Separator and secondary battery including 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 including inorganic particles in at least one surface of the porous base material. The surface roughness (Ra) of the inorganic particle layer is in the range of 180nm to 230nm of the inorganic particle layer.SELECTED DRAWING: None

Description

Technical Field

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

Background Art

[0002] In an electrochemical device, the separator of a battery is very important for improving the stability, lifespan, and performance of the battery. The main function of the separator is to provide a path for ion movement within the battery and prevent physical contact between the negative electrode and the positive electrode. By improving the characteristics of the separator, a battery with excellent performance can be manufactured.

[0003] To improve the characteristics of the separator used in a battery, a multilayer separator is formed by laminating porous polymers such as polyolefin-based or polypropylene-based polymers, or a separator is developed in which a porous polymer is used as a base material and a coating layer is formed by mixing a binder and inorganic particles. The coating layer mixed with a multilayer separator or a binder can improve various characteristics of the separator compared to a single-layer separator. However, the thickness of the separator can increase, and the performance of the battery may rather decrease due to low permeability, reduced wettability, and decreased impregnation. To solve such problems, research has been conducted to manufacture a separator that can improve the performance of the battery by being sufficiently suitable for the separator of the battery in terms of various characteristics, having a thin thickness, and satisfying mechanical and chemical stability.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] One embodiment provides a separator with excellent heat resistance, 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 180 nm to 230 nm.

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

Advantages 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 180 nm to 230 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.

Modes for Carrying Out the Invention

[0010] The embodiments described in this specification may be modified into various other forms, and the technology according to one embodiment is not limited to the embodiments described below. Further, throughout the specification, when a component is described as "comprising", "including", "containing", or "having", it means that other components can be further included, rather than excluding other components, unless there is a description to the contrary, and does not exclude elements, materials, or steps not further mentioned.

[0011] The numerical ranges used in this specification include the lower limit value and the upper limit value, all values within that range, increments logically derivable from the form and width of the defined range, all of the limited values among them, and all possible combinations of the upper and lower limits of numerical ranges limited to different forms from each other. As an example, when the content of a composition is limited to 10% to 80% or 20% to 50%, numerical ranges of 10% to 50% or 50% to 80% should also be interpreted as being described in this specification. Unless otherwise specifically defined in this specification, values outside the numerical range that may occur due to experimental error or rounding of values are also included in the defined numerical range.

[0012] Hereinafter, unless otherwise specifically defined in this specification, "about" is considered to be a value within 30%, 25%, 20%, 15%, 10%, 5%, 3%, 2%, 1% or 0.5% of the explicitly stated value.

[0013] Hereinafter, unless otherwise specifically defined in this specification, "(meth)acryl" means acrylic and / or methacrylic.

[0014] Unless otherwise defined in this specification, the average particle diameter of the inorganic particles is D 50 means the value.

[0015] Unless otherwise defined in this specification, when a part such as a layer, film, thin 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 is another part in between.

[0016] Unless otherwise defined herein, "polymer" means a molecule of relatively high molecular weight, the structure of which may include multiple repetitions of units derived from low molecular weight molecules. In one embodiment, the 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 that includes all of these (e.g., a polymer that includes more than one monomer). In other embodiments, the polymer may be a homopolymer (e.g., a polymer that includes one type of monomer).

[0017] One embodiment provides a separator that has high heat resistance and can suppress a decrease in battery performance during charge and discharge. Specifically, the separator according to one embodiment includes a porous substrate and an inorganic particle layer including inorganic particles on at least one surface of the porous substrate, wherein the inorganic particle layer is characterized in that the surface roughness (Ra) is 180 nm to 230 nm. The inorganic particle layer included in the separator according to one embodiment was devised by first recognizing that by satisfying the surface roughness (Ra) of 180 nm to 230 nm, lithium ions can move uniformly during charge and discharge of the battery, and the problem of side reactions caused by moisture can be effectively suppressed.

[0018] The above effect is an effect caused by adjusting the surface roughness (Ra) of the inorganic particle layer to 180 nm to 230 nm, and is not an effect affected only by a specific element during the components of the separator or the manufacturing process of the separator. As confirmed from one embodiment, it can be realized by various means including various factors such as the average particle size of the inorganic substance, the solid content of the slurry, and the coating speed, and there is no limitation on how the surface roughness (Ra) of the inorganic particle layer is realized.

