Separator for secondary battery and secondary battery including same

Abstract

The present invention relates to a separator for a secondary battery and a secondary battery including same. The separator for a secondary battery comprises: a porous substrate; and a coating layer disposed on at least one surface of the porous substrate, wherein the coating layer contains a filler and a binder, the filler has a specific surface area of 5-10 m2 / g, the binder includes an aqueous binder, and the porous substrate has a ratio of the tensile strength in the machine direction to the tensile strength in the transverse direction of 1:0.9 to 1:1.1, and a ratio of the elongation in the machine direction to the elongation in the transverse direction of 1:0.9 to 1:1.1.

Description

Separator for secondary batteries and secondary battery including the same

[0001] This invention relates to a separator for a secondary battery and a secondary battery including the same.

[0002]

[0003] Recently, accompanied by the rapid proliferation of battery-powered electronic devices such as mobile phones, laptop computers, and electric vehicles, the demand for high-energy-density, high-capacity rechargeable batteries is rapidly increasing. Accordingly, research and development to improve the performance of lithium-ion batteries is actively underway.

[0004] A lithium secondary battery is a battery comprising a positive electrode and a negative electrode containing an active material capable of lithium ion intercalation and deintercalation, and an electrolyte, which produces electrical energy through oxidation and reduction reactions when lithium ions are intercalated or deintercalated from the positive and negative electrodes.

[0005] The separator is used by being injected into the cell while impregnated with the electrolyte. Therefore, it may be desirable for the separator to have a low shrinkage rate in the width direction within the cell. Meanwhile, since lithium secondary batteries are susceptible to moisture, they may be assembled in a dry room with low moisture content. The temperature and relative humidity of the dry room differ from the production, shipping, and storage environment of the separator. Therefore, it may be desirable for the separator to have a low rate of change in width not only within the cell but also within the dry room.

[0006]

[0007] One embodiment provides a separator for a secondary battery with a low width shrinkage rate not only within the cell but also within the dry room.

[0008] Another embodiment provides a separator for a secondary battery that has no core detachment during winding, a low thermal shrinkage rate, and high puncture strength.

[0009] Another embodiment provides a secondary battery comprising the above-mentioned separator for the secondary battery.

[0010]

[0011] 1. One embodiment comprises a porous substrate; and a coating layer positioned on at least one surface of the porous substrate, wherein the coating layer comprises a filler and a binder, and the filler has a specific surface area of ​​5 to 10 m² 2 / g, the binder comprises a water-based binder, the porous substrate has a ratio of tensile strength in the mechanical direction to tensile strength in the width direction of 1:0.9 to 1:1.1, and a ratio of elongation in the mechanical direction to elongation in the width direction of 1:0.9 to 1:1.1, and provides a separator for a secondary battery.

[0012] A porous substrate; and a coating layer positioned on at least one surface of the porous substrate, wherein the coating layer comprises a filler and a binder.

[0013] The above filler has a specific surface area of ​​5 to 10 m² 2 / g and,

[0014] The above binder includes a water-based binder, and

[0015] The above porous substrate is a separator for a secondary battery, wherein the ratio of tensile strength in the mechanical direction to tensile strength in the width direction is 1:0.9 to 1:1.1 and the ratio of elongation in the mechanical direction to elongation in the width direction is 1:0.9 to 1:1.1.

[0016] 2.1. The filler is a separator for a secondary battery having an average particle size D50 of 0.1 to 1 μm.

[0017] 3.1 or 2, wherein the filler is spherical, a separator for a secondary battery.

[0018] 4.1 to 3, wherein the filler comprises Al2O3, SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, GaO, ZnO, ZrO2, Y2O3, SrTiO3, BaTiO3, Mg(OH)2, boehmite, or a combination thereof, for a separator for a secondary battery.

[0019] In 5.1 to 4, the specific surface area of ​​the coating layer is 5 to 10 m 2 A separator for a secondary battery, wherein the filler in / g comprises 95% by weight or more of the total filler in the coating layer.

[0020] 6.1 to 5, wherein the binder : filler in the coating layer is included in a mass ratio of 1:10 to 1:50. A separator for a secondary battery.

[0021] In 7.1 to 6, the porous substrate has a tensile strength in the mechanical direction of 1800 to 4000 kgf / cm² 2 , tensile strength in the width direction is 1600 to 3800 kgf / cm 2 Phosphor, separator for secondary batteries.

[0022] 8.1 to 7, wherein the porous substrate has a mechanical elongation of 20 to 200% and a tensile strength in the width direction of 25 to 220%, a separator for a secondary battery.

[0023] A separator for a secondary battery according to 9.1 to 8, wherein the ratio of moisture content to the thickness of the coating layer is 250 ppm / ㎛ or less.

[0024] A separator for a secondary battery according to 10.1 to 9, wherein the ratio of the thermal shrinkage rate in the width direction of the coating layer according to Formula 2 below to the thermal shrinkage rate in the width direction of the porous substrate according to Formula 1 below is 0.05 or less:

[0025] [Equation 1]

[0026] Thermal shrinkage rate = (L0 - L1) / L0 x 100

[0027] (L0 is the initial width of the porous substrate, L1 is the width of the porous substrate after being left at 120°C for 1 hour)

[0028] [Equation 2]

[0029] Thermal shrinkage rate = (L0 - L1) / L0 x 100

[0030] (L0 is the initial width of the coating layer, L1 is the width of the coating layer after being left at 130°C for 1 hour).

[0031] 11.1 to 10, wherein the aqueous binder is a (meth)acrylic binder, a separator for a secondary battery.

[0032] A separator for a secondary battery according to 12.1 to 11, wherein the porous substrate is a polyolefin-based substrate, and the polyolefin-based substrate comprises a polyolefin-based resin having a weight-average molecular weight of 1 million g / mol or more and a melting temperature of 130 to 140°C.

[0033] Another embodiment provides a secondary battery comprising a positive electrode; a negative electrode; and a separator for the secondary battery located between the positive electrode and the negative electrode.

[0034]

[0035] A separator for a secondary battery according to one embodiment has a low shrinkage rate not only in the cell but also in the dry room, does not lose its core during winding, has a low thermal shrinkage rate, and has high puncture strength, which can improve the manufacturing processability and reliability of the secondary battery.

[0036]

[0037] FIG. 1 is a cross-sectional view of a separator according to one embodiment.

[0038] FIGS. 2 to 5 are cross-sectional views schematically illustrating a lithium secondary battery according to one embodiment.

