

[0138] The aforementioned substances, which are used in the manufacture of the positive electrode, can be used as the adhesive, conductive material, and thickener.

[0139] In some embodiments, styrene-butadiene rubber (SBR) adhesives, carboxymethyl cellulose (CMC), polyacrylic acid adhesives, and poly(3,4-ethylenedioxythiophene) (PEDOT) adhesives can be used as negative electrode adhesives.

[0140] [Electrode Assembly]

[0141] According to exemplary embodiments, the positive electrode, negative electrode, and separator can be repeatedly configured to form an electrode assembly. In some embodiments, the electrode assembly can be of the winding type, stacking type, z-folding type, or stack-folding type.

[0142] [Electrolytes]

[0143] A lithium secondary battery can be defined by housing the electrode assembly and the electrolyte together within a casing. According to an exemplary embodiment, a non-aqueous electrolyte can be used as the electrolyte.

[0144] (Lithium salt / organic solvent)

[0145] Non-aqueous electrolytes include a lithium salt as the electrolyte and an organic solvent, wherein the lithium salt is, for example, represented by Li. + X - As the negative ion of the lithium salt (X) - ), can instantiate 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<​​​​​The organic solvent may include an organic compound that has sufficient solubility for the lithium salt and additives and is non-reactive in the battery. For example, the organic solvent 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), butene 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), and diethylene glycol dimethyl ether can be used. These substances include ether (DEGDME), dimethoxyethane, tetrahydrofuran (THF), 2-methyltetrahydrofuran, ethyl alcohol, isopropyl alcohol, dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, sulfolane, γ-butyrolactone, and propylene sulfite, among others. They can be used alone or in combination of two or more.

[0147] (additive)

[0148] The non-aqueous electrolyte may also contain additives. These additives may include, for example, cyclic carbonate compounds, fluorocarbonate compounds, sulcolepsy 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 fluorocarbonate compounds may be fluorocyclic carbonate compounds. The fluorocyclic carbonate compounds may include fluoroethylene carbonate (FEC), etc. The sulcolepsy compounds may include 1,3-propane sultone, 1,3-propene sultone, 1,4-butane sultone, etc. The cyclic sulfate compounds may include 1,2-ethylene sulfate, 1,2-propylene sulfate, etc. The cyclic sulfite compounds may include ethylene sulfite, buthylene sulfite, etc. The phosphate compounds may include lithium difluorobis-oxalatophosphate, lithium difluorophosphate, etc. The borate compounds may include lithium bis(oxalate) borate, etc.

[0149] 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 merely illustrative of this disclosure and do not limit the scope of the appended claims. Various changes and modifications can be made to the embodiments within the scope and technical concept of this disclosure, which will be obvious to those skilled in the art, and it is only natural that such variations and modifications fall within the scope of the appended claims.

[0150] First, the methods for measuring the physical properties of the diaphragm and evaluating the characteristics of the secondary battery are explained.

[0151] Glass transition temperature

[0152] The glass transition temperature was measured using a differential scanning calorimeter (DSC). The manufacturer was Mettler Toledo, and the model name was DSC1.

[0153] The measurement method is as follows: Prepare 5-10 mg test strips according to the DSC pan size, place the test strips in a container, and press them using a corrugated press. The prepared sample and reference were placed, and the temperature range, heating rate, and reactive gas were selected for analysis.

[0154] The measurement conditions are as follows:

[0155] Temperature range: -100~250℃

[0156] Reactive gas: N2

[0157] Heating / cooling rate: 10℃ / min

[0158] [Average Particle Size]

[0159] The average particle size was derived from the particle size distribution results obtained by collecting samples of the particles to be tested according to ISO 13320-1 and analyzing them using a Microtrac S3500. This method was used to determine the average particle size of inorganic particles and particulate adhesives.

[0160] [Molecular weight]

[0161] Weight-average molecular weight was measured using a GPC (Tosoh, EcoSEC HLC-8320 GPC reflective index detector). A Tskgel Guard PWxl column, two TSKgel GMPWxl columns, and a TSKgel G2500PWxl column (7.8 × 300 mm) were connected together as the GPC column. The solvent used was 0.1 M NaNO3 aqueous solution, and the standard was PEG / PEO. The analysis was performed at 40 °C and a flow rate of 1 mL / min.

