Separator and secondary battery containing the same

Abstract

To provide a separator which are excellent in the heat resistance, the charge-discharge characteristics, and life characteristics.SOLUTION: The separator includes: a porous base material; and an inorganic particle layer containing inorganic particles on at least one surface of the porous base material. The surface roughness (Ra) of the inorganic particle layer is 100nm to 160nm.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This disclosure relates to separators and secondary batteries including them. [Background technology]

[0002] In electrochemical devices, the separator in a battery is crucial for improving battery stability, lifespan, and performance. The separator's primary function is to provide ion movement pathways within the battery and prevent physical contact between the negative and positive electrodes. Improving the separator's properties allows for the manufacture of batteries with superior performance.

[0003] To improve the properties of separators used in batteries, multilayer separators have been developed by laminating porous polymers such as polyolefins and polypropylenes, or by using porous polymers as a base material and forming a coating layer by mixing a binder and inorganic particles. While multilayer separators and coating layers mixed with binders can improve various properties of the separator compared to single-layer separators, the separator thickness may increase, potentially leading to reduced permeability, decreased wettability, and decreased impregnation, which could actually decrease battery performance. To solve these problems, research is being conducted to manufacture separators that have various properties that are sufficiently suitable for battery separators, are thin, and satisfy mechanical and chemical stability requirements, thereby improving battery performance. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Korean Published Patent Gazette No. 2016-0109669 (September 21, 2016) [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] One embodiment provides a separator that is excellent in heat resistance and has excellent charge / discharge characteristics and life characteristics.

[0006] Another embodiment provides a secondary battery including the separator.

Means for Solving the Problems

[0007] One embodiment provides a separator including a porous substrate and an inorganic particle layer including inorganic particles on at least one surface of the porous substrate, wherein the surface roughness (Ra) of the inorganic particle layer is 100 nm to 160 nm.

[0008] Another embodiment provides a secondary battery including the separator according to the one embodiment.

Effects of the Invention

[0009] The present disclosure relates to a separator including a porous substrate and an inorganic particle layer including inorganic particles on at least one surface of the porous substrate, wherein the surface roughness (Ra) of the inorganic particle layer is 100 nm to 160 nm. The separator according to one embodiment can improve the heat resistance, charge / discharge characteristics, and life characteristics of a battery by having the surface roughness.

Brief Description of the Drawings

[0010] [Figure 1] It is a diagram schematically showing the structure of a separator according to one embodiment (100: separator, 10: porous substrate, 20: inorganic particle layer).

Mode for Carrying Out the Invention

[0011] The embodiments described herein may be modified into various other forms, and the technology of one embodiment is not limited to the embodiments described below. Furthermore, throughout this specification, the terms "comprising, including, containing," "equipping," "containing," or "having" a component mean, unless otherwise stated, that it may further include other components rather than excluding other components, and do not exclude any other elements, materials, or processes not listed.

[0012] Numerical ranges as used herein include lower and upper limits, all values ​​within those limits, increments logically derived from the form and width of the defined range, all limited values, and all possible combinations of upper and lower limits of numerical ranges limited in different forms. For example, if the composition content is limited to 10% to 80% or 20% to 50%, the numerical ranges of 10% to 50% or 50% to 80% should also be interpreted as being described herein. Unless otherwise specifically defined herein, values ​​outside the numerical range that may occur due to experimental error or rounding of values ​​are also included in the defined numerical range.

[0013] Hereafter, unless otherwise defined in this specification, "about" is understood to mean a value within 30%, 25%, 20%, 15%, 10%, 5%, 3%, 2%, 1%, or 0.5% of the explicitly stated value.

[0014] Hereafter, unless otherwise defined, "(meth)acrylic" means acrylic and / or methacrylic.

[0015] Unless otherwise defined herein, the average particle size of inorganic particles is D 50 It means a value.

[0016] Unless otherwise defined herein, when a part such as a layer, film, thin film, region, or plate is said to be "on top of" or "on top of" another part, this includes not only when it is "immediately on top of" the other part, but also when there are other parts in between.

[0017] Unless otherwise defined herein, “polymer” means a molecule with a relatively high molecular weight, whose structure may include multiple repeats of units derived from low molecular weight molecules. In one mode, a polymer may be an alternating copolymer, a block copolymer, a random copolymer, a graft copolymer, a gradient copolymer, a branched copolymer, a crosslinked copolymer, or a copolymer containing all of these (e.g., a polymer containing more than one monomer). In other modes, a polymer may be a homopolymer (e.g., a polymer containing one monomer).

[0018] One embodiment provides a separator that has high heat resistance and can suppress the degradation of battery performance during charging and discharging. Specifically, the separator 100 according to one embodiment includes a porous substrate 10 and an inorganic particle layer 20 containing inorganic particles on at least one surface of the porous substrate, wherein the inorganic particle layer is characterized by having a surface roughness (Ra) of 100 nm to 160 nm. The inorganic particle layer included in the separator according to one embodiment was devised based on the first recognition that by satisfying a surface roughness (Ra) of 100 nm to 160 nm, lithium ions can move uniformly during battery charging and discharging, and the problem of side reactions due to moisture can be effectively suppressed.

[0019] The aforementioned effect is due to the adjustment of the surface roughness (Ra) of the inorganic particle layer to 100 nm to 160 nm, and is not an effect that is solely influenced by the separator components or any specific element in the separator manufacturing process. As confirmed from one embodiment, the surface roughness (Ra) of the inorganic particle layer can be achieved by various means, including various factors such as the average particle size of the inorganic material, the solid content of the slurry, and the coating rate, and is not limited to how the surface roughness (Ra) of the inorganic particle layer is achieved.