[0039]

[0040] Hereinafter, embodiments of the present invention will be described in detail. However, these are presented as examples and are not intended to limit the present invention, and the present invention is defined only by the scope of the claims set forth below.

[0041] Unless otherwise specifically stated in this specification, when a part such as a layer, film, region, plate, etc. is described as being "on" another part, this includes not only cases where it is "immediately on" another part, but also cases where there is another part in between.

[0042] Unless otherwise specified in this specification, a singular form may also include a plural form. Additionally, unless otherwise specified, "A or B" may mean "including A, including B, or including A and B."

[0043] In this specification, "combination of these" may mean a mixture of components, a laminate, a composite, a copolymer, an alloy, a blend, and a reaction product, etc.

[0044] Unless otherwise defined in this specification, the particle size may be the average particle size. Additionally, the particle size refers to the average particle size (D50), which means the diameter of the particle whose cumulative volume in the particle size distribution is 50% by volume. The average particle size (D50) may be measured by methods widely known to those skilled in the art, for example, by measuring with a particle size analyzer, or by measuring with a transmission electron microscope (TEM) image or a scanning electron microscope (SEM) image. Alternatively, the average particle size (D50) value may be obtained by measuring using a measuring device utilizing dynamic light scattering, performing data analysis to count the number of particles for each particle size range, and then calculating from this. Alternatively, it may be measured using a laser diffraction method. When measuring by laser diffraction, more specifically, after dispersing the particles to be measured in a dispersion medium, they are introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac MT 3000) and irradiated with ultrasound of about 28 kHz at an output of 60 W, and then the average particle size (D50) at 50% of the particle size distribution in the measuring device can be calculated.

[0045] A separator for a secondary battery according to one embodiment has a low width shrinkage rate not only within the cell but also within the dry room, which can improve the manufacturing processability and reliability of the lithium secondary battery.

[0046] Here, the 'dry room' may be a space having conditions of a temperature of 20 to 28°C and a relative humidity of 30 to 50%.

[0047] Here, 'width shrinkage rate' refers to the shrinkage rate of the porous substrate in the width direction (transverse direction, TD) of the above-mentioned separator.

[0048] Here, the 'width direction' may refer to a direction perpendicular to the direction in which the unoriented film is manufactured, when the porous substrate is manufactured by stretching an unoriented film produced by melt extrusion or solvent casting of a composition containing a resin for a porous substrate. The direction in which the unoriented film is manufactured may be the machine direction (MD).

[0049] The above separator may have a shrinkage rate in the width direction in the above dry room of 0.3% or less, for example, 0 to 0.3%. Within this range, the deformation of the separator is reduced during the assembly process of a secondary battery using the above separator, thereby improving the manufacturing processability of the secondary battery.

[0050] The above separator may have a thermal shrinkage rate of 15% or less in MD and TD, respectively. Within this range, the reliability of the battery can be increased. The thermal shrinkage rate in MD and TD, respectively, can be measured by the method described below.

[0051] The above separator may have a puncture strength of 45 gf / µm or higher. Within this range, the reliability of the battery can be increased. The puncture strength may be measured by the method described below.

[0052] The above separator may have a moisture content of 550 ppm or less. Within this range, the reliability of the battery can be increased. The moisture content may be measured by the method described below. For example, the above moisture content is 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, 200, 210, 220, 230, 240, 250, 260, 270, 280, 290, 300, 310, 320, 330, 340, 350, 360, 370, 380, 390, 400, 410, 420, 430, 440, 450, 460, 470, 480, 490, It can be 500, 510, 520, 530, 540, 550 ppm.

[0053] In one embodiment, the ratio of moisture content to the thickness of the coating layer may be 250 ppm / µm or less, for example, 100, 105, 110, 115, 120, 125, 130, 135, 140, 145, 150, 155, 160, 165, 170, 175, 180, 185, 190, 195, 200, 205, 210, 215, 220, 225, 230, 235, 240, 245, 250 ppm / µm, for example, 100 to 230 ppm / µm. Within this range, the shrinkage rate in the width direction within the dry room may be lower. The moisture content of the coating layer may be measured in substantially the same way as the moisture content of the separation membrane.

[0054] The separator for the secondary battery comprises a porous substrate; and a coating layer located on at least one surface of the porous substrate, wherein the coating layer comprises a filler and a binder, and the filler has a specific surface area of ​​5 to 10 m² 2 / g, and the binder includes a water-based binder, and the porous substrate has a ratio of tensile strength in the mechanical direction to tensile strength in the width direction of 1:0.9 to 1:1.1, and a ratio of elongation in the mechanical direction to elongation in the width direction of 1:0.9 to 1:1.1.

[0055] The porous substrate satisfies the ratio of tensile strength and the ratio of elongation simultaneously. By satisfying the ratio of tensile strength and the ratio of elongation simultaneously, the porous substrate may facilitate a reduction in width shrinkage rate within the cell. If the ratio of tensile strength is satisfied but the ratio of elongation deviates from 1:0.9 to 1:1.1, there may be a problem as the rate of change in width deviates from a suitable range for the cell. If the ratio of elongation is satisfied but the ratio of tensile strength deviates from 1:0.9 to 1:1.1, there may be a problem as the rate of change in width deviates from a suitable range for the cell.

[0056] In one embodiment, the ratio of the tensile strengths may be 1:0.95 to 1:1, for example, 1:0.95 to 1:0.99, 1:0.96 to 1:0.99, 1:0.97 to 1:0.99, or 1:0.97 to 1:0.98. Within this range, the porous substrate can be manufactured easily, and the shrinkage rate in the width direction within the dry room can be further reduced.

[0057] In one embodiment, the ratio of the elongation may be 1:0.95 to 1:1, for example, 1:0.95 to 1:0.99, 1:0.96 to 1:0.99, 1:0.97 to 1:0.99, or 1:0.97 to 1:0.98. Within this range, the porous substrate can be manufactured easily, and the shrinkage rate in the width direction within the dry room can be further reduced.

[0058] The tensile strength in the mechanical direction of the above porous substrate is 1,800 to 4,000 kgf / cm 2 , for example, 1800 to 3000 kgf / cm² 2It can be. Within the above range, it is easy to satisfy the ratio of the tensile strength and easy to manufacture the porous substrate.

[0059] The tensile strength in the width direction of the above porous substrate is 1600 to 3800 kgf / cm 2 , for example, 1600 to 2800 gf / cm² 2 It can be. Within the above range, it is easy to satisfy the ratio of the tensile strength and easy to manufacture the porous substrate.

