Separator and secondary battery including the same

Abstract

To provide a separator and a secondary battery including the same.SOLUTION: According to one aspect of the present disclosure, there is provided a separator including: a porous substrate; and an inorganic particle layer which is formed on at least one surface of the porous substrate and includes a binder and inorganic particles. The separator has a first peak appearing in a range of 3,800-3,400 cm-1 and a second peak appearing in a range of 1,800-1,500 cm-1 in a spectrum by Fourier-transform infrared spectroscopy (FT-IR) measured after performing 600 cycles of charge and discharge.SELECTED DRAWING: Figure 2

Description

Technical Field

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

Background Art

[0002] Recently, lithium secondary batteries are required to have increased capacity so that they can be applied to electric vehicles and energy storage devices. As the capacity of lithium secondary batteries increases, the risk of fire and explosion also increases, and various studies have been conducted to improve this.

[0003] A normal lithium secondary battery is manufactured by winding or laminating cells composed of a negative electrode, a positive electrode, and a separator located between the negative electrode and the positive electrode into a cylinder, inserting them into a pouch, and injecting a liquid electrolyte into the pouch. The electrolyte plays a role in allowing the charges between the electrodes to move smoothly and generally contains a non-aqueous organic solvent and a salt.

[0004] As described above, when a lithium secondary battery using an electrolyte containing a non-aqueous organic solvent and a salt is stored at a high temperature for a long time, problems such as ignition and explosion of the lithium secondary battery may occur due to various factors.

[0005] As an example, in a lithium secondary battery using a carbonate-based organic solvent, a negative electrode passive film (SEI film: solid electrolyte interphase film), which is an electrolyte decomposition product, is formed on the surface of the negative electrode, causing decomposition of the carbonate-based organic solvent, so that gas may be generated inside the secondary battery. Or, in the lithium secondary battery, the electrolyte reacts very sensitively to moisture and may generate gas. Such gases include hydrogen gas (H2), carbon monoxide gas (CO), carbon dioxide gas (CO2), methane gas (CH4), hydrogen fluoride, hydrogen sulfide, etc., depending on the type of non-aqueous organic solvent and negative electrode active material.

[0006] Due to the generation of such gas, the thickness expands during charging. When the lithium secondary battery is left at a high temperature in a fully charged state up to its maximum capacity, a side reaction may occur where the electrolyte reacts with the surface of the negative electrode. Therefore, in the lithium secondary battery, gas continues to be generated due to the side reaction, causing the internal pressure to rise, the volume to expand, and performance degradation such as a reduction in the lifespan of the lithium secondary battery at high temperatures.

[0007] Therefore, in order to improve such performance degradation, research continues to be conducted, such as changing the constituent components of the electrolyte or changing the type of negative electrode material.

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0009] According to one aspect of the present disclosure, it is possible to provide a separator that can significantly reduce the amount of gas generation.

[0010] In addition, it is possible to provide a secondary battery that is excellent in resistance characteristics and lifespan characteristics during long-term driving.

[0011] In addition, it is possible to provide a secondary battery that can significantly suppress volume expansion.

[0012] The separator of the present disclosure and the secondary battery including the same are widely applicable in the fields of green technologies such as electric vehicles, battery charging stands, and other uses of batteries in solar power generation, wind power generation, etc. Further, the separator of the present disclosure and the secondary battery including the same can be used in eco-friendly electric vehicles, hybrid vehicles, etc. that suppress air pollution and greenhouse gas emissions to prevent climate change.

Means for Solving the Problems

[0013] 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. In the spectrum measured by Fourier transform infrared spectroscopy (FT-IR) after performing 600 cycles of charge and discharge, a first peak appearing in the range of 3800 to 3400 cm -1 and a second peak appearing in the range of 1800 to 1500 cm -1 are present. The charge and discharge is defined as one cycle by constant current charging to 4.2 V at 1C at room temperature, followed by constant voltage charging while maintaining 4.2 V until the current reaches 0.01C, and then discharging to 2.5 V at a constant current of 1C.

[0014] In one embodiment, the binder may include a nitrile group.

[0015] In one embodiment, the binder may include a structural unit derived from a (meth)acrylonitrile-based monomer.

[0016] In one embodiment, the binder may further include any one or more structural units selected from the group consisting of a structural unit derived from a (meth)acrylamide-based monomer and a structural unit derived from a (meth)acrylate-based monomer having a polar group.

[0017] In one embodiment, the binder may have a weight average molecular weight of 10,000 to 2,000,000 g / mol.

[0018] In one embodiment, the binder may be a particulate binder.

[0019] In one embodiment, the binder may be an aqueous dispersion binder.

[0020] In one embodiment, the binder may have a glass transition temperature of 40 to 80°C.

[0021] In one embodiment, the binder may be contained in an amount of 1 to 30% by weight based on the total weight of the inorganic particle layer.

[0022] 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, metal carbides, and metal sulfates.

[0023] In one embodiment, the porous substrate may include polar functional groups on its surface.

[0024] The method for manufacturing a separator according to the present disclosure includes a step of manufacturing a slurry composition containing a binder and inorganic particles, and a step of applying the slurry composition to at least one surface of a porous substrate to form an inorganic particle layer. In the spectrum obtained by Fourier transform infrared spectroscopy (FT-IR) measured by performing charge and discharge 600 cycles, a first peak appearing in the range of 3800 to 3400 cm -1 and a second peak appearing in the range of 1800 to 1500 cm -1 are present. The charge and discharge is performed at room temperature. One cycle consists of constant current charging to 4.2 V at 1C, constant voltage charging until the current becomes 0.01C while maintaining 4.2 V, and then discharging to 2.5 V at a constant current of 1C.

[0025] In one embodiment, the binder may include nitrile groups.

[0026] In one embodiment, the binder may include a structural unit derived from a (meth)acrylonitrile-based monomer.

[0027] In one embodiment, the binder may be a particulate binder.

[0028] In one embodiment, the binder may have a glass transition temperature of 40 to 80°C.

[0029] In one embodiment, before the step of forming the inorganic particle layer, the step of introducing polar functional groups to the surface of the porous substrate by hydrophilic surface treatment may be further included.

[0030] In one embodiment, the hydrophilic surface treatment may be performed including any one or more of corona discharge treatment and plasma discharge treatment.

[0031] In one embodiment, after the step of forming the inorganic particle layer, the step of aging the porous substrate on which the inorganic particle layer is formed may be further included.

[0032] The secondary battery according to the present disclosure includes a positive electrode, a negative electrode, a separator as described above interposed between the positive electrode and the negative electrode, and an electrolyte.

Advantages of the Invention

[0033] The separator according to one embodiment of the present disclosure can significantly reduce the gas generation amount.

[0034] The secondary battery using the separator according to one embodiment of the present disclosure can have excellent resistance characteristics and life characteristics during long-term driving.

[0035] In addition, the secondary battery using the separator according to one embodiment of the present disclosure can have the effect of significantly suppressing volume expansion.

Brief Description of the Drawings

[0036]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Mode for Carrying Out the Invention

[0037] Hereinafter, the present disclosure will be described in detail. However, this is merely exemplary and the present disclosure is not limited to the specific embodiments illustrated.

[0038] Also, the singular forms used in the specification and the appended claims are intended to include the plural forms as well, unless the context clearly dictates otherwise.

