Separator for lithium secondary battery and method for manufacturing same

Abstract

The present invention relates to a separator for a lithium secondary battery and a method for manufacturing same. According to the present invention, provided are a separator for a lithium secondary battery, which can exhibit excellent insulating properties while minimizing the occurrence of defects, and a method for manufacturing same.

Description

Separator for lithium secondary battery and method for manufacturing same

[0001] Cross-citation with related applications

[0002] This application claims the benefit of priority to Republic of Korea Patent Application No. 10-2023-0109886, dated August 22, 2023, and Republic of Korea Patent Application No. 10-2024-0110509, dated August 19, 2024, the entire contents of which are incorporated herein by reference.

[0003]

[0004] The present invention relates to a separator for a lithium secondary battery and a method for manufacturing the same.

[0005]

[0006] With the advancement of functionality in devices such as mobile phones, laptops, tablets, mobile batteries, electric vehicles, and personal mobility devices, demand for secondary batteries used as power sources is steadily increasing. In particular, lithium secondary batteries, with their high operating voltage and high energy density per unit weight, are the most widely used.

[0007] Lithium secondary batteries typically have a structure in which a rechargeable electrode assembly comprising a positive electrode, a separator, and a negative electrode is mounted in a battery case. The positive and negative electrodes are manufactured by applying a slurry containing an electrode active material to one or both sides of a metal current collector, followed by drying and rolling.

[0008] The separator is one of the key elements that determines the lifespan of a secondary battery, electrically insulating the anode and cathode. Separators require ion permeability and mechanical strength to ensure the smooth passage of the electrolyte. As the applications of high-energy lithium secondary batteries expand, the need for separator safety at high temperatures is also increasing.

[0009] Typically, separators composed of a substrate and an inorganic coating layer lack sufficient adhesion to the electrode due to their material properties. Consequently, partial lifting or wrinkling occurs at the electrode-separator interface. Furthermore, polyolefin, commonly used as the substrate, suffers from thermal stability issues, such as melting at high temperatures.

[0010] To address these issues, a method has been proposed that removes the substrate and constructs a separator solely from an inorganic coating film. However, these separators still lack sufficient adhesion to the electrodes and have significantly low insulation, making them vulnerable to internal short circuits when applied to electrochemical devices. These separators also suffer from the critical drawback of low tensile strength and elongation, which can easily tear the separator, causing microscopic short circuits within the electrode assembly.

[0011]

[0012] The present invention provides a separator for a lithium secondary battery that can exhibit excellent insulation properties while minimizing the occurrence of defects.

[0013] And, the present invention provides a method for manufacturing a separator for a lithium secondary battery.

[0014]

[0015] According to one embodiment of the invention,

[0016] A porous polymer substrate, and a porous coating layer formed on the porous polymer substrate,

[0017] The above porous coating layer comprises a polymer binder and inorganic fine particles dispersed on the polymer binder,

[0018] The above inorganic fine particles include two or more types of inorganic fine particles having different green densities measured under the same pressure conditions.

[0019] A separator for a lithium secondary battery is provided.

[0020]

[0021] According to another embodiment of the invention,

[0022] A step of forming a porous coating layer by applying a slurry including a polymer binder, inorganic fine particles, and a solvent onto a porous polymer substrate,

[0023] The above inorganic fine particles include two or more types of inorganic fine particles having different green densities measured under the same pressure conditions.

[0024] A method for manufacturing a separator for the above lithium secondary battery is provided.

[0025]

[0026] Hereinafter, the separator for a lithium secondary battery and the method for manufacturing the same according to embodiments of the invention will be described in more detail.

[0027]

[0028] The terms and words used in this specification and claims should not be interpreted as limited to their usual or dictionary meanings, but should be interpreted with meanings and concepts that conform to the technical idea of ​​the invention, based on the principle that the inventor can appropriately define the concept of the term to explain his or her own invention in the best way.

[0029] Unless otherwise defined herein, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein is for the purpose of describing specific embodiments only and is not intended to be limiting.

[0030] As used herein, the singular forms also include the plural forms unless the context clearly dictates otherwise.

[0031] As used herein, the term "including" means specifying a particular characteristic, region, integer, step, operation, element and / or component, but does not exclude the presence or addition of other particular characteristics, regions, integers, steps, operations, elements, components and / or groups.

[0032] The present invention is susceptible to various modifications and takes various forms. Specific embodiments are illustrated and described in detail below. However, this is not intended to limit the present invention to specific disclosed forms, but rather to encompass all modifications, equivalents, and alternatives falling within the spirit and scope of the invention.

[0033] In this specification, when the positional relationship between two parts is described as, for example, ‘on top of’, ‘upper part of’, ‘lower part of’, ‘next to’, etc., one or more other parts may be located between the two parts unless the expression ‘right’ or ‘directly’ is used.

[0034] In this specification, when a temporal relationship is described as, for example, ‘after’, ‘following’, ‘next to’, or ‘before’, it may also include cases where it is not continuous, unless the expression ‘immediately’ or ‘directly’ is used.

[0035] The term 'at least one' in this specification should be understood to include all possible combinations of one or more associated items.

[0036] In this specification, 'green density' means the density (g / cm) of a green pellet made by filling a mold with a specific amount of inorganic particles and applying pressure. 3 ) means.

[0037] In addition, terms including ordinal numbers, such as "first" and "second," are used in this specification to distinguish one component from another and are not limited by the ordinal numbers. For example, within the scope of the present invention, the first component may also be referred to as the second component, and similarly, the second component may be referred to as the first component.

[0038]

[0039] According to one embodiment of the invention,

[0040] A porous polymer substrate, and a porous coating layer formed on the porous polymer substrate,

[0041] The above porous coating layer comprises a polymer binder and inorganic fine particles dispersed on the polymer binder,

[0042] The above inorganic fine particles include two or more types of inorganic fine particles having different green densities measured under the same pressure conditions.

[0043] A separator for a lithium secondary battery is provided.

[0044]

[0045] As a result of the inventors' continued research, it was confirmed that a separator for a lithium secondary battery satisfying the above characteristics can exhibit excellent insulating properties while minimizing the occurrence of defects.

[0046] In particular, since the porous coating layer includes two or more types of inorganic fine particles having different compact densities, the porous coating layer can be provided with a dense pore structure and high pore tortuosity. Such a porous coating layer can exhibit low resistance and high ionic conductivity while minimizing the occurrence of defects. In addition, the porous coating layer enables the formation of a uniform electric potential in the separator for a lithium secondary battery, thereby enabling the expression of excellent insulating properties.

[0047]

[0048] The above-mentioned separator for a lithium secondary battery includes a porous polymer substrate and a porous coating layer formed on the porous polymer substrate.

[0049]

[0050] The above porous polymer substrate has high porosity that allows movement of lithium ions between two electrodes, and can be applied without special restrictions as long as it does not cause chemical changes in a lithium secondary battery.

[0051] According to one embodiment, the porous polymer substrate may include at least one polymer selected from the group consisting of polyethylene, polypropylene, polyethylene terephthalate, polypropylene terephthalate, polybutylene terephthalate, polyester, polyacetal, polyamide, polycarbonate, polyimide, polyamideimide, polyetherimide, polyetheretherketone, polyethersulfone, polyphenylene oxide, polyphenylene sulfide, and polyethylene naphthalate.

[0052] According to one embodiment, the porous polymer substrate may have a thickness of 5 μm to 100 μm. In order to secure the mechanical properties required for the substrate, the thickness of the porous polymer substrate is preferably 5 μm or more. However, if the substrate is too thick, the ionic conductivity may decrease, which may cause a deterioration in the performance of the lithium secondary battery. Therefore, the thickness of the porous polymer substrate is preferably 100 μm or less.

[0053] In one embodiment, the porous polymer substrate has a density of 300 kgf / cm in the machine direction (MD) and the transverse direction (TD). 2 Up to 1000 kgf / cm 2It may be desirable to have a tensile strength of . In order to prevent defects from occurring in the porous polymer substrate during the manufacturing and operation of a lithium secondary battery, it is desirable for the porous polymer substrate to satisfy the tensile strength range.

[0054]

[0055] Meanwhile, the separator for the lithium secondary battery includes a porous coating layer laminated on the porous polymer substrate.

[0056] According to one embodiment, the porous coating layer comprises a polymer binder and inorganic fine particles dispersed on the polymer binder.