[0060] The mechanical elongation of the porous substrate can be 20 to 200%, for example, 30 to 180%. Within this range, it is easy to satisfy the ratio of the tensile strength and easy to manufacture the porous substrate.

[0061] The elongation in the width direction of the porous substrate can be 25 to 220%, for example, 40 to 200%. Within this range, it is easy to satisfy the ratio of the tensile strength and easy to manufacture the porous substrate.

[0062] Here, the tensile strength and elongation can each be measured by the method described below.

[0063] A porous substrate satisfying the above ratio of tensile strength and elongation can be achieved by controlling the elongation ratio during the manufacture of the porous substrate. This is explained in detail below.

[0064] porous substrate

[0065] The above porous substrate has a number of pores and can be applied as a substrate for a separator to facilitate the movement of lithium ions.

[0066] The porous substrate may be a polymer membrane formed from any one polymer selected from the group consisting of polyolefins such as polyethylene and polypropylene, polyesters such as polyethylene terephthalate and polybutylene terephthalate, polyacetal, polyamide, polyimide, polycarbonate, polyetheretherketone, polyaryletherketone, polyetherimide, polyamideimide, polybenzimidazole, polyethersulfone, polyphenylene oxide, cyclic olefin copolymer, polyphenylene sulfide, polyethylene naphthalate, glass fiber, Teflon, and polytetrafluoroethylene, or a copolymer or mixture of two or more of these.

[0067] In one embodiment, the porous substrate may be a polyolefin-based substrate including polyolefin, and may be, for example, a polyethylene substrate.

[0068] The above polyolefin-based substrate has excellent shutdown capabilities and can contribute to improving the safety of the battery. The above polyolefin-based substrate may be selected from, for example, a polyethylene single membrane, a polypropylene single membrane, a polyethylene / polypropylene double membrane, a polypropylene / polyethylene / polypropylene triple membrane, and a polyethylene / polypropylene / polyethylene triple membrane. In addition, the above polyolefin-based resin may include a non-olefin resin in addition to an olefin resin, or may include a copolymer of an olefin and a non-olefin monomer.

[0069] A porous substrate satisfying the above ratio of tensile strength and ratio of elongation can be realized by controlling the weight-average molecular weight, melting temperature (TM), and / or stretching temperature and / or stretching ratio of the polyolefin resin used in the porous substrate when manufacturing the porous substrate.

[0070] In one embodiment, the polyolefin resin has a weight average molecular weight of 1 million g / mol or more, 1 million, 1.1 million, 1.2 million, 1.3 million, 1.4 million, 1.5 million, 1.6 million, 1.7 million, 1.8 million, 1.9 million, 2 million, 2.1 million, 2.2 million, 2.3 million, 2.4 million, 2.5 million, 2.6 million, 2.7 million, 2.8 million, 2.9 million, 3 million, 3.1 million, 3.2 million, 3.3 million, 3.4 million, 3.5 million, 3.6 million, 3.7 million, 3.8 million, 3.9 million, 4 million, 4.1 million, 4.2 million, 4.3 million, 4.4 million, 4.5 million, It can be 4.6 million, 4.7 million, 4.8 million, 4.9 million, 5 million g / mol, for example, 1 million to 5 million g / mol, or 1 million to 3 million g / mol. Within the above range, the ratio of tensile strength and the ratio of elongation can be easily reached. Here, the weight-average molecular weight can be obtained as a polystyrene equivalent value by gel permeation chromatography.

[0071] In one embodiment, the polyolefin resin may have a melting temperature (Tm) of 130 to 140°C. Within this range, the ratio of tensile strength to elongation can be easily reached. Here, Tm can be determined by referring to a product catalog of polyolefin-based materials or by methods known to those skilled in the art. For example, the melting temperature may be measured by the following method:

[0072] Using a Differential Scanning Calorimeter (DSC, device name: DSC Q20, manufacturer: TA instrument), the temperature was raised to heat the polyethylene composition to 200°C at a rate of 10°C / min (Cycle 1), isothermal at 200°C for 1 minute, then cooled to 40°C at a rate of 10°C / min, and isothermal at 40°C for 1 minute, then heated again to 200°C at a rate of 10°C / min (Cycle 2). In the DSC curve obtained through this process, the temperature at the point of maximum endothermic peak was measured as the melting temperature (Tm, °C), and the temperature at the point of maximum exothermic peak was measured as the crystallization temperature (Tc, °C). At this time, the melting temperature (Tm) and crystallization temperature (Tc) are the results measured in the second temperature rising and falling section (Cycle 2), respectively.

[0073] The porous substrate described above may be manufactured by stretching an unoriented film containing the polyolefin resin using a wet method. Specifically, the porous substrate may be manufactured by a filler extraction method, but is not limited thereto. The filler extraction method involves mixing a polyolefin resin with a filler, forming pores by extracting the filler after rolling, and then manufacturing the porous substrate through a stretching process.

[0074] In one embodiment, the elongation temperature may be 90 to 130°C, for example, 90 to 110°C. Within this range, the ratio of tensile strength to elongation can be easily reached.

[0075] In one embodiment, the elongation ratio may be 4 to 10 times, for example, 5 to 8 times. Within this range, the ratio of tensile strength and the ratio of elongation can be easily reached.

[0076] In one embodiment, the stretching may be performed by MD and TD uniaxial stretching of the unstretched film, MD and TD biaxial stretching, etc.

[0077] The porous substrate may have a thickness of 1 μm to 40 μm, for example, 1 μm to 30 μm, 1 μm to 20 μm, or 5 μm to 15 μm.

[0078] The above separation membrane can reduce the width shrinkage rate in a dry room by having a coating layer described below.

[0079] Coating layer

[0080] The coating layer comprises a filler and a binder, and the filler has a specific surface area of ​​5 to 10 m² 2 / g, and the binder includes a water-based binder. The coating layer can significantly reduce the width shrinkage rate in a dry room of a separation membrane having a porous substrate satisfying the ratio of tensile strength and the ratio of elongation.

[0081] The above filler has a specific surface area of ​​5 to 10 m² 2 / g. The specific surface area of ​​the above filler is 5m² 2 A separator having a coating layer of less than / g may have a high rate of width shrinkage within the cell. The specific surface area of ​​the filler is 10m² 2 Separators having a coating layer exceeding 1g may have an excessively high width shrinkage rate in the dry room, which can lower the processability of battery manufacturing.