[0039] Also, the numerical ranges used in this specification include the lower and upper limits, all values within that range, increments logically derived from the form and width of the defined range, including all of the limited values and all possible combinations of the upper and lower limits of different numerical ranges limited to different forms. In this specification, unless otherwise specified, values outside the numerical range that may occur due to experimental error or rounding of values are also included in the defined numerical range.

[0040] Furthermore, throughout the specification, stating that a component "includes" means that it can further include other components, rather than excluding other components, unless specifically stated to the contrary.

[0041] 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 other parts in between.

[0042] In this specification, normal temperature means 20 ± 5°C and can be 25°C as an example.

[0043] In this specification, "average particle size" means "D50", and "D50" means the particle size of inorganic particles corresponding to 50% in terms of the cumulative fraction based on volume. The average particle size can be derived from the results of the particle size distribution analyzed using S3500 manufactured by MICROTRAC after sampling the inorganic particles to be measured according to the ISO 13320-1 standard.

[0044] In the present disclosure, 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).

[0045] According to an embodiment of the present disclosure, after performing charge and discharge during a long-term cycle, in the measured FT-IR spectrum, a separator having a first peak and a second peak at specific positions can effectively suppress the decomposition reaction of the electrolyte and significantly reduce the gas generation amount. When using the separator, the resistance of the battery can be reduced, and a secondary battery having significantly excellent life characteristics can be provided. Also, a secondary battery having characteristics of significantly reducing changes such as volume expansion of the battery over time can be provided.

[0046] 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. In the spectrum obtained by Fourier transform infrared spectroscopy (FT-IR) measured by performing charge and discharge cycles 600 times, there are a first peak appearing in the range of 3800 to 3400 cm -1 and a second peak appearing in the range of 1800 to 1500 cm -1 . A separator having the peaks is provided. Here, the charge and discharge may be defined as follows: at room temperature, constant current charging is performed at 1C up to 4.2V, followed by constant voltage charging while maintaining 4.2V until the current reaches 0.01C, and then discharging at a constant current of 1C down to 2.5V, which is regarded as one cycle. Further, the charge and discharge may be performed using a test battery manufactured by injecting a liquid electrolyte after winding and assembling a separator according to an embodiment between a positive electrode and a negative electrode. The test battery may include a positive electrode including a positive electrode active material layer containing a lithium composite oxide, a negative electrode including a negative electrode active material layer containing a graphite-based material, a separator according to an embodiment of the present disclosure interposed between the positive electrode and the negative electrode, and an electrolyte in which LiPF6 is dissolved at a concentration of 1M in a mixed solvent in which ethylene carbonate and diethyl carbonate are mixed at a volume ratio of 1:1.

[0047] As one embodiment, the first peak is a peak having a maximum intensity in the range of 3800 to 3400 cm -1 , specifically, it may be a peak having a maximum intensity in the range of 3700 to 3500 cm -1 or in the range of 3650 to 3550 cm -1 .

[0048] As one embodiment, the second peak is a peak having a maximum intensity in the range of 1800 to 1500 cm -1 , specifically, it may be a peak having a maximum intensity in the range of 1750 to 1500 cm -1 or in the range of 1700 to 1500 cm -1 .

[0049] As one embodiment, the separator is in the range of 1800 to 1500 cm -1In addition to the second peak within the range, it may further have a third peak. Here, the third peak means a peak having an intensity smaller than that of the second peak within the range of 1800 to 1500 cm -1 In addition to the second peak within the range, it may further have a third peak. Here, the third peak means a peak having an intensity smaller than that of the second peak within the range of 1800 to 1500 cm -1 It may be a peak having an intensity smaller than that of the second peak within the range of 1750 to 1500 cm -1 or within the range of 1700 to 1500 cm

[0050] As a specific example, the second peak may be a peak having a maximum intensity within the range of 1580 to 1500 cm -1 or within the range of 1550 to 1500 cm -1 and the third peak may be a peak having a maximum intensity within the range of 1800 to 1600 cm -1 or within the range of 1700 to 1600 cm -1 or within the range of 1700 to 1600 cm

[0051] As an embodiment, the separator before performing charge and discharge may not have either the first peak appearing within the range of 3800 to 3400 cm -1 or the second peak appearing within the range of 1800 to 1500 cm -1 during the measurement of the FT-IR spectrum.

[0052] The separator has a first peak and a second peak that appear at specific positions on the FT-IR spectrum measured under the above-described conditions, thereby removing the decomposition products of the electrolyte that are a cause of performance degradation and significantly reducing the gas generation amount. Specifically, the decomposition products of the electrolyte may be removed by a chemical reaction with a functional group located on the surface of the separator, and the first peak and the second peak may be generated after charge and discharge by such a chemical reaction. Examples of the decomposition products of the electrolyte include hydrogen gas (H2), carbon monoxide gas (CO), carbon dioxide gas (CO2), methane gas (CH4), hydrogen fluoride, hydrogen sulfide, etc., but are not limited thereto and may be changed according to the types of the non-aqueous organic solvent and the negative electrode active material used. For example, the functional group located on the surface of the separator may be reduced by a reaction with hydrogen gas, thereby removing hydrogen gas, which is an example of the decomposition products of the electrolyte, and significantly reducing the gas generation amount, but is not particularly limited thereto. As another example, the functional group reduced by a reaction with hydrogen gas may react with the decomposition products of the non-aqueous organic solvent used in the electrolyte, thereby removing the decomposition products of the non-aqueous organic solvent that are a cause of performance degradation, but is not particularly limited thereto.

[0053] As one embodiment, the chemical reaction between the functional group located on the surface of the separator and the decomposition products of the electrolyte may be promoted by a metal contained in the positive electrode active material acting as a catalyst, but is not particularly limited thereto. The metal contained in the positive electrode active material may be a metal contained in a positive electrode active material capable of reversibly intercalating and deintercalating lithium ions, and as an example, may be any one or more selected from the group consisting of cobalt, manganese, nickel, iron, and aluminum.

[0054] As one embodiment, the binder may include a nitrile group, and specifically, may include a structural unit derived from a (meth)acrylonitrile-based monomer.

[0055] As one embodiment, the binder may further include any one or more structural units selected from the group consisting of structural units derived from (meth)acrylonitrile monomers, structural units derived from (meth)acrylamide monomers, and structural units derived from (meth)acrylate monomers having a polar group. Together with the structural unit derived from the (meth)acrylonitrile monomer, when further including the structural unit derived from the (meth)acrylamide monomer and / or the structural unit derived from the (meth)acrylate monomer having a polar group, the adhesive force with the active material layer of the positive electrode increases, the reaction with the decomposition products of the electrolyte is more effectively carried out, the gas generation amount can be further reduced, which is more preferable.

[0056] Here, the polar group of the (meth)acrylate monomer having a polar group may be a hydroxy group, a carboxylic acid group, or an aldehyde group, and specifically, it may be a hydroxy group, but is not limited thereto.

[0057] As one embodiment, the binder can be a particulate binder, and the specific shape of the particles is not particularly limited. For example, the particulate binder may have a spherical, elliptical, plate-like, or irregular particle form.