[0057] The polymer binder may be gelled when impregnated with a liquid electrolyte, thereby exhibiting a high degree of swelling. After assembling a lithium secondary battery, the electrolyte injected permeates the polymer binder, and the polymer binder retaining the absorbed electrolyte has electrolyte ion conductivity. Therefore, the polymer binder may have a solubility index of 15 to 45 MPa. 1 / 2 Polymers of human origin can be preferably applied.

[0058] For example, the polymer binder may be at least one compound selected from the group consisting of polyvinylidene fluoride, poly(vinylidene fluoride-co-trichloroethylene), poly(vinylidene fluoride-co-chlorotrifluoroethylene), poly(vinylidene fluoride-co-trifluoroethylene), poly(vinylidene fluoride-co-tetrafluoroethylene), poly(vinylidene fluoride-co-hexafluoropropylene), spandex, butylacrylate, polymethylmethacrylate, polyacrylonitrile, polyvinylpyrrolidone, and polyvinylacetate.

[0059] As another example, the binder may further comprise at least one compound selected from the group consisting of polyimide, polyetherimide, ethylene vinyl acetate copolymer, polyethylene oxide, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethyl pullulan, cyanoethylated polyvinyl alcohol, cyanoethyl cellulose, cyanoethyl sucrose, pullulan, carboxymethylcellulose, acrylonitrile-styrene-butadiene copolymer, ethylene-propylene-diene terpolymer, sulfonated ethylene-propylene-diene terpolymer, styrene butadiene rubber, and fluororubber, together with the above-described exemplary compound.

[0060]

[0061] The above inorganic fine particles form micropores due to empty spaces between particles, maintain their physical form at high temperatures, and are electrochemically stable.

[0062] In one embodiment, the inorganic fine particles comprise two or more types of inorganic fine particles having different green densities measured under the same pressure conditions. Alternatively, the inorganic fine particles may be composed of two types of inorganic fine particles having different green densities measured under the same pressure conditions.

[0063]

[0064] The green pellet density of the above inorganic fine particles is the density of a green pellet made by filling a specific amount of inorganic particles into a mold and applying pressure, and may vary depending on the material of the inorganic fine particles, the shape of the particles, the size of the particles, or the porosity of the particles.

[0065]

[0066] By including two or more types of inorganic fine particles having different compact densities in the porous coating layer, the porous coating layer can be provided with a dense pore structure and high pore tortuosity. Such a porous coating layer can exhibit low resistance and high ionic conductivity while minimizing the occurrence of defects. In addition, the porous coating layer enables the formation of a uniform potential in the separator for a lithium secondary battery, thereby enabling the expression of excellent insulating properties.

[0067]

[0068] In one embodiment, the inorganic fine particles are 1 ton / cm 2 1.2 g / cm measured under a pressure of 3 1.5 g / cm 3 First inorganic fine particles having a compaction density of 1 ton / cm 2 0.7 g / cm measured under a pressure of 3 1.1 g / cm 3 It may include second inorganic fine particles having a compaction density of .

[0069] Here, the size of the mold applied to the compaction of the first and second inorganic fine particles and the amount of each inorganic fine particle are the same. For example, 1 g of any inorganic fine particle is filled into a cylindrical mold with a diameter of 16 mm and 1 ton / cm 2 When a green pellet is manufactured by applying pressure, the first and second inorganic fine particles satisfying the green pellet density range can be preferably applied.

[0070] Specifically, the first inorganic fine particles are 1.20 g / cm 3 Ideal, or 1.21 g / cm 3 Ideal, or 1.22 g / cm 3 Ideal, or 1.23 g / cm 3 Ideal, or 1.24 g / cm 3Ideal, or 1.25 g / cm 3 Ideal, or 1.26 g / cm 3 Ideal, or 1.27 g / cm 3 Ideal, or 1.28 g / cm 3 Ideal, or 1.29 g / cm 3 Ideal, or 1.30 g / cm 3 Ideal, or 1.31 g / cm 3 Ideal, or 1.32 g / cm 3 Ideal, or 1.33 g / cm 3 Ideal, or 1.34 g / cm 3 Ideal, or 1.35 g / cm 3 above; and 1.50 g / cm 3 or less, or 1.49 g / cm 3 or less, or 1.48 g / cm 3 or less, or 1.47 g / cm 3 or less, or 1.46 g / cm 3 It may have a compaction density below. And, the second inorganic fine particles are 0.70 g / cm 3 Ideal, or 0.71 g / cm 3 Ideal, or 0.72 g / cm 3 Ideal, or 0.73 g / cm 3 Ideal, or 0.74 g / cm 3 Ideal, or 0.75 g / cm 3 Ideal, or 0.76 g / cm 3 Ideal, or 0.77 g / cm 3 Ideal, or 0.78 g / cm 3 Ideal, or 0.79 g / cm 3 Ideal, or 0.80 g / cm 3 above; and 1.10 g / cm 3 or less, or 1.09 g / cm 3 or less, or 1.08 g / cm 3 or less, or 1.07 g / cm 3 or less, or 1.06 g / cm 3 or less, or 1.05 g / cm 3or less, or 1.04 g / cm 3 or less, or 1.03 g / cm 3 or less, or 1.02 g / cm 3 or less, or 1.01 g / cm 3 or less, or 1.00 g / cm 3 It may have a compact density below.

[0071] Preferably, the first inorganic fine particles are 1.20 g / cm 3 1.50 g / cm 3 , or 1.21 g / cm 3 1.50 g / cm 3 , or 1.22 g / cm 3 1.50 g / cm 3 , or 1.23 g / cm 3 1.50 g / cm 3 , or 1.24 g / cm 3 1.50 g / cm 3 , or 1.25 g / cm 3 1.50 g / cm 3 , or 1.25 g / cm 3 1.49 g / cm 3 , or 1.25 g / cm 3 1.48 g / cm 3 , or 1.26 g / cm 3 1.48 g / cm 3 , or 1.27 g / cm 3 1.48 g / cm 3 , or 1.28 g / cm 3 1.48 g / cm 3 , or 1.29 g / cm 3 1.48 g / cm 3 , or 1.30 g / cm 3 1.48 g / cm 3 , or 1.30 g / cm 3 1.47 g / cm 3 , or 1.30 g / cm 3 1.46 g / cm 3, or 1.31 g / cm 3 1.46 g / cm 3 , or 1.32 g / cm 3 1.46 g / cm 3 , or 1.33 g / cm 3 1.46 g / cm 3 , or 1.34 g / cm 3 1.46 g / cm 3 , or 1.35 g / cm 3 1.46 g / cm 3 It may have a compaction density of . And, the second inorganic fine particles may have a compaction density of 0.70 g / cm 3 1.10 g / cm 3 , or 0.71 g / cm 3 1.10 g / cm 3 , or 0.72 g / cm 3 1.10 g / cm 3 , or 0.73 g / cm 3 1.10 g / cm 3 , or 0.74 g / cm 3 1.10 g / cm 3 , or 0.75 g / cm 3 1.10 g / cm 3 , or 0.75 g / cm 3 1.09 g / cm 3 , or 0.75 g / cm 3 1.08 g / cm 3 , or 0.75 g / cm 3 1.07 g / cm 3 , or 0.75 g / cm 3 1.06 g / cm 3 , or 0.75 g / cm 3 1.05 g / cm 3 , or 0.76 g / cm 3 1.05 g / cm 3 , or 0.77 g / cm 3 1.05 g / cm 3 , or 0.78 g / cm 31.05 g / cm 3 , or 0.79 g / cm 3 1.05 g / cm 3 , or 0.80 g / cm 3 1.05 g / cm 3 , or 0.80 g / cm 3 1.04 g / cm 3 , or 0.80 g / cm 3 1.03 g / cm 3 , or 0.80 g / cm 3 1.02 g / cm 3 , or 0.80 g / cm 3 1.01 g / cm 3 , or 0.80 g / cm 3 1.00 g / cm 3 It may have a compact density of .

[0072]

[0073] In order to provide the porous coating layer with a dense pore structure and high tortuosity of the pores, it is preferable that the porous coating layer include first and second inorganic fine particles that satisfy the compact density range.