[0162] 1) Sample preparation for gel permeation chromatography (GPC)

[0163] (1) Sample pretreatment: The provided sample is used directly.

[0164] (2) Sample dissolution state: completely dissolved

[0165] (3) Sample solution filtration: 0.45µm nylon filter

[0166] 2) Gel permeation chromatography (GPC) analytical equipment conditions

[0167] (1) Analytical equipment: Tosoh EcoSEC HLC-8320 GPC

[0168] (2) Detector: RI detector

[0169] (3) Developing solvent: 0.1M NaNO3

[0170] (4) Column (maker, model no.): Tskgel guard PWxl + 2 x TSKgel GMPWxl + TSKgel G2500PWxl (7.8 x 300mm)

[0171] (5) Temperature: 40℃

[0172] (6) Flow rate: 1.0 mL / min

[0173] (7) Injection volume: 100µl, 10mg / mL

[0174] (8) Standard material: PEG / PEO

[0175] [Viscosity]

[0176] Using a Brookfield viscometer (model RVDV2) and a spindle CPA-52Z, the viscosity was measured at 25°C with the rpm set to 60-70% torque.

[0177] Porosity

[0178] A rectangular sample of porous substrate, measuring A cm × B cm, was taken and its porosity was calculated using the following mathematical formula. Measurements were performed on samples A and B ranging from 5 to 20 cm. The unit is %.

[0179] Porosity = {1 - (M ÷ ρ) ÷ (A × B × T)} × 100

[0180] Where T = diaphragm thickness (cm)

[0181] M = Sample thickness (g)

[0182] ρ = True density of porous substrate (g / cm³) 3 )

[0183] [Gree Breathability]

[0184] The Gurley permeability of porous substrates was measured according to ASTM D726 using a densometer from Toyoseiki Corporation. The time required for 100 cc of air to pass through a 1 square inch area of ​​porous substrate was recorded in seconds and compared.

[0185] [Pin Puncture Strength]

[0186] The puncture strength of the diaphragm was measured in accordance with ASTM D3763_02 standard, with each sample measured three times and the average value taken.

[0187] Speed: 120mm / minute

[0188] Needle diameter: 1.0mm

[0189] [FT-IR spectroscopy measurement]

[0190] The diaphragm was cut into 1cm × 1cm pieces to prepare the measurement samples. Measurements were performed using an FT-IR instrument (Thermo Scientific, Nicolet iN10 Infrared Microscope) equipped with a mercury cadmium telluride (MCT) detector under the following conditions. The average values ​​of the major peaks appearing in the measured FT-IR spectra are shown in Table 2 below.

[0191] - Resolution: 4cm -1

[0192] - Number of scans: 16

[0193] - Range: 4000~675cm -1

[0194] - Measurement points for each sample: 15 points (10µm interval) * 15 points (10µm interval) to map three positions.

[0195] [Average thickness (µm) of diaphragm and porous substrate]

[0196] After stacking 10 layers of membrane, use a Mitutoyo thickness gauge to measure the thickness at any 5 points in the width direction, sum the results, divide by 5 to obtain the average thickness of the 10 membrane layers, and then divide by 10 to obtain the overall average thickness of a single membrane.

[0197] To determine the average thickness of the porous substrate, after stacking 10 layers of the porous substrate, the thickness was measured at any 5 points along the width using a Mitutoyo thickness gauge. The sum of the measurements was then divided by 5 to derive the average thickness of the 10 porous substrate layers. This summation was then divided by 10 to derive the average thickness of the porous substrate. If an inorganic particle layer has already been formed, the inorganic particle layer was removed and thoroughly dried. The average thickness of the porous substrate after the inorganic particle layer was removed was then derived using the same method.

