Separator, and lithium secondary battery comprising same

Abstract

The present invention relates to a separator comprising: a substrate layer; and a porous coating layer located on one surface or both surfaces of the substrate layer and including first inorganic particles, second inorganic particles, and an acrylic binder, wherein the ratio of the average particle diameter (D50) of the second inorganic particles to the average particle diameter (D50) of the first inorganic particles is 1.4 to 2.0, the content of the first inorganic particles is greater than the content of the second inorganic particles with respect to the total weight of the porous coating layer, and the thickness of the porous coating layer is 1.2-2.0 µm.

Description

Separator and lithium secondary battery containing same Cross-citation with related applications This application claims the benefit of priority to Korean Patent Application No. 10-2023-0166120, filed on November 24, 2023, and Korean Patent Application No. 10-2024-0164623, filed on November 18, 2024, the entire contents of which are incorporated herein by reference. Technical field The present invention relates to a separator and a lithium secondary battery including the same, and more particularly, to a bimodal distribution of an inorganic material having a specific average particle diameter (D 50 ) and a porous coating layer mixed at a specific weight ratio, and the porous coating layer has a thickness of 1.2 ㎛ to 2.0 ㎛, thereby improving wet shrinkage and dry shrinkage, and a lithium secondary battery including the same. As technology development and demand for mobile devices increase, the demand for secondary batteries as an energy source is rapidly increasing. Among these secondary batteries, lithium secondary batteries, which have high energy density and voltage, long cycle life, and low self-discharge rate, are commercialized and widely used. Typically, lithium secondary batteries are manufactured using a cathode and an anode, a separator interposed between them, and an electrolyte that serves as a transport medium for lithium ions. Among these, the separator is an inactive material that does not participate in electrochemical reactions, but it provides a path for lithium ions to move in order to operate the battery and is a material that separates the physical contact between the positive and negative electrodes, making it one of the key materials that greatly affects the performance and stability of the battery. Meanwhile, lithium secondary batteries can easily generate heat due to the kinetic energy generated during repeated charging and discharging, and the separator is vulnerable to this heat. In particular, in the case of a separator using polyethylene (PE), it may start to melt around 130℃ and a 'shutdown' phenomenon may occur in which the pores are closed, and at 150℃ or higher, it may completely melt and collapse without preventing an internal short circuit. To overcome this problem, research has been ongoing on separators with enhanced durability by coating the surface of the separator with inorganic particles. However, the membranes developed to date have not been durable enough. For example, when a cylindrical cell using an existing membrane was disassembled after being evaluated in a hot box at 130°C, there was a problem that the free-standing membrane located in the cell core was excessively contracted in the TD direction, exposing the electrode portion. Meanwhile, since the separator in a lithium secondary battery is used in a state impregnated with an electrolyte, the dimensional change rate of the separator in a wet state is more significant than in a dry state. Therefore, there is a need to develop a separator that can secure high-temperature dimensional stability of a wet-state separator in a high-temperature electrolyte environment. The present invention is intended to solve the above problems, and provides a separator capable of suppressing shrinkage even when immersed in a high-temperature electrolyte, and a lithium secondary battery including the same. [1] The present invention comprises a substrate layer and a porous coating layer positioned on one or both sides of the substrate layer and including first inorganic particles, second inorganic particles, and an acrylic binder, wherein the average particle diameter (D) of the first inorganic particles 50 ) for the average particle diameter (D) of the second inorganic particles 50) is 1.4 to 2.0, the content of the first inorganic particles is greater than the content of the second inorganic particles based on the total weight of the porous coating layer, and the thickness of the porous coating layer is 1.2 ㎛ to 2.0 ㎛. [2] The present invention, in the above [1], the average particle diameter (D) of the first inorganic particles 50 ) provides a separation membrane of 0.32 μm to 0.5 μm. [3] The present invention, in the above [1] or [2], the average particle diameter (D) of the second inorganic particles 50 ) provides a separation membrane having a thickness of 0.45 μm to 0.70 μm. [4] The present invention provides a separation membrane according to any one of the above [1] to [3], wherein the porous coating layer comprises the first inorganic particles: the second inorganic particles in a weight ratio of 55:45 to 95:5. [5] The present invention, in any one of [1] to [4], wherein the first inorganic particle and the second inorganic particle are each independently composed of aluminum oxide (Al 2 O 3 ), boehmite (AlOOH), silicon dioxide (SiO 2 ), magnesium oxide (MgO), titanium oxide (TiO 2 ) and zeolite. [6] The present invention provides a separation membrane in which the porous coating layer has a porosity of 60% or less in any one of [1] to [5]. [7] The present invention, in any one of [1] to [6], wherein the loading amount of the porous coating layer is 4.9 g / cm 2 7.0g / cm2 2 It provides a separation membrane. [8] The present invention, in any one of [1] to [7], has a packing density of the porous coating layer of 1.4 g / cm 3 2.0 g / cm 3 It provides a separation membrane. [9] The present invention provides a separation membrane according to any one of [1] to [8] above, wherein the porous coating layer is formed by applying a slurry composition having a solid content of 20 wt% to 50 wt% on one side or both sides of the substrate layer.

[0010] The present invention provides a separation membrane having a thickness of 11 µm to 14 µm in any one of the above [1] to [9].

[0011] The present invention provides a separator having an MD shrinkage of 0.5% to 7.0% and a TD shrinkage of 0.5% to 5.5% when the separator is immersed in an electrolyte and then left at 130°C for 30 minutes, in any one of the above [1] to

[0010] .