[0020] Therefore, regardless of the average particle size, distribution, or combination of inorganic materials, regardless of the separator manufacturing conditions, i.e., the content and type of binder, dispersant, and lubricant, the solid content of the slurry, the rotation speed and / or bead size in the slurry manufacturing step, whether or not a smoothing bar is used, the drying temperature, the porous substrate, or the electrolyte of the battery, as long as the surface roughness (Ra) of the inorganic particle layer of the above embodiment is satisfied, the separator will have excellent heat resistance, and the battery manufactured using it will have excellent lifespan and charge / discharge characteristics.

[0021] In one embodiment, the surface roughness (Ra) of the separator may be 100 nm to 160 nm, 110 nm to 150 nm, 120 nm to 140 nm, or an average of approximately 130 nm. In one embodiment, the surface roughness (Ra) value of the separator may be the surface roughness value of the initial (fresh) separator before cycle driving.

[0022] In one embodiment, the inorganic particles contained in the inorganic particle layer are not particularly limited in type, as long as they are known to be electrochemically stable inorganic particles. For example, they may include one or more of the following: boehmite, CeO2, MgO, CaO, ZnO, Al2O3, TiO2, BaTiO3, HfO2, SrTiO3, SnO2, NiO, ZrO2, Y2O3, and / or SiC.

[0023] In one embodiment, the average particle size (D) of the inorganic particles 50The average particle size of the inorganic particles (D) can be appropriately selected according to the experimental conditions and purpose, as long as it can satisfy the range of surface roughness of the separator according to one embodiment, and is not necessarily limited to a specific range. For example, the average particle size of the inorganic particles may be 0.01 μm to 10.0 μm, 0.01 μm to 5.0 μm, 0.1 μm to 3.0 μm, 0.05 μm to 2.0 μm, or 0.1 μm to 1.0 μm. 50 The particle size was measured using a particle size analyzer (Microtrac, Microtrac S3500) in accordance with the ISO standard (ISO13320-1).

[0024] Alternatively, the inorganic particles may be a mixture of one, two, three, or more types of inorganic particles having different average particle sizes. For example, one or more of the following may be used: first inorganic particles with an average particle size of 0.1 μm to 0.6 μm, 0.1 μm to 0.5 μm, or about 0.3 μm; second inorganic particles with an average particle size of 0.3 μm to 1.0 μm, 0.5 μm to 1.0 μm, or about 0.7 μm; and third inorganic particles with an average particle size of 1.0 μm to 3.0 μm, 1.0 μm to 2.0 μm, or about 1.6 μm. For example, the inorganic particles may include the first inorganic particles and the second inorganic particles, or the first inorganic particles and the third inorganic particles. Here, the first inorganic particles, second inorganic particles, and third inorganic particles may be the same inorganic particles or different inorganic particles.

[0025] In one embodiment, when using inorganic particles having two different average particle sizes, the weight ratio is not particularly limited, but may be mixed in, for example, 20:80-80:20, 30:70-70:30, 50:50-80:20, 70:30, or 50:50. For example, the inorganic particles may include first inorganic particles and second inorganic particles in a weight ratio of 30:70-80:20, 50:50-80:20, 60:40-80:20, or about 70:30. Alternatively, the inorganic particles may include first inorganic particles and third inorganic particles in a weight ratio of 30:70-70:30, 40:60-60:40, or about 50:50. However, this is merely an example, and the inorganic particles do not necessarily have to be mixed in such weight ratios. Here, the first inorganic particle, the second inorganic particle, and the third inorganic particle may be the same inorganic particle or different inorganic particles.

[0026] In one embodiment, the inorganic particle layer may further include a binder. The binder can be appropriately selected from binders known to the ordinary skill of the art disclosed herein, according to the purpose and circumstances. In one embodiment, the binder may include a polymer, for example, one or more selected from the group consisting of ester polymers, amide polymers, imide polymers, acrylic polymers, acrylamide polymers, vinyl alcohol polymers, fluorine polymers, and / or vinylpyrrolidone polymers. In one embodiment, the binder may include an acrylamide polymer. Alternatively, for example, the binder may include a polymer produced from one or more monomers of (meth)acrylamide monomers, hydroxyl group-containing (meth)acrylic monomers, and / or polyfunctional (meth)acrylamide monomers, and is not limited as long as the inorganic particles formed on the surface of the porous substrate layer of the secondary battery separator are used as a binder for the inorganic particle layer in which pores are formed by linking the inorganic particles together by the binder.

[0027] In one embodiment, the binder content can be appropriately adjusted according to the situation and purpose, within a range that satisfies the surface roughness (Ra) range of the inorganic particle layer being 100 nm to 160 nm. For example, the binder content may be 0.1 to 20.0 parts by weight, 0.1 to 15.0 parts by weight, 1.0 to 10.0 parts by weight, 1.0 to 5.0 parts by weight, or about 3.0 parts by weight per 100 parts by weight of inorganic particles.