[0019] Therefore, regardless of the average particle size, distribution, or combination of inorganic substances, the manufacturing conditions of the separator, namely, the content and type of binder, dispersant, lubricant, the solid content of the slurry, the rotation speed and / or bead size in the slurry manufacturing step, the use or non-use of a smoothing bar, and the drying temperature, regardless of the porous substrate and the electrolyte of the battery, when the surface roughness (Ra) of the inorganic particle layer of the above embodiment is satisfied, the separator has excellent heat resistance, and the battery manufactured using the same has excellent life characteristics and charge / discharge characteristics.

[0020] In one embodiment, the surface roughness (Ra) of the separator may be 180 nm to 230 nm, 190 nm to 220 nm, or about 205 nm on average. 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.

[0021] In one embodiment, the inorganic particles contained in the inorganic particle layer are not particularly limited in type as long as they are inorganic particles known to be electrochemically stable. For example, 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 , and / or any one or more of SiC may be included.

[0022] In one embodiment, the average particle size (D 50) can be appropriately selected according to experimental conditions and purposes as long as the surface roughness range of the separator according to one embodiment can be satisfied, 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, 0.1 μm to 1.0 μm. The average particle size (D 50 ) was measured using a particle size analyzer (Microtrac, Microtrac S3500) in accordance with the ISO standard (ISO13320-1).

[0023] Alternatively, the inorganic particles may be used by mixing one, two, three or more inorganic particles having different average particle sizes. For example, the first inorganic particles having an average particle size of 0.1 μm to 0.6 μm, 0.1 μm to 0.5 μm, or about 0.3 μm, the second inorganic particles having 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 the average particle size is 1.0 μm to 3.0 μm, 1.0 μm to 2.0 μm, or one or more of the third inorganic particles having an average particle size of about 1.6 μm may be mixed and used. For example, the inorganic particles may include the first inorganic particles and the second inorganic particles, or may include the first inorganic particles and the third inorganic particles. Here, the first inorganic particles, the second inorganic particles, and the third inorganic particles may be the same inorganic particles as each other, or may be different inorganic particles from each other.

[0024] In one embodiment, when using inorganic particles having two different average particle sizes, their weight ratio is not particularly limited. For example, they may be mixed at 20:80 to 80:20, 30:70 to 70:30, 50:50 to 80:20, 70:30, or 50:50. For example, the inorganic particles may include the first inorganic particles and the second inorganic particles in a weight ratio of 30:70 to 80:20, 50:50 to 80:20, 60:40 to 80:20, or about 70:30. Or the inorganic particles may include the first inorganic particles and the third inorganic particles in a weight ratio of 30:70 to 70:30, 40:60 to 60:40, or about 50:50. However, this is only an example, and the inorganic particles do not necessarily have to be mixed in the above weight ratio. Here, the first inorganic particles, the second inorganic particles, and the third inorganic particles may be the same inorganic particles as each other, or may be different inorganic particles from each other.

[0025] In one embodiment, the inorganic particle layer may further include a binder. The binder can be appropriately selected according to the purpose and situation from binders known to ordinary technicians in the technical field disclosed in the present application. In one embodiment, the binder may include a polymer. For example, it may include any one or more selected from the group consisting of ester-based polymers, amide-based polymers, imide-based polymers, acrylic-based polymers, acrylamide-based polymers, vinyl alcohol-based polymers, fluorine-based polymers, and / or vinyl pyrrolidone-based polymers. In one embodiment, the binder may include an acrylic-based polymer. Or, for example, the binder may include a polymer produced from any one or more of (meth)acrylamide-based monomers, (meth)acrylic-based monomers containing a hydroxy group, and / or polyfunctional (meth)acrylamide-based monomers. As long as the inorganic particles formed on the surface of the porous base material layer of the secondary battery separator are used as the binder for the inorganic particle layer in which the pores are formed by being connected to each other by the binder, there is no limitation.

[0026] In one embodiment, the content of the binder can be appropriately adjusted according to the situation and purpose within the range where the surface roughness (Ra) of the inorganic particle layer satisfies 180 nm to 230 nm. For example, the content of the binder may be 0.1 part by weight to 20.0 parts by weight, 0.1 part by weight to 15.0 parts by weight, 1.0 part by weight to 10.0 parts by weight, 5.0 parts by weight to 10.0 parts by weight, or about 7.0 parts by weight with respect to 100 parts by weight of the inorganic particles.