[0074] However, if the compaction density of the first and second inorganic fine particles is outside the above range, a dense pore structure may not be formed in the porous coating layer, and thus an uneven potential may be formed in the separator for a lithium secondary battery. In addition, if the compaction density of the first and second inorganic fine particles does not meet the above range, an appropriate level of curvature may not be provided, and thus the possibility of defects in the porous coating layer may increase and resistance may increase.

[0075]

[0076] According to one embodiment, the difference in compaction density of the first and second inorganic fine particles is 0.20 or more, or 0.21 or more, or 0.22 or more, or 0.23 or more, or 0.24 or more, or 0.25 or more, or 0.26 or more, or 0.27 or more, or 0.28 or more, or 0.29 or more, or 0.30 or more, or 0.31 or more, or 0.32 or more, or 0.33 or more, or 0.34 or more, or 0.35 or more; And it may be 0.80 or less, or 0.79 or less, or 0.78 or less, or 0.77 or less, or 0.76 or less, or 0.75 or less, or 0.74 or less, or 0.73 or less, or 0.72 or less, or 0.71 or less, or 0.70 or less, or 0.69 or less, or 0.68 or less, or 0.67 or less, or 0.66 or less, or 0.65 or less.

[0077] In order to provide the porous coating layer with a dense pore structure and high tortuosity of the pores, it is preferable that the difference in the compact density of the first and second inorganic fine particles be 0.20 or more, or 0.21 or more, or 0.22 or more, or 0.23 or more, or 0.24 or more, or 0.25 or more, or 0.26 or more, or 0.27 or more, or 0.28 or more, or 0.29 or more, or 0.30 or more, or 0.31 or more, or 0.32 or more, or 0.33 or more, or 0.34 or more, or 0.35 or more.

[0078] However, if the difference in compaction density of the first and second inorganic fine particles is excessively large, a dense pore structure may not be formed in the porous coating layer and an appropriate level of curvature may not be provided. Therefore, it is preferable that the difference in compaction density of the first and second inorganic fine particles be 0.80 or less, or 0.79 or less, or 0.78 or less, or 0.77 or less, or 0.76 or less, or 0.75 or less, or 0.74 or less, or 0.73 or less, or 0.72 or less, or 0.71 or less, or 0.70 or less, or 0.69 or less, or 0.68 or less, or 0.67 or less, or 0.66 or less, or 0.65 or less.

[0079] Preferably, the difference in the compact density of the first and second inorganic fine particles is 0.20 to 0.80, or 0.21 to 0.80, or 0.22 to 0.80, or 0.23 to 0.80, or 0.24 to 0.80, or 0.25 to 0.80, or 0.25 to 0.79, or 0.25 to 0.78, or 0.25 to 0.77, or 0.25 to 0.76, or 0.25 to 0.75, or 0.26 to 0.75, or 0.27 to 0.75, or 0.28 to 0.75, or 0.29 to 0.75, or 0.30 to 0.75, or 0.30 to 0.74, or 0.30 to 0.73, or 0.30 to 0.72, or 0.30 to 0.71, or 0.30 to 0.70, or 0.31 to 0.70, or 0.32 to 0.70, or 0.33 to 0.70, or 0.34 to 0.70, or 0.35 to 0.70, or 0.35 to 0.69, or 0.35 to 0.68, or 0.35 to 0.67, or 0.35 to 0.66, or 0.35 to 0.65.

[0080]

[0081] In one embodiment, the first inorganic fine particles are 40 m by nitrogen adsorption / desorption. 2 / g to 80 m 2 / g Bruner-Emmitt-Teller (BET) surface area, and the second inorganic fine particles have a surface area of ​​90 m by nitrogen adsorption / desorption. 2 / g to 120 m 2 / g can have a Bruner-Emmitt-Teller (BET) surface area.

[0082] Specifically, the first inorganic fine particles are 40 m by nitrogen adsorption / desorption. 2 / g or more, or 41 m 2 / g or more, or 42 m 2 / g or more, or 43 m 2 / g or more, or 44 m 2 / g or more, or 45 m 2 / g or more; and 80 m 2 / g or less, or 79 m 2 / g or less, or 78 m 2 / g or less, or 77 m 2 / g or less, or 76 m 2 / g or less, or 75 m 2 / g or less, or 74 m 2 / g or less, or 73 m 2 / g or less, or 72 m 2 / g or less, or 71 m 2 / g or less, or 70 m 2 / g or less. And, the second inorganic fine particles may have a Bruner-Emmitt-Teller (BET) specific surface area of ​​90 m by nitrogen adsorption / desorption. 2 / g or more, or 91 m 2 / g or more, or 92 m 2 / g or more, or 93 m 2 / g or more, or 94 m 2 / g or more, or 95 m 2 / g or more; and 120 m 2 / g or less, or 119 m2 / g or less, or 118 m 2 / g or less may have a Bruner-Emmitt-Teller (BET) surface area.

[0083] In order to provide the porous coating layer with a dense pore structure and high tortuosity of the pores, the porous coating layer preferably includes first and second inorganic fine particles that satisfy the BET specific surface area range. However, if the BET specific surface area of ​​the first and second inorganic fine particles falls outside the range, a dense pore structure may not be formed in the porous coating layer and an appropriate level of tortuosity may not be provided.

[0084] Preferably, the first inorganic fine particles have a diameter of 40 m by nitrogen adsorption / desorption. 2 / g to 80 m 2 / g, or 41 m 2 / g to 80 m 2 / g, or 42 m 2 / g to 80 m 2 / g, or 42 m 2 / g to 79 m 2 / g, or 42 m 2 / g to 78 m 2 / g, or 42 m 2 / g to 77 m 2 / g, or 42 m 2 / g to 76 m 2 / g, or 42 m 2 / g to 75 m 2 / g, or 43 m 2 / g to 75 m 2 / g, or 44 m 2 / g to 75 m 2 / g, or 45 m 2 / g to 75 m 2 / g, or 45 m 2 / g to 74 m 2 / g, or 45 m 2 / g to 73 m2 / g, or 45 m 2 / g to 72 m 2 / g, or 45 m 2 / g to 71 m 2 / g, or 45 m 2 / g to 70 m 2 / g of BET surface area. And, the second inorganic fine particles may have a BET surface area of ​​90 m by nitrogen adsorption / desorption. 2 / g to 120 m 2 / g, or 91 m 2 / g to 120 m 2 / g, or 92 m 2 / g to 120 m 2 / g, or 93 m 2 / g to 120 m 2 / g, or 94 m 2 / g to 120 m 2 / g, or 95 m 2 / g to 120 m 2 / g, or 95 m 2 / g to 119 m 2 / g, or 95 m 2 / g to 118 m 2 It may have a BET surface area of ​​ / g.

[0085] The above first inorganic fine particles are 1 ton / cm 2 1.2 g / cm measured under a pressure of 3 1.5 g / cm 3 40 m by compaction density and nitrogen adsorption / desorption 2 / g to 80 m 2 / g Bruner-Emmitt-Teller (BET) specific surface area. And, the second inorganic fine particles may have a surface area of ​​1 ton / cm 2 0.7 g / cm measured under a pressure of 3 1.1 g / cm 3 90 m by compaction density and nitrogen adsorption / desorption 2 / g to 120 m 2 / g may have a Bruner-Emmitt-Teller (BET) surface area.

[0086]

[0087] According to one embodiment, the first inorganic fine particles may have a primary particle diameter of 40 nm to 70 nm, or 45 nm to 70 nm, or 45 nm to 65 nm; and the second inorganic fine particles may have a primary particle diameter of 10 nm to 35 nm, or 15 nm to 35 nm, or 20 nm to 35 nm.

[0088] And, the first inorganic fine particles may have a secondary particle diameter of 250 nm to 550 nm, or 260 nm to 550 nm, or 260 nm to 540 nm, or 270 nm to 540 nm, or 270 nm to 530 nm; and the second inorganic fine particles may have a secondary particle diameter of 50 nm to 230 nm, or 60 nm to 230 nm, or 70 nm to 230 nm, or 70 nm to 220 nm, or 70 nm to 210 nm, or 70 nm to 200 nm, or 80 nm to 200 nm, or 90 nm to 200 nm, or 100 nm to 200 nm, or 100 nm to 190 nm, or 100 nm to 180 nm.

[0089] In order to secure appropriate dispersibility and pore size of the inorganic fine particles in the porous coating layer and prevent the thickness of the porous coating layer from becoming too thick, it is preferable that the porous coating layer include first and second inorganic fine particles that satisfy the primary particle diameter range and the secondary particle diameter range.