[0058] The particulate binder may have an average particle size (D50) of 10 nm or more, 20 nm or more, 50 nm or more, 10 μm or less, 5 μm or less, 2 μm or less, 500 nm or less, or a value between the above numerical values. As one embodiment, the particulate binder may have an average particle size (D50) of 10 nm to 10 μm, 20 nm to 5 μm, 50 nm to 2 μm, or 50 nm to 500 nm. When having the above average particle size, the binder is uniformly dispersed in the aqueous slurry composition, the reaction between the functional groups on the surface of the separator and the decomposition products of the electrolyte is more effectively carried out, and the gas generation amount can be further reduced.

[0059] As one embodiment, the binder may have a glass transition temperature of 40 to 80°C. By including a binder having a glass transition temperature within the above range, the separator according to one embodiment can trap hydrogen and / or decomposed electrolyte components generated during the charge and discharge process of the battery. Further, a battery to which the separator as described above is applied can suppress volume expansion and achieve a remarkable improvement in charge and discharge performance.

[0060] The binder used in the separator of the present disclosure may be a particulate binder having a glass transition temperature of 40 to 80°C and containing a nitrile group. The separator having an inorganic particle layer containing the particulate binder of the present disclosure can trap hydrogen and / or decomposed electrolyte components generated during the charge and discharge process of the battery. Further, a battery to which the separator as described above is applied can suppress volume expansion and achieve a remarkable improvement in charge and discharge performance. As one embodiment, the binder may have a glass transition temperature of 80°C or less, 70°C or less, 65°C or less, 60°C or less, 40°C or more, 45°C or more, 50°C or more, or a value between the above numerical values. As one embodiment, the binder may have a glass transition temperature of 40 to 80°C, 40 to 70°C, 45 to 65°C, or 50 to 60°C. The particulate binder satisfying the glass transition temperature exists in a particulate form in the slurry composition, and the reaction between the functional groups on the separator surface and the decomposition products of the electrolyte can be carried out more effectively, thereby further reducing the gas generation amount.

[0061] As one embodiment, the binder may be a copolymer containing a structural unit derived from a (meth)acrylonitrile-based monomer, a structural unit derived from a (meth)acrylamide-based monomer, and a structural unit derived from a (meth)acrylate-based monomer having a polar group. Thereby, the reaction between the functional groups on the separator surface and the decomposition products of the electrolyte can be carried out more effectively, and the gas generation amount can be further reduced.

[0062] As one embodiment, the binder may further include an acrylic monomer not included in the above-mentioned monomer. For example, the binder may further include one or more of a structural unit derived from a (meth)acrylate monomer having no polar group and a structural unit derived from a (meth)acrylic acid monomer.

[0063] As an example, the binder may be a copolymer containing 0.1 to 20% by weight of a (meth)acrylonitrile monomer, 20 to 70% by weight of a (meth)acrylamide monomer, 10 to 50% by weight of a (meth)acrylic acid monomer, 0.1 to 10% by weight of a (meth)acrylate monomer having no polar group, and 0.1 to 20% by weight of a (meth)acrylate monomer having a polar group. As one embodiment, the particulate binder may be a copolymer containing 40 to 60% by weight of a (meth)acrylamide monomer, 1 to 15% by weight of a (meth)acrylonitrile monomer, 20 to 40% by weight of a (meth)acrylic acid monomer, 1 to 10% by weight of a (meth)acrylate monomer having no polar group, and 1 to 15% by weight of a (meth)acrylate monomer having a polar group.

[0064] In one embodiment, the binder has 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 these numerical values. In one embodiment, the 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. Specifically, the measurement of the weight average molecular weight is performed using GPC (manufactured by Tosoh, EcoSEC HLC-8320GPC Reflective Index detector). The GPC column is Tskgel guard PWx, two TSKgel GMPWxl, and TSKgel G2500PWxl (7.8×300 mm). The developing solvent is an aqueous solution of 0.1 M NaNO3. The standard is polyethylene glycol, and the analysis is performed at 40 °C with a flow rate of 1 mL / min.

[0065] In one embodiment, the particulate binder may be a water-dispersible binder provided in particulate form within an aqueous slurry composition. The binder is water-dispersible, and even when the content of the binder is increased, the viscosity is low and the coating properties are excellent. Further, the water-dispersible binder may be uniformly dispersed together with inorganic particles in the applied state, and may melt and locally diffuse and be applied under drying conditions of about 60 °C or lower or aging conditions of about 80 °C or lower. Thereby, the separator of one embodiment can improve the adhesive force with the positive electrode, widen the contact surface area with the positive electrode and the electrolyte, and can have the hydrogen trap effect, the decomposed electrolyte component trap effect, etc. to be achieved in the present disclosure. Further, a battery to which the separator as described above is applied can suppress the volume expansion and can achieve an effect of significantly improving the charge and discharge performance.

[0066] As long as it is possible to provide the binder according to the above-described embodiment, the method for manufacturing the binder is not particularly limited. However, in one embodiment, the binder may be provided by emulsion polymerization or suspension polymerization.

[0067] When coating with a slurry containing a water-soluble binder produced by solution polymerization and inorganic particles, no specific peak is observed in the FT-IR spectrum measured after 600 charge-discharge cycles that the present disclosure aims to achieve, and it is not possible to have a sufficient hydrogen trapping effect.

[0068] As one embodiment, the binder may be 1% by weight or more, 3% by weight or more, 3.5% by weight or more, 5% by weight or more, 7% by weight or more, 30% by weight or less, 20% by weight or less, 15% by weight or less, or a value between the above numerical values with respect to the total weight of the inorganic particle layer. As one embodiment, the binder may contain 1 to 30% by weight, 3 to 30% by weight, 3.5 to 20% by weight, 5 to 20% by weight, or 7 to 15% by weight with respect to the total weight of the inorganic particle layer. The content may correspond to a very large excess compared to the content of the binder less than 3% by weight that is usually used as the binder in the inorganic particle layer. The separator according to one embodiment can strengthen the adhesive force with the positive electrode active material layer and more effectively trap hydrogen and / or decomposed electrolyte components in the battery, which are by-products of the electrolyte, by using an excessive amount of the binder. Specifically, hydrogen gas generated by moisture contained in the electrolyte can be trapped by the nitrile group of the binder (see Chemical Formula 1 below). Also, by trapping hydrogen gas, hydrogen fluoride (HF), water vapor (H2O), etc., which cause the generation of hydrogen gas, can be removed. Here, the metal contained in the positive electrode active material can act as a catalyst in the reaction between the nitrile group and hydrogen gas as shown in Chemical Formula 1 below. R-CN in Chemical Formula 1 below means the binder according to one embodiment of the present disclosure.

[0069] [Chemical Formula 1] R-CN + H2 → R-CH2NH2

[0070] Also, although the cause of the amine group generated by the reaction of the nitrile group and hydrogen gas is not clear, it is considered that the effect of being able to trap electrolyte by-products as described below also increases. The following Chemical Formula 2 shows the case of using an electrolyte containing ethylene carbonate, and is an example for explaining the present disclosure, and is not limited thereto.

[0071] [Chem.] [Chemical Formula 2]

[0072] In one embodiment, the inorganic particle layer can include a binder and inorganic particles, and the inorganic particles can be a porous inorganic particle layer 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 can 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 can be formed on 100% of the area of the porous substrate.