[0198] [BDV / t (kV / µm)]

[0199] The insulation breakdown voltage (BDV) was measured according to ASTM D 3755. The diaphragm was placed between the electrodes of a withstand voltage tester (Croma Model 19052) in a dry chamber (dew point temperature: -60°C) and the voltage was evaluated as the voltage (kV) at which the leakage current was 5mA when the voltage was increased by 5kV / 10sec.

[0200] Regarding the overall average thickness t (µm) of the diaphragm, after stacking 10 layers of diaphragm as above, use a Mitutoyo thickness gauge to measure the thickness at any 5 points on TD, divide by 5 to derive the average thickness of the 10 layers of diaphragm, and then divide by 10 to derive the overall average thickness of a single diaphragm.

[0201] Subsequently, in order to compare the insulation breakdown voltage relative to the thickness, the value of BDV / t, which is the ratio of the insulation breakdown voltage BDV measured above to the overall average thickness t of the diaphragm, was determined.

[0202] Bulk density of inorganic particle layer (g / (m³)) 2 ·µm))]

[0203] After measuring the average thickness of the porous substrate and the overall average thickness of the membrane with the inorganic particle layer on the porous substrate using 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 membrane. The membrane with the inorganic particle layer on the porous substrate was cut into 10mm × 10mm (0.01m) pieces. 2 Area (S, m) 2The weight (W, g) of the inorganic particle layer is calculated by subtracting only the weight of the porous substrate after measuring its weight. The bulk density of the inorganic particle layer is calculated as W / (T*S)(g / (m³)). 2 Calculated using µm.

[0204] [ΔGree Breathability]

[0205] The ΔGurley permeability was measured using a Toyoseiki densometer according to ASTM D726 standard. The time required for 100cc of air to pass through a 1 square inch diaphragm was measured in seconds. The Gurley permeability was then calculated using the following formula.

[0206] ΔGree air permeability (sec / 100cc) = P m -P s

[0207] The P m For the air permeability of the diaphragm, P s The air permeability of porous substrates.

[0208] [Heat shrinkage rate (%)]

[0209] Cut the diaphragm into a square with sides of 10cm and mark the transverse direction (TD) and machine direction (MD). Place the sample in the center, and place five sheets of paper on the top and bottom of the sample respectively, wrapping the four edges of the paper with tape. Place the paper-wrapped sample in a hot air drying oven at 150℃ for 60 minutes. Then remove the sample and measure the diaphragm with a camera, and calculate the heat shrinkage rate in the machine direction (MD) and transverse direction (TD) using the following formulas.

[0210] MD heat shrinkage rate (%) = (MD length before heating - MD length after heating) / MD length before heating × 100

[0211] TD heat shrinkage rate (%) = (TD length before heating - TD length after heating) / TD length before heating × 100

[0212] [Adhesive strength]

[0213] Cut the diaphragm to a size of 50mm wide × 50mm long and arrange it with the inorganic particle layer on top. Place a piece of black drawing paper (20mm wide × 150mm long × 0.25mm thick) with a dynamic friction coefficient of 0.15 on top and apply a certain pressure (200g / cm²) using a pressing device. 2 Then, the black drawing paper was forcibly pulled to the side to confirm the degree of inorganic matter adhering to the surface, and the degree of adhesion was graded to A / B / C / D / E / F.

[0214] A: Not attached

[0215] B: Adhered with a small amount of inorganic matter

[0216] C to F represent the levels where both adhesives and inorganic substances adhere; the closer to F, the more severe the adhesion.

[0217] [Battery resistance characteristics]

[0218] Each battery manufactured according to the embodiments and comparative examples was charged and then discharged using a charge / discharge cycling device at a constant current-constant voltage (CC-CV) of 4.2V. Specifically, each battery was charged at 25°C with a constant current at a rate of 0.5C until the voltage reached 4.2V, and then charged at a constant voltage until the current reached 0.01C while maintaining 4.2V. Subsequently, it was discharged at a constant current of 0.5C until the voltage reached 3.0V, and this cycle was repeated 300 times. Furthermore, the Direct Current Internal Resistance (DC-IR) of the first cycle and the 300th cycle was measured using the J-Pulse method when the State of Charge (SoC) was 60%, and the resistance increase rate was calculated using the following formula.