[0027] In one embodiment, the binder (or the 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 120,000 g / mol. However, this is only an example, and it may be appropriately selected according to the experimental conditions as long as the surface roughness range of the separator according to the present application can be satisfied. The weight average molecular weight may be measured by gel permeation chromatography (GPC). The weight average molecular weight is measured using GPC (Tosoh Corporation, EcoSEC HLC-8320 GPC Refractive Index detector), with TSKgel guard PWx as the guard column, two columns of TSKgel GMPWxl and TSKgel G2500PWxl (7.8×300 mm) as the GPC columns, 0.1 M NaNO 3 aqueous solution, using polyethylene glycol as the standard substance, and analyzing at a flow rate of 1 mL / min at 40°C for measurement.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] 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 is 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), 1.0 g / (m 2 ·μm) to 1.5 g / (m 2 ·μm), 1.1 g / (m 2 ·μm) to 1.4 g / (m 2 ·μm), or 1.1 g / (m 2 ·μm) to 1.3 g / (m 2 ·μm) may be sufficient. The coating density is defined as the value obtained by dividing the weight (g) per unit area (m 2 ) of the inorganic particle layer by the thickness (μm) of the inorganic particle layer.

[0032] In one embodiment, after the separator is left at 150 °C for 60 minutes, the shrinkage rates in the machine direction (MD) and the transverse direction (TD) can both be 5.0% or less, where the lower limit can 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%.

[0033] In one embodiment, the separator may have an air permeability (Gurley permeability) of 150 s / 100 cc to 180 s / 100 cc, 160 s / 100 cc to 175 s / 100 cc, or 160 s / 100 cc to 170 s / 100 cc in accordance with ASTM D726 standard.

[0034] In one embodiment, the separator has a moisture content measured while heating at 150°C after drying at 80°C for 12 hours in a dry room with a dew point of -40°C or lower, then leaving it standing in the dry room for 30 minutes, which can be 300 ppm to 1000 ppm, 550 ppm to 800 ppm, 550 ppm to 700 ppm, or 580 ppm to 680 ppm. In one embodiment, the moisture content was measured by the following method. For the measurement of the moisture content, first, the separator was dried. The 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. Then, the separator was taken out of the oven and stored in the dry room for 30 minutes. Next, after collecting 0.3 g of the dried separator, a moisture measuring machine (Metrohm, 917 Coulometer) was utilized to measure the amount of moisture generated while heating the test piece at 150°C according to the Karl Fischer moisture measurement method.

[0035] A separator with a surface roughness (Ra) of 180 nm to 230 nm according to one embodiment has a low thermal shrinkage rate, and the packing density and air permeability of the inorganic matter reach the most appropriate levels for realizing separator performance and battery performance, and the moisture content is low. As a result, the separator has excellent charge and discharge performance and life characteristics of the battery. On the other hand, when the surface roughness (Ra) of the separator is higher than 230 nm, the packing of the inorganic matter is not well performed, and the air permeability, moisture content, and initial resistance are low. However, when the battery is charged and discharged, lithium ions cannot move uniformly, and a performance degradation may occur. Also, when the surface roughness (Ra) of the separator is lower than 180 nm, the packing of the inorganic matter is too dense, and the air permeability, moisture content, and initial resistance are high. Therefore, when the battery is charged and discharged, a performance degradation may occur due to the problem of side reactions caused by moisture.

[0036] When the separator according to one embodiment is used to charge and discharge a secondary battery manufactured using the same 600 times, the change rate of the surface roughness (Ra) may be 15.0% or less, or 0.1% to 15.0%, 0.1% to 10.0%, 0.1% to 5.0%, 0.1% to 3.0%, 0.1% to 2.0%, or 0.1% to 1.0%. Here, the change rate 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)). When the separator according to one embodiment satisfies a surface roughness (Ra) value of 180 nm to 230 nm and, after 600 charge and discharge cycles of the battery, its change value is 15.0% or less at the same time, better battery performance can be achieved.

[0037] The separator with a surface roughness (Ra) of 180 nm to 230 nm according to one embodiment may be manufactured from the steps of preparing a composition for forming an inorganic particle layer containing inorganic particles and applying (or coating) the composition for forming the inorganic particle layer on at least one surface of the porous substrate and then drying to form an inorganic particle layer.

[0038] In one embodiment, the solvent used in the composition for forming the inorganic particle layer is not particularly limited, and when the composition contains a binder, a solvent that is easy to dissolve or disperse 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.