[0073] In one embodiment, the inorganic particle layer can be coated on one or both surfaces of the porous substrate. When the inorganic particle layer is coated on both surfaces of the porous substrate, the thicknesses of the inorganic particle layers coated on one surface and the other surface may be the same or different from each other. Although not particularly limited, in one embodiment, the total thickness of the inorganic particle layer formed on the porous substrate may be 0.1 μm or more, 0.5 μm or more, 1 μm or more, 15 μm or less, 10 μm or less, 5 μm or less, or a value between the above numerical values. In a specific embodiment, the total thickness of the inorganic particle layer may be 0.1 to 15 μm, 0.5 to 10 μm, or 1 to 5 μm.

[0074] 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, metal carbides, and metal sulfates. 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), barium titanate (BaTiO₃), barium sulfate (BaSO₄), 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).

[0075] In one embodiment, the form of the inorganic particles is not limited and may be spherical, elliptical, needle-shaped, or the like.

[0076] In one embodiment, the inorganic particles may have an average particle size (D50) of 0.01 μm or more, 0.1 μm or more, 0.5 μm or more, 1.5 μm or less, 1.0 μm or less, or a value between these numerical values. As one embodiment, the D50 of the inorganic particles may be 0.01 to 1.5 μm, 0.1 to 1.5 μm, or 0.5 to 1.0 μm, but this can be changed as long as it does not deviate from the scope of the present disclosure.

[0077] In one embodiment, the porous substrate can be variously used, such as a porous polymer film, sheet, non-woven fabric, woven fabric, etc. made of a polymer used as a separator, and may also include a porous substrate having a laminated structure in which two or more of the above layers are laminated.

[0078] 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, and any porous substrate known as a porous substrate for a separator of an electrochemical device may be used.

[0079] 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 these numerical values, specifically 1 to 100 μm, and for the realization of a high-capacity battery, it may be 3 to 50 μm, 5 to 20 μm, or 5 to 15 μm. Although not limited thereto, the porous substrate may be manufactured by stretching.

[0080] In one embodiment, the porosity of the porous substrate may be 20 to 60% or 30 to 60%, but is not limited thereto.

[0081] 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 these numerical values, specifically 10 to 500 sec / 100 cc, 25 to 200 sec / 100 cc, or 25 to 150 sec / 100 cc, but is not limited thereto.

[0082] In one embodiment, the porous substrate may include polar functional groups on its surface. Here, the polar functional groups may be, for example, carboxylic acid groups, aldehyde groups or hydroxy groups, but are not limited thereto. By including a porous substrate having polar functional groups on its surface, the separator according to one embodiment has a glass transition temperature of 40 to 80°C, and the binding property between the particulate binder containing nitrile groups and the polar functional groups can be increased. Thereby, the separation between the positive electrode active material layer and the separator can be prevented, and they can be brought into closer contact, and the trapping effect of hydrogen generated by the catalytic action of the positive electrode active material can be further improved.

[0083] The polar groups may be introduced by hydrophilic surface treatment. As one embodiment, the surface treatment is not limited in its means, and may be performed including any one or more of corona discharge treatment and plasma discharge treatment, and may be performed in the presence of one or more selected from oxygen, air and ozone.

[0084] Hereinafter, the method for manufacturing the separator of the present disclosure will be described.

[0085] The method for manufacturing a separator according to an embodiment of the present disclosure includes a step of manufacturing a slurry composition containing a binder and inorganic particles, and a step of applying the slurry composition to at least one surface of a porous substrate to form an inorganic particle layer. The separator may have a first peak appearing in the range of 3800 to 3400 cm -1 and a second peak appearing in the range of 1800 to 1500 cm -1 in the spectrum measured by Fourier transform infrared spectroscopy (FT-IR) after performing 600 charge-discharge cycles.

[0086] The descriptions of the separator, the porous substrate, the inorganic particle layer, the inorganic particles and the binder are as described above, and specific descriptions are omitted.

[0087] Any ordinary method known in the art may be applied without limitation to produce the slurry composition. Without particular limitation, by way of non-limiting example, stirring may be carried out to disperse inorganic particles and a binder to produce a slurry, or an agglomerated inorganic particle may be dispersed using a ball mill.

[0088] The slurry composition includes inorganic particles, a binder, and a dispersion medium. The dispersion medium may be water, a lower alcohol such as ethanol, methanol, propanol, dimethylformamide, acetone, tetrahydrofuran, diethyl ether, methylene chloride, DMF, N-methyl-2-pyrrolidone, hexane, cyclohexane, or a mixture thereof, but is not necessarily limited thereto.

[0089] In one embodiment, the solid content of the slurry composition is not particularly limited. For example, it may be 1 to 50% by weight, 5 to 40% by weight, 10 to 35% by weight, but is not limited thereto.

[0090] In one embodiment, the slurry composition may include 70 to 99% by weight of inorganic particles and 1 to 30% by weight of a binder based on the total weight of the solid content. Specifically, the inorganic particles may be included in the slurry composition at 70 to 97% by weight, 80 to 96.5% by weight, 80 to 95% by weight, or 85 to 93% by weight based on the total weight of the solid content. Specifically, the binder may be included in the slurry composition at 3 to 30% by weight, 3.5 to 20% by weight, 5 to 20% by weight, or 7 to 15% by weight based on the total weight of the solid content. A method for manufacturing a separator according to one embodiment may further include a step of introducing a polar functional group onto the surface of a porous substrate by hydrophilic surface treatment before the step of forming the inorganic particle layer. Here, the polar functional group may be, for example, a carboxylic acid group, an aldehyde group, or a hydroxy group, but is not limited thereto. In one embodiment, the hydrophilic surface treatment may be carried out including any one or more of corona discharge treatment and plasma discharge treatment.

[0091] As a method for applying the slurry composition, any ordinary method known in the art may be applied without limitation. By way of non-limiting example, roll coating, spin coating, dip coating, bar coating, die coating, slit coating, inkjet printing, and methods combining these may be applied. The applied slurry can be dried and formed as an inorganic particle layer. The drying for forming the inorganic particle layer is not particularly limited, but it may be dried at 100°C or lower, or at 30 to 60°C.

[0092] The method for manufacturing a separator according to one embodiment may further include a step of aging a porous substrate on which an inorganic particle layer is formed after the step of forming the inorganic particle layer.

[0093] In a specific embodiment, after drying for forming the inorganic particle layer, a step of aging the porous substrate on which the inorganic particle layer is formed may further be included. As one embodiment, the drying may be performed at 60°C or lower, or at 50°C or lower. The aging may be performed at 50 to 100°C, or at 65 to 90°C, and the aging time may be 2 to 24 hours. By the aging, the adhesiveness between the porous substrate and the inorganic particle layer, not only between the inorganic particles but also between the inorganic particle layer and the electrode, particularly between the inorganic particle layer and the positive electrode active material layer, can be increased. Thereby, the reaction between the functional groups on the separator surface and the decomposition products of the electrolyte can be more effectively performed, and the gas generation amount can be further reduced.

[0094] A secondary battery according to an embodiment of the present disclosure may include a positive electrode, a negative electrode, the above-described separator interposed between the positive electrode and the negative electrode, and an electrolyte. Here, the positive electrode, the negative electrode, and the electrolyte can be used without limitation as long as they are those usually used in secondary batteries. In one embodiment, the secondary battery may be a lithium secondary battery.