[0090] The particle size of the above-mentioned inorganic fine particles can be confirmed through a scanning electron microscope image (SEM) or transmission electron microscope image (TEM) taken of a cross-section of the above-mentioned porous coating layer.

[0091] The above first inorganic fine particles are 1 ton / cm 2 1.2 g / cm measured under a pressure of 3 1.5 g / cm 3 It may have a compaction density of 1 ton / cm and a secondary particle diameter of 250 nm to 550 nm. And, the second inorganic fine particles may have a secondary particle diameter of 1 ton / cm. 2 0.7 g / cm measured under a pressure of 3 1.1 g / cm 3 It may have a compaction density of 50 nm and a secondary particle diameter of 50 nm to 230 nm.

[0092] The above first inorganic fine particles are 1 ton / cm 2 1.2 g / cm measured under a pressure of 3 1.5 g / cm 3 Compaction density of 40 m by nitrogen adsorption / desorption 2 / g to 80 m 2 / g Bruner-Emmitt-Teller (BET) specific surface area and a secondary particle diameter of 250 nm to 550 nm. And, the second inorganic fine particles may have a particle size of 1 ton / cm 2 0.7 g / cm measured under a pressure of 3 1.1 g / cm 3 Compaction density of 90 m by nitrogen adsorption / desorption 2 / g to 120 m 2 / g and a Bruner-Emmitt-Teller (BET) surface area and a secondary particle diameter of 50 nm to 230 nm.

[0093]

[0094] According to one embodiment, the inorganic fine particles may have a particle shape selected from the group consisting of acicular particles, angular particles, dendritic particles, fibrous particles, flaky particles, granular particles, irregular particles, nodular particles, and spheroidal particles.

[0095] Preferably, the first inorganic fine particles and the second inorganic fine particles may have different particle shapes.

[0096] For example, the first inorganic fine particles may be angular particles, and the second inorganic fine particles may be acicular particles. As another example, the first inorganic fine particles may be irregular particles, and the second inorganic fine particles may be fibrous particles.

[0097] However, since the compaction density of the above-mentioned inorganic fine particles may vary depending on the material of the inorganic fine particles, the shape of the particles, the size of the particles, or the porosity of the particles, the shapes of the first inorganic fine particles and the second inorganic fine particles do not necessarily need to be different.

[0098]

[0099] According to one embodiment, the inorganic fine particles may include the first inorganic fine particles and the second inorganic fine particles in a weight ratio of 1:1 to 100:1.

[0100] Specifically, the inorganic fine particles may include the first inorganic fine particles and the second inorganic fine particles in a weight ratio of 1:1 to 100:1, or 1:1 to 80:1, or 1:1 to 60:1, or 1:1 to 40:1, or 1:1 to 20:1, or 1:1 to 10:1.

[0101] In order to provide the porous coating layer with a dense pore structure and high tortuosity of the pores, it is preferable that the inorganic fine particles include the first inorganic fine particles and the second inorganic fine particles in the weight ratio range.

[0102] However, if the weight ratio of the first and second inorganic fine particles is outside the above range, a dense pore structure may not be formed in the porous coating layer, and an appropriate level of curvature may not be provided.

[0103]

[0104] According to one embodiment, it is preferable that the inorganic fine particles do not undergo oxidation and / or reduction reactions within the operating voltage range of the secondary battery (e.g., 0 to 5 V based on Li / Li+). It is preferable that the inorganic fine particles have a high electrolyte ion transfer capability. In order to be well dispersed within the polymer binder, it is preferable that the inorganic fine particles have as low a density as possible. In addition, it is preferable that the inorganic fine particles have a high dielectric constant so as to contribute to increasing the dissociation of the electrolyte salt within the electrolyte.

[0105] Preferably, the inorganic fine particles may be at least one selected from the group consisting of inorganic particles having a dielectric constant of 1 or more, inorganic particles having piezoelectricity, and inorganic particles having lithium ion transfer capability.

[0106] For example, inorganic particles such as SrTiO3, SnO2, CeO2, MgO, NiO, CaO, ZnO, ZrO2, Y2O3, Al2O3, boehmite (AlO(OH)), Al(OH)3, TiO2, and SiC have a dielectric constant of 1 or greater and can be preferably applied as the inorganic fine particles.

[0107] As another example, the piezoelectric inorganic particle is a material that is an insulator at normal pressure, but exhibits conductivity due to a change in its internal structure when a certain pressure is applied. The piezoelectric inorganic particle has a high dielectric constant of 100 or more. In addition, when the piezoelectric inorganic particle is stretched or compressed by applying a certain pressure, a charge is generated, so that one side is charged positively (+) and the opposite side is charged negatively (-), thereby generating a potential difference between the two sides. Due to the above-described characteristics of the piezoelectric inorganic particle, when an internal short circuit occurs in the electrode of a secondary battery due to an external impact, direct contact between the positive and negative electrodes can be prevented, and a gradual decrease in voltage and improved safety can be achieved. Examples of the piezoelectric inorganic particle include BaTiO3, Pb(Zr,Ti)O3(PZT), Pb 1-x La x Zr 1-y Ti y O3(PLZT), Pb(Mg 1 / 3 Nb 2 / 3 )O3-PbTiO3(PMN-PT), and inorganic particles such as HfO2 can be preferably applied.

[0108] As another example, the inorganic particles having the lithium ion transport capability refer to inorganic particles that contain lithium elements but have the function of transporting lithium ions without storing lithium. The inorganic particles having the lithium ion transport capability enable improvement of lithium ion conductivity in a battery. Such inorganic particles include Li3PO4, Li x Ti y (PO4)3(0 <x<2, 0<y<3), Li x Al y Ti z (PO4)3(0 <x< 2, 0<y<1, 0<z<3), (LiAlTiP) x O y (0 <x<4, 0<y<13), Li x La y TiO3(0 <x<2, 0<y<3), Li x Gey P z S w (0 <x<4, 0<y<1, 0<z<1, 0<w<5), Li x N y (0 <x<4, 0<y<2), Li x Si y S z (0 <x<3, 0<y<2, 0<z< 4), 및 Li x P y S z (0 <x<3, 0<y<3, 0<z<7) 와 같은 무기 입자를 예로 들 수 있다.

[0109] Preferably, the inorganic fine particles are SrTiO3, SnO2, CeO2, MgO, NiO, CaO, ZnO, ZrO2, Y2O3, Al2O3, AlO(OH), Al(OH)3, TiO2, SiC, BaTiO3, Pb(Zr,Ti)O3, Pb 1-x La x Zr 1-y Ti y O3, Pb(Mg 1 / 3 Nb 2 / 3 )O3-PbTiO3, HfO2, Li3PO4, Li x Ti y (PO4)3(0 <x<2, 0<y<3), Li x Al y Ti z (PO4)3(0 <x< 2, 0<y<1, 0<z<3), (LiAlTiP) x O y (0 <x<4, 0<y<13), Li x La y TiO3(0 <x<2, 0<y<3), Li x Ge y P z S w (0 <x<4, 0<y<1, 0<z<1, 0<w<5), Li x N y (0 <x<4, 0<y<2), Li x Si y S z (0 <x<3, 0<y<2, 0<z< 4), 및 Li x Py S z (0 <x<3, 0<y<3, 0<z<7)로 이루어진 군에서 선택된 1종 이상일 수 있다.

[0110]

[0111] According to one embodiment, the inorganic fine particles include first inorganic fine particles and second inorganic fine particles having different compact densities measured under the same pressure conditions; and the first and second inorganic fine particles may have different particle shapes and be composed of the same type of components.

[0112]

[0113] According to one embodiment, the porous coating layer may include 1 to 90 wt% of the polymer binder and 10 to 99 wt% of the inorganic fine particles. In order to provide the porous coating layer with an appropriate porosity and insulating properties, the inorganic fine particles are preferably included in an amount of 10 wt% or more. However, if the inorganic fine particles are included in an excessive amount, the mechanical properties of the porous coating layer may deteriorate due to weakened adhesive strength. Therefore, the inorganic fine particles are preferably included in an amount of 99 wt% or less.

[0114]

[0115] According to one embodiment, the thickness of the porous coating layer is preferably controlled in the range of 2 μm to 100 μm, or 2 μm to 80 μm, or 2 μm to 50 μm, or 2 μm to 20 μm to exhibit appropriate performance.