[0039] 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 wt% to 40 wt%, 20 wt% to 40 wt%, or 20 wt% to 35 wt%.

[0040] In one embodiment, the method of applying or coating the composition for forming the inorganic particle layer on the porous substrate is not particularly limited. For example, roll coating, spin coating, dip coating, bar coating, die coating, slit coating, or inkjet printing may be used.

[0041] In one embodiment, the drying may be performed by drying with warm air, hot air, low humidity air, vacuum drying, or irradiation methods such as far-infrared rays or electron beams. Since the drying temperature is not particularly limited, it may be appropriately adjusted according to 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.

[0042] As described above, the surface roughness (Ra) of the separator according to one embodiment may be realized 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, the flattening means using a smoothing bar, etc.

[0043] Another embodiment provides a secondary battery including the separator according to the above embodiment.

[0044] In one embodiment, after 100 charge-discharge cycles, the capacity change rate of the secondary battery may be 20% or less, 10% or less, 9% or less, 8% or less, 7% or less, or may be 2% to 10%, 3% to 8%, or 4% to 6%. Here, the change rate is an absolute value, and the absolute value is calculated by {│(capacity after 100 cycles) - (initial capacity)│} / (initial capacity).

[0045] Hereinafter, the components of the secondary battery according to the present disclosure will be further described.

[0046] [Positive Electrode] The positive electrode can include a positive electrode current collector and a positive electrode mixture layer disposed on at least one surface of the positive electrode current collector.

[0047] (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 include carbon, nickel, titanium, aluminum surface-treated with silver, or stainless steel. The positive electrode current collector is not limited thereto, and can be, for example, 10 μm to 50 μm.

[0048] (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.

[0049] According to an exemplary embodiment, any conventionally used positive electrode active material can be used without limitation. For example, the positive electrode active material can 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).

[0050] The positive electrode active material can 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 can be used as the coating element or the doping element. For example, one or more of the above-described elements can be used alone or in combination as the coating element or the doping element.

[0051] 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.

[0052] Among the NCM-based lithium oxides, the content of Ni (e.g., the molar fraction of nickel among the total moles of nickel, cobalt, and manganese) may be 0.6 or more, 0.7 or more, or 0.8 or more. In some embodiments, the content of Ni may be 0.8 to 0.95, 0.82 to 0.95, 0.83 to 0.95, 0.84 to 0.95, 0.85 to 0.95, or 0.88 to 0.95.

[0053] In some embodiments, the cathode active material may include a lithium cobalt oxide-based active material, a lithium manganese oxide-based active material, a lithium nickel oxide-based active material, or a lithium iron phosphate-based (LFP) active material (e.g., LiFePO 4 ) may be included.

[0054] (Method for manufacturing the cathode) For example, the cathode active material may be mixed in a solvent to produce a cathode slurry. After coating the cathode slurry on a cathode current collector, it may be dried and rolled to produce a cathode 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 cathode mixture layer may further include a binder, and optionally, may further include a conductive material, a thickening agent, etc.

[0055] (Cathode solvent) Non-limiting examples of the solvent used in the production of the cathode mixture include N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, N,N-dimethylaminopropylamine, ethylene oxide, tetrahydrofuran, etc.

[0056] (Cathode binder) The binder may include polyvinylidene fluoride (PVDF), polyvinylidene fluoride - co - hexafluoropropylene, polyacrylonitrile, polymethylmethacrylate, acrylonitrile - butadiene rubber (NBR), polybutadiene rubber (BR), styrene - butadiene rubber (SBR), etc. In one embodiment, a PVDF - based binder may be used as the positive electrode binder.

[0057] (Positive electrode conductive material) The conductive material may be added to enhance the conductivity of the positive electrode mixture layer and / or the mobility of lithium ions or electrons. For example, the conductive material may include carbon - based conductive materials such as graphite, carbon black, acetylene black, ketjen black, graphene, carbon nanotubes, VGCF (vapor - grown carbon fiber), carbon fiber, etc. and / or metal - based conductive materials including perovskite substances such as tin, tin oxide, titanium oxide, LaSrCoO 3 , LaSrMnO 3 and is not limited thereto, including perovskite substances such as those of LaSrMnO and the like.