[0095] Hereinafter, the components of the secondary battery according to the present disclosure will be further described.

[0096] [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.

[0097] (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 or stainless steel surface-treated with silver. The positive electrode current collector is not limited thereto, and may be, for example, 10 μm to 50 μm.

[0098] (Positive electrode active material layer) 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.

[0099] 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 composite oxide. The positive electrode active material may be a composite oxide of lithium and any one or more metals selected from the group consisting of cobalt, manganese, nickel, iron, and aluminum. In this case, the metal other than lithium contained in the composite oxide can play a role of a catalyst for the reaction between the functional group on the separator surface and the decomposition product of the electrolyte, and can more effectively reduce the gas generation amount.

[0100] 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.

[0101] The positive electrode active material may include a lithium cobalt oxide-based active material, a lithium manganese oxide-based active material, a lithium nickel oxide-based active material, or a lithium iron phosphate-based (LFP) active material (for example, LiFePO4).

[0102] 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.

[0103] The content of Ni (for example, the molar fraction of nickel among the total number of moles of nickel, cobalt, and manganese) in the NCM-based lithium oxide may be 0.4 to 0.8 or 0.6 to 0.8, and the contents of Co and Mn may each independently be 0.1 to 0.3 or 0.1 to 0.2.

[0104] (Method for manufacturing the positive electrode) For example, the positive electrode active material may be mixed in a solvent to produce a positive electrode slurry. After coating the positive electrode slurry on a positive electrode current collector, it may be dried and rolled to produce a positive electrode active material layer. The coating process may be performed by methods such as gravure coating, slot die coating, simultaneous multilayer die coating, imprinting, doctor blade coating, dip coating, bar coating, casting, etc., and is not limited thereto. The positive electrode active material layer may further include a binder, and optionally, may further include a conductive material, a thickener, etc.

[0105] (Positive electrode solvent) Non-limiting examples of the solvent used in the production of the positive electrode active material layer include N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, N,N-dimethylaminopropylamine, ethylene oxide, tetrahydrofuran, pure water, deionized water, distilled water, ethanol, isopropanol, methanol, acetone, n-propanol, t-butanol, and the like.

[0106] (Positive electrode binder) The binder may include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (Polyvinylidene fluoride-co-hexafluoropropylene), polyacrylonitrile, polymethyl methacrylate, acrylonitrile-butadiene rubber (NBR), polybutadiene rubber (BR), styrene-butadiene rubber (SBR), and the like. In one embodiment, a PVDF-based binder may be used as the positive electrode binder.

[0107] (Positive electrode conductive material) The conductive material may be added to enhance the conductivity of the positive electrode active material layer and / or the mobility of lithium ions or electrons. For example, the conductive material may include carbon-based conductive materials such as graphite, carbon black, acetylene black, ketjen black, graphene, carbon nanotubes, VGCF (vapor-grown carbon fiber), carbon fibers, and / or metal-based conductive materials including perovskite substances such as tin, tin oxide, titanium oxide, LaSrCoO3, LaSrMnO3, but is not limited thereto.

[0108] (Positive electrode thickener / dispersant) Optionally, the positive electrode active material layer may further include a thickener and / or a dispersant, etc. In one embodiment, the positive electrode active material layer may include a thickener such as carboxymethyl cellulose (CMC).

[0109] [Negative electrode] The negative electrode may include a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector.

[0110] (Negative electrode current collector) Non-limiting examples of the negative electrode current collector include copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, and a polymer substrate coated with a conductive metal. The negative electrode current collector is not limited thereto, and may be, for example, 10 to 50 μm.

[0111] (Negative electrode active material layer) 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, the negative electrode active material may be a carbon-based material such as crystalline carbon, amorphous carbon, carbon composite, carbon fiber, lithium metal, lithium alloy, silicon (Si)-containing substance, or tin (Sn)-containing substance.

[0112] Examples of the amorphous carbon include hard carbon, soft carbon, coke, mesocarbon microbead (MCMB), and mesophase pitch-based carbon fiber (MPCF).

[0113] Examples of the crystalline carbon include graphite-based carbon such as natural graphite, artificial graphite, graphitized coke, graphitized MCMB, and graphitized MPCF.

[0114] Examples of the lithium metal include pure lithium metal and 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.

[0115] Examples of the elements contained in the lithium alloy include aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium, or indium.

[0116] The silicon-containing substance can provide increased capacity characteristics. The silicon-containing substance may include Si, SiO x (0 < x < 2), metal-doped SiO x (0 < x < 2), and may include a silicon-carbon composite. The metal may include lithium and / or magnesium, and metal-doped SiO x (0 < x < 2) may include metal silicate.

[0117] (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.

[0118] 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.

[0119] (Negative electrode solvent) Non-limiting examples of the solvent used in the production of the negative electrode active material layer include N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, N,N-dimethylaminopropylamine, ethylene oxide, tetrahydrofuran, water, pure water, deionized water, distilled water, ethanol, isopropanol, methanol, acetone, n-propanol, t-butanol, and the like.

[0120] (Negative electrode binder / conductive material / thickener) As the binder, conductive material, and thickener, the above-described substances that can be used during the production of the positive electrode may be used.

[0121] In some embodiments, as the negative electrode binder, a styrene-butadiene rubber (SBR)-based binder, carboxymethyl cellulose (CMC), polyacrylic acid-based binder, poly(3,4-ethylenedioxythiophene) (PEDOT)-based binder, or the like may be used.

[0122] [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.

[0123] [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.

[0124] (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- ) as F - , Cl - , Br - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , PF6 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , CF3SO3 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - and (CF3CF2SO2)2N - and the like. According to an exemplary embodiment, when applying the separator of the present disclosure, the gas generation amount can be significantly reduced in an electrolyte containing LiPF6, but is not necessarily limited thereto.

[0125] 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.

[0126] (Additive) The non-aqueous electrolyte may further contain an additive. The additive may include, for example, a cyclic carbonate compound, a fluorine-substituted carbonate compound, a sultone compound, a cyclic sulfate compound, a cyclic sulfite compound, a phosphate compound, and a borate compound. The cyclic carbonate compound may include vinylene carbonate (VC), vinyl ethylene carbonate (VEC), and the like. The fluorine-substituted 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.

[0127] 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 patent 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. It is natural that such variations and modifications belong to the scope of the appended patent claims.

[0128] First, the separator and the method for evaluating the characteristics of the secondary battery will be described.

[0129] [FT-IR Spectrum Analysis] Each battery manufactured by the examples and comparative examples was charged at 4.2V with CCCV (Constant current-constant voltage) at room temperature (25°C) using a charge / discharge cycle device and then discharged. Specifically, each battery was charged at a constant current of 1C to 4.2V at room temperature (25°C), and then charged at a constant voltage while maintaining 4.2V until the current reached 0.01C. After that, discharging at a constant current of 1C to 2.5V was defined as one cycle. After performing a total of 600 charge / discharge cycles, the separator was separated from the battery, and then surface-washed with a solvent in which ethylene carbonate and diethyl carbonate were mixed at a volume ratio of 1:1, and the solvent was vacuum-dried. Next, the dried separator was cut into a size of 1 cm × 1 cm to prepare a measurement sample. Thereafter, an FT-IR spectrum was obtained under the following conditions using an FT-IR equipment (Nicolet iN10 Infrared Microscope manufactured by Thermo Scientific) equipped with an MCT (mercury cadmium telluride) detector.