[0028] In one embodiment, the binder (or polymer contained in the binder) may have a weight-average molecular weight (Mw) of 10,000 g / mol to 2,000,000 g / mol, 50,000 g / mol to 2,000,000 g / mol, 50,000 g / mol to 1,000,000 g / mol, 50,000 g / mol to 500,000 g / mol, 50,000 g / mol to 300,000 g / mol, 100,000 g / mol to 300,000 g / mol, or about 150,000 g / mol. This is merely an example, and the weight-average molecular weight may be appropriately selected depending on the experimental conditions, as long as it satisfies the range of surface roughness of the separator according to this application. The weight-average molecular weight may be measured by gel permeation chromatography (GPC). The aforementioned weight-average molecular weight can be measured using a GPC (Tosoh Corporation, EcoSEC HLC-8320 GPC Refractive Index detector) with two GPC columns, TSKgel guard PWx, TSKgel GMPWxl and TSKgel G2500PWxl (7.8 × 300 mm), a 0.1 M NaNO3 aqueous solution as the developing solvent, and polyethylene glycol as the standard substance. The analysis is performed at a flow rate of 1 mL / min at 40°C.

[0029] In one embodiment, the porous substrate is not particularly limited as long as it is commonly used in the art, and can be, for example, a woven fabric, a non-woven fabric, or a porous film. Specifically, the porous substrate may be made of polyolefins such as polyethylene and polypropylene, polyesters such as polyethylene terephthalate and polybutylene terephthalate, polyacetal, polyamide, polyimide, polycarbonate, polyether ether ketone, polyaryl ether ketone, polyether imide, polyamide imide, polybenzimidazole, polyether sulfone, polyphenylene oxide, cyclic olefin copolymer, polyphenylene sulfide, polyethylene naphthalate, glass fiber, Teflon (registered trademark), and / or polytetrafluoroethylene, or any two or more of these may be used.

[0030] In one embodiment, the thickness of the porous substrate is not particularly limited, and may be, for example, 1 μm to 100 μm, 1 μm to 50 μm, 1 μm to 30 μm, 5 μm to 20 μm, or about 9 μm.

[0031] In one embodiment, the thickness of the inorganic particle layer formed on either side of the porous substrate may be, for example, 0.1 μm to 10.0 μm, 0.1 μm to 5.0 μm, 0.5 μm to 3.0 μm, 1.0 μm to 2.0 μm, or about 1.5 μm. When the inorganic particle layer is formed on both sides of the porous substrate, the thickness may be 0.2 μm to 15.0 μm, 0.3 μm to 10.0 μm, 1.0 μm to 8.0 μm, 2.0 μm to 5.0 μm, or about 3.0 μm.

[0032] In one embodiment, the coating density of the inorganic particle layer may be 0.8 g / (m 2 ·μm) or more, where the upper limit may be 3.0 g / (m 2 ·μm). Specifically, the coating density may be 1.0 g / (m 2 ·μm) to 3.0 g / (m 2 ·μm), 1.0 g / (m 2 ·μm) to 2.0 g / (m 2(μm), 1.0g / (m 2 (μm) ~ 1.5g / (m 2 ·μm), 1.1g / (m 2 (μm) ~ 1.4g / (m 2 ·μm), or 1.1g / (m 2 (μm) ~ 1.3g / (m 2 The coating density may be (μm). The coating density is the unit area (m²) of the inorganic particle layer. 2 It is defined as the value obtained by dividing the weight per unit (g) by the thickness of the inorganic particle layer (μm).

[0033] In one embodiment, after being left at 150°C for 60 minutes, the separator may have a shrinkage rate of 5.0% or less in both the mechanical direction (MD) and the width direction (TD), where the lower limit may be 0.5%. Specifically, the shrinkage rate may be 0.5% to 5.0%, 1.0% to 4.0%, or 1.0% to 3.0%.

[0034] In one embodiment, the separator may have an air permeability (Gurley permeability) of 150s / 100cc to 190s / 100cc, 160s / 100cc to 175s / 100cc, or 160s / 100cc to 170s / 100cc in accordance with the ASTM D726 standard.

[0035] In one embodiment, the separator may have a moisture content of 300 ppm to 1000 ppm, 550 ppm to 800 ppm, 550 ppm to 700 ppm, or 580 ppm to 680 ppm, measured while heating at 150°C after being dried at 80°C for 12 hours in a dry room with a dew point of -40°C or lower, left in the dry room for 30 minutes. In one embodiment, the moisture content was measured by the following method. To measure the moisture content, the separator was first dried. Drying was carried out in a dry room with a dew point of -40°C and dried in a convection oven at 80°C for 12 hours. After that, the separator was removed from the oven and stored in a dry room for 30 minutes. Next, 0.3 g of dried separator was taken, and the amount of moisture generated while heating the test specimen at 150°C was measured using a moisture meter (Metrohm, 917 Coulometer) according to the Karl Fischer moisture metering method.

[0036] In one embodiment, a separator with a surface roughness (Ra) of 100 nm to 160 nm has a low thermal shrinkage rate, and the density and air permeability of the inorganic packing are at the most appropriate level for achieving separator performance and battery performance, and the moisture content is low. As a result, the battery has excellent charge / discharge performance and life characteristics. On the other hand, if the surface roughness (Ra) of the separator is higher than 160 nm, the inorganic packing is not done well, resulting in low air permeability, moisture content, and initial resistance. However, during battery charging and discharging, lithium ions cannot move uniformly, which can lead to a decrease in performance. Also, if the surface roughness (Ra) of the separator is lower than 100 nm, the inorganic packing is too dense, resulting in high air permeability, moisture content, and initial resistance. Therefore, during battery charging and discharging, a decrease in performance may occur due to side reactions caused by moisture.