[0058] (Positive electrode thickener / dispersant) Optionally, the positive electrode mixture may further include a thickener and / or a dispersant, etc. In one embodiment, the positive electrode mixture may include a thickener such as carboxymethyl cellulose (CMC).

[0059] [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.

[0060] (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 polymer substrates coated with conductive metals. The negative electrode current collector is not limited thereto, but may be, for example, 10 to 50 μm.

[0061] (Negative electrode material) The negative electrode binder 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.

[0062] Examples of the amorphous carbon include hard carbon, soft carbon, coke, mesocarbon microbead (MCMB), and mesophase pitch-based carbon fiber (MPCF).

[0063] Examples of the crystalline carbon include graphite-based carbons such as natural graphite, artificial graphite, graphitized coke, graphitized MCMB, and graphitized MPCF.

[0064] 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.

[0065] Examples of the elements included in the lithium alloy include aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium, or indium.

[0066] 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, etc. The metal may include lithium and / or magnesium, and metal-doped SiO x (0 < x < 2) may include metal silicates.

[0067] (Method for manufacturing 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, etc.

[0068] 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.

[0069] (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, etc.

[0070] (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.

[0071] In some embodiments, as the negative electrode binder, a styrene-butadiene rubber (SBR)-based binder, carboxymethyl cellulose (CMC), polyacrylic acid-based binder, poly(3,4-ethylenedioxythiophene) (PEDOT)-based binder, etc. may be used.

[0072] [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.

[0073] [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.

[0074] (Lithium salt / Organic solvent) The non-aqueous electrolyte contains a lithium salt as an electrolyte and an organic solvent. The lithium salt is represented by, for example, Li + X - and the anion (X - ) of the lithium salt includes F - , Cl - , Br - , I - , NO 3 - , N(CN) 2 - , BF 4 - , ClO 4 - , PF 6 - , (CF 3 ) 2 PF 4 - , (CF 3 ) 3 PF3 - , (CF 3 ) 4 PF 2 - , (CF 3 ) 5 PF - , (CF 3 ) 6 P - , CF 3 SO 3 - , CF 3 CF 2 SO 3 - , (CF 3 SO 2 ) 2 N - , (FSO 2 ) 2 N - , CF 3 CF 2 (CF 3 ) 2 CO - , (CF 3 SO 2 ) 2 CH - , (SF 5 ) 3 C - , (CF 3 SO 2 ) 3 C - , CF 3 (CF 2 ) 7 SO 3 - , CF 3 CO 2 - , CH 3 CO 2 - , SCN - and (CF 3 CF 2 SO 2 ) 2 N - etc. can be mentioned.

[0075] The organic solvent may include an organic compound that has sufficient solubility in the lithium salt and the additive and has 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 thereof.

[0076] (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, butylene 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.

[0077] Hereinafter, examples and experimental examples will be specifically illustrated and described below. However, the examples and experimental examples described below illustrate a part of one embodiment, and it should not be construed that the technology described in this specification is limited thereto.

[0078] <Experimental Method> 1. Measurement of Surface Roughness (Ra) After cutting the manufactured separator into a square shape with a side length of 1 cm, it was fixed on a slide glass substrate using double-sided tape, and the roughness was measured using an atomic force microscope (Atomic Force Microscopy, Bruker, Icon). Here, the measurement mode was the tapping mode, the tip used was TESPA-V2, the scan speed was set to 1.0 Hz, and the resolution was set to 256.

[0079] 2. Measurement of Coating Density The weight per unit area (g / m 2 ) of the inorganic particle layer formed on the porous substrate was divided by the thickness (μm) of the inorganic particle layer for calculation (unit: g / (m 2 ·μm))

[0080] 3. Measurement of Air Permeability Using a densometer (Toyoseiki Ltd.), in accordance with the ASTM D726 standard, the air permeability (Gurley permeability) was measured, and the time taken for 100 cc of air to pass through an area of 1 square inch of the separator was recorded in seconds.

[0081] 4. Measurement of Thermal Shrinkage Rate The manufactured separator was cut into a square shape with a side length of 10 cm, and the machine direction (MD, Machine Direction) and the transverse direction (TD, Transverse Direction) were marked. The sample was placed in the center, 5 sheets of paper were placed above and below the sample respectively, and the four sides of the paper were wrapped with tape. The sample wrapped with paper was left in a hot air drying oven at a temperature of 150 °C for 60 minutes. Then, the sample was taken out and the separator was measured with a camera, and the shrinkage rate in the machine direction (MD) of the following Mathematical Formula 1 and the shrinkage rate in the transverse direction (TD) of the following Mathematical Formula 2 were calculated.