[0130] -resolution:4cm -1 -scans:16 -range:4000~675cm -1 - Measurement points per sample: 15 point (10μm interval) × 15 point (10μm interval) mapping 3 positions

[0131] [Analysis of life characteristics] For each battery manufactured by the examples and comparative examples in the same manner as described in the FT-IR spectrum measurement, charge and discharge were performed for a total of 400 cycles. Resistance (mΩ) and discharge capacity (mAh) were measured every 100 cycles. Specifically, the resistance was measured by the J-Pulse method for DC-IR (Direct Current Internal Resistance). Calculated by the following formula, and the resistance (mΩ) or discharge capacity (mAh) of the examples was relatively evaluated based on the resistance (mΩ) or discharge capacity (mAh) of Comparative Example 1 for each cycle.

[0132] [(Resistance at the nth cycle of Comparative Example 1 - Resistance at the nth cycle of the Example) / Resistance at the nth cycle of Comparative Example 1] × 100

[0133] [(Discharge capacity at the nth cycle of the Example - Discharge capacity at the nth cycle of Comparative Example 1) / Discharge capacity at the nth cycle of Comparative Example 1] × 100

[0134] [Analysis of gas generation amount] The gas generation amount was measured by preparing an SOC battery charged to 100%, measuring the volume using a density meter, storing it in an oven at 60°C for 10 weeks, and then measuring the volume in the same way. The changed volume (volume increase rate △V) with respect to the volume at the 0th week of storage was calculated by the following formula. For the batteries of the examples and comparative examples, the difference from the value of Comparative Example 1 was obtained and relatively evaluated.

[0135] Volume increase rate △V (%) = [(Volume after 10 weeks - Volume after 0 weeks) / Volume after 0 weeks] × 100

[0136] <Production Example 1> A monomer component consisting of 38 parts by weight of methacrylamide, 23 parts by weight of acrylic acid, 3 parts by weight of butyl acrylate, 7 parts by weight of acrylonitrile and 7 parts by weight of 2-hydroxyethyl acrylate, 100 parts by weight of distilled water, and 0.60 parts by weight of n-dodecyl mercaptan as an emulsifier were mixed to produce a monomer solution.

[0137] A reactor of a four-necked flask equipped with a stirrer, a thermometer, a nitrogen inlet, and a circulation condenser was prepared. When the internal temperature of the reactor reached 35°C, 0.001 parts by weight of benzoyl peroxide as a polymerization initiator and 0.020 parts by weight of sodium formaldehyde sulfoxylate (SFS) were added dropwise to the monomer solution over 3 hours to proceed with the reaction. Then, 0.0001 parts by weight of benzoyl peroxide and 0.002 parts by weight of sodium formaldehyde sulfoxylate were further added to remove residual monomers, and the reaction was carried out for 2 hours to produce latex-like binder particles. The produced binder particles had an average particle size (D50) of 110 nm, a weight average molecular weight (Mw) of 300,000 g / mol, and a glass transition temperature (Tg) of 57.8°C.

[0138] <Production Example 2> Latex-like binder particles were produced in the same manner as in Production Example 1, except that 61 parts by weight of acrylic acid and 19 parts by weight of acrylonitrile were used as the monomer components. The produced binder particles had an average particle size (D50) of 110 nm, a weight average molecular weight (Mw) of 250,000 g / mol, and a glass transition temperature (Tg) of 55°C.

[0139] <Example 1> Production of Slurry Composition 92.8% by weight of boehmite (γ-AlO(OH)) having an average particle size (D50) of 800 nm and 7.2% by weight of the binder particles produced in Production Example 1 were added to water based on the total weight of the solid content, and then stirred to produce a slurry composition having a solid content concentration of 33% by weight.

[0140] Production of Separator As the porous substrate, both sides of a polyethylene porous film with a thickness of 9 μm (porosity: 50%, Gurley permeability: 70 sec / 100 cc) were subjected to corona discharge treatment to introduce polar functional groups on the surface. Here, the corona discharge treatment was carried out at a power density of 2 W / mm and a speed of 3 - 5 mpm (meter per minute). It was confirmed by Fourier transform infrared spectroscopy (FT-IR) that there were carboxylic acid groups and hydroxy groups on both sides of the corona discharge-treated porous substrate. The manufactured slurry composition was applied to both sides of the porous substrate and dried at 50 °C to form an inorganic particle layer with a thickness of 2.0 μm on each side of the porous substrate. The separator was manufactured through the step of aging the substrate with the inorganic particle layer formed thereon at 80 °C for 12 hours. The FT-IR spectrum of the manufactured separator is shown in Figure 1.

[0141] Manufacture of the positive electrode As the positive electrode active material, LiNi x Co y Mn z O2 (x = 0.4 - 0.8, y = 0.1 - 0.3, z = 0.1 - 0.3) 92 wt%, 4 wt% of carbon black as the conductive material, and 4 wt% of polyvinylidene fluoride (PVdF) as the binder were added to N-methyl-2-pyrrolidone (NMP) as the solvent and stirred to manufacture a uniform positive electrode slurry. The positive electrode slurry was applied to an aluminum (Al) thin film with a thickness of 30 μm, dried, and crimped to manufacture a positive electrode with a total thickness of 150 μm.

[0142] Manufacture of the negative electrode As the negative electrode active material, 96 wt% of graphite carbon, 3 wt% of carbon black as the conductive material, and 1 wt% of PVdF as the binder were added to NMP as the solvent and stirred to manufacture a uniform negative electrode slurry. The negative electrode slurry was applied to a copper (Cu) thin film with a thickness of 20 μm, dried, and crimped to manufacture a negative electrode with a total thickness of 150 μm.

[0143] Manufacture of the battery The manufactured separator was placed between the positive electrode and the negative electrode, and the resulting assembly was wound and placed in an aluminum pack. Then, an electrolyte in which 1 M lithium hexafluorophosphate (LiPF6) was dissolved in a solution containing ethylene carbonate and diethyl carbonate in a volume ratio of 1:1 was injected, and then the battery was sealed to produce a secondary battery with a capacity of 2 Ah. The characteristics of the secondary battery are summarized in Table 1 below.

[0144] After performing charge and discharge cycles 600 times under the above conditions on the manufactured battery, the separator was separated from the battery. After surface cleaning with a solvent in which ethylene carbonate and diethyl carbonate were mixed at a volume ratio of 1:1, the solvent was vacuum dried. Then, the FT-IR spectrum of the dried separator is shown in Figure 2. Referring to Figures 1 and 2, as charge and discharge were carried out, peaks with maximum intensity at 3591 cm -1 ~3500 cm -1 in the range of 3800 cm -1 and peaks with maximum intensity at 1625 cm -1 ~1500 cm -1 and 1511 cm -1 in the range of 1800 cm -1 appeared, which did not appear in the FT-IR spectrum of the separator before the charge and discharge. Also, in the FT-IR spectra of the separators manufactured by the remaining examples below after charge and discharge, peaks in the range of 3800 cm -1 ~3500 cm -1 and peaks in the range of 1800 cm -1 ~1500 cm -1 were confirmed to appear.