[0012] The present invention provides a separator having an MD shrinkage rate of 1% to 50% and a TD shrinkage rate of 2% to 40% when the separator is left at 150°C for 30 minutes in any one of the above [1] to

[0011] .

[0013] The present invention provides a lithium secondary battery including a separator according to any one of [1] to

[0012] . The separation membrane according to the present invention has a specific average particle diameter (D 50) By using a porous coating layer having a thickness of 1.2 ㎛ to 2.0 ㎛ including first inorganic particles and second inorganic particles satisfying the ratio and weight ratio, the effect of suppressing shrinkage of the separator in a high-temperature electrolyte phase is achieved. Accordingly, when the separator of the present invention is used, it has the characteristic of high heat resistance due to high dimensional stability compared to existing separators, so that the positive and negative electrodes can be isolated in a high-temperature electrolyte phase, thereby preventing internal short circuit. The effects according to the present invention are not limited to those exemplified above, and further diverse effects are included in the present specification. Hereinafter, the present invention will be described in detail. The terms or words used in this specification and claims should not be interpreted as limited to their usual or dictionary meanings, but should be interpreted as having meanings and concepts that conform to the technical idea of ​​the present invention, based on the principle that the inventor can appropriately define the concept of the term in order to explain his or her own invention in the best manner. The terminology used herein is for the purpose of describing embodiments only and is not intended to limit the invention. In this specification, the singular also includes the plural unless specifically stated otherwise. The terms "comprises" and / or "comprising" as used herein do not exclude the presence or addition of one or more other components in addition to the components mentioned. In the present invention, the average particle diameter (D 50 ) means the particle size based on 50% of the volume cumulative particle size distribution of the target powder, such as inorganic particles. The average particle diameter (D 50) can be measured using the laser diffraction method. For example, the target powder is dispersed in a dispersion medium, introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac MT 3000), and ultrasonic waves of about 28 kHz are irradiated at an output of 60 W, and then a volume-cumulative particle size distribution graph is obtained, and then the particle size corresponding to 50% of the volume-cumulative amount is measured. In the present invention, the porosity can be obtained from the ratio of the packing density of the porous coating layer and the packing density of the non-porous coating. The packing density of the non-porous coating can be obtained by applying the bulk density of the raw material used and the coating composition, assuming a porosity of 0%. In the present invention, the loading amount of the porous coating layer (R, unit: g / cm 2 ) can be measured by measuring the average values ​​W1 and W2 of the weights of each of the coated separator and base film cut into 5 cm X 5 cm sizes, measured 6 times, and then substituting them into Equation 1 below. [Formula 1] R = (W1-W2) / 25 In the present invention, the packing density (D, unit: g / cm) of the porous coating layer 3 ) is the loading amount (R) of the porous coating layer and the total thickness (T) of the membrane. total ) and the thickness of the substrate layer of the membrane (T c ) can be calculated by substituting it into Equation 2 below. [Formula 2] D = R / {(T total - T c ) × 0.0001} In the present invention, the MD direction (Machine Direction) means the length direction of the membrane, and the TD direction (Transverse Direction) means the width direction of the membrane. In the present invention, the wet shrinkage is a value obtained by cutting a separator into a size of 5 cm × 5 cm, placing it in a 10 cm × 9 cm pouch together with an electrolyte, impregnating it, storing it in a 130°C convection oven for 30 minutes, and then separating the separator from the pouch and measuring the shrinkage in the MD and TD directions. In the present invention, the dry shrinkage is a value obtained by measuring the shrinkage in the MD and TD directions after cutting the separator into a size of 5 cm × 5 cm, storing it in a 150℃ convection oven for 30 minutes, and then taking it out. <Separator> First, the separation membrane according to the present invention will be described. A separation membrane according to the present invention comprises a substrate layer and a porous coating layer positioned on one or both sides of the substrate layer and including first inorganic particles, second inorganic particles, and an acrylic binder. In the present invention, the substrate layer is a thin film of an insulating material to allow only lithium ions to pass through and prevent a short circuit, and may be a porous polymer film, and for example, may be a polymer film formed of 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, polyether ether ketone, polyarylether ketone, polyetherimide, polyamide imide, polybenzimidazole, polyether sulfone, polyphenylene oxide, cyclic olefin copolymer, polyphenylene sulfide, polyethylene naphthalate, Teflon, and polytetrafluoroethylene, or a copolymer or mixture of two or more thereof. Preferably, the substrate layer may be a polyolefin-based substrate including polyolefin. The polyolefin-based substrate has an excellent shutdown function and thus may contribute to improving the safety of the battery. The polyolefin-based substrate may be selected from, for example, a polyethylene single film, a polypropylene single film, a polyethylene / polypropylene double film, a polypropylene / polyethylene / polypropylene triple film, and a polyethylene / polypropylene / polyethylene triple film. In addition, the 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. The substrate layer may have a thickness of about 1 ㎛ to 20 ㎛, preferably 1 ㎛ to 15 ㎛, more preferably 1 ㎛ to 10 ㎛. When the substrate layer thickness satisfies the above range, it has good breathability, can have a mechanical tensile strength that can be bent during a cell assembly process, can have a strong puncture strength that does not break through lithium precipitates in the form of dendrites formed on the surface of the negative electrode during overcharge, and is advantageous in that it increases the output and capacity of the battery. The porous coating layer is positioned on one or both sides of the substrate layer to improve the mechanical strength and heat resistance of the substrate layer. The porous