[0082] Here, the specific surface area refers to the BET specific surface area. Here, the specific surface area may be the average value of the specific surface areas of the fillers included in the coating layer. The BET specific surface area may be measured using MOUNTECH’s Macsorb HM Model-1208, but is not limited thereto.

[0083] The above specific surface area is 5 to 10 m² 2 It can be implemented by including a filler having / g. In one embodiment, the specific surface area of ​​the coating layer is 5 to 10 m 2The filler in / g may be included in an amount of 95% or more by weight, for example, 95 to 100% by weight, of the total filler in the coating layer. Within this range, it may be easy to achieve the effect of the separator described above.

[0084] The above specific surface area is 5 to 10 m 2 The filler in / g may have an average particle size D50 of 0.1 to 1㎛. Within the above range, it is easy to have the above specific surface area, excellent uniformity, and the peeling of the coating layer may not occur.

[0085] The filler may have a specific surface area of ​​5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, or 10 m² / g. In one embodiment, the filler may have an average particle size D50 of 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, or 1 µm. For example, the specific surface area is 5 to 10 m² 2 The filler in / g may have an average particle size D50 of 0.6 to 1.0㎛ or 0.6 to 0.8㎛. Within the above range, the width shrinkage rate in the dry room may be lower.

[0086] The above specific surface area is 5 to 10 m 2 The filler in / g may include one or more types of organic fillers and inorganic fillers.

[0087] In one embodiment, the organic filler may include a cross-linked polymer filler. The cross-linked polymer filler can lower the moisture content, thereby further lowering the thermal shrinkage rate of the separator and improving insulation properties. The cross-linked polymer filler may be included in the combination of the (meth)acrylic binder and the inorganic filler to facilitate lowering the thermal shrinkage rate of the separator.

[0088] The inorganic filler may be a ceramic material. For example, the inorganic filler may include, for instance, metal oxides, metal metal oxides, metal fluorides, metal hydroxides, or combinations thereof. The inorganic filler may include, for example, alumina (Al2O3), SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, GaO, ZnO, ZrO2, Y2O3, SrTiO3, BaTiO3, Mg(OH)2, boehmite, or combinations thereof, but is not limited thereto. For example, the inorganic filler may be boehmite.

[0089] The above filler may be one or more of plate-shaped, cubic-shaped, amorphous, and spherical. For example, the above filler may be spherical. The above spherical shape may facilitate the realization of the effect of the above-described separation membrane.

[0090] The above specific surface area is 5 to 10 m 2 The filler in / g may be included in the coating layer in an amount of 50% to 99% by weight, for example 70% to 99% by weight, for example 75% to 99% by weight, for example 80% to 99% by weight, for example 85% to 99% by weight, for example 90% to 99% by weight, for example 95% to 99% by weight. When the filler is included within the above range, it may exhibit excellent heat resistance, durability, oxidation resistance, and stability.

[0091] In one embodiment, the binder and the filler in the coating layer may be included in a mass ratio of 1:10 to 1:50, for example, 1:20 to 1:30, or 1:20. Within this range, it is easy to implement the effect of the aforementioned separation membrane, and there may be an effect of improving heat resistance and durability.

[0092] In one embodiment, the ratio of the thermal shrinkage rate in the width direction of the coating layer according to Formula 2 below to the thermal shrinkage rate in the width direction of Formula 1 below of the porous substrate may be 0.05 or less, for example, greater than 0 and less than 0.05: within the above range, the thermal shrinkage rate of the separator is lowered and there may be no core detachment during winding.

[0093] [Equation 1]

[0094] Thermal shrinkage rate = (L0 - L1) / L0 x 100

[0095] (L0 is the initial width of the porous substrate, L1 is the width of the porous substrate after being left at 120°C for 1 hour)

[0096] [Equation 2]

[0097] Thermal shrinkage rate = (L0 - L1) / L0 x 100

[0098] (L0 is the initial width of the coating layer, L1 is the width of the coating layer after being left at 130°C for 1 hour).

[0099] The above binder includes a water-based binder. The water-based binder may preferably be a (meth)acrylic binder, for example, an acrylic binder. The above water-based (meth)acrylic binder may be manufactured by conventional methods known to those skilled in the art.

[0100] According to one embodiment, the (meth)acrylic binder may have a weight-average molecular weight of 100,000 to 1 million g / mol, for example, 200,000 to 500,000 g / mol. Within this range, it may be easy to achieve the effect of the aforementioned separation membrane.

[0101] Each of the above coating layers may have a thickness of 0.01㎛ to 20㎛, 0.1㎛ to 10㎛, or 0.1㎛ to 5㎛, or 0.5㎛ to 2㎛.

[0102] The ratio of the thickness of the coating layer to the thickness of the porous substrate may be 0.05 to 0.5, for example, 0.05 to 0.4, or 0.05 to 0.3, or 0.1 to 0.2. Within the above range, the separator may exhibit excellent air permeability, heat resistance, and adhesion. Here, 'thickness of the coating layer' refers to the thickness of one coating layer when the coating layer is formed only on one side of the porous substrate, and refers to the total thickness of two coating layers when the coating layer is formed on both sides of the porous substrate.

[0103] A separator for a secondary battery according to one embodiment may exhibit excellent air permeability and may have an air permeability value of, for example, 200 sec / 100cc or less, for example, 190 sec / 100cc or less, or 180 sec / 100cc or less. That is, it may have an air permeability value of less than 40 sec / 100cc·1㎛ per unit thickness, for example, 30 sec / 100cc·1㎛ or less, or 25 sec / 100cc·1㎛ or less. Here, air permeability refers to the time (in seconds) required for 100cc of air to pass through a unit thickness of the separator. The air permeability per unit thickness can be obtained by measuring the air permeability over the entire thickness of the separator and then dividing by the thickness. The air permeability can be measured by using an air permeability measuring device (Asahi Seiko, EG01-55-1MR) to measure the time (in seconds) required for 100cc of air to pass through.

[0104] A separator for a secondary battery according to one embodiment can be formed by applying the above-described composition for forming a coating layer to one or both sides of a porous substrate and then drying. The drying can be performed using conventional methods known to those skilled in the art.

[0105] FIG. 1 is a cross-sectional view of a separator according to one embodiment. Referring to FIG. 1, the separator comprises a porous substrate 1 and a coating layer 2 laminated on both sides of the porous substrate 1, and the coating layer 2 comprises a filler 3 and a water-based binder 4.