[0116]

[0117]

[0118] Meanwhile, according to another embodiment of the invention,

[0119] A step of forming a porous coating layer by applying a slurry including a polymer binder, inorganic fine particles, and a solvent onto a porous polymer substrate,

[0120] The above inorganic fine particles include two or more types of inorganic fine particles having different green densities measured under the same pressure conditions.

[0121] A method for manufacturing a separator for the above lithium secondary battery is provided.

[0122]

[0123] The above separator for a lithium secondary battery can be provided through the above manufacturing method.

[0124] In the step of forming the porous coating layer, the porous polymer substrate, the polymer binder, and the inorganic fine particles are each replaced with the previously described contents.

[0125]

[0126] According to one embodiment, the slurry including the polymer binder, inorganic fine particles, and a solvent can be obtained by first preparing a dispersion in which two or more types of inorganic fine particles having different green densities are dispersed in the solvent, and then mixing the polymer binder into the dispersion.

[0127]

[0128] According to one embodiment, as the solvent included in the slurry, a solvent that exhibits a solubility of 1 wt% or more, or 2.5 wt% or more, or 5 wt% or more, or 7.5 wt% or more, or 10 wt% or more with respect to the polymer binder at room temperature (25°C) can be preferably used.

[0129] Preferably, the solvent may be at least one selected from the group consisting of methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone, dibutyl ether, tetrahydrofuran, cyclohexanone, benzene, fluorobenzene, N-methyl-2-pyrrolidone, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, ethyl methyl carbonate, ethylene carbonate, propylene carbonate, dimethylformamide, 1,3-dioxolane, and sulfolane.

[0130]

[0131] In one embodiment, the slurry preferably has a solids content of 20 wt% to 80 wt%.

[0132] If the solid content of the slurry is too high, the viscosity may increase, preventing the slurry from penetrating into the pores of the porous polymer substrate, thereby reducing the interfacial adhesive strength between the porous polymer substrate and the porous coating layer. However, if the solid content of the slurry is too low, pinholes may occur during the coating of the slurry, and the drying efficiency of the slurry coating may be reduced.

[0133] Specifically, the solids content of the slurry may be 20 wt% or more; and 80 wt% or less, or 70 wt% or less, or 60 wt% or less. Preferably, the solids content of the slurry may be 20 wt% to 80 wt%, or 20 wt% to 70 wt%, or 20 wt% to 60 wt%.

[0134]

[0135] A slurry containing the polymer binder, the inorganic fine particles, and the solvent is coated on the porous polymer substrate.

[0136] As a coating method for the above slurry, any conventional method known in the technical field to which the present invention pertains may be applied. For example, spin coating, dip coating, die coating, roll coating, comma coating, gravure coating, bar coating, curtain coating, screen printing, inkjet printing, doctor blade, or a combination thereof may be used for coating the above slurry.

[0137] In the coating step of the slurry, the thickness of the coating layer formed on the porous polymer substrate can be controlled by considering the composition of the slurry and the thickness of the porous coating layer to be ultimately formed.

[0138]

[0139] According to one embodiment, the step of forming the porous coating layer can be performed by vaporizing the solvent from the slurry coated on the porous polymer substrate.

[0140] Preferably, the step of forming the porous coating layer may be performed at a temperature of 80° C. to 130° C. or 80° C. to 120° C. If the temperature does not meet the above range, drying efficiency may be reduced or the shape of the porous polymer substrate or the porous coating layer may change, resulting in defects.

[0141]

[0142] According to one embodiment, the porous coating layer formed by the above method may include 1 to 90 wt% of the polymer binder and 10 to 99 wt% of the inorganic fine particles. In order to provide the porous coating layer with an appropriate porosity and insulation, the inorganic fine particles are preferably included in an amount of 10 wt% or more. However, if the inorganic fine particles are included in an excessive amount, the mechanical properties of the porous coating layer may deteriorate due to weakened adhesive strength. Therefore, the inorganic fine particles are preferably included in an amount of 99 wt% or less.

[0143]

[0144]

[0145] According to another embodiment of the invention, a lithium secondary battery including the above-described separator for a lithium secondary battery is provided.

[0146] For example, the lithium secondary battery may include an electrode assembly including the lithium secondary battery separator interposed between two electrodes; an electrolyte impregnated in the electrode assembly; and a battery case that seals and stores the electrode assembly and the electrolyte.

[0147] The above lithium secondary battery can exhibit excellent durability and stable performance by having the above-described electrode assembly.

[0148] The above lithium secondary battery can have various shapes such as square, cylindrical, and pouch shapes.

[0149] The above lithium secondary battery can be used as an energy source with improved performance and safety in the field of portable electronic devices such as mobile phones, laptop computers, tablet computers, mobile batteries, and digital cameras; and in the field of transportation means such as electric vehicles, electric motorcycles, and personal mobility devices.

[0150]

[0151] The two electrodes included in the above lithium secondary battery each include an electrode current collector layer and an electrode active material layer laminated on the electrode current collector layer.

[0152]

[0153] The electrode current collector layer may be formed of an electrode current collector known in the art to which the present invention pertains to have conductivity without causing chemical changes in a lithium secondary battery. For example, the electrode current collector may be formed of stainless steel; aluminum; nickel; titanium; sintered carbon; or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, or the like.

[0154] Preferably, the electrode current collector may have a thickness of 3 μm to 500 μm. In order to increase adhesion to the electrode material, the electrode current collector may have fine unevenness formed on its surface. The electrode current collector may have various forms, such as a film, sheet, foil, net, porous body, foam, or non-woven fabric.

[0155]

[0156] The above electrode active material layer includes an electrode material composition which is a mixture of an electrode active material, a conductive material, and a binder.

[0157] The above conductive material can be used to impart electronic conductivity to the electrode.

[0158] As the conductive material, any material that has electronic conductivity and does not cause a chemical change in the lithium secondary battery may be used without particular limitation. Non-limiting examples thereof include carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, summer black, and carbon fiber; graphite such as natural graphite or artificial graphite; metal powder or metal fiber such as copper, nickel, aluminum, and silver; conductive whiskey such as zinc oxide or potassium titanate; conductive metal oxide such as titanium oxide; or conductive polymers such as polyphenylene derivatives. The conductive material may be one or a mixture of two or more of the above-described examples.

[0159] The content of the conductive material can be adjusted within a range that exhibits an appropriate level of conductivity while not causing a decrease in the capacity of the lithium secondary battery. Preferably, the content of the conductive material may be 1 wt% to 10 wt% or 1 wt% to 5 wt% relative to the total weight of the electrode material composition.

[0160]

[0161] The above binder is used to properly attach the electrode material composition to the electrode current collector.

[0162] As non-limiting examples, the binder may be a polymer including polyvinyl alcohol, polyacrylate, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon resin, etc. The binder may be one or a mixture of two or more of the above-described examples.

[0163] The content of the binder can be adjusted within a range that exhibits an appropriate level of adhesiveness while not causing a decrease in the capacity of the lithium secondary battery. Preferably, the content of the binder may be 1 wt% to 10 wt% or 1 wt% to 5 wt% relative to the total weight of the electrode material composition.

[0164]

[0165] When the above electrode is a positive electrode, any material capable of reversible insertion and de-insertion of lithium ions can be used as the positive electrode active material without any special restrictions.

[0166] For example, the positive electrode active material may be a composite oxide or phosphate containing lithium and a metal such as cobalt, manganese, nickel, iron, or a combination thereof.

[0167] As another example, the positive electrode active material may be a compound represented by any one of the following chemical formulas: Li a A 1-b R b D2(0.90≤a≤1.8, 0≤b≤0.5); Li a E 1-b R b O 2-c D c (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05); LiE 2-b R b O 4-c D c (0≤b≤0.5, 0≤c≤0.05); Li a Ni 1-b-c Co b R c D d (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05, 0 <d≤2); Li a Ni 1-b-c Co b R c O 2-d Z d (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05, 0 <d<2); Li a Ni 1-b-c Co b R c O 2-d Z2(0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05, 0 <d<2); Li a Ni 1-b-c Mn b R c D d (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05, 0 <d≤2); Li a Ni 1-b-c Mn b R c O 2-d Z d (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05, 0 <d<2); Li a Ni 1-b-c Mn b R c O 2-dZ2(0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05, 0 <d<2); Li a Ni b E c G d O2(0.90≤a≤1.8, 0≤b≤0.9, 0≤c≤0.5, 0.001≤d≤0.1.); Li a Ni b Co c Mn d G e O2(0.90≤a≤1.8, 0≤b≤0.9, 0≤c≤0.5, 0≤d≤0.5, 0.001≤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 MnG 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); QO2; QS2; LiQS2; V2O5; LiV2O5; LiTO2; LiNiVO4; Li (3-f) J2(PO4)3(0≤f≤2); Li (3-f) Fe2(PO4)3(0≤f≤2); and LiFePO4.