coating layer according to the present invention has an average particle diameter (D 50 ) includes different first inorganic particles and second inorganic particles, and an acrylic binder. Average particle diameter (D 50 ) When two different types of inorganic particles are included in the porous coating layer, the average particle diameter (D 50 ) between the large particles, the average particle diameter (D) 50 ) are arranged so that the ratio of voids between inorganic particles is reduced, which increases the packing density of the porous coating layer and increases thermal stability. However, the average particle diameter (D 50) Even if two different types of inorganic particles are used, the average particle diameter (D) between the inorganic particles 50 ) If the difference is too large, the pore size or void ratio in the porous coating layer becomes too small, resulting in poor electrolyte impregnation, which may result in deterioration of electrochemical properties, and the average particle diameter (D) between inorganic particles may be reduced. 50 ) If the difference is too small, the effect of improving thermal stability is minimal. Therefore, in the present invention, the average particle diameter (D) of the first inorganic particle and the second inorganic particle 50 ) By ensuring that the amount of water satisfies a specific range, the thermal shrinkage of the membrane can be reduced while minimizing the deterioration of electrochemical properties. Specifically, in the present invention, the average particle diameter (D) of the first inorganic particles 50 ) for the average particle diameter (D) of the second inorganic particles 50 ) may be 1.4 to 2.0, preferably 1.4 to 1.8, more preferably 1.4 to 1.5. The average particle diameter (D) of the first inorganic particle 50 ) for the average particle diameter (D) of the second inorganic particles 50 ) exceeds 2.0, there is a problem that the wet shrinkage and dry shrinkage increase due to excessively large pores, which increases the probability of internal short-circuiting of the battery, and the average particle diameter (D) of the first inorganic particles 50 ) for the average particle diameter (D) of the second inorganic particles 50 ) is less than 1.4, there is a problem that the dispersibility of inorganic particles is reduced or the particles are distributed within the already formed pores, thereby reducing the air permeability. In comparison, the average particle diameter (D) of the first inorganic particle and the second inorganic particle 50) satisfies the range of the present invention, the first inorganic particles having a small particle diameter can be included between the second inorganic particles having a large particle diameter, and accordingly, the ratio of pores existing between the inorganic particles is reduced. As a result, the packing density of the porous coating layer is increased, so that shrinkage due to heat is reduced when left at room temperature and high temperature, and the high-temperature stability of the battery can be increased. That is, the average particle diameter (D) of the first inorganic particles described above 50 ) for the average particle diameter (D) of the second inorganic particles 50 ) is 1.4 to 2.0, preferably 1.4 to 1.8, more preferably 1.4 to 1.5, the adhesion of the separator to the substrate as well as the heat resistance and moisture resistance can be improved, and thus the safety and life characteristics of the battery can be improved. In the present invention, the average particle diameter (D) of the first inorganic particles 50 ) may be 0.32 ㎛ to 0.5 ㎛, preferably 0.32 ㎛ to 0.45 ㎛, more preferably 0.32 ㎛ to 0.4 ㎛. The average particle diameter (D of the first inorganic particles 50 ) is less than 0.32㎛, there is a problem that the ion conductivity is reduced because it is difficult to form a porous shape within the coating layer, the surface area is relatively increased, and the contact area with the binder is widened, so there is a problem that the binder is excessively consumed and the coating layer becomes thick, and agglomeration occurs between the first inorganic particles, so there is a problem that the dispersibility is reduced. In addition, the average particle diameter (D) of the first inorganic particles 50 ) exceeds 0.5㎛, there is a problem that the electrolyte is not distributed uniformly due to the formation of non-uniform pores during the porous structure formation process. The average particle diameter (D) of the first inorganic particles 50 ) when the above range is satisfied, the effect of improving thermal stability can be exhibited because the optimal size ratio in terms of packing density with the second inorganic particles is satisfied. In addition, the average particle diameter (D) of the second inorganic particles 50 ) may be 0.45 ㎛ to 0.70 ㎛, preferably 0.45 ㎛ to 0.60 ㎛, more preferably 0.48 ㎛ to 0.55 ㎛. The average particle diameter (D) of the second inorganic particles 50 ) is less than 0.45㎛, the cohesion between particles becomes strong, the particle distribution within the porous coating layer becomes uneven, and when the electrolyte penetrates into the porous coating layer, the degree of expansion of the porous coating layer is uneven, causing cracks to occur, and the average particle diameter (D) of the second inorganic particles 50 ) exceeds 0.70㎛, it means that the particle size is excessively large, and in this case, when the electrolyte penetrates into the porous coating layer, it is not evenly distributed inside but is locally aggregated, so that the expansion rate increases in a specific area, which increases the wet shrinkage rate, and since it is difficult for large particles to sufficiently maintain moisture, there is a problem that the porous coating layer shrinks rapidly when moisture is lost, causing cracks to grow. The average particle diameter (D) of the second inorganic particles 50 ) when the above range is satisfied, the BET surface area decreases, which may be advantageous in terms of moisture adsorption and interfacial resistance. Meanwhile, the present invention includes the first inorganic particles having a smaller particle size than the second inorganic particles having a larger particle size in the porous coating layer. That is, the content of the first inorganic particles in the coating layer is greater than the content of the second inorganic particles. When the content of the second inorganic particles is greater than the content of the first inorganic particles, the wet shrinkage and the dry shrinkage increase due to a decrease in the substrate bonding strength. Preferably, the porous coating layer may include the first inorganic particles:the second inorganic particles in a weight ratio of 55:45 to 95:5, more preferably 60:40 to 85:15, and even more preferably 65:35 to 75:25. When