[0106] Another embodiment provides a lithium secondary battery comprising a positive electrode, a negative electrode, and a separator for the secondary battery located between the positive electrode and the negative electrode.

[0107] The above-mentioned separator for the secondary battery is omitted as it has been described above.

[0108] anode

[0109] A positive electrode for a lithium secondary battery may include a current collector and a positive electrode active material layer formed on the current collector. The positive electrode active material layer may include a positive electrode active material and may further include a binder and / or a conductive material.

[0110] For example, the above anode may further include an additive that can serve as a sacrificial anode.

[0111] The content of the positive active material is 90% to 99.5% by weight with respect to 100% by weight of the positive active material layer, and the content of the binder and the conductive material may each be 0.5% to 5% by weight with respect to 100% by weight of the positive active material layer.

[0112] As a positive electrode active material, a compound capable of reversible intercalation and deintercalation of lithium (a lithated intercalation compound) may be used. Specifically, one or more composite oxides of lithium and a metal selected from cobalt, manganese, nickel, and combinations thereof may be used.

[0113] The above composite oxide may be a lithium transition metal composite oxide, and specific examples include a lithium nickel-based oxide, a lithium cobalt-based oxide, a lithium manganese-based oxide, a lithium iron phosphate-based compound, a cobalt-free nickel-manganese-based oxide, or a combination thereof.

[0114] As an example, a compound represented by any one of the following chemical formulas may be used. Li a A 1-b X b O 2-c D c (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05); Li a Mn 2-b X b O 4-c D c (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05); Li a Ni 1-b-c Co b X c O 2-α D α (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.5, 0<α<2); Li a Ni 1-b-c Mn b X c O 2-α D α (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.5, 0<α<2); Li a Ni b Co c L 1 d G e O2(0.90≤a≤1.8, 0≤b≤0.9, 0≤c≤0.5, 0≤d≤0.5, 0≤e≤0.1); Li a NiG b O2(0.90≤a≤1.8, 0.001≤b≤0.1); Li a CoG b O2(0.90≤a≤1.8, 0.001≤b≤0.1); Li a Mn 1-b G b O2(0.90≤a≤1.8, 0.001≤b≤0.1); Li a Mn2G b O4(0.90≤a≤1.8, 0.001≤b≤0.1); Li a Mn 1-g G g PO4(0.90≤a≤1.8, 0≤g≤0.5); Li(3-f) Fe2(PO4)3(0≤f≤2); Li a FePO4(0.90≤a≤1.8).

[0115] In the above chemical formula, A is Ni, Co, Mn, or a combination thereof; X is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, a rare earth element, or a combination thereof; D is O, F, S, P, or a combination thereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, or a combination thereof; L 1 is Mn, Al, or a combination thereof.

[0116] For example, the above-mentioned positive electrode active material may be a high-nickel positive electrode active material in which the nickel content relative to 100 mol% of the metal excluding lithium in the lithium transition metal composite oxide is 80 mol% or more, 85 mol% or more, 90 mol% or more, 91 mol% or more, or 94 mol% or more and 99 mol% or less. The high-nickel positive electrode active material can achieve high capacity and can be applied to high-capacity, high-density lithium secondary batteries.

[0117] The above binder serves to adhere the positive active material particles well to each other and also to adhere the positive active material well to the current collector. Representative examples of binders include, but are not limited to, polyvinyl alcohol, carboxymethylcellulose, hydroxypropylcellulose, diacetylcellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, epoxy resin, (meth)acrylic resin, polyester resin, nylon, etc.

[0118] The above conductive material is used to impart conductivity to the electrode, and any electronically conductive material that does not cause chemical changes can be used in the battery being constructed. Examples of conductive materials include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, carbon nanofiber, carbon nanotube; metal-based materials in the form of metal powder or metal fibers containing copper, nickel, aluminum, silver, etc.; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0119] Al may be used as the current collector mentioned above, but is not limited thereto.

[0120] cathode

[0121] A negative electrode for a lithium secondary battery comprises a current collector and a negative electrode active material layer located on the current collector. The negative electrode active material layer comprises a negative electrode active material and may further comprise a binder and / or a conductive material.

[0122] For example, the negative electrode active material layer may comprise 90% to 99% by weight of negative electrode active material, 0.5% to 5% by weight of binder, and 0% to 5% by weight of conductive material.

[0123] The negative electrode active material includes a material capable of reversibly intercalating / deintercalating lithium ions, lithium metal, an alloy of lithium metal, a material capable of doping and dedoping lithium, or a transition metal oxide.

[0124] A material capable of reversibly intercalating / deintercalating the above lithium ions may be a carbon-based negative electrode active material, such as crystalline carbon, amorphous carbon, or a combination thereof. Examples of the crystalline carbon include graphite such as amorphous, plate-like, flake-like, spherical, or fibrous natural graphite or artificial graphite, and examples of the amorphous carbon include soft carbon or hard carbon, mesophase pitch carbide, calcined coke, etc.

[0125] As the above lithium metal alloy, an alloy of lithium and a metal selected from Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn may be used.

[0126] As a material capable of doping and undoping the above lithium, a Si-based negative electrode active material or a Sn-based negative electrode active material may be used. The Si-based negative electrode active material may be silicon, a silicon-carbon composite, SiOx (0 < x < 2), a Si-Q alloy (wherein Q is selected from alkali metals, alkaline earth metals, group 13 elements, group 14 elements (excluding Si), group 15 elements, group 16 elements, transition metals, rare earth elements, and combinations thereof), or a combination thereof. The Sn-based negative electrode active material may be Sn, SnO2, a Sn-based alloy, or a combination thereof.

[0127] The silicon-carbon composite may be a composite of silicon and amorphous carbon. According to one embodiment, the silicon-carbon composite may be in the form of silicon particles and amorphous carbon coated on the surface of the silicon particles. For example, it may include a secondary particle (core) assembled from silicon primary particles and an amorphous carbon coating layer (shell) located on the surface of the secondary particle. The amorphous carbon may also be located between the silicon primary particles, so that, for example, the silicon primary particles may be coated with amorphous carbon. The secondary particles may be dispersed in an amorphous carbon matrix.

[0128] The silicon-carbon composite may further include crystalline carbon. For example, the silicon-carbon composite may include a core comprising crystalline carbon and silicon particles and an amorphous carbon coating layer located on the surface of the core.