[0145] <Example 2> The same type of components contained in the slurry composition were used, and a separator and a secondary battery were manufactured in the same manner as in Example 1, except that the content was changed to 96.8% by weight of boehmite and 3.2% by weight of the binder particles of Production Example 1. The characteristics of the secondary battery are summarized in Table 1 below.

[0146] <Example 3> When manufacturing the slurry composition, a separator and a secondary battery were manufactured in the same manner as in Example 1, except that the binder particles manufactured in Production Example 2 were used instead of the binder particles manufactured in Production Example 1. The characteristics of the secondary battery are summarized in Table 1 below.

[0147] <Example 4> When manufacturing the separator, a separator and a secondary battery were manufactured in the same manner as in Example 1, except that the aging step was not performed. The characteristics of the secondary battery are summarized in Table 1 below.

[0148] <Comparative Example 1> Manufacture of Slurry Composition A polyacrylamide-based water-soluble polymer (Mw: 300,000 g / mol) prepared using a monomer component of 932 mmol of acrylamide, 89 mmol of 2-hydroxyethyl methacrylate, and 0.324 mmol of N,N'-methylenebisacrylamide was prepared.

[0149] 96.8% by weight of boehmite (γ-AlO(OH)) having an average particle diameter (D50) of 800 nm with respect to the total weight of the solid content and 3.2% by weight of the above polyacrylamide-based water-soluble polymer were added to water, and then stirred to produce a slurry composition having a solid content concentration of 32% by weight.

[0150] Manufacture of Separator As a porous substrate, both sides of a polyethylene porous film with a thickness of 9 μm (porosity: 50%, Gurley permeability: 70 sec / 100 cc) were subjected to corona discharge treatment to introduce polar functional groups onto the surface. Here, the corona discharge treatment was carried out at a power density of 2 W / mm and a speed of 3 - 5 mpm (meter per minute). It was confirmed by Fourier transform infrared spectroscopy (FT-IR) that carboxylic acid groups and hydroxy groups were present on both sides of the corona discharge-treated porous substrate. The manufactured slurry composition was applied to both sides of the porous substrate and dried at 50 °C to form inorganic particle layers with a thickness of 2.0 μm on both sides of the porous substrate. A separator was manufactured through a step of aging the substrate with the inorganic particle layer formed thereon at 80 °C for 12 hours. The FT-IR spectrum of the manufactured separator is shown in Figure 3.

[0151] Manufacture of the positive electrode, negative electrode, and battery The positive electrode and the negative electrode were manufactured in the same manner as described in Example 1, and then a secondary battery was manufactured together with the manufactured separator. The characteristics of the secondary battery are summarized in Table 1 below.

[0152] For the manufactured battery, after performing charge and discharge 600 cycles under the above conditions, the separator was separated from the battery, and then surface cleaning was carried out with a solvent in which ethylene carbonate and diethyl carbonate were mixed at a volume ratio of 1:1, and the solvent was dried under vacuum. Next, the FT-IR spectrum of the dried separator is shown in Figure 4. Referring to Figures 3 and 4, in the case of Comparative Example 1, different from the example, no peak was found in the spectrum after charge and discharge in the range of 3800 - 3400 cm -1 .

[0153] <Comparative Example 2> Manufacture of the slurry composition 61 parts by weight of methacrylamide, 10 parts by weight of acrylic acid, 1 part by weight of butyl acrylate, 3 parts by weight of acrylonitrile and 3 parts by weight of 2-hydroxyethyl acrylate as monomer components, 100 parts by weight of distilled water, and 0.60 parts by weight of n-dodecyl mercaptan as an emulsifier were mixed to produce a monomer solution.

[0154] A reactor of a four-necked flask equipped with a stirrer, a thermometer, a nitrogen inlet, and a circulation condenser was prepared. When the internal temperature of the reactor reached 35°C, 0.001 parts by weight of benzoyl peroxide as the monomer solution and a polymerization initiator, and 0.020 parts by weight of sodium formaldehyde sulfoxylate (SFS) were added dropwise over 3 hours to proceed with the reaction. Then, 0.0001 parts by weight of benzoyl peroxide and 0.002 parts by weight of sodium formaldehyde sulfoxylate were further added to remove residual monomers, and the reaction was carried out for 2 hours to produce latex-like binder particles. The produced binder particles had an average particle size (D50) of 120 nm, a weight average molecular weight (Mw) of 320,000 g / mol, and a glass transition temperature (Tg) of 105.5°C.

[0155] 92.8% by weight of boehmite (γ-AlO(OH)) with an average particle size (D50) of 800 nm and 7.2% by weight of the above binder particles were added to water with respect to the total weight of the solid content, and then stirred to produce a slurry composition with a solid content concentration of 33% by weight.

[0156] Manufacture of separator As the porous substrate, both surfaces of a polyethylene porous film with a thickness of 9 μm (porosity: 50%, Gurley permeability: 70 sec / 100 cc) were treated by corona discharge to introduce polar functional groups on the surface. Here, the corona discharge treatment was carried out at a power density of 2 W / mm and a speed of 3 - 5 mpm (meter per minute). It was confirmed by Fourier transform infrared spectroscopy (FT-IR) that there were carboxylic acid groups and hydroxy groups on both surfaces of the corona discharge-treated porous substrate. The above-prepared slurry composition was applied to both surfaces of the porous substrate and dried at 50 °C to form inorganic particle layers with a thickness of 2.0 μm on both surfaces of the porous substrate. A separator was manufactured through the step of aging the substrate with the inorganic particle layer formed thereon at 80 °C for 12 hours.

[0157] Manufacture of the 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 above-manufactured separator. The characteristics of the secondary battery are summarized in Table 1 below. As a result of measuring the FT-IR spectra of the manufactured separator before and after cycle driving, similar to Comparative Example 1, in the spectrum after performing charge and discharge 600 cycles, no peak was found in the range of 3800 - 3400 cm -1 .

[0158] <Comparative Example 3> Manufacture of the slurry composition A water-soluble polymer prepared using a monomer component of 12 parts by weight of methacrylamide, 43 parts by weight of acrylic acid, 1 part by weight of butyl acrylate, 7 parts by weight of acrylonitrile and 14 parts by weight of 2-hydroxyethyl acrylate was prepared. Here, the water-soluble polymer used had a weight average molecular weight (Mw) of 250,000 g / mol and a glass transition temperature of 56 °C.

[0159] To the total weight of the solid content, 96.8% by weight of boehmite (γ-AlO(OH)) with an average particle size (D50) of 800 nm and 3.2% by weight of the above water-soluble polymer were added to water, and then stirred to manufacture a slurry composition with a solid content concentration of 32% by weight.

[0160] Manufacture of Separator As the porous substrate, both sides of a polyethylene porous film with a thickness of 9 μm (porosity: 50%, Gurley permeability: 70 sec / 100 cc) were subjected to corona discharge treatment to introduce polar functional groups on the surface. Here, the corona discharge treatment was carried out at a power density of 2 W / mm and a speed of 3 - 5 mpm (meter per minute). It was confirmed by Fourier transform infrared spectroscopy (FT-IR) that both sides of the corona discharge-treated porous substrate had carboxylic acid groups and hydroxy groups. The prepared slurry composition was applied to both sides of the porous substrate and dried at 50 °C to form inorganic particle layers with a thickness of 2.0 μm on both sides of the porous substrate. The separator was manufactured through the step of aging the substrate with the inorganic particle layer formed thereon at 80 °C for 12 hours.