the weight ratio of the first inorganic particles to the second inorganic particles satisfies the above range, the packing density of the porous coating layer increases, so that the effect of improving thermal safety is more excellent. The first inorganic particle and the second inorganic particle are each independently made of aluminum oxide (Al 2 O 3 ), boehmite (AlOOH), silicon dioxide (SiO 2 ), magnesium oxide (MgO), titanium oxide (TiO 2 ) and zeolite, preferably comprising at least one selected from the group consisting of aluminum oxide (Al 2 O 3 ) may be included. Such inorganic particles can improve the thermal stability of the membrane and prevent the membrane from shrinking at high temperatures. Specifically, aluminum oxide (Al 2 O 3 ) has high thermal stability, maintains its shape and properties at high temperatures, can have a particle shape and size distribution that are advantageous for maintaining a porous structure, and has affinity for moisture, so it binds well with the electrolyte and has the effect of being uniformly dispersed within the coating layer, ultimately improving the wet shrinkage and dry shrinkage of the separator. On the other hand, if the first inorganic particle or the second inorganic particle is aluminum hydroxide (Al(OH)), respectively, 3 ) or magnesium hydroxide (Mg(OH) 2 ) contains inorganic substances such as barium sulfate (BaSO), it can easily be thermally decomposed at high temperatures or dehydrated, causing changes in physical properties, which may result in deformation of the porous coating layer.4 ) is included, there is a problem that the inorganic particles are difficult to disperse uniformly within the porous coating layer due to the hydrophobic nature, and compatibility with the binder is poor. Meanwhile, the acrylic binder provides adhesive strength so that the porous coating layer adheres well to the substrate layer, and plays a role in improving the heat resistance, air permeability, and oxidation resistance of the separator. As the above acrylic binder, acrylic binders used in the relevant technical field can be used, and examples thereof include, but are not limited to, PAA, PAA-PAM copolymer, PAA-PU copolymer, etc. Meanwhile, the acrylic binder may be included in an amount of 1 wt% to 6 wt%, preferably 1 wt% to 4 wt%, and more preferably 1 wt% to 2 wt%, based on the total weight of the porous coating layer. When the above range is satisfied, the wet shrinkage, peel strength, and mechanical tensile / puncture strength of the separator can be maintained at a high level while lowering the resistance and increasing the output and capacity. Meanwhile, the porous coating layer of the present invention as described above has the function of lowering surface resistance and providing conductivity to insulate the negative electrode and the positive electrode, while improving the ion movement of lithium ions and reducing the wet shrinkage and dry shrinkage of the separator. The above porous coating layer is positioned on one or both sides of the base layer, and may have a thickness of 1.2 ㎛ to 2.0 ㎛, preferably 1.4 ㎛ to 1.9 ㎛, and more preferably 1.6 ㎛ to 1.8 ㎛. When the thickness of the porous coating layer is less than 1.2 ㎛, it is difficult to maintain stability in a high temperature environment due to the thin thickness, and the insulating function cannot be exhibited, so the effect of increasing conductivity cannot be obtained. When it exceeds 2.0 ㎛, the excessively thick thickness makes it difficult to penetrate the electrolyte, and since the expansion and contraction that occurs when the porous coating layer comes into contact with the electrolyte occurs unevenly on the inside and the surface, there is a problem that cracks occur in the porous coating layer, and there is a problem that the performance of the battery is deteriorated due to an increase in the movement distance of lithium ions. When the thickness of the porous coating layer satisfies the above range, the performance of the battery can be improved by reducing the internal resistance, improving the rate characteristics, reducing the movement distance of lithium ions, etc. The porosity of the above porous coating layer may be 60% or less, preferably 52% to 60%, and more preferably 54% to 57%. If the porosity exceeds 60%, the effective cohesive bonding surface area may become smaller, which may result in a decrease in the mechanical properties of the separator due to weakened adhesion between inorganic substances, thereby deteriorating electrolyte impregnation properties and high-efficiency charge / discharge characteristics. The loading amount of the above porous coating layer is 4.9 g / cm 2 7.0g / cm2 2 may be, preferably 5.6 g / cm 2 6.7g / cm2 2 may be, more preferably, 6.0 g / cm 2 6.3g / cm2 2 If the above range is satisfied, the resistance can be reduced while preventing heat shrinkage in a high-temperature electrolyte environment. The packing density of the above porous coating layer is 1.4 g / cm 3 2.0 g / cm 3may be, preferably 1.6 g / cm 3 1.9 g / cm 3 may be, more preferably, 1.7 g / cm 3 1.8g / cm2 3 If the above range is satisfied, the resistance can be reduced while preventing heat shrinkage in a high-temperature electrolyte environment. Meanwhile, the porous coating layer can be formed by applying a slurry composition on one or both sides of the substrate layer. At this time, the slurry composition can be prepared by adding the first inorganic particles, the second inorganic particles, and the acrylic binder to a solvent. At this time, water, an organic solvent, or a mixture thereof can be used as the solvent, and water can be preferably used. When water is used as the solvent, a high dielectric constant, polarity, and hydrogen bonding effects can be achieved, so that a high reaction rate can be obtained. Meanwhile, the slurry composition may have a solid content of 20 wt% to 50 wt%, preferably 30 wt% to 40 wt%, and more preferably 33 wt% to 37 wt%. When the solid content of the slurry composition satisfies the above range, an appropriate viscosity and particle size distribution for high packing density and coatability can be secured. <Lithium secondary battery> Next, a lithium secondary battery according to the present invention will be described. The secondary battery of the present invention comprises a cathode, an anode, a separator disposed between the cathode and the anode, and an electrolyte, and uses the separator according to the present invention described above as the separator. Since the separator has been described above, the remaining components will be described below. (1) Bipolar Specifically, the positive electrode according to the present invention may include a positive electrode active material layer including a positive electrode active material, and, if necessary, the positive electrode active material