[0037] In one embodiment, when a secondary battery manufactured using the separator is charged and discharged 600 times, the rate of change in surface roughness (Ra) may be 30% or less, 20% or less, or 15% or less, and may be 1% to 20%, 5% to 20%, 5% to 15%, 10% to 15%, or 10% to 13%. Here, the rate of change is an absolute value, and the absolute value is calculated by {│(Surface roughness (Ra) after 600 cycles)-(Initial surface roughness (Ra))│} / (Initial surface roughness (Ra)). In one embodiment, if the separator satisfies a surface roughness (Ra) value of 100 nm to 160 nm and simultaneously satisfies the condition that the change value is 30% or less after 600 charge-discharge cycles of the battery, then superior battery performance can be achieved.

[0038] A separator having a surface roughness (Ra) of 100 nm to 160 nm according to one embodiment may be manufactured by the steps of preparing a composition for forming an inorganic particle layer containing inorganic particles, and applying (or coating) the composition for forming an inorganic particle layer onto at least one surface of a porous substrate, followed by drying to form an inorganic particle layer.

[0039] In one embodiment, the solvent used in the composition for forming the inorganic particle layer is not particularly limited, and if the composition contains a binder, a solvent that readily dissolves or disperses the binder may be selected. For example, water, acetone, ethanol, tetrahydrofuran, methylene chloride, chloroform, cyclohexane, dimethylformamide, and / or N-methyl-2-pyrrolidone may be used.

[0040] In one embodiment, the composition for forming the inorganic particle layer may be a slurry, and the solid content of the slurry may be, for example, 15% to 40% by weight, 20% to 40% by weight, or 20% to 35% by weight.

[0041] In one embodiment, the method for applying or coating the inorganic particle layer-forming composition onto a porous substrate is not particularly limited, but may include, for example, roll coating, spin coating, dip coating, bar coating, die coating, slit coating, or inkjet printing.

[0042] In one embodiment, the drying may be performed by drying with warm air, hot air, low-humidity air, vacuum drying, or irradiation by far-infrared rays or electron beams. The drying temperature is not particularly limited and may be adjusted as appropriate depending on the experimental environment and purpose, for example, it may be 30°C to 120°C, 30°C to 100°C, 30°C to 50°C, or about 45°C.

[0043] As described above, the surface roughness (Ra) of the separator according to one embodiment may be achieved by various means and can be adjusted by the size of the inorganic particles, the degree of distribution of the inorganic particles, the type and content of the binder, the solid content of the slurry, the manufacturing conditions of the slurry, the viscosity of the slurry, the drying conditions (temperature, speed), the coating speed, and the planarization means using a smoothing bar.

[0044] Another embodiment provides a secondary battery including the separator according to the above embodiment.

[0045] In one embodiment, the secondary battery may have a capacity change rate of 20% or less, 10% or less, 9% or less, 8% or less, 7% or less after 100 charge-discharge cycles, or it may be 2% to 10%, 3% to 8%, or 4% to 5%. Here, the rate of change is an absolute value, and the absolute value is calculated by {│(Capacity after 100 cycles)-(Initial capacity)│} / (Initial capacity).

[0046] The components of the secondary battery described herein will be explained further below.

[0047] [Positive electrode] The positive electrode may include a positive electrode current collector and a positive electrode mixture layer disposed on at least one surface of the positive electrode current collector.

[0048] (Positive electrode current collector) The positive electrode current collector may include stainless steel, nickel, aluminum, titanium, or alloys thereof. The positive electrode current collector may also include aluminum or stainless steel surface-treated with carbon, nickel, titanium, or silver. The thickness of the positive electrode current collector can be, for example, 10 μm to 50 μm, but is not limited thereto.

[0049] (Positive electrode material) The positive electrode mixture 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.

[0050] According to exemplary embodiments, any conventionally used positive electrode active material can be used without limitation. For example, the positive electrode active material may include a lithium-nickel metal oxide. The lithium-nickel metal oxide may further include at least one of cobalt (Co), manganese (Mn), and aluminum (Al).

[0051] The positive electrode active material may further include coating elements or doping elements. For example, elements substantially identical or similar to the auxiliary elements described above may be used as coating elements or doping elements. For example, one or more of the above elements may be used as coating elements or doping elements.

[0052] The positive electrode active material may include nickel-cobalt-manganese (NCM) lithium oxide. In this case, an NCM lithium oxide with an increased nickel content may be used.

[0053] The Ni content in the NCM-based lithium oxide (for example, the mole fraction of nickel in the total number of moles of nickel, cobalt, and manganese) may be 0.6 or higher, 0.7 or higher, or 0.8 or higher. In some embodiments, the Ni content may be 0.8 to 0.95, 0.82 to 0.95, 0.83 to 0.95, 0.84 to 0.95, 0.85 to 0.95, or 0.88 to 0.95.

[0054] In some embodiments, the positive electrode active material may include a lithium cobalt oxide-based active material, a lithium manganese oxide-based active material, a lithium nickel oxide-based active material, or a lithium iron phosphate (LFP)-based active material (e.g., LiFePO4).

[0055] (Method of manufacturing the positive electrode) For example, a positive electrode slurry may be produced by mixing the positive electrode active material in a solvent. The positive electrode slurry may be coated onto a positive electrode current collector, and then dried and rolled to produce a positive electrode mixture layer. The coating process may be carried out by methods such as gravure coating, slot die coating, simultaneous multilayer die coating, imprinting, doctor blade coating, dip coating, bar coating, and casting, and is not limited to these. The positive electrode mixture layer may further contain a binder, and optionally further contain conductive materials, thickeners, and the like.