[0168] In the above chemical formula, A is Ni, Co, Mn or a combination thereof; R 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; E is Co, Mn or a combination thereof; Z is F, S, P or a combination thereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V or a combination thereof; Q is Ti, Mo, Mn or a combination thereof; T is Cr, V, Fe, Sc, Y or a combination thereof; J is V, Cr, Mn, Co, Ni, Cu or a combination thereof.

[0169] A positive electrode active material having a coating layer on the surface thereof may also be used, or a positive electrode active material having a coating layer may be mixed and used. As the coating element included in the coating layer, Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, or a mixture thereof may be used.

[0170] According to one embodiment, the positive electrode active material may be included in an amount of 80 wt% to 95 wt% based on the total weight of the electrode material composition. Preferably, the content of the positive electrode active material may be 82 wt% to 95 wt%, or 82 wt% to 93 wt%, or 85 wt% to 93 wt%, or 85 wt% to 90 wt% based on the total weight of the electrode material composition.

[0171]

[0172] When the above electrode is a negative electrode, the negative electrode active material may include a material capable of reversibly intercalating and deintercalating lithium ions, lithium metal, an alloy of lithium metal, a material capable of doping and dedoping lithium, and a transition metal oxide.

[0173] Examples of the material capable of reversibly intercalating and deintercalating the lithium ions include carbonaceous materials such as crystalline carbon, amorphous carbon, or mixtures thereof. Specifically, the carbonaceous material may be natural graphite, artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitches, mesophase pitch-based carbon fiber, meso-carbon microbeads, petroleum or coal tar pitch derived cokes, soft carbon, and hard carbon.

[0174] The above lithium metal alloy may be an alloy of lithium and a metal selected from the group consisting of Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, Sn, Bi, Ga, and Cd.

[0175] The above lithium doping and dedoping materials include Si, Si-C complex, SiOx (0 <x<2), Si-Q 합금(상기 Q는 알칼리 금속, 알칼리 토금속, 13족 원소, 14족 원소, 15족 원소, 16족 원소, 전이 금속, 희토류 원소, 및 이들의 조합으로 이루어진 군에서 선택되는 원소이다; 단, Si는 제외한다), Sn, SnO2, Sn-R 합금(상기 R은 알칼리 금속, 알칼리 토금속, 13족 원소, 14족 원소, 15족 원소, 16족 원소, 전이 금속, 희토류 원소, 및 이들의 조합으로 이루어진 군에서 선택되는 원소이다; 단, Sn은 제외한다.) 등일 수 있다. 그리고, 상기 리튬에 도프 및 탈도프 가능한 물질로는 상기 예들 중 적어도 하나와 SiO2를 혼합하여 사용할 수 있다. 상기 Q 및 R은 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, Tl, Ge, P, As, Sb, Bi, S, Se, Te, Po 등일 수 있다.

[0176] And, the transition metal oxide may be vanadium oxide, lithium vanadium oxide, lithium titanium oxide, etc.

[0177] Preferably, the negative electrode active material may include at least one compound selected from the group consisting of carbonaceous materials and silicon compounds. Here, the carbonaceous material is at least one material selected from the group consisting of natural graphite, artificial graphite, kish graphite, pyrolytic carbon, mesophase pitch, mesophase pitch-based carbon fiber, carbon microspheres, petroleum or coal-based coke, softened carbon, and hardened carbon, as exemplified above. And, the silicon compound is a compound including Si as exemplified above, i.e., Si, Si-C composite, SiOx (0 <x<2), 상기 Si-Q 합금, 이들의 혼합물, 또는 이들 중 적어도 하나와 SiO2의 혼합물일 수 있다.

[0178] According to one embodiment, the negative active material may be included in an amount of 85 wt% to 98 wt% based on the total weight of the electrode material composition. Preferably, the content of the negative active material may be 85 wt% to 97 wt%, or 87 wt% to 97 wt%, or 87 wt% to 95 wt%, or 90 wt% to 95 wt% based on the total weight of the negative electrode material.

[0179]

[0180] According to one embodiment, the thickness of the electrode active material layer is preferably controlled in the range of 5 µm to 500 µm, or 5 µm to 450 µm, or 10 µm to 450 µm to achieve appropriate performance.

[0181]

[0182] According to one embodiment, the electrolyte may be used without particular limitation as long as it is known in the technical field to which the present invention pertains to be applicable to lithium secondary batteries. For example, the electrolyte may be an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel-type polymer electrolyte, a solid inorganic electrolyte, a molten inorganic electrolyte, etc.

[0183] Specifically, the electrolyte may include a non-aqueous organic solvent and a lithium salt.

[0184] Any non-aqueous organic solvent that can serve as a medium through which ions involved in the electrochemical reaction of the battery can move may be used without any particular restrictions.

[0185] Specifically, the non-aqueous organic solvent includes ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether and tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; carbonate solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); Alcohol solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (wherein R is 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 sulfolane.

[0186] Among the above examples, a carbonate solvent can be preferably used as the non-aqueous organic solvent.

[0187] In particular, considering the charge / discharge performance of the battery and compatibility with the positive electrode material, a mixture of a cyclic carbonate (e.g., ethylene carbonate, propylene carbonate) having high ionic conductivity and high dielectric constant and a linear carbonate (e.g., ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate) having low viscosity can be preferably used as the non-aqueous organic solvent. In this case, mixing and using the cyclic carbonate and the linear carbonate in a volume ratio of 1:1 to 1:9 can be advantageous for exhibiting the above-described performance.

[0188] In addition, as the non-aqueous organic solvent, a mixture of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 1:2 to 1:10; or a mixture of ethylene carbonate (EC), ethyl methyl carbonate (EMC) and dimethyl carbonate (DMC) in a volume ratio of 1 to 3:1 to 9:1 can be preferably used.

[0189] The lithium salt included in the electrolyte is dissolved in the non-aqueous organic solvent and acts as a source of lithium ions within the battery, enabling the basic operation of a lithium secondary battery and promoting the movement of lithium ions between the positive and negative electrodes.

[0190] Specifically, the lithium salt may be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiFSI, LiTFSI, LiCl, LiI, and LiB(C2O4)2, etc. Preferably, the lithium salt may be LiPF6, LiFSI, LiTFSI, and mixtures thereof.

[0191] The lithium salt may be included in the electrolyte at a concentration of 0.1 M to 2.0 M. The lithium salt included in the above concentration range enables the electrolyte to exhibit excellent electrolyte performance by providing appropriate conductivity and viscosity to the electrolyte.

[0192] Optionally, the electrolyte may include additives for the purpose of improving the life characteristics of the battery, suppressing battery capacity reduction, and improving the discharge capacity of the battery.

[0193] For example, the additive may be a haloalkylene carbonate compound such as difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, a cyclic ether, ethylene diamine, n-glyme, hexaphosphoric acid triamide, a nitrobenzene derivative, sulfur, a quinone imine dye, an N-substituted oxazolidinone, an N,N-substituted imidazolidine, an ethylene glycol dialkyl ether, an ammonium salt, a pyrrole, 2-methoxyethanol, aluminum trichloride, or the like. The additive may be included in an amount of 0.1 wt% to 5 wt% based on the total weight of the electrolyte.

[0194]

[0195] According to the present invention, a separator for a lithium secondary battery and a method for manufacturing the same are provided, which can exhibit excellent insulating properties while minimizing the occurrence of defects.

[0196]

[0197] FIG. 1 is a scanning electron microscope (SEM) image of the surface of a porous coating layer in a separator for a lithium secondary battery according to Example 1 of the present specification.

[0198] FIG. 2 is an SEM image of the surface of a porous coating layer in a separator for a lithium secondary battery according to Example 2 of the present specification.