[0129] The above Si-based or Sn-based negative electrode active material can be used in combination with a carbon-based negative electrode active material.

[0130] The above binder serves to effectively bond the negative electrode active material particles to each other and also to effectively bond the negative electrode active material to the current collector. As the binder, a non-aqueous binder, an aqueous binder, a dry binder, or a combination thereof may be used.

[0131] Examples of the above-mentioned non-aqueous binders include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene propylene copolymer, polystyrene, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide imide, polyimide, or combinations thereof.

[0132] The above-mentioned water-based binder may be selected from styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, (meth)acrylonitrile-butadiene rubber, (meth)acrylic rubber, butyl rubber, fluororubber, polyethylene oxide, polyvinylpyrrolidone, polyepichlorohydrin, polyphosphazene, poly(meth)acrylonitrile, ethylenepropylenediene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, (meth)acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, and combinations thereof.

[0133] When a water-based binder is used as the above-mentioned cathode binder, a cellulose-based compound capable of imparting viscosity may be further included. As this cellulose-based compound, one or more types such as carboxymethyl cellulose, hydroxypropylmethyl cellulose, methyl cellulose, or alkali metal salts thereof may be mixed and used. Na, K, or Li may be used as the alkali metal.

[0134] The above dry binder is a polymer material capable of fiberization, and may be, for example, polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or a combination thereof.

[0135] The above conductive material is used to impart conductivity to the electrode, and any electronically conductive material that does not cause chemical changes can be used in the battery being constructed. Specific examples include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, carbon nanofiber, carbon nanotube; metal-based materials in the form of metal powder or metal fibers including copper, nickel, aluminum, silver, etc.; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0136] As the above-mentioned cathode current collector, a material selected from copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, and combinations thereof may be used.

[0137] Lithium secondary batteries may also contain an electrolyte.

[0138] electrolyte

[0139] The electrolyte for lithium secondary batteries contains a non-aqueous organic solvent and a lithium salt.

[0140] The above-mentioned non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can move.

[0141] The above-mentioned non-aqueous organic solvent may be a carbonate-based, ester-based, ether-based, ketone-based, or alcohol-based solvent, an aprotic solvent, or a combination thereof.

[0142] The above carbonate-based solvents may include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), methyl ethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), etc.

[0143] Ester-based solvents such as methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methylpropionate, ethylpropionate, decanolide, mevalonolactone, valerolactone, and caprolactone may be used.

[0144] As ether-based solvents, dibutyl ether, tetraglame, diglame, dimethoxyethane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, tetrahydrofuran, etc. may be used. Additionally, as ketone-based solvents, cyclohexanone, etc. may be used. As alcohol-based solvents, ethyl alcohol, isopropyl alcohol, etc. may be used, and as aprotic solvents, nitriles such as R-CN (where R is a straight-chain, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms and may include a double bond, an aromatic ring, or an ether group); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane, 1,4-dioxolane; sulfolanes, etc. may be used.

[0145] The above-mentioned non-aqueous organic solvent can be used alone or in a mixture of two or more types.

[0146] In addition, when using a carbonate-based solvent, a mixture of cyclic carbonates and chain carbonates can be used, and the cyclic carbonates and chain carbonates can be mixed in a volume ratio of 1:1 to 1:9.

[0147] The above lithium salt is a substance that dissolves in an organic solvent and acts as a source of lithium ions within the battery, enabling the basic operation of a lithium secondary battery and facilitating the movement of lithium ions between the anode and cathode. Representative examples of lithium salts include LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiAlO2, LiAlCl4, LiPO2F2, LiCl, LiI, LiN(SO3C2F5)2, Li(FSO2)2N (lithium bis(fluorosulfonyl)imide (LiFSI), LiC4F9SO3, LiN(C x F 2x+1 SO2)(C y F 2y+1 It may include one or more selected from SO2)(x and y are integers from 1 to 20), lithium trifluoromethane sulfonate, lithium tetrafluoroethane sulfonate, lithium difluorobis(oxalate)phosphate (LiDFOB), and lithium bis(oxalate)borate (LiBOB).

[0148] lithium secondary battery

[0149] Lithium secondary batteries can be classified into cylindrical, prismatic, pouch, coin, etc., depending on their shape. FIGS. 2 to 5 are schematic diagrams illustrating lithium secondary batteries according to one embodiment, where FIG. 2 is a cylindrical battery, FIG. 3 is a prismatic battery, and FIGS. 4 and 5 are pouch-type batteries. Referring to FIGS. 2 to 5, the lithium secondary battery (100) may include an electrode assembly (40) having a separator (30) interposed between a positive electrode (10) and a negative electrode (20), and a case (50) in which the electrode assembly (40) is housed. The positive electrode (10), the negative electrode (20), and the separator (30) may be impregnated with an electrolyte (not shown). The lithium secondary battery (100) may include a sealing member (60) that seals the case (50) as in FIG. 2. In addition, in FIG. 3, the lithium secondary battery (100) may include a positive lead tab (11) and a positive terminal (12), a negative lead tab (21) and a negative terminal (22). As shown in FIG. 4 and FIG. 5, the lithium secondary battery (100) may include electrode tabs (70), namely a positive tab (71) and a negative tab (72), which serve as electrical passages for inducing current formed in the electrode assembly (40) to the outside.

[0150] A lithium secondary battery according to one embodiment of the present invention may be applied to automobiles, mobile phones, and / or various types of electric devices, etc., but the present invention is not limited thereto.

[0151]

[0152] Examples and comparative examples of the present invention are described below. However, the following examples are merely one example of the present invention, and the present invention is not limited to the following examples.

[0153]

[0154] Example 1:

[0155] Boehmite (spherical, average particle size D50: 0.6㎛, specific surface area: 5m² 2 / g) and an acrylic binder (ZEON, weight-average molecular weight 200,000 to 500,000 g / mol) as a water-based binder were dispersed in water, and then milled using a bead mill at 25°C for 30 minutes to prepare a dispersion. A composition for a coating layer was prepared by adding water so that the total solid content was 20% by weight. In the composition for the coating layer, the weight ratio of acrylic binder to boehmite is 1:20.

[0156] A polyethylene film (weight-average molecular weight of the polyethylene resin is 3 million g / mol, Tm is 132 to 136°C, thickness: 8 μm, manufactured by stretching) was used as the porous substrate. The tensile strength (unit: kgf / cm²) of the MD and TD of the porous substrate was 2 ) and elongation (unit: %) were measured by the following methods, respectively:

[0157] [MD Tensile Strength]

[0158] A porous substrate was cut into 10 cm × 1 cm pieces in MD × TD to prepare specimens, and the tensile strength was measured by stretching the specimens in MD using a tensile strength measuring device (3343, instron), and the average value of the six porous substrates was determined as the tensile strength.