[0219] △R (%) = (R2-R1) / R1 X 100

[0220] R1 is the resistor for the first cycle (DC-IR), and R2 is the resistor for the 300th cycle (DC-IR).

[0221] <Example 1>

[0222] Preparation of coating slurry

[0223] Based on the total weight of solid components, a coating slurry with a solid component concentration of 25% was prepared by adding 95% by weight of boehmite (γ-AlO(OH)) with an average particle size (D50) of 0.3µm as inorganic particles, 4.2% by weight of polyacrylate (Tg: -45℃, D50: 250nm, Sigma Aldrich Inc.) as a particulate binder, and 0.8% by weight of polyacrylamide (Mw=230000g / mol, Tg: 200℃, Sigma Aldrich Inc.) as a water-soluble binder to water and stirring. The polyacrylamide was added in the form of a dispersion with a solid content of 12% by weight and a viscosity of 2000 mPas.

[0224] Diaphragm manufacturing

[0225] A porous polyethylene membrane 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. The prepared coating slurry was coated onto 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 manufacturing the diaphragm.

[0226] Manufacturing of secondary batteries

[0227] A uniform 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 the binder), and 3.5% by weight of carbon black (as the conductive material) to N-methyl-2-pyrrolidone (NMP) (as the solvent) and stirring. The prepared slurry was coated onto an aluminum foil with a thickness of 30 µm, dried, and pressed to produce a positive electrode with a total thickness of 150 µm. A uniform 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 the binder), and 2% by weight of carboxymethyl cellulose (CMC) (as the thickener) to water (as the solvent) and stirring. The prepared slurry was coated onto a 20µm thick copper foil, dried, and pressed to create a negative electrode with a total thickness of 150µm. A pouch cell was assembled by stacking the prepared separator between the positive and negative electrodes. The assembled cell was then hot-pressed at 80°C and 1MPa using a hot press to fuse the positive, negative, and separator components together. Finally, a 2Ah secondary battery was manufactured by dissolving 1M lithium hexafluorophosphate (LiPF6) in a solution containing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a 3:5:2 volume ratio, followed by sealing.

[0228] <Example 2>

[0229] Except that boehmite with an average particle size (D50) of 0.27 µm was used as the inorganic particles when preparing the coating slurry, the separator and secondary battery were manufactured in the same manner as in Example 1.

[0230] <Example 3>

[0231] Except that boehmite with average particle sizes (D50) of 0.3µm and 0.7µm, respectively, was mixed at a weight ratio of 8:2 to be used as inorganic particles when preparing the coating slurry, the separator and secondary battery were manufactured in the same manner as in Example 1.

[0232] <Example 4>

[0233] Except that boehmite with average particle sizes (D50) of 0.3µm and 0.7µm were mixed at a weight ratio of 7:3 to be used as inorganic particles when preparing the coating slurry, the separator and secondary battery were manufactured in the same manner as in Example 1.

[0234] <Example 5>

[0235] Except that boehmite with average particle sizes (D50) of 0.3µm and 0.7µm, respectively, was mixed in a weight ratio of 6:4 to use as inorganic particles when preparing the coating slurry, the separator and secondary battery were manufactured in the same manner as in Example 1.

[0236] <Comparative Example 1>

[0237] Preparation of coating slurry

[0238] Based on the total weight of solid components, 95% by weight of boehmite (γ-AlO(OH)) with an average particle size (D50) of 1.3µm as inorganic particles and 5% by weight of polyacrylate (Mw=120000g / mol, Tg: -45℃, D50: 250nm, Sigma Aldrich Inc.) as particulate binder were added to water and stirred to prepare a coating slurry with a solid component concentration of 25% by weight.

[0239] Diaphragm manufacturing

[0240] A porous polyethylene membrane 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. The prepared coating slurry was coated onto 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 manufacturing the diaphragm.

[0241] Manufacturing of positive electrode, negative electrode and battery

[0242] After manufacturing the positive and negative electrodes in the same manner as described in Example 1, a secondary battery was manufactured together with the separator manufactured above.