[0199] Figure 3 is an SEM image of the surface of a porous coating layer in a separator for a lithium secondary battery according to Comparative Example 1 of the present specification.

[0200] FIG. 4 is an SEM image of the surface of a porous coating layer in a separator for a lithium secondary battery according to Comparative Example 4 of the present specification.

[0201]

[0202] The following specific examples of the invention will illustrate its functions and effects in greater detail. However, these examples are provided solely to aid understanding of the invention. The following examples are not intended to limit the scope of the invention in any way, and it will be apparent to those skilled in the art that various modifications and variations are possible within the scope and spirit of the invention.

[0203]

[0204] Example 1

[0205] (1) Manufacturing of membrane

[0206] Boehmite (AlO(OH)) with fine inorganic particles; compaction density 1.35 g / cm 3 ; BET surface area by nitrogen adsorption / desorption 63 m 2 / g; primary particle diameter 50 nm; secondary particle diameter 350 nm) and needle-like boehmite (AlO(OH); compact density 0.99 g / cm 3 ; BET surface area by nitrogen adsorption / desorption 101 m 2 / g; primary particle diameter 30 nm; secondary particle diameter 155 nm) were prepared.

[0207] A dispersion was prepared by dispersing a mixture of 9.0 g of the above-mentioned boehmite and 1.0 g of the above-mentioned needle-shaped boehmite in N-methyl-2-pyrrolidone (NMP). A polymer binder, poly(vinylidene fluoride-co-hexafluoropropylene), was added to the dispersion and uniformly mixed using a homogenizer to prepare a slurry having a solid content of 20%.

[0208] The above slurry was applied onto a porous polyethylene substrate (manufacturer: Senior) having a thickness of 9 μm using a dual slot die, and the solvent was vaporized at 80°C to form a porous coating layer having a thickness of 6 μm. The composition of the porous coating layer was 90 wt% of the inorganic fine particles and 10 wt% of the polymer binder.

[0209]

[0210] (2) Manufacturing of the cathode

[0211] An electrode material composition was prepared, comprising 95.6 wt% of an active material composed of 90 wt% of a graphite active material in which artificial graphite and natural graphite are mixed in a ratio of 3:7 and 10 wt% of SiO; 1 wt% of acetylene black as a conductive material; and 1.1 wt% of carboxymethyl cellulose (CMC) and 2.3 wt% of styrene butadiene rubber (SBR) as binders. The electrode material composition was applied to one side of a copper current collector having a thickness of 8 μm using a comma coater. This was dried and rolled at 130°C to manufacture a negative electrode plate having a layer of negative electrode active material. The negative electrode active material layer had a porosity of 24% and a thickness of 44 μm. The negative electrode plate was punched into a size of 31 x 43 mm using a die puncher to prepare a negative electrode portion.

[0212]

[0213] (3) Manufacturing of the anode part

[0214] A slurry was prepared by uniformly dispersing a mixture of 94 wt% LiNiCoMnO2 (Ni:Co:Mn=8:1:1) as a cathode active material, 3 wt% conductive carbon black (Super P; IMERYS Graphite & Carbon) as a conductive material, and 3 wt% polyvinylidene fluoride as a binder in NMP. The slurry was applied to one surface of an aluminum current collector, dried, and rolled to prepare a cathode plate having a layer of cathode active material laminated thereon. The cathode plate was punched into a size of 30 x 42 mm using a die puncher to prepare a cathode part.

[0215]

[0216] (4) Battery manufacturing

[0217] The above negative electrode, the separator, and the positive electrode were sequentially laminated and pressurized at 90°C to manufacture an electrode assembly. The electrode assembly was placed in a pouch to form a small cell, and an electrolyte was injected into the pouch to manufacture five lithium secondary batteries.

[0218] At this time, the electrolyte used was a non-aqueous organic solvent containing ethylene carbonate (EC) and ethyl methyl carbonate (EMC) mixed in a volume ratio of 3:7, in which 0.5 M LiFSI, 0.7 M LiPF6, and 2 wt% vinylene carbonate (VC) were dissolved.

[0219]

[0220] Example 2

[0221] A separator and a lithium secondary battery including the same were manufactured in the same manner as in Example 1, except that a mixture of 5.0 g of the above-described boehmite and 5.0 g of the above-described needle-shaped boehmite was used as inorganic fine particles in the manufacture of the above-described separator.

[0222]

[0223] Example 3

[0224] In the manufacture of the above separation membrane, instead of the mixture of the above-mentioned angular boehmite and the above-mentioned needle-shaped boehmite as inorganic fine particles, 9.0 g of angular boehmite (AlO(OH); green density 1.46 g / cm 3 ; BET surface area 45 m by nitrogen adsorption / desorption 2 / g; primary particle diameter 65 nm; secondary particle diameter 500 nm) and 1.0 g of needle-like boehmite (AlO(OH); green density 0.81 g / cm 3 ; BET surface area by nitrogen adsorption / desorption 118 m 2 / g; primary particle diameter 25 nm; secondary particle diameter 136 nm) was used, and a separator and a lithium secondary battery including the same were manufactured in the same manner as in Example 1.

[0225]

[0226] Comparative Example 1

[0227] In the manufacture of the above separation membrane, instead of the mixture of the above-mentioned angular boehmite and the above-mentioned needle-shaped boehmite as inorganic fine particles, the above-mentioned angular boehmite (AlO(OH); compact density 1.35 g / cm 3 ; BET surface area by nitrogen adsorption / desorption 63 m 2 / g; primary particle diameter 50 nm; secondary particle diameter 350 nm) was used alone, 10.0 g of the separator and a lithium secondary battery including the same were manufactured in the same manner as in Example 1.

[0228]

[0229] Comparative Example 2

[0230] In the manufacture of the above separation membrane, instead of the mixture of the above angular boehmite and the above needle-shaped boehmite as inorganic fine particles, the needle-shaped boehmite (AlO(OH); compact density 0.99 g / cm 3 ; BET surface area by nitrogen adsorption / desorption 101 m 2 / g; primary particle diameter 30 nm; secondary particle diameter 155 nm) was used alone, 10.0 g of the separator and a lithium secondary battery including the same were manufactured in the same manner as in Example 1.

[0231]

[0232] Comparative Example 3

[0233] In the manufacture of the above separation membrane, instead of the mixture of the above-mentioned angular boehmite and the above-mentioned needle-shaped boehmite as inorganic fine particles, angular boehmite (AlO(OH); green density 1.38 g / cm 3 ; BET surface area by nitrogen adsorption / desorption 18 m 2 / g; primary particle diameter 300 nm; secondary particle diameter 700 nm) was used alone, 10.0 g of the separator and a lithium secondary battery including the same were manufactured in the same manner as in Example 1.

[0234]

[0235] Comparative Example 4

[0236] In the manufacture of the above separation membrane, instead of the mixture of the above angular boehmite and the above needle-shaped boehmite as inorganic fine particles, alumina (Al2O3; compact density 2.05 g / cm 3 ; BET surface area by nitrogen adsorption / desorption 6.4 m 2 / g; primary particle diameter 350 nm; secondary particle diameter 900 nm) was used alone, 10.0 g of the separator and a lithium secondary battery including the same were manufactured in the same manner as in Example 1.

[0237]

[0238] Experimental Example 1

[0239] The surface of the porous coating layer formed on the separator according to Examples 1 and 2 and Comparative Examples 1 and 4 was observed using a scanning electron microscope, and the results are shown in FIG. 1 (Example 1), FIG. 2 (Example 2), FIG. 3 (Comparative Example 1), and FIG. 4 (Comparative Example 4).

[0240] Referring to FIGS. 1 and 2, it can be observed that in the porous coating layer according to the embodiments, inorganic fine particles are evenly distributed on the surface, and small pores are densely formed.

[0241] On the other hand, referring to FIGS. 3 and 4, the porous coating layers according to Comparative Examples 1 and 4 have larger pore sizes and an uneven surface shape compared to the examples.

[0242]

[0243] Experimental Example 2

[0244] For each of the inorganic fine particles used in the above examples and comparative examples, the compaction density was obtained by the following method.

[0245] 1 g of inorganic fine particles was filled into a cylindrical mold with a diameter of 16 mm and 1 ton / cm 2 A green pellet was manufactured by applying pressure. The green pellet density (g / cm) was calculated from the volume measurement value of the green pellet and the weight (1 g) of the green pellet. 3 ) was calculated.