[0082] [Mathematical Formula 1] Shrinkage rate in the machine direction (MD) (%) = (Length in the machine direction before heating - Length in the machine direction after heating) × 100 / Length in the machine direction before heating

[0083] [Mathematical formula 2] Shrinkage rate in the transverse direction (TD) (%) = (Length in the transverse direction before heating - Length in the transverse direction after heating) × 100 / Length in the transverse direction before heating

[0084] 5. Measurement of moisture content For the measurement of moisture content, first, the separator was dried. The 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. Then, the separator was taken out of the oven and stored in the dry room for 30 minutes. Next, after collecting 0.3 g of the dried separator, a moisture measuring machine (Metrohm, 917 Coulometer) was utilized to measure the amount of moisture generated while heating the test piece at 150°C according to the Karl Fischer moisture measurement method.

[0085] 6. Performance measurement after initial and 100 - cycle driving The resistance (DC - IR) evaluation of the secondary battery was carried out using the J - pulse (Japan Electric Vehicle Association Standards, JEVS D 713) method, which evaluates the 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 by the above - mentioned method, and the initial resistance value was calculated.

[0086] After 100 cycles, in the case of DC - IR and capacity, from 2.7V (Constant Current) to 4.3V (Constant Current Constant Voltage), after charging / discharging at 0.1C for the first cycle and 0.2C for the second cycle, and then charging / discharging at 0.5C for 100 cycles from the third cycle onwards, similar to the initial resistance, the DC - IR after 100 cycles (Cycle) was measured by the J - pulse method, and at this time, the capacity was measured.

[0087] 7. Measurement of surface roughness after 600 - cycle driving After performing 600 cycles in the same manner as the 6th one, the battery was discharged three times until the voltage reached 2.7 V, and then the pouch was disassembled. After that, the separator was washed with dimethyl carbonate and then left in an oven at 80 °C for one week to be sufficiently dried. Next, the surface roughness was measured in the same way as the 1st one.

[0088] 8. Measurement of Thickness Thickness of separator: After stacking 10 separators, the thickness was measured at five arbitrary points in the width direction using a thickness measuring instrument manufactured by Mitutoyo. Then, the average thickness of the 10 - layer separator was derived, and further divided by 10 to obtain the overall average thickness of a single separator.

[0089] Thickness of porous film: After stacking only 10 porous films, the thickness was measured at five arbitrary points in the width direction using a thickness measuring instrument manufactured by Mitutoyo. Then, the average thickness of the 10 - layer porous film was derived, and further divided by 10 to obtain the average thickness of a single porous film.

[0090] Thickness of inorganic particle layer: It was derived by calculating the value obtained by subtracting the average thickness of a single porous film from the overall average thickness of a single separator obtained by the above method.

[0091] 9. Measurement of Weight - Average Molecular Weight The measurement of the weight - average molecular weight was carried out using GPC (manufactured by Tosoh, EcoSEC HLC - 8320GPC Reflective Index detector). The GPC columns used were Tskgel guard PWx, two TSKgel GMPWxl, and TSKgel G2500PWxl (7.8×300 mm). The eluent was 0.1M NaNO 3 aqueous solution. The standard substance used was polyethylene glycol, and the analysis was carried out at 40 °C with a flow rate of 1 mL / min.

[0092] <Example 1> Manufacture of Separator In water, the average particle size (D 50) having particle sizes of 300 nm and 700 nm respectively, boehmite (γ-AlOOH) was added at a weight ratio of 3:7, and 0.7 parts by weight of dispersant BYK-2018 (BYK GmbH) was added to 100 parts by weight of the boehmite. After stirring for 30 minutes, an aqueous dispersion with a solid content of 45% by weight was produced. Subsequently, the aqueous dispersion was further stirred for 3 minutes at a rotational speed of 250 rpm using a planetary mixer (Planetary mixer, bead size: 0.65 nm). Next, 7 parts by weight of polyacrylate (Mw: 120,000 g / mol, Sigma Aldrich Inc.) was added to 100 parts by weight of the boehmite, and then water was added to produce an aqueous slurry with a final solid content of 29% by weight.