[0161] Manufacture of Positive Electrode, Negative Electrode and Battery In the same manner as the method described in Example 1, after manufacturing the positive electrode and the negative electrode, a secondary battery was manufactured together with the manufactured separator. The characteristics of the secondary battery are summarized in Table 1 below. As a result of measuring the FT-IR spectra of the manufactured separator before and after cycle driving, in the spectrum after performing 600 charge and discharge cycles, similar to Comparative Example 1, no peak was found in the range of 3800 - 3400 cm -1 There was no peak in the range of.

[0162] <Comparative Example 4> Manufacture of Slurry Composition A water-soluble polymer prepared using a monomer component of 12 parts by weight of methacrylamide, 43 parts by weight of acrylic acid, 1 part by weight of butyl acrylate, 7 parts by weight of acrylonitrile and 14 parts by weight of 2-hydroxyethyl acrylate was prepared. Here, the water-soluble polymer used had a weight average molecular weight (Mw) of 250,000 g / mol and a glass transition temperature of 56 °C.

[0163] After adding 92.8% by weight of boehmite (γ-AlO(OH)) with an average particle size (D50) of 800 nm and 7.2% by weight of the above-mentioned water-soluble polymer to the total weight of the solid content to water, it was stirred to produce a slurry composition with a solid content concentration of 33% by weight.

[0164] Manufacture of separator As a porous substrate, both sides of a 9-μm-thick polyethylene porous film (porosity: 50%, Gurley permeability: 70 sec / 100 cc) were subjected to corona discharge treatment to introduce polar functional groups to the surface. Here, the corona discharge treatment was carried out at a power density of 2 W / mm and a speed of 3 - 5 mpm (meter per minute). It was confirmed by Fourier transform infrared spectroscopy (FT-IR) that there were carboxylic acid groups and hydroxy groups on both sides of the corona discharge-treated porous substrate. The slurry composition prepared above was coated on both sides of the porous substrate and dried at 50 °C to form inorganic particle layers with a thickness of 2.0 μm on both sides of the porous substrate. A separator was manufactured through the step of aging the substrate with the inorganic particle layer formed thereon at 80 °C for 12 hours. As a result, the viscosity of the slurry composition was too high and the coating was not properly carried out.

[0165] Manufacture of positive electrode, negative electrode and battery In the same manner as the method described in Example 1, after manufacturing the positive electrode and the negative electrode, a secondary battery was manufactured together with the separator manufactured above. The characteristics of the secondary battery are summarized in Table 1 below. As a result of measuring the FT-IR spectra of the manufactured separator before and after cycle driving, similar to Comparative Example 1, no peak was found in the range of 3800 - 3400 cm -1 in the spectrum after 600 charge and discharge cycles.

[0166]

Table 1

[0167] Referring to Table 1, the secondary batteries of Examples 1 to 4 used a separator having a combination of peaks at specific positions on the FT-IR spectrum after 600 cycles of charge and discharge, and it was confirmed that they were superior in the effect of suppressing volume increase, resistance characteristics, and life characteristics compared to the case of using a separator of a comparative example that did not have such a combination of peaks.

[0168] Thereby, it can be seen that the separator according to one embodiment can effectively suppress the decomposition reaction of the electrolyte and significantly reduce the gas generation amount, and when using the separator, a secondary battery with reduced battery resistance and significantly excellent life characteristics can be provided.

[0169] On the other hand, it was confirmed that the batteries of Comparative Examples 1 to 4 using a separator that did not have a combination of peaks at specific positions on the FT-IR spectrum after 600 cycles of charge and discharge had a decrease in the effect of suppressing volume increase, resistance characteristics, and life characteristics compared to the examples.

[0170] The above content is merely an exemplification of applying the principle of the present disclosure, and other configurations may be further included without departing from the scope of the present disclosure.

Claims

1. A porous substrate; an inorganic particle layer formed on at least one surface of the porous substrate and including a binder and inorganic particles; In the spectrum measured by Fourier transform infrared spectroscopy (FT-IR) after 600 cycles of charge and discharge, －１ The first peak appears in the range of 1800 to 1500 cm －１ A second peak appears in the range of The charge and discharge cycle is a cycle of charging at a constant current of 1C up to 4.2V at room temperature, charging at a constant voltage of 0.01C while maintaining 4.2V, and then discharging at a constant current of 1C down to 2.5V.

2. The separator of claim 1 , wherein the binder comprises a nitrile group.

3. The separator according to claim 2 , wherein the binder comprises a structural unit derived from a (meth)acrylonitrile monomer.

4. 4. The separator according to claim 3, wherein the binder further comprises at least one structural unit selected from the group consisting of a structural unit derived from a (meth)acrylamide-based monomer and a structural unit derived from a (meth)acrylate-based monomer having a polar group.

5. The separator according to claim 1, wherein the binder has a weight average molecular weight of 10,000 to 2,000,000 g / mol.

6. The separator according to claim 1 , wherein the binder is a particulate binder.

7. The separator according to claim 1 , wherein the binder is a water-dispersible binder.

8. The separator according to claim 1, wherein the binder has a glass transition temperature of 40 to 80°C.

9. The separator according to claim 1, wherein the binder is contained in an amount of 1 to 30% by weight based on the total weight of the inorganic particle layer.

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

11. The separator according to claim 1 , wherein the porous substrate comprises polar functional groups on a surface thereof.

12. preparing a slurry composition comprising a binder and inorganic particles; and applying the slurry composition to at least one surface of a porous substrate to form an inorganic particle layer. In the spectrum measured by Fourier transform infrared spectroscopy (FT-IR) after 600 cycles of charge and discharge, －１ The first peak appears in the range of 1800 to 1500 cm －１ A second peak appears in the range of The charge and discharge cycle is one cycle of constant current charging at 1C up to 4.2V at room temperature, constant voltage charging while maintaining 4.2V until the current becomes 0.01C, and then discharging at a constant current of 1C down to 2.5V.

13. The method for producing a separator according to claim 12 , wherein the binder contains a nitrile group.

14. The method for producing a separator according to claim 13 , wherein the binder contains a structural unit derived from a (meth)acrylonitrile monomer.

15. The method for producing a separator according to claim 12, wherein the binder is a particulate binder.

16. The method for producing a separator according to claim 12, wherein the binder has a glass transition temperature of 40 to 80°C.

17. Prior to the step of forming an inorganic particle layer, The method for producing a separator according to claim 12, further comprising the step of introducing polar functional groups onto the surface of the porous substrate by hydrophilic surface treatment.

18. The method for producing a separator according to claim 17, wherein the hydrophilic surface treatment includes at least one of a corona discharge treatment and a plasma discharge treatment.

19. After the step of forming the inorganic particle layer, The method for producing a separator according to claim 12, further comprising a step of aging the porous substrate on which the inorganic particle layer is formed.

20. A secondary battery comprising: a positive electrode; a negative electrode; the separator according to any one of claims 1 to 11 interposed between the positive electrode and the negative electrode; and an electrolyte.

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