layer may further include a conductive material and / or a binder. The above cathode active material is a compound capable of reversible intercalation and deintercalation of lithium, and may include a lithium transition metal oxide containing lithium and at least one metal selected from cobalt, manganese, nickel, or aluminum, and specifically, a lithium-manganese oxide having high capacity characteristics and safety of the battery, lithium iron phosphate, and a lithium-nickel-manganese-cobalt oxide (for example, Li(Ni) p Co q Mn r1 )O 2 (Here, it can include at least one of 0<p<1, 0<q<1, 0<r1<1, p+q+r1=1). Specifically, the lithium-manganese oxide is LiMnO 2 or LiMn 2 O 4 , and the lithium iron phosphate may be LiFePO 4 Examples include: In addition, the lithium-nickel-manganese-cobalt oxide is Li(Ni 1 / 3 Mn 1 / 3 Co 1 / 3 )O 2 , Li(Ni 0.6 Mn 0.2 Co 0.2 )O 2 , Li(Ni 0.5 Mn 0.3 Co 0.2 )O 2 , Li(Ni 0.7 Mn 0.15 Co 0.15 )O 2 and Li(Ni 0.8 Mn 0.1 Co 0.1 )O 2It may include at least one of the transition metals, and among them, it is preferable to include a lithium transition metal oxide having a nickel content of 60 atm% or more among the transition metals. That is, since a higher capacity can be implemented as the content of nickel among the transition metals increases, it is more advantageous to use one having a nickel content of 60 atm% or more for implementing high capacity. Such a lithium composite metal oxide is Li(Ni 0.6 Mn 0.2 Co 0.2 )O 2 , Li(Ni 0.7 Mn 0.15 Co 0.15 )O 2 and Li(Ni 0.8 Mn 0.1 Co 0.1 )O 2 At least one selected from the group consisting of: Meanwhile, the cathode active material of the present invention includes, in addition to the lithium transition metal oxide, a lithium-cobalt oxide (e.g., LiCoO). 2 etc.), lithium-nickel oxides (e.g., LiNiO 2 etc.), lithium-nickel-manganese oxides (e.g., LiNi 1-Y Mn Y O 2 (0 <Y<1), LiMn 2-z Ni z O 4 (0<Z<2), lithium-nickel-cobalt oxide (e.g., LiNi 1-Y1 Co Y1 O 2 (0 <Y1<1), 리튬-망간-코발트계 산화물(예를 들면, LiCo 1-Y2 Mn Y2 O 2 (0 <Y2<1), LiMn 2-z1 Co z1 O 4 (0<Z1<2), lithium-nickel-manganese-cobalt oxide (e.g., Li(Ni p1 Co q1 Mn r2 )O 4(0<p1<2, 0<q1<2, 0<r2<2, p1+q1+r2=2), or lithium-nickel-cobalt-transition metal (M) oxide (e.g., Li(Ni p2 Co q2 Mn r3 M S2 )O 2 (M is selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg, and Mo, and p2, q2, r3, and s2 are atomic fractions of independent elements, respectively, such that 0<p2<1, 0<q2<1, 0<r3<1, 0<s2<1, p2+q2+r3+s2=1), and one or more compounds thereof may be further included. The above positive electrode active material may be included in an amount of 90 wt% to 99 wt%, specifically 93 wt% to 98 wt%, based on the total weight of the solid content in the positive electrode active material layer. The conductive material is not particularly limited as long as it is conductive and does not cause a chemical change in the battery, and for example, carbon powder such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, or thermal black; graphite powder such as natural graphite, artificial graphite, or graphite with a highly developed crystal structure; conductive fibers such as carbon fibers or metal fibers; conductive powder such as fluorinated carbon powder, aluminum powder, or nickel powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; conductive materials such as polyphenylene derivatives, etc. can be used. The above-mentioned conductive agent is typically added in an amount of 1 to 30 wt% based on the total weight of the solid content in the positive electrode active material layer. The above binder is a component that improves the adhesion between positive electrode active material particles and the adhesive strength between the positive electrode active material and the current collector, and is typically added in an amount of 1 to 30 wt% based on the total weight of the solid content in the positive electrode active material layer. Examples of such binders include a fluorine resin binder including polyvinylidene fluoride (PVDF) or polytetrafluoroethylene (PTFE); a rubber binder including styrene butadiene rubber (SBR), acrylonitrile-butadiene rubber, and styrene-isoprene rubber; a cellulose binder including carboxyl methyl cellulose (CMC), starch, hydroxy propyl cellulose, and regenerated cellulose; a polyalcohol binder including polyvinyl alcohol; a polyolefin binder including polyethylene and polypropylene; Examples thereof include polyimide binders; polyester binders; and silane binders. The positive electrode of the present invention can be manufactured according to a positive electrode manufacturing method known in the art. For example, the positive electrode can be manufactured by a method in which a positive electrode slurry is manufactured by dissolving or dispersing a positive electrode active material, a binder, and / or a conductive agent in a solvent, and then applying the positive electrode slurry onto a positive electrode current collector, followed by drying and rolling to form a positive electrode active material layer, or a method in which the positive electrode active material layer is cast onto a separate support, and then the support is peeled off to obtain a film, and then laminating the obtained film onto a positive electrode current collector. The above positive electrode current collector is not particularly limited as long as it is conductive and does not cause a chemical change in the battery, and for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. can be used. The solvent may include an organic solvent such as NMP (N-methyl-2-pyrrolidone), and may be used in an amount that provides a desirable viscosity when including the positive electrode active material and optionally a binder and a conductive material. For example, the solvent may be included so that the solid concentration in the active material slurry including the positive electrode active material and optionally a binder and a conductive material is 10 wt% to 70 wt%, preferably 20 wt% to 60 wt%. (2) Cathode Next, let's explain the cathode. The negative electrode according to the present invention includes a negative electrode active material layer including a negative electrode active material, and the negative electrode active material layer may further include a conductive material and / or a binder, if necessary. The above negative electrode active material may include at least one selected from the group consisting of lithium metal, a carbon material capable of reversibly intercalating / deintercalating lithium ions, a metal or an alloy of these metals and lithium, a metal composite oxide, a material capable of doping and dedoping lithium, and a transition metal oxide. As the carbon material capable of reversibly intercalating / deintercalating the lithium ion, any carbon-based negative electrode active material generally used in lithium ion secondary batteries