[0093] The aqueous slurry was coated on both sides of a porous polyolefin film (ENPASS, SK Innovation, average pore diameter: 40 nm) with a thickness of 9 μm at a speed of 10 m per minute to form inorganic particle layers with a thickness of approximately 1.5 μm each. For the flattening of the inorganic particle layers, after passing through a patternless smoothing bar, it was put into a hot air dryer at 45 °C to produce a separator.

[0094] Manufacture of Battery Manufacture of the positive electrode: As the positive electrode active material, 92% by weight of lithium cobalt composite oxide (LiCoO 2 ) 92% by weight, 4% by weight of carbon black as the conductive material, and 4% by weight of polyvinylidene fluoride (PVdF) as the binder were added to N-methyl-2-pyrrolidone (NMP) as the solvent to produce a positive electrode mixture slurry. The produced slurry was coated on an aluminum (Al) thin film with a thickness of 30 μm, dried at a temperature of 120 °C, and then roll-pressed to produce a positive electrode with a thickness of 140 μm.

[0095] Manufacture of the negative electrode: Graphite carbon, PVdF as the binder, and carbon black as the conductive agent were added to NMP, which is a solvent, at 96 wt%, 3 wt%, and 1 wt%, respectively, to produce a negative electrode mixture slurry. The produced slurry was applied to a 20-μm-thick copper (Cu) thin film, dried at 120 °C, and roll-pressed to produce a 150-μm-thick negative electrode.

[0096] A separator manufactured between the positive electrode and the negative electrode was stacked to assemble a pouch-type battery, and 1 M lithium hexafluorophosphate (LiPF 6 ) dissolved in ethylene carbonate (EC) / ethyl methyl carbonate (EMC) / dimethyl carbonate (DMC) = 3:5:2 (volume ratio) was injected into each assembled battery to manufacture a lithium secondary battery. Thereby, a pouch-type lithium ion secondary battery with a capacity of 80 mAh was manufactured.

[0097] <Example 2> In the manufacture of the separator of Example 1, boehmite with an average particle size (D 50 ) of 300 nm and 1600 nm, respectively, was used at a weight ratio of 1:1, and a battery was manufactured in the same manner as in Example 1 except that a rotation speed of 150 rpm was applied.

[0098] <Example 3> In the manufacture of the separator of Example 1, the final solid content of the aqueous slurry was set to 25 wt%, and a battery was manufactured in the same manner as in Example 1 except that the slurry was applied at a speed of 5 m per minute during the application of the slurry.

[0099] <Example 4> In the manufacture of the separator of Example 2, the final solid content of the aqueous slurry was set to 37 wt%, and a battery was manufactured in the same manner as in Example 2 except that the slurry was applied at a speed of 13 m per minute during the application of the slurry.

[0100] <Example 5> In the production of the separator of Example 1, a battery was produced in the same manner as in Example 1, except that a rotation speed of 300 rpm was applied and the drying temperature of the hot air dryer was adjusted to 40°C.

[0101] <Comparative Example 1> In the production of the separator of Example 1, a battery was produced in the same manner as in Example 1, except that the final solid content of the aqueous slurry was adjusted to 37% by weight, and when applying the slurry, it was applied at a speed of 20 m per minute and no smoothing bar was applied.

[0102] <Comparative Example 2> In the production of the separator of Example 2, a battery was produced in the same manner as in Example 2, except that the final solid content of the aqueous slurry was adjusted to 37% by weight, and when applying the slurry, it was applied at a speed of 20 m per minute and no smoothing bar was applied.

[0103] <Comparative Example 3> In the production of the separator of Example 1, a battery was produced 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 23% by weight, when applying the slurry, it was applied at a speed of 5 m per minute, and a hot air dryer at 35°C was applied as the dryer.

[0104] <Comparative Example 4> In the production of the separator of Example 2, a battery was produced in the same manner as in Example 2, except that a rotation speed of 250 rpm was applied, the final solid content of the aqueous slurry was adjusted to 23% by weight, when applying the slurry, it was applied at a speed of 5 m per minute, and a hot air dryer at 35°C was applied as the dryer.

[0105] <Comparative Example 5> In the production of the separator of Example 1, a battery was produced 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 32% by weight, when applying the slurry, it was applied at a speed of 5 m per minute, and a hot air dryer at 40°C was applied as the dryer.

[0106] <Comparative Example 6> In the production of the separator of Example 2, the final solid content of the aqueous slurry was adjusted to 37% by weight, and when applying the slurry, it was applied at a speed of 20 m per minute. A battery was produced in the same manner as in Example 2 except that a hot air dryer at 45 °C was applied as the dryer.