[0246]

[0247] Experimental Example 3

[0248] The nitrogen adsorption / desorption Bruner-Emmitt-Teller (BET) surface area of ​​the inorganic fine particles used in the above examples and comparative examples was measured using a surface area analyzer (BEL Japan Inc., BELSORP-max). In the measurement of the above characteristics, the temperature of the air oven equipped with the analyzer was maintained at 40°C.

[0249]

[0250] Experimental Example 4

[0251] The breakdown voltage (kV / mil) of the porous coating layer was measured for the lithium secondary batteries (five samples each) obtained in the above examples and comparative examples using the following method. Using a Hi-pot meter (Chroma 19055), the maximum voltage allowed before breakdown occurred was measured at a voltage increase rate of 100 V / sec. The measured maximum voltage was divided by the thickness of the porous coating layer to calculate the maximum voltage allowed per unit thickness, which is shown in Table 1 below.

[0252]

[0253] Experimental Example 5

[0254] The resistance (ohm) of the porous coating layer of the lithium secondary batteries (five samples each) obtained in the above examples and comparative examples was measured by the following method. The resistance of the porous coating layer was measured by the Nyquist plot method using electrochemical impedance spectroscopy (EIS) under AC voltage conditions of amplitude 10 Mv and frequency 104-105 Hz.

[0255]

[0256] Experimental Example 6

[0257] The air permeability (sec / 100cc) of the membranes manufactured in the above examples and comparative examples was measured using the following method. The membranes were mounted on an air-permeability tester device according to the method of JIS P8117, and the time taken for 100 cc of air to permeate the membrane under a constant pressure was measured.

[0258]

[0259] Insulation Breakdown Voltage (kV / mil) Resistance (ohm) Air Permeability (sec / 100cc) Example 14.26 0.74 122.4 Example 24.42 0.76 135.0 Example 34.46 0.75 120.1 Comparative Example 13.8 10.76 121.3 Comparative Example 23.99 0.80 156.5 Comparative Example 33.78 0.75 114.8 Comparative Example 43.70 0.75 107.5

[0260] Referring to the results of the above experimental examples, it was confirmed that the porous coating layer according to the examples was provided with high tortuosity and exhibited a high insulation breakdown voltage.

[0261] On the other hand, the porous coating layer according to the comparative examples showed a poorer insulation breakdown voltage compared to the above examples.

[0262]

[0263] Although the present invention has been described above with reference to limited embodiments and drawings, the present invention is not limited thereto, and it is obvious that various modifications and variations are possible within the scope of the technical idea of ​​the present invention and the equivalent scope of the patent claims to be described below by a person having ordinary skill in the art to which the present invention pertains.

Claims

1. A porous polymer substrate, and a porous coating layer formed on the porous polymer substrate, The above porous coating layer comprises a polymer binder and inorganic fine particles dispersed on the polymer binder, The above inorganic fine particles include two or more types of inorganic fine particles having different green densities measured under the same pressure conditions. Separator for lithium secondary batteries.

2. In paragraph 1, The above inorganic fine particles are 1 ton / cm 2 1.2 g / cm measured under a pressure of 3 1.5 g / cm 3 First inorganic fine particles having a compaction density of , 1 ton / cm 2 0.7 g / cm measured under a pressure of 3 1.1 g / cm 3 comprising second inorganic fine particles having a compaction density of . Separator for lithium secondary batteries.

3. In paragraph 1, The above inorganic fine particles are 40 m by nitrogen adsorption / desorption 2 / g to 80 m 2 A first inorganic fine particle having a Bruner-Emmitt-Teller (BET) surface area of ​​ / g, 90 m by nitrogen adsorption / desorption 2 / g to 120 m 2 / g comprising second inorganic fine particles having a Bruner-Emmitt-Teller (BET) surface area of Separator for lithium secondary batteries.

4. In paragraph 1, The above inorganic fine particles are First inorganic fine particles having a secondary particle diameter of 250 nm to 550 nm, Comprising a second inorganic fine particle having a secondary particle diameter of 50 nm to 230 nm, Separator for lithium secondary batteries.

5. In paragraph 2, A separator for a lithium secondary battery, wherein the first inorganic fine particles and the second inorganic fine particles have different particle shapes.

6. In paragraph 5, A separator for a lithium secondary battery, wherein the first inorganic fine particles and the second inorganic fine particles are made of the same type of components.

7. In paragraph 5, The above first inorganic fine particles are angular particles, The above second inorganic fine particles are acicular particles, Electrode-integrated separator for lithium secondary batteries.

8. In paragraph 2, A separator for a lithium secondary battery, wherein the above inorganic fine particles include the first inorganic fine particles and the second inorganic fine particles in a weight ratio of 1:1 to 100:

1.

9. In paragraph 1, The above inorganic fine particles are SrTiO3, SnO2, CeO2, MgO, NiO, CaO, ZnO, ZrO2, Y2O3, Al2O3, boehmite (AlO(OH)), Al(OH)3, TiO2, SiC, BaTiO3, Pb(Zr,Ti)O3, Pb 1-x La x Zr 1-y Ti y O3, Pb(Mg 1 / 3 Nb 2 / 3 )O3-PbTiO3, HfO2, Li3PO4, Li x Ti y (PO4)3(0 <x<2, 0<y<3), Li x Al y Ti z (PO4)3(0 <x< 2, 0<y<1, 0<z<3), (LiAlTiP) x O y (0 <x<4, 0<y<13), Li x La y TiO3(0 <x<2, 0<y<3), Li x Ge y P z S w (0 <x<4, 0<y<1, 0<z<1, 0<w<5), Li x N y (0 <x<4, 0<y<2), Li x Si y S z (0 <x<3, 0<y<2, 0<z< 4), 및 Li x P y S z (0 <x<3, 0<y<3, 0<z<7)로 이루어진 군에서 선택된 1종 이상인, 리튬 이차 전지용 분리막.

10. In paragraph 1, A separator for a lithium secondary battery, wherein the polymer binder is at least one compound selected from the group consisting of polyvinylidene fluoride, poly(vinylidene fluoride-co-trichloroethylene), poly(vinylidene fluoride-co-chlorotrifluoroethylene), poly(vinylidene fluoride-co-trifluoroethylene), poly(vinylidene fluoride-co-tetrafluoroethylene), poly(vinylidene fluoride-co-hexafluoropropylene), spandex, butylacrylate, polymethylmethacrylate, polyacrylonitrile, polyvinylpyrrolidone, and polyvinylacetate.

11. In paragraph 1, A separator for a lithium secondary battery, wherein the porous coating layer comprises 1 to 90 wt% of the polymer binder and 10 to 99 wt% of the inorganic fine particles.

12. In paragraph 1, A separator for a lithium secondary battery, wherein the porous polymer substrate comprises at least one polymer selected from the group consisting of polyethylene, polypropylene, polyethylene terephthalate, polypropylene terephthalate, polybutylene terephthalate, polyester, polyacetal, polyamide, polycarbonate, polyimide, polyamideimide, polyetherimide, polyetheretherketone, polyethersulfone, polyphenylene oxide, polyphenylene sulfide, and polyethylene naphthalate.

13. A step of forming a porous coating layer by applying a slurry including a polymer binder, inorganic fine particles, and a solvent onto a porous polymer substrate, The above inorganic fine particles include two or more types of inorganic fine particles having different green densities measured under the same pressure conditions. A method for manufacturing a separator for a lithium secondary battery according to claim 1.

14. In paragraph 13, A method for producing a separator for a lithium secondary battery, wherein the slurry has a solid content of 20 wt% to 80 wt%.

15. In paragraph 13, A method for producing a separator for a lithium secondary battery, wherein the solvent is at least one selected from the group consisting of methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone, dibutyl ether, tetrahydrofuran, cyclohexanone, benzene, fluorobenzene, N-methyl-2-pyrrolidone, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, ethyl methyl carbonate, ethylene carbonate, propylene carbonate, dimethylformamide, 1,3-dioxolane, and sulfolane.

16. In paragraph 13, A method for manufacturing a separator for a lithium secondary battery, wherein the step of forming the porous coating layer is performed by vaporizing the solvent from the slurry coated on the porous polymer substrate at a temperature of 80°C to 130°C.

17. A lithium secondary battery comprising a separator for a lithium secondary battery according to Article 1.

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