can be used without particular limitation, and representative examples thereof include crystalline carbon, amorphous carbon, or a combination of these. Examples of the crystalline carbon include graphite such as amorphous, plate-shaped, flake-shaped, spherical, or fibrous natural graphite or artificial graphite, and examples of the amorphous carbon include soft carbon (low-temperature calcined carbon) or hard carbon, mesophase pitch carbide, calcined coke, and the like. As the above metal or an alloy of these metals with lithium, a metal selected from the group consisting of Cu, Ni, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al and Sn or an alloy of these metals with lithium can be used. The above metal composite oxides include PbO, PbO 2 , Pb 2 O 3 , Pb 3 O 4 , Sb 2 O 3 , Sb 2 O 4 , Sb 2 O 5 , GeO, GeO 2 , Bi 2 O 3 , Bi 2 O 4 , Bi 2 O 5 , Li x Fe 2 O 3 (0≤x≤1), Li x WO 2 (0≤x≤1) and Sn x Me 1-x Me' y O z (Me: Mn, Fe, Pb, Ge; Me': Al, B, P, Si, elements of group 1, 2, and 3 of the periodic table, halogens; 0 <x≤1; 1≤y≤3; 1≤z≤8) 로 이루어진 군에서 선택되는 것이 사용될 수 있다. Materials capable of doping and dedoping the above lithium include Si, SiO. x (0 <x<2), Si-Y 합금(상기 Y는 알칼리 금속, 알칼리 토금속, 13족 원소, 14족 원소, 전이금속, 희토류 원소 및 이들의 조합으로 이루어진 군에서 선택되는 원소이며, Si은 아님), Sn, SnO 2, Sn-Y (wherein Y is an element selected from the group consisting of alkali metals, alkaline earth metals, group 13 elements, group 14 elements, transition metals, rare earth elements and combinations thereof, but not Sn), and also at least one of these and SiO 2 can also be used in combination. The element Y may be selected from the group consisting of Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Ge, P, As, Sb, Bi, S, Se, Te, Po, and combinations thereof. Examples of the above transition metal oxides include lithium-containing titanium composite oxide (LTO), vanadium oxide, and lithium vanadium oxide. The above negative active material may be included in an amount of 80 wt% to 99 wt% based on the total weight of the solid content in the negative active material layer. The conductive agent is a component for further improving the conductivity of the negative electrode active material, and can be added in an amount of 1 to 20 wt% based on the total weight of the solid content in the negative electrode active material layer. The conductive agent is not particularly limited as long as it has conductivity without causing a chemical change in the battery, and for example, graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, or thermal black; conductive fibers such as carbon fiber or metal fiber; conductive powder such as fluorinated carbon powder, aluminum powder, or nickel powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; conductive materials such as polyphenylene derivatives, etc. can be used. The above binder is a component that assists in bonding between the conductive agent, the active material, and the current collector, and is typically added in an amount of 1 to 30 wt% based on the total weight of the solid content in the negative electrode active material layer. Examples of such binders include a fluororesin binder including polyvinylidene fluoride (PVDF) or polytetrafluoroethylene (PTFE); a rubber binder including styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber, and styrene-isoprene rubber; a cellulose binder including carboxymethyl cellulose (CMC), starch, hydroxy propyl cellulose, and regenerated cellulose; a polyalcohol binder including polyvinyl alcohol; a polyolefin binder including polyethylene and polypropylene; a polyimide binder; a polyester binder; and a silane binder. The above negative electrode can be manufactured according to a negative electrode manufacturing method known in the art. For example, the negative electrode can be manufactured by a method of forming a negative electrode active material layer by applying a negative electrode active material slurry prepared by dissolving or dispersing a negative electrode active material and, optionally, a binder and a conductive material in a solvent on a negative electrode current collector, rolling and drying the same, or by casting the negative electrode active material layer on a separate support, then peeling off the support, and laminating the obtained film on a negative electrode current collector. The above negative electrode current collector generally has a thickness of 3 to 500 μm. The negative electrode current collector is not particularly limited as long as it has high conductivity and does not cause a chemical change in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloy, etc. can be used. In addition, like the positive electrode current collector, the bonding strength of the negative electrode active material can be strengthened by forming fine unevenness on the surface, and can be used in various forms such as a film, sheet, foil, net, porous body, foam, and non-woven fabric. The solvent may include water or an organic solvent such as NMP or alcohol, and may be used in an amount that provides a desirable viscosity when including the negative active material and optionally a binder and a conductive material. For example, the solid content concentration in the active material slurry including the negative active material and optionally a binder and a conductive material may be 50 wt% to 75 wt%, preferably 50 wt% to 65 wt%. (3) Electrolyte Next, let's talk about electrolytes. The above electrolyte may include an organic solvent and a lithium salt. As the organic solvent, any solvent that can act as a medium through which ions involved in the electrochemical reaction of the battery can move may be used without particular limitation. Specifically, the organic solvent may include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; Examples of solvents that can be used include carbonate solvents, such as dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol solvents, such as ethyl alcohol and isopropyl alcohol; nitriles, such as R-CN (wherein R represents a C2 to C20 linear, branched, or cyclic hydrocarbon group, which may include a double-bonded aromatic ring or an ether bond); amides, such as dimethylformamide; dioxolanes, such as 1,3-dioxolane; and sulfolanes. Among these, a carbonate solvent is preferable, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate, etc.) having high ionic conductivity and high dielectric constant that can improve the charge / discharge performance of the battery and a low-viscosity linear carbonate compound (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate, etc.) is more preferable. The above lithium salt can be used without any special limitation as long as it is a compound capable of providing lithium ions used in a lithium secondary battery. Specifically, the above lithium salt is LiPF 6 , LiClO 4 , LiAsF 6 , LiBF 4 , LiSbF 6 , LiAl0 4 , LiAlCl 