[0107] The surface roughness and physical properties of the separators produced in the above Examples and Comparative Examples were measured and shown in Table 1 below.

[0108]

Table 1

[0109] The performance of the batteries produced in the above Examples and Comparative Examples was evaluated and shown in Tables 2 and 3 below.

[0110]

Table 2

[0111] As can be confirmed from Table 2 above, the separators of the Examples having a surface roughness of 180 nm to 230 nm show an increase in battery resistance and a decrease in capacity of 10% or less even after 100 cycles of driving, while for the separators with a surface roughness value higher than 230 nm (Comparative Examples 1, 2, 6) or lower than 180 nm (Comparative Examples 3, 4, 5), after 100 cycles of driving, the battery resistance of all of them increased by 10% or more and the capacity of all of them decreased by 8% or more.

[0112] Specifically, the separators of Comparative Examples 1, 2, and 6 have a relatively loose packing of inorganic particles due to their high surface roughness, resulting in low air permeability and moisture content of the separators. Although the initial resistance of the battery is low, during charge and discharge, lithium ions cannot move uniformly, leading to a decrease in battery performance. The separators of Comparative Examples 3, 4, and 5 have a relatively dense packing of inorganic particles due to their low surface roughness, resulting in high air permeability and moisture content of the separators. The initial resistance of the battery is high, and during charge and discharge, side reactions caused by moisture lead to a decrease in battery performance. On the other hand, in the case of the separator of the Example that satisfies the range of surface roughness of 180 nm to 230 nm, it has excellent heat resistance. Moreover, it can be confirmed that the battery manufactured using this separator can achieve high output performance and discharge efficiency and improve the battery life.

[0113]

Table 3

[0114] As can be confirmed from Table 3 above, for the separator according to the Example, even after 600 cycles of charge and discharge, the change rate of the surface roughness is significantly lower than that of the Comparative Example. Thus, it can be seen that the surface characteristics of the separator are maintained even after long-term battery operation, indicating excellent life characteristics.

[0115] As described above in detail by way of Examples and Experimental Examples for one embodiment, the scope of one embodiment is not limited to specific Examples and should be interpreted according to the appended claims.

Claims

1. A porous substrate; an inorganic particle layer comprising inorganic particles on at least one surface of the porous substrate; The separator, wherein the inorganic particle layer has a surface roughness (Ra) of 180 nm to 230 nm.

2. The inorganic particles include 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 2. The separator of claim 1, comprising one or more selected from the group consisting of:

3. The separator according to claim 1 , wherein the inorganic particle layer further comprises a binder.

4. 4. The separator according to claim 3, wherein the binder comprises at least one selected from the group consisting of ester-based polymers, amide-based polymers, imide-based polymers, acrylic-based polymers, acrylamide-based polymers, vinyl alcohol-based polymers, fluorine-based polymers, and vinylpyrrolidone-based polymers.

5. The separator according to claim 3, wherein the binder is contained in an amount of 0.1 to 20.0 parts by weight based on 100 parts by weight of the inorganic particles.

6. The separator according to claim 3, wherein the binder has a weight average molecular weight of 10,000 g / mol to 2,000,000 g / mol.

7. The inorganic particles have different average particle sizes (D ５０ 2. The separator of claim 1, comprising one or more inorganic particles having a molecular weight of 1.2 or more.

8. The inorganic particles have an average particle size (D ５０ 2. The separator of claim 1, comprising inorganic particles having a particle size of 0.05 μm to 2.0 μm.

9. The separator according to claim 1, wherein the inorganic particle layer has a thickness of 0.1 μm to 10.0 μm.

10. The coating density of the inorganic particle layer is 0.8 g / (m ２ The separator according to claim 1, wherein the thickness of the separator is equal to or greater than 1 μm.

11. 2. The separator according to claim 1, wherein the separator has a shrinkage rate of 5.0% or less in both the machine direction (MD) and the transverse direction (TD) after being left at 150°C for 60 minutes.

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

13. 2. The separator according to claim 1, wherein a rate of change in surface roughness (Ra) is 15% or less when a secondary battery manufactured using the separator is charged and discharged for 600 cycles.

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

15. The secondary battery according to claim 14, wherein the capacity change rate after 100 charge / discharge cycles is 20% or less.

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