[0056] (Positive electrode solvent) Non-limiting examples of solvents used in the production of the aforementioned cathode mixture include N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, N,N-dimethylaminopropylamine, ethylene oxide, and tetrahydrofuran.

[0057] (Positive electrode binder) The binder may include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer, polyacrylonitrile, polymethyl methacrylate, acrylonitrile butadiene rubber (NBR), polybutadiene rubber (BR), styrene-butadiene rubber (SBR), and the like. In one embodiment, a PVDF-based binder may be used as the positive electrode binder.

[0058] (Positive electrode conductive material) The conductive material may be added to enhance the conductivity and / or the mobility of lithium ions or electrons in the positive electrode mixture layer. For example, the conductive material may include, but is not limited to, carbon-based conductive materials such as graphite, carbon black, acetylene black, Ketjenblack, graphene, carbon nanotubes, VGCF (vapor-grown carbon fiber), and carbon fibers, and / or metallic conductive materials such as tin, tin oxide, titanium oxide, LaSrCoO3, and LaSrMnO3.

[0059] (Positive electrode thickener / dispersant) If necessary, the cathode mixture may further include a thickener and / or a dispersant. In one embodiment, the cathode mixture may include a thickener such as carboxymethylcellulose (CMC).

[0060] [Negative electrode] The negative electrode may include a negative electrode current collector and a negative electrode mixture layer disposed on at least one surface of the negative electrode current collector.

[0061] (Negative electrode current collector) Non-limiting examples of negative electrode current collectors include copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, and polymer substrates coated with conductive metals. The negative electrode current collector is not limited to these, but may be, for example, 10 to 50 μm thick.

[0062] (Negative electrode material) The negative electrode mixture layer may include a negative electrode active material. The negative electrode active material may be a substance capable of adsorbing and desorbing lithium ions. For example, the negative electrode active material may be a carbon-based material such as crystalline carbon, amorphous carbon, carbon composite, or carbon fiber, or a lithium metal, lithium alloy, silicon (Si)-containing material, or tin (Sn)-containing material.

[0063] Examples of amorphous carbon include hard carbon, soft carbon, coke, mesocarbon microbeads (MCMB), and mesophase pitch-based carbon fiber (MPCF).

[0064] Examples of the aforementioned crystalline carbon include graphite-based carbons such as natural graphite, artificial graphite, graphitized coke, graphitized MCMB, and graphitized MPCF.

[0065] The lithium metal may be pure lithium metal or lithium metal with a protective layer formed on it to suppress dendrite growth, etc. In one embodiment, a lithium metal-containing layer deposited or coated on a negative electrode current collector may be used as the negative electrode active material layer. In one embodiment, a lithium thin film layer may be used as the negative electrode active material layer.

[0066] Examples of elements contained in the aforementioned lithium alloy include aluminum, zinc, vizmus, cadmium, antimony, silicon, lead, tin, gallium, or indium.

[0067] The silicon-containing substance can provide increased capacity characteristics. The silicon-containing substance may include Si, SiO x (0 < x < 2), metal-doped SiO x (0 < x < 2), and may include silicon-carbon composites and the like. The metal may include lithium and / or magnesium, and metal-doped SiO x (0 < x < 2) may include metal silicates.

[0068] (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 can be dried and rolled to produce a negative electrode mixture 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 mixture layer may further include a binder, and optionally, may further include a conductive material, a thickening agent, and the like.

[0069] 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.

[0070] (Negative electrode solvent) Non-limiting examples of the solvent for the negative electrode mixture include water, pure water, deionized water, distilled water, ethanol, isopropanol, methanol, acetone, n-propanol, t-butanol, and the like.

[0071] (Negative electrode binder / conductive material / thickening agent) As the binder, conductive material, and thickening agent, the above-mentioned substances that can be used during the manufacture of the positive electrode may be used.

[0072] In some embodiments, the negative electrode binder may be a styrene-butadiene rubber (SBR) binder, a carboxymethylcellulose (CMC) binder, a polyacrylic acid (PEDOT) binder, or the like.

[0073] [Electrode assembly] According to exemplary embodiments, an electrode assembly may be formed by repeatedly arranging a positive electrode, a negative electrode, and a separator. In some embodiments, the electrode assembly may be of the winding, stacking, z-folding, or stack-folding type.

[0074] [Electrolyte] A lithium secondary battery may be defined by housing the electrode assembly together with the electrolyte in a case. According to an exemplary embodiment, a non-aqueous electrolyte may be used as the electrolyte.

[0075] (Lithium salt / organic solvent) The non-aqueous electrolyte contains a lithium salt, which is the electrolyte, and an organic solvent, wherein the lithium salt is, for example, Li + X - Represented by 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 - These are some examples.

[0076] The organic solvent may include organic compounds that have sufficient solubility in the lithium salt and additives and that do not react within the battery. The organic solvent may include, for example, at least one of carbonate solvents, ester solvents, ether solvents, ketone solvents, alcohol solvents, and aprotic solvents.Examples of the aforementioned organic solvents include propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate, diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), methyl propyl carbonate, ethyl propyl carbonate, dipropyl carbonate, vinylene carbonate, methyl acetate (MA), ethyl acetate (EA), n-propyl acetate (n-PA), 1,1-dimethylethyl acetate (DMEA), methyl propionate (MP), ethyl propionate (EP), fluoroethyl acetate (FEA), difluoroethyl acetate (DFEA), trifluoroethyl acetate (TFEA), and dibutyl ether (dibutyl Other substances that may be used include ether, tetraethylene glycol dimethyl ether (TEGDME), diethylene glycol dimethyl ether (DEGDME), dimethoxyethane, tetrahydrofuran (THF), and 2-methyltetrahydrofuran, ethanol (ethyl alcohol), isopropyl alcohol, dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, sulfolane, gamma-butyrolactone, and propylene sulfite. These may be used individually or in combination of two or more.