[0243] <Comparative Example 2>

[0244] Preparation of coating slurry

[0245] A coating slurry with a solid content of 28 wt% was prepared by adding 95 wt% boehmite (γ-AlO(OH)) with an average particle size (D50) of 0.7 µm as inorganic particles, 4.2 wt% polyacrylate (Mw: 120000 g / mol, Tg: -45℃, D50: 250 nm, Sigma Aldrich Inc.) as a binder, and 0.8 wt% polyacrylamide (Mw: 150000 g / mol, Tg: 200℃, Sigma Aldrich Inc.) to water and stirring. The polyacrylamide was added in the form of a dispersion with a solid content of 12 wt% and a viscosity of 2000 mPas.

[0246] Diaphragm manufacturing

[0247] A porous polyethylene membrane 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. The prepared coating slurry was coated onto 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 manufacturing the diaphragm.

[0248] Manufacturing of positive electrode, negative electrode and battery

[0249] After manufacturing the positive and negative electrodes in the same manner as described in Example 1, a secondary battery was manufactured together with the separator manufactured above.

[0250] <Comparative Example 3>

[0251] Preparation of coating slurry

[0252] Based on the total weight of solid components, 90% by weight of inorganic particles (a mixture of boehmite (γ-AlO(OH)) with average particle sizes (D50) of 0.3µm and 0.7µm respectively) in a weight ratio of 8:2, and 10% by weight of polyacrylate (Mw: 120000g / mol, Tg: -45℃, D50: 250nm, Sigma Aldrich Inc.) as a binder were added to water and stirred to prepare a coating slurry with a solid component concentration of 25% by weight.

[0253] Diaphragm manufacturing

[0254] A porous polyethylene membrane 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. The prepared coating slurry was coated onto 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 manufacturing the diaphragm.

[0255] Manufacturing of positive electrode, negative electrode and battery

[0256] After manufacturing the positive and negative electrodes in the same manner as described in Example 1, a secondary battery was manufactured together with the separator manufactured above.

[0257] <Comparative Example 4>

[0258] Preparation of coating slurry

[0259] Based on the total weight of solid components, 93% by weight of inorganic particles (a mixture of boehmite (γ-AlO(OH)) with average particle sizes (D50) of 0.3µm and 0.7µm respectively) in a weight ratio of 8:2, and 7% by weight of polyacrylamide (Mw: 150000g / mol, Tg: 200℃, Sigma Aldrich Inc.) as a binder were added to water and stirred to prepare a coating slurry with a solid component concentration of 25% by weight.

[0260] Diaphragm manufacturing

[0261] A porous polyethylene membrane 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. The prepared coating slurry was coated onto 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 manufacturing the diaphragm.

[0262] Manufacturing of positive electrode, negative electrode and battery

[0263] After manufacturing the positive and negative electrodes in the same manner as described in Example 1, a secondary battery was manufactured together with the separator manufactured above.

[0264] <Comparative Example 5>

[0265] Preparation of coating slurry

[0266] Based on the total weight of solid components, 95% by weight of inorganic particles (γ-AlO(OH)) with average particle sizes (D50) of 0.3µm and 0.7µm respectively, mixed in a weight ratio of 8:2, along with 4.2% by weight of polyacrylate (Mw: 120000g / mol, Tg: -45℃, D50: 250nm, Sigma Aldrich Inc.) as a binder, and 0.8% by weight of polyethylene oxide (Mv: 200000g / mol, Tg: 65℃, Sigma Aldrich Inc.) as a binder, were added to water and stirred to prepare a coating slurry with a solid component concentration of 25% by weight.

[0267] Preparation of diaphragm

[0268] A porous polyethylene membrane 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. The prepared coating slurry was coated onto 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 manufacturing the diaphragm.

[0269] Manufacturing of positive electrode, negative electrode and battery

[0270] After manufacturing the positive and negative electrodes in the same manner as described in Example 1, a secondary battery was manufactured together with the separator manufactured above.