4 , LiCF 3 SO 3 , LiC 4 F 9 SO 3 , LiN(C 2 F 5 SO 3 ) 2 , LiN(C 2 F 5 SO 2 ) 2 , LiN(CF 3 SO 2 ) 2 . LiCl, LiI, or LiB(C 2 O 4 ) 2 The concentration of the lithium salt may be used within the range of 0.1 to 5.0 M, preferably 0.1 to 3.0 M. When the concentration of the lithium salt is within the range, the electrolyte has appropriate conductivity and viscosity, so that it can exhibit excellent electrolyte performance, and lithium ions can move effectively. In addition to the electrolyte components, the electrolyte may further contain additives for the purposes of improving the life characteristics of the battery, suppressing battery capacity decrease, and improving the discharge capacity of the battery. For example, the additives may include, but are not limited to, haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, cyclic ethers, ethylene diamine, n-glyme, hexamethylphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxy ethanol, or aluminum trichloride. The additives may be contained in an amount of 0.1 to 10 wt%, preferably 0.1 to 5 wt%, based on the total weight of the electrolyte. Hereinafter, the present invention will be described in more detail by way of examples. However, the following examples are intended to illustrate the present invention and the scope of the present invention is not limited to these examples. Examples and Comparative Examples Example 1 Average particle diameter (D 50 ) First inorganic particle Al having a size of 0.35 μm 2 0 3 and the average particle diameter (D 50 ) is a second inorganic particle Al having a size of 0.5 μm 2 0 3 30 g of inorganic particles and 1.9 g of acrylic binder were mixed in a weight ratio of 7:3, added to water as a solvent, and stirred to prepare a slurry composition having a solid content of 35 wt%. The slurry composition was coated on both sides of a polyethylene substrate to a thickness of 1.7 μm. At this time, the porous coating layer had a porosity of 53%. Comparative Example 1 Average particle diameter (D 50) A membrane was manufactured using the same method as in Example 1, except that only the first inorganic particle having a size of 0.35 μm was added. Comparative Example 2 Average particle diameter (D 50 ) of the first inorganic particle having an average particle diameter (D) of 0.35 ㎛ 50 ) A separation membrane was manufactured in the same manner as in Example 1, except that the second inorganic particles having a size of 0.5 μm were mixed in a weight ratio of 5:5. Comparative Example 3 Average particle diameter (D 50 ) of the first inorganic particle having an average particle diameter (D) of 0.35 ㎛ 50 ) A separation membrane was manufactured in the same manner as in Example 1, except that the second inorganic particles having a size of 0.5 μm were mixed in a weight ratio of 3:7. Comparative Example 4 Average particle diameter (D 50 ) A separation membrane was manufactured in the same manner as in Example 1, except that only second inorganic particles having a size of 0.5 μm were added. Comparative Example 5 Average particle diameter (D 50 ) is 0.1㎛ and the average particle diameter (D) is 50 ) A separation membrane was manufactured in the same manner as in Example 1, except that the second inorganic particles having a size of 0.5 μm were mixed in a weight ratio of 7:3. Comparative Example 6 Average particle diameter (D 50 ) is 0.1㎛ and the average particle diameter (D) is 50 ) A separation membrane was manufactured in the same manner as in Example 1, except that the second inorganic particles having a size of 0.8 μm were mixed in a weight ratio of 7:3. The average particle diameter (D) of each of the first inorganic particles and the second inorganic particles used in manufacturing the separation membrane according to Example 1 and Comparative Examples 1 to 6 50 ), the average particle diameter (D) of the first inorganic particle and the second inorganic particle 50 ) The ratio of the amount and weight is shown in Table 1 below. Average particle diameter (D 50 )[㎛]Average particle size(D 50 ) Average particle diameter of the first inorganic particle (D) 50 )[㎛] Average particle diameter of the second inorganic particle (D 50 )[㎛] Example 10.350.51.427:3 Comparative Example 10.35--10:0 Comparative Example 20.350.51.425:5 Comparative Example 30.350.51.423:7 Comparative Example 4-0.5-0:10 Comparative Example 50.10.557:3 Comparative Example 60.10.887:3 Experimental Example 1: Wet shrinkage measurement The wet shrinkage of the membranes manufactured according to Example 1 and Comparative Examples 1 to 6 was measured by the following method. The above membranes were each cut into 5 cm × 5 cm pieces, placed in a 10 cm × 9 cm pouch with 1 g of 1 M LiPF6 electrolyte, impregnated, and stored in a 130° C. convection oven for 30 minutes. After the membranes were separated from the pouch, the shrinkage in the MD and TD directions was measured. The measurement results are shown in Table 2 below. Experimental Example 2: Dry shrinkage measurement The membranes manufactured according to Example 1 and Comparative Examples 1 to 6 were each cut into 5 cm × 5 cm pieces, stored in a 150°C convection oven for 30 minutes, and then taken out to measure the shrinkage ratio in the MD and TD directions. The measurement results are shown in Table 2 below. Experimental Example 3: Loading Amount Measurement The loading amount of the porous coating layer included in the separators manufactured by Example 1 and Comparative Examples 1 to 6 was calculated by measuring the average value difference of the weight of each of the coated separator and the base film cut into a size of 5 cm × 5 cm six times. The calculation results are shown in Table 2 below. Experimental Example 4: Calculating Packing Density The packing density of the porous coating layer included in the separators manufactured by Example 1 and Comparative Examples 1 to 6 was calculated by dividing the loading amount of the porous coating layer calculated in Experimental Example 3 by 3.4 μm, which is the difference between the total thickness of the separator, 13 μm, and the thickness of the substrate layer of the separator, 9.6 μm. The calculation results are shown in Table 2 below. Wet shrinkage [%]Dry shrinkage [%]Loading [g / cm 2 ]Packing density [g / cm 3 ]MD [%]TD [%]MD [%]TD [%]Example 121236.31.85Comparative Example 111869685.01.47Comparative Example 28649425.81.71Comparative Example 39751455.71.68Comparative Example 4111056495.41.59Comparative Example 511967655.51.62Comparative Example 6121073715.01.47 Referring to Table 2, it can be seen that the separator according to Example 1 has significantly improved wet shrinkage and dry shrinkage compared to the separators according to Comparative Examples 1 to 6. Accordingly, it can be expected that the heat resistance of the separator will be significantly different when applied to an actual cell.