[0077] (Additives) The non-aqueous electrolyte may further contain additives. These additives may include, for example, cyclic carbonate compounds, fluorine-substituted carbonate compounds, sultone compounds, cyclic sulfate compounds, cyclic sulfite compounds, phosphate compounds, and borate compounds. The cyclic carbonate compounds may include vinylene carbonate (VC), vinyl ethylene carbonate (VEC), etc. The fluorine-substituted cyclic carbonate compounds may include fluoroethylene carbonate (FEC), etc. The sultone compounds may include 1,3-propane sultone, 1,3-propene sultone, 1,4-butane sultone, etc. The cyclic sulfate compound may include 1,2-ethylene sulfate, 1,2-propylene sulfate, etc. The cyclic sulfite compound may include ethylene sulfite, butylene sulfite, etc. The phosphate compound may include lithium difluorobis-oxalato phosphate, lithium difluoro phosphate, etc. The borate compound may include lithium bis(oxalate)borate, etc.

[0078] Examples and experimental cases are described below with specific illustrations. However, the examples and experimental cases described later are merely illustrative of one mode of implementation and should not be construed as limiting the technology described herein to these examples.

[0079] <Experimental Method> 1. Measurement of surface roughness (Ra) The manufactured separator was cut into a square shape with sides of 1 cm, fixed onto a glass slide substrate using double-sided tape, and its roughness was measured using an atomic force microscope (Bruker, Icon). The measurement mode was tapping mode, using a TESPA-V2 tip, with a scan speed of 1.0 Hz and a resolution of 256.

[0080] 2. Measurement of coating density Weight per unit area (g / m²) of an inorganic particle layer formed on a porous substrate 2 ) was calculated by dividing by the thickness of the inorganic particle layer (μm) (unit: g / (m 2 (μm))

[0081] 3. Measurement of air permeability Using a Densometer (Toyoseiki Ltd.), air permeability (Gurley permeability) was measured in accordance with the ASTM D726 standard, and the time taken for 100cc of air to pass through a 1 square inch area of ​​the separator was recorded in seconds.

[0082] 4. Measurement of thermal shrinkage rate The manufactured separator was cut into a square shape with sides of 10 cm, and the machine direction (MD) and transverse direction (TD) were marked. The sample was placed in the center, and five sheets of paper were placed above and below the sample, and the four sides of the paper were wrapped with tape. The paper-wrapped sample was left in a hot air drying oven at 150°C for 60 minutes. After that, the sample was removed, and the separator was measured with a camera, and the shrinkage rate in the machine direction (MD) and the transverse direction (TD) were calculated using the following mathematical formula 1 and 2.

[0083] [Mathematical formula 1] Shrinkage rate in the mechanical direction (MD) (%) = (Length in the mechanical direction before heating - Length in the mechanical direction after heating) × 100 / Length in the mechanical direction before heating

[0084] [Mathematical formula 2] Shrinkage rate in the width direction (TD) (%) = (width length before heating - width length after heating) × 100 / width length before heating

[0085] 5. Measurement of moisture content To measure the moisture content, the separator was first dried. Drying was carried out in a dry room with a dew point of -40°C, and then in a convection oven at 80°C for 12 hours. After that, the separator was removed from the oven and stored in the dry room for 30 minutes. Next, 0.3 g of the dried separator was taken, and the amount of moisture generated was measured using a moisture analyzer (Metrohm, 917 Coulometer) while heating the test specimen at 150°C according to the Karl Fischer moisture analysis method.

[0086] 6. Performance measurements at initial stage and after 100 cycles of operation. The DC-IR resistance (DC-IR) of the secondary batteries was evaluated using the J-pulse (Japan Electric Vehicle Association Standards, JEVS D 713) method, which evaluates discharge and charge characteristics for 10 seconds at 0.25C, 0.5C, 1.0C, 1.5C, 2.0C, and 2.5C. The average impedance of three batteries was calculated using the above method, and the initial resistance value was then calculated.

[0087] After 100 cycles, for both DC-IR and capacitance, the voltage changed from 2.7V (Constant Current) to 4.3V (Constant Current Constant Voltage) by charging / discharging at 0.1C for the first cycle, 0.2C for the second cycle, and then at 0.5C for 100 cycles from the third cycle onward. Similar to the initial resistance, the DC-IR after 100 cycles was measured using the J-pulse method, and the capacitance was also measured at this time.

[0088] Measurement of surface roughness after 7,600 cycles of operation. After performing 600 cycles using the same method as in step 6, the battery was discharged three times until the voltage reached 2.7V, and then the pouch was disassembled. The battery was then cleaned with dimethyl carbonate and left in an 80°C oven for one week to dry thoroughly. Next, the surface roughness was measured using the same method as in step 1.

[0089] 8. Measuring Thickness Separator thickness: After stacking 10 separators, the thickness was measured at 5 arbitrary points in the width direction using a thickness measuring instrument manufactured by Mitutoyo. The average thickness of the 10 separators was then calculated, and this was divided by 10 to obtain the overall average thickness of a single separator.