[0271] The physical properties of the separators manufactured in the above embodiments and comparative examples and the performance (resistance characteristics) of the secondary batteries are measured and shown in Table 1 below. Furthermore, the FT-IR spectral measurement results of the separators manufactured in the above embodiments and comparative examples are shown in Table 2 below.

[0272] Table 1

[0273]

[0274] Table 2

[0275]

[0276] As can be seen from Tables 1 and 2 above, a BDV / t value greater than 0.15 and exhibiting good performance in the FT-IR spectrum between 1070 and 1082 cm⁻¹ -1The separator in this embodiment exhibits excellent voltage resistance even at a thin thickness, with peaks appearing within the specified range, a ΔGreley permeability of less than 100 sec / 100 cc, and a heat shrinkage rate of less than 5%. It also boasts high packing density of the inorganic particle layer, low ΔGreley permeability and heat shrinkage rate at high temperatures (150°C), and excellent adhesion. Furthermore, batteries using this separator exhibit low initial discharge resistance and low discharge resistance after 300 cycles.

[0277] The separators of Comparative Examples 1 to 5, which fail to meet the requirements of at least one of the following: BDV / t value, presence of a peak at a specific position in the FT-IR spectrum, ΔGerley permeability value, and heat shrinkage rate value, exhibit a significant decrease in any one of the voltage resistance, heat resistance, adhesion, and permeability characteristics. The initial discharge resistance and discharge resistance after 300 cycles of the battery using the separator are higher than those of the Examples.

[0278] The above description is merely an example of applying the principles of this disclosure, and may include other components without departing from the scope of this disclosure.

Claims

1. A diaphragm, comprising: Porous substrate; as well as An inorganic particle layer, formed on at least one side of the porous substrate, comprises an adhesive and inorganic particles. The bulk density of the inorganic particle layer is 1.2 g / m³. 2 Above µm, The inorganic particles include first inorganic particles with an average particle size D50 of 0.01µm to 0.5µm. The adhesives include acrylic adhesives and acrylamide-based water-soluble adhesives. The ratio of the diaphragm's insulation breakdown voltage (kV) to its overall average thickness (μm) is above 0.15 kV / µm, and it exhibits good performance at 1070 cm⁻¹ in Fourier transform infrared spectroscopy (FT-IR). -1 Up to 1082cm -1 The peaks appearing within the specified range, and the thermal shrinkage rates in the mechanical and width directions measured after being placed at 150℃ for 60 minutes are below 5%. The ΔGerley air permeability calculated using the following formula 1 is below 40 sec / 100cc. [Equation 1] ΔGree air permeability (sec / 100cc) = P m -P s In the above formula 1, P m For the air permeability of the diaphragm, P s The air permeability of porous substrates.

2. The diaphragm according to claim 1, wherein the inorganic particles comprise any one or more of the group consisting of metal hydroxides, metal oxides, metal nitrides and metal carbides.

3. The membrane according to claim 1, wherein the average particle size D50 of the inorganic particles is from 0.01µm to 0.65µm.

4. The diaphragm according to claim 1, wherein the inorganic particles further include second inorganic particles with an average particle size D50 greater than that of the first inorganic particles.

5. The diaphragm according to claim 4, wherein the content of the second inorganic particles is less than 50% by weight, based on the total weight of the first inorganic particles and the second inorganic particles.

6. The diaphragm according to claim 1, wherein the acrylic adhesive comprises an acrylic particulate adhesive.

7. The diaphragm according to claim 6, wherein the glass transition temperature of the acrylic particulate adhesive is -60°C to 0°C.

8. The diaphragm according to claim 6, wherein the glass transition temperature of the acrylamide-based water-soluble adhesive is 180°C to 220°C.

9. The diaphragm according to claim 1, wherein the content of the binder is from 0.1 parts by weight to 20 parts by weight relative to 100 parts by weight of the inorganic particles.

10. The diaphragm according to claim 6, wherein the weight ratio of the acrylamide-based water-soluble adhesive to the acrylic-based particulate adhesive is 1:1 to 1:

10.

11. A lithium secondary battery comprising a separator according to any one of claims 1 to 10.

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