Claims

1. Base layer; and A porous coating layer positioned on one or both sides of the above-mentioned substrate layer and including first inorganic particles, second inorganic particles, and an acrylic binder; The average particle diameter (D) of the first inorganic particle 50 ) for the average particle diameter (D) of the second inorganic particles 50 ) is between 1.4 and 2.0, The content of the first inorganic particles is greater than the content of the second inorganic particles based on the total weight of the porous coating layer, A membrane having a thickness of the porous coating layer of 1.2 ㎛ to 2.0 ㎛.

2. In claim 1, The average particle diameter (D) of the first inorganic particle 50 ) is a separation membrane having a thickness of 0.32 μm to 0.5 μm.

3. In claim 1, The average particle diameter (D) of the second inorganic particles 50 ) is a separation membrane having a thickness of 0.45 μm to 0.70 μm.

4. In claim 1, A separation membrane wherein the porous coating layer comprises the first inorganic particles: the second inorganic particles in a weight ratio of 55:45 to 95:

5.

5. In claim 1, The first inorganic particle and the second inorganic particle are each independently made of aluminum oxide (Al 2 O 3 ), boehmite (AlOOH), silicon dioxide (SiO 2 ), magnesium oxide (MgO), titanium oxide (TiO 2 ) and a separation membrane comprising at least one selected from the group consisting of zeolite.

6. In claim 1, The above porous coating layer is a separation membrane having a porosity of 60% or less.

7. In claim 1, The loading amount of the above porous coating layer is 4.9 g / cm 2 7.0g / cm2 2 A membrane that is.

8. In claim 1, The packing density of the above porous coating layer is 1.4 g / cm 3 2.0 g / cm 3 A membrane that is.

9. In claim 1, A separation membrane in which the porous coating layer is formed by applying a slurry composition having a solid content of 20 to 50 wt% on one or both sides of the substrate layer.

10. In claim 1, A separation membrane having a thickness of 11 ㎛ to 14 ㎛.

11. In claim 1, A separator having an MD shrinkage rate of 0.5% to 7.0% and a TD shrinkage rate of 0.5% to 5.5% when the separator is immersed in an electrolyte and left at 130°C for 30 minutes.

12. In claim 1, A separator having an MD shrinkage rate of 1% to 50% and a TD shrinkage rate of 2% to 40% when the separator is left at 150°C for 30 minutes.

13. A lithium secondary battery comprising the separator of claim 1.