[0090] Thickness of porous film: The average thickness of the porous film was determined by stacking 10 layers of porous film and measuring the thickness at 5 arbitrary points in the width direction using a thickness measuring instrument manufactured by Mitutoyo. The average thickness of the 10 layers of porous film was then calculated, and the average thickness of a single porous film was obtained by dividing by 10.

[0091] Thickness of the inorganic particle layer: This was calculated by subtracting the average thickness of the single porous film from the overall average thickness of the single separator obtained using the method described above.

[0092] 9. Measurement of weight-average molecular weight Weight-average molecular weight was measured using GPC (EcoSEC HLC-8320GPC Reflective Index detector, Tosoh Corporation). The GPC columns used were Tskgel guard PWx, two TSKgel GMPWxl columns, and TSKgel G2500PWxl (7.8 × 300 mm). The developing solvent was a 0.1 M NaNO3 aqueous solution, and the standard was polyethylene glycol. The analysis was performed at 40°C and a flow rate of 1 mL / min.

[0093] <Example 1> Manufacturing of separators In water, the average particle size (D 50Boehmite (γ-AlOOH) with wavelengths of 300 nm and 700 nm, respectively, was added in a weight ratio of 3:7. Dispersant BYK-2018 (BYK GmbH) was added at a rate of 0.7 parts by weight per 100 parts by weight of the boehmite, and the mixture was stirred for 30 minutes to produce an aqueous dispersion with a solid content of 45% by weight. The aqueous dispersion was then further stirred for 3 minutes at a rotation speed of 250 rpm using a planetary mixer (bead size: 0.65 nm). Next, polyacrylamide (Mw: 150,000 g / mol, Sigma Aldrich Inc.) was added at a rate of 3 parts by weight per 100 parts by weight of the boehmite, and then water was added to produce an aqueous slurry with a final solid content of 32% by weight.

[0094] The aqueous slurry was applied to both sides of a 9 μm thick porous polyolefin film (ENPASS, SK Innovation, average pore size: 40 nm) at a speed of 10 m per minute, forming an inorganic particle layer approximately 1.5 μm thick on each side. To flatten the inorganic particle layer, it was passed through a smoothing bar without a pattern, and then placed in a 45°C hot air dryer to produce a separator.

[0095] Battery manufacturing Cathode Manufacturing: A cathode mixture slurry was prepared by adding 92% by weight of lithium cobalt composite oxide (LiCoO2) as the cathode active material, 4% by weight of carbon black as the conductive material, and 4% by weight of polyvinylidene fluoride (PVdF) as the binder to N-methyl-2-pyrrolidone (NMP) as the solvent. The prepared slurry was coated onto a 30 μm thick aluminum (Al) thin film, dried at a temperature of 120°C, and then roll-pressed to produce a 140 μm thick cathode.

[0096] Negative electrode manufacturing: Graphite carbon, PVdF as a binder, and carbon black as a conductive agent were added to the solvent NMP in concentrations of 96% by weight, 3% by weight, and 1% by weight, respectively, to produce a negative electrode mixture slurry. The manufactured slurry was applied to a 20 μm thick copper (Cu) thin film, dried at 120°C, and pressed using a roll press to produce a 150 μm thick negative electrode.

[0097] A pouch-type battery was assembled using a stacking method, with a separator manufactured between the positive and negative electrodes. An electrolyte solution consisting of ethylene carbonate (EC) / ethyl methyl carbonate (EMC) / dimethyl carbonate (DMC) = 3:5:2 (volume ratio), in which 1M lithium hexafluorophosphate (LiPF6) was dissolved, was injected into each assembled battery to produce a lithium secondary battery. This resulted in the production of a pouch-type lithium-ion secondary battery with a capacity of 80mAh.

[0098] <Example 2> In the manufacturing of the separator in Example 1, the average particle size (D) of boehmite is used. 50 The battery was manufactured in the same manner as in Example 1, except that boehmite with wavelengths of 300 nm and 1600 nm, respectively, was used in a 1:1 weight ratio, and a rotation speed of 150 rpm was applied.

[0099] <Example 3> In the production of the separator of Example 1, the battery was manufactured in the same manner as in Example 1, except that the final solid content of the aqueous slurry was adjusted to 22% by weight.

[0100] <Example 4> In the production of the separator of Example 2, the battery was manufactured in the same manner as in Example 2, except that the final solid content of the aqueous slurry was adjusted to 39% by weight.

[0101] <Example 5> In the manufacturing of the separator in Example 2, the battery was manufactured in the same manner as in Example 1, except that the rotation speed was set to 200 rpm and the drying temperature of the hot air dryer was adjusted to 40°C.

[0102] <Comparative Example 1> In the production of the separator of Example 1, the final solid content of the aqueous slurry was adjusted to 39% by weight, the slurry was applied at a speed of 20 m per minute, and a smoothing bar was not applied; otherwise, the battery was manufactured in the same manner as in Example 1.

[0103] <Comparative Example 2> In the production of the separator of Example 2, the battery was manufactured in the same manner as in Example 2, except that the final solid content of the aqueous slurry was adjusted to 39% by weight, the slurry was applied at a speed of 20 m per minute, and a smoothing bar was not applied.

[0104] <Comparative Example 3> In the production of the separator of Example 1, the battery was manufactured in the same manner as in Example 1, except that a rotation speed of 300 rpm was applied, the final solid content of the aqueous slurry was adjusted to 22% by weight, the slurry was applied at a speed of 5 m per minute, and a hot air dryer at 35°C was used.