[0159] [TD Tensile Strength]

[0160] A porous substrate was cut into 1 cm × 10 cm pieces in MD × TD to prepare specimens, and the tensile strength was measured by tensile testing with TD using a tensile strength measuring device (3343, instron), and the average value of the 6 porous substrates was determined as the tensile strength.

[0161] [MD Elongation Rate]

[0162] A porous substrate was cut into 10 cm × 1 cm pieces in MD × TD to prepare specimens, and the length of the specimen was measured by pulling it at 100 mm / min in MD at room temperature using an Instron (3343) machine until fracture. The ratio of the increase to the length of the initial specimen was calculated, and the average value for six porous substrates was determined as the elongation rate.

[0163] [TD Elongation Rate]

[0164] A porous substrate was cut into a size of 1 cm × 10 cm in MD × TD to prepare specimens, and the length of the specimen was measured by pulling it at 100 mm / min at room temperature using an Instron (3343) machine until fracture. The ratio of the increase to the length of the initial specimen was calculated, and the average value for six porous substrates was determined as the elongation rate.

[0165] A separation membrane was manufactured by forming a coating layer (thickness: 2㎛) by coating the composition for the coating layer on one surface of the porous substrate using a die-coating method and then drying it at 70°C for 10 minutes.

[0166] Example 2

[0167] A separator was prepared in the same manner as in Example 1, except that the polyethylene film in Example 1 was changed to a polyethylene film having the composition of Table 1 below. The polyethylene film was prepared by increasing the stretching temperature compared to the polyethylene film in Example 1.

[0168] Example 3

[0169] A separator was prepared in the same manner as in Example 1, except that the polyethylene film in Example 1 was changed to a polyethylene film having the composition of Table 1 below. The polyethylene film was prepared by increasing the stretching temperature compared to the polyethylene film in Example 1.

[0170] Example 4

[0171] A separator was prepared in the same manner as in Example 1, except that the polyethylene film in Example 1 was changed to a polyethylene film having the composition of Table 1 below. The polyethylene film was prepared by increasing the stretching temperature compared to the polyethylene film in Example 1.

[0172] Example 5

[0173] In Example 1, boehmite (spherical, average particle size D50: 0.6 μm, specific surface area: 5 m² 2 Instead of / g), boehmite (spherical, average particle size D50: 1.0㎛, specific surface area: 10m² 2 A separation membrane was prepared in the same manner as in Example 1, except that / g) was used.

[0174] Comparative Example 1

[0175] A separator was prepared in the same manner as in Example 1, except that the polyethylene film in Example 1 was changed to a polyethylene film having the composition of Table 1 below. The polyethylene film was prepared by increasing the stretching temperature compared to the polyethylene film in Example 1.

[0176] Comparative Example 2

[0177] A separator was prepared in the same manner as in Example 1, except that the polyethylene film in Example 1 was changed to a polyethylene film having the composition of Table 1 below. The polyethylene film was prepared by increasing the stretching temperature compared to the polyethylene film in Example 1.

[0178] Comparative Example 3

[0179] In Example 1, boehmite (spherical, average particle size D50: 0.6 μm, specific surface area: 5 m² 2 Instead of / g), boehmite (spherical, average particle size D50: 1.5㎛, specific surface area: 2m² 2 A separation membrane was prepared in the same manner as in Example 1, except that / g) was used.

[0180] Comparative Example 4

[0181] In Example 1, boehmite (spherical, average particle size D50: 0.6 μm, specific surface area: 5 m² 2 Instead of / g), boehmite (spherical, average particle size D50: 0.3㎛, specific surface area: 13m² 2 A separation membrane was prepared in the same manner as in Example 1, except that / g) was used.

[0182] Comparative Example 5

[0183] A separator was prepared in the same manner as in Example 1, except that an organic binder, specifically a polyvinylidene fluoride (PVdF) binder, was used instead of an acrylic binder in Example 1.

[0184] Comparative Example 6

[0185] A separator was prepared in the same manner as in Example 1, except that an organic binder, specifically a polyimide (PI) binder, was used instead of an acrylic binder in Example 1.

[0186]

[0187] The following properties were evaluated for the separation membranes prepared in the examples and comparative examples, and the results are shown in Table 1 below.

[0188] (1) Width shrinkage rate of the separator (Unit: %): Prepare samples by cutting the separator of the example and comparative example into pieces 30 cm in the MD direction and 30 cm in the TD direction. Lay them flat on the measurement surface of the projector (or 3-D). Using the projector (or 3-D), measure the width at least 3 points in 1 reel and use the data.

[0189] The TD direction length (T1) between any first point and any adjacent second point among the above samples is measured. After leaving the above samples at 23°C and 60% relative humidity for 3 days, the TD direction length (T2) between the first point and the second point is measured. The width shrinkage rate is calculated according to the following formula.

[0190] [ceremony]

[0191] Width shrinkage rate = (T1 - T2) / T1 × 100

[0192] The TD direction length (T1) between any first point and any adjacent second point among the above samples is measured. After leaving the above samples at 23°C and 40% relative humidity for 5 minutes, the TD direction length (T2) between the first point and the second point is measured. The width shrinkage rate of the membrane is calculated according to the above formula.

[0193] (2) Core detachment of the separator: The separator of the example and comparative example is wound onto a reel, placed in a constant temperature and humidity chamber, and left for 24 hours at 55°C and 70% relative humidity. The winding condition of the separator is evaluated based on whether it has detached from the center of the core. If there is no core detachment, it is evaluated as OK, and if there is core detachment, it is evaluated as NG.

[0194] (3) Moisture content of the membrane (unit: ppm): The amount of moisture evaporated from the membranes of the examples and comparative examples using the Karl-Fisher method (which measures moisture by utilizing the quantitative reaction of water with iodine and sulfur dioxide) with a Metrohm 831KF Coulometer at 150°C was measured in ppm units. The moisture content was evaluated after leaving the membranes at a temperature of 25 to 28°C and a relative humidity of 65 to 70% for 24 hours.