[0105] <Comparative Example 4> In the manufacturing of the separator of Example 2, the battery was manufactured in the same manner as in Example 2, except that a rotation speed of 300 rpm was applied, the final solid content of the aqueous slurry was adjusted to 22% by weight, the slurry was applied at a speed of 5 m per minute, and a hot air dryer at 35°C was used.

[0106] <Comparative Example 5> In the production of the separator of Example 1, the battery was manufactured in the same manner as in Example 1, except that a rotation speed of 350 rpm was applied, the final solid content of the aqueous slurry was adjusted to 39% by weight, the slurry was applied at a speed of 5 m per minute, and a hot air dryer at 35°C was used.

[0107] <Comparative Example 6> In the production of the separator of Example 2, the battery was manufactured in the same manner as in Example 2, except that the final solid content of the aqueous slurry was adjusted to 39% by weight, the slurry was applied at a speed of 20 m per minute, and a 45°C hot air dryer was used.

[0108] The surface roughness and physical properties of the separators manufactured in the above examples and comparative examples were measured and are shown in Table 1 below.

[0109] [Table 1]

[0110] The performance of the batteries manufactured in the above examples and comparative examples was evaluated and is shown in Tables 2 and 3 below.

[0111] [Table 2]

[0112] As can be seen from Table 2 above, the separators of the examples having a surface roughness of 100 nm to 160 nm showed an increase in battery resistance and a decrease in capacity of 15% or less even after 100 cycles of operation. In contrast, for separators with a surface roughness value higher than 160 nm (Comparative Examples 1, 2, 6) or lower than 100 nm (Comparative Examples 3, 4, 5), the battery resistance increased by 14% or more and the capacity decreased by 10% or more after 100 cycles of operation.

[0113] Specifically, the separators of Comparative Examples 1, 2, and 6 have high surface roughness, resulting in relatively inconsistent packing of inorganic particles, low air permeability and moisture content, and low initial battery resistance. However, during charging and discharging, lithium ions cannot move uniformly, leading to a decrease in battery performance. The separators of Comparative Examples 3, 4, and 5 have low surface roughness, resulting in relatively inconsistent packing of inorganic particles, high air permeability and moisture content, and high initial battery resistance. During charging and discharging, side reactions caused by moisture lead to a decrease in battery performance. On the other hand, the separators of the Examples, with a surface roughness in the range of 100 nm to 160 nm, exhibit excellent heat resistance. Furthermore, batteries manufactured using these separators can achieve high output performance and discharge efficiency, and their battery life can be improved.

[0114] [Table 3]

[0115] As can be seen from Table 3 above, the separator according to the example shows a significantly lower rate of change in surface roughness even after 600 charge-discharge cycles compared to the comparative example. This indicates that the surface characteristics of the separator are maintained even after long-term battery operation, resulting in superior lifespan characteristics.

[0116] Although one embodiment has been described in detail above with reference to examples and experimental examples, the scope of this embodiment is not limited to a specific embodiment and should be interpreted according to the attached claims.

Claims

1. Porous substrate and The porous substrate comprises an inorganic particle layer containing inorganic particles on at least one surface of the porous substrate, The surface roughness (Ra) of the inorganic particle layer is 100 nm to 160 nm. The inorganic particle layer includes a binder, The binder is a separator for secondary batteries, having a weight-average molecular weight of 50,000 g / mol to 300,000 g / mol.

2. The inorganic particles are boehmite, CeO ２ , MgO, CaO, ZnO, Al ２ O ３ , TiO ２ , BaTiO ３ , HfO ２ , SrTiO ３ , SnO ２ , NiO, ZrO ２ , Y ２ O ３ The separator according to claim 1, comprising one or more selected from the group consisting of SiC.

3. The separator according to claim 1, wherein the binder comprises one or more selected from the group consisting of ester polymers, amide polymers, imide polymers, acrylic polymers, acrylamide polymers, vinyl alcohol polymers, fluorine polymers, and vinylpyrrolidone polymers.

4. The separator according to claim 1, wherein the binder is contained in an amount of 0.1 to 20.0 parts by weight per 100 parts by weight of inorganic particles.

5. The inorganic particles have different average particle sizes (D ５０ The separator according to claim 1, comprising one or more inorganic particles having ).

6. The inorganic particles have an average particle size (D ５０ The separator according to claim 1, comprising inorganic particles having a size of 0.05 μm to 2.0 μm.

7. The separator according to claim 1, wherein the thickness of the inorganic particle layer is 0.1 μm to 10.0 μm.

8. The coating density of the inorganic particle layer is 0.8 g / (m²). ２ The separator according to claim 1, wherein the particle size is 1 μm or larger.

9. The separator according to claim 1, wherein, after being left at 150°C for 60 minutes, the shrinkage rate in the mechanical direction (MD) and the width direction (TD) is 5.0% or less in all directions.

10. The separator according to claim 1, wherein the separator is dried in a dry room with a dew point of -40°C or lower at 80°C for 12 hours, left in the dry room for 30 minutes, and then the moisture content measured while heating at 150°C is 300 ppm to 1000 ppm.

11. The separator according to claim 1, wherein the rate of change in surface roughness (Ra) is 30% or less when a secondary battery manufactured using the separator is subjected to 600 charge-discharge cycles.

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

13. The secondary battery according to claim 12, wherein the rate of change in capacity after 100 charge-discharge cycles is 20% or less.

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