[0195] (4) Thermal shrinkage rate of the separator (Unit: %): The separator of the example and comparative example is cut into a size of 8 cm × 8 cm to prepare a sample. A square of 5 cm × 5 cm is drawn on the surface of the sample, placed between paper or alumina powder, and left in an oven at 150°C for 1 hour. After removing the sample, the dimensions of the side of the drawn square are measured to calculate the thermal shrinkage rate in the mechanical direction (MD) and perpendicular direction (TD), respectively. The thermal shrinkage rate is calculated according to the following formula.

[0196] [ceremony]

[0197] Thermal shrinkage rate = (L0 - L1) / L0 x 100

[0198] (L0 is the initial length of the membrane, L1 is the length of the membrane after standing at 150°C for 1 hour)

[0199] (5) Prick strength of the membrane (unit: gf / ㎛): Ten specimens were prepared by cutting the membranes of the examples and comparative examples at 10 different points with a width (MD) of 50 mm and a length (TD) of 50 mm. Then, using a GATO Tech G5 machine, the specimens were placed over a 10 cm hole and the force of penetration was measured while pressing with a 1 mm probe. The piercing strength of each specimen was measured three times, and the average value was calculated.

[0200] Example 1 2 3 4 5 Porous substrate Tensile strength (MD:TD) 1:0.9 1:1.11:0.9 1:1.11:0.9 Elongation (MD:TD) 1:0.9 1:1.11:1.11:0.9 1:0.9 BET of coating layer filler 5 5 5 5 10 Binder Acrylic Acrylic Acrylic Acrylic Acrylic Width Shrinkage rate 3 days 0.0 10.0 20.0 10.0 10.0 5 5 minutes 0.2 30.2 60.2 40.2 40.2 8 Core release OK OK OK OK OK Moisture content 460 460 460 460 5 20 Thermal shrinkage rate (MD / TD) 12 / 10 10 / 13 11 / 13 13 / 13 9 / 8 Prick strength 45 5 14 8 48 46

[0201]

[0202] Comparative Example 123456 Porous Substrate Tensile Strength (MD:TD) 1:0.7 1:1.3 1:0.9 1:0.9 1:0.9 1:0.9 1:0.9 Elongation (MD:TD) 1:0.7 1:1.3 1:0.9 1:0.9 1:0.9 1:0.9 BET of Coating Layer Filler 5521344 Binder Acrylic-based Acrylic-based Acrylic-based PV dF-based PI-based Width Shrinkage Rate 3 days 0.1 5 0.1 9 0.0 2 0.0 8 0.1 0.1 3 5 minutes 0.6 7 0.7 3 0.2 4 0.4 8 0.5 5 0.6 2 Core Detachment OK OK OK NG NG OK Moisture Content 4 60 460 320 1230 15 00 2200 Heat Shrinkage Rate (MD / TD) 15 / 79 / 1825 / 226 / 537 / 323 / 2 Piercing Strength 415445474547

[0203]

[0204] As shown in Table 1 above, the separator of the example has a low shrinkage rate not only in the cell but also in the dry room, and there is no core detachment during winding, and has a low thermal shrinkage rate and high puncture strength, which can improve the manufacturing processability and reliability of the secondary battery.

[0205]

[0206] Although preferred embodiments of the present invention have been described above, the present invention is not limited thereto and can be implemented with various modifications within the scope of the claims, the detailed description of the invention, and the attached drawings, and it is obvious that such modifications also fall within the scope of the present invention.

Claims

1. A porous substrate; and a coating layer positioned on at least one surface of the porous substrate, wherein the coating layer comprises a filler and a binder, and The above filler has a specific surface area of ​​5 to 10 m² 2 / g and, The above binder includes a water-based binder, and The above porous substrate is a separator for a secondary battery, wherein the ratio of tensile strength in the mechanical direction to tensile strength in the width direction is 1:0.9 to 1:1.1 and the ratio of elongation in the mechanical direction to elongation in the width direction is 1:0.9 to 1:1.

1.

2. In claim 1, the filler is a separator for a secondary battery having an average particle size D50 of 0.1 to 1 μm.

3. A separator for a secondary battery, wherein the filler is spherical, in accordance with claim 1 or 2.

4. A separator for a secondary battery according to any one of claims 1 to 3, wherein the filler comprises Al2O3, SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, GaO, ZnO, ZrO2, Y2O3, SrTiO3, BaTiO3, Mg(OH)2, boehmite, or a combination thereof.

5. In any one of claims 1 to 4, the specific surface area of ​​the coating layer is 5 to 10 m 2 A separator for a secondary battery, wherein the filler in / g comprises 95% by weight or more of the total filler in the coating layer.

6. A separator for a secondary battery according to any one of claims 1 to 5, wherein the binder : filler in the coating layer is included in a mass ratio of 1:10 to 1:

50.

7. In any one of claims 1 to 6, the porous substrate has a tensile strength in the mechanical direction of 1800 to 4000 kgf / cm² 2 , tensile strength in the width direction is 1600 to 3800 kgf / cm 2 Phosphor, separator for secondary batteries.

8. A separator for a secondary battery according to any one of claims 1 to 7, wherein the porous substrate has a mechanical elongation of 20 to 200% and a widthwise tensile strength of 25 to 220%.

9. A separator for a secondary battery according to any one of claims 1 to 8, wherein the ratio of moisture content to the thickness of the coating layer is 250 ppm / ㎛ or less.

10. A separator for a secondary battery according to any one of claims 1 to 9, wherein the ratio of the width-direction shrinkage rate of the coating layer according to the following formula 2 to the width-direction thermal shrinkage rate of the porous substrate according to the following formula 1 is 0.05 or less: [Equation 1] Thermal shrinkage rate = (L0 - L1) / L0 x 100 (L0 is the initial width of the porous substrate, L1 is the width of the porous substrate after being left at 120°C for 1 hour) [Equation 2] Shrinkage rate = (L0 - L1) / L0 x 100 (L0 is the initial width of the coating layer, L1 is the width of the coating layer after being left at 130°C for 1 hour).

11. A separator for a secondary battery, wherein, in any one of claims 1 to 10, the aqueous binder is a (meth)acrylic binder.

12. In any one of claims 1 to 11, the porous substrate is a polyolefin-based substrate, and The above polyolefin-based substrate comprises a polyolefin-based resin having a weight-average molecular weight of 1 million g / mol or more and a melting temperature of 130 to 140°C, and is a separator for a secondary battery.

13. A secondary battery comprising an anode, a cathode, and a separator for a secondary battery according to any one of claims 1 to 12 located between the anode and the cathode.

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