Binder resin and method for manufacturing the same and binder composition for coating separator of secondary battery

Abstract

A binder resin for coating a separator of a secondary battery, a method for manufacturing the same, and a binder composition are disclosed. A binder resin for coating a separator of a secondary battery according to one embodiment is a copolymer of a plurality of monomers, wherein the plurality of monomers may include methyl methacrylate, butyl acrylate, ethylhexyl acrylate, hydroxyethyl methacrylate, acrylic acid, and glycidyl methacrylate.

Description

Technology Field

[0001] The present disclosure relates to a binder resin coated on a separator of a secondary battery, a method for manufacturing the binder resin, and a binder composition comprising the binder resin. Background Technology

[0002] The separator is one of the core materials of a secondary battery, and conventionally, polyolefin-based separators have been widely used. However, polyolefin-based separators have poor thermal stability and physical strength at high temperatures, so there was a concern that they would lose their function as separators when exposed to a temperature of 150°C for about an hour, as the thermal shrinkage rate would reach 50–90%. Additionally, existing secondary battery separators had the problem of a high possibility of internal short circuits occurring upon external impact.

[0003] Recently, to address these issues, a coating layer is being formed on the surface of the separator. For example, when a coating layer is formed on one side of a polyolefin separator with a thickness of 9 μm, the thickness of the coating layer is set to 3 μm or more, and when a coating layer is formed on both sides of the polyolefin separator, the thickness of the coating layer on each side is set to 1.5 μm to 2 μm. Efforts are being made to manufacture a separator with excellent heat resistance even at 150 to 200°C.

[0004] As the thickness of the coating layer applied to the surface of the separator increases, the thermal stability of the separator improves, but electrical conductivity decreases and battery efficiency may decline; therefore, there is a need to develop new technology that can improve the heat resistance and electrical conductivity of the separator while implementing the coating layer as a thin film. Prior art literature

[0005] Republic of Korea Published Patent Application No. 10-2023-0093674 The problem to be solved

[0006] The technical concept of the present disclosure is intended to solve the aforementioned problems, and aims to provide a technology for manufacturing a separator with excellent thermal stability while reducing the thickness of the coating layer coated on the surface of the separator.

[0007] Another objective of the technical concept of the present disclosure is to provide a technology that can maintain an excellent level of electrical conductivity of a separator even when a coating layer is formed on the separator.

[0008] Another objective of the technical concept of the present disclosure is to provide a technology capable of maintaining an excellent level of adhesion of a coating layer coated on a separator.

[0009] The problems that this disclosure aims to solve are not limited to the problems described above, and other technical problems not mentioned will be clearly understood by those skilled in the art to which this disclosure belongs from the following description. means of solving the problem

[0010] In order to achieve this purpose, as an embodiment of the present disclosure, a binder resin for coating a separator of a secondary battery is copolymerized from a plurality of monomers, wherein the plurality of monomers may include methyl methacrylate, butyl acrylate, ethylhexyl acrylate, hydroxyethyl methacrylate, acrylic acid, and glycidyl methacrylate.

[0011] In one embodiment, a plurality of monomers may further include a crosslinking agent.

[0012] In one embodiment, the crosslinking agent may include hexanediol diacrylate.

[0013] In one embodiment, the content of methyl methacrylate is 10 to 25 weight%, the content of butyl acrylate is 13 to 25 weight%, the content of ethylhexyl acrylate is 13 to 25 weight%, the content of hydroxyethyl methacrylate is 5 to 20 weight%, the content of acrylic acid is 1 to 5 weight%, the content of glycidyl methacrylate is 5 to 25 weight%, and the content of the crosslinking agent may be 0.1 to 1 weight%.

[0014] In order to achieve this purpose, as another embodiment of the present disclosure, a binder composition for coating a separator of a secondary battery comprises the aforementioned binder resin; and particles; wherein the particles may comprise at least one of inorganic particles and organic particles.

[0015] In order to achieve this purpose, as another embodiment of the present disclosure, the separator may comprise a porous substrate; and a coating layer formed by applying the aforementioned binder composition to one or both sides of the porous substrate.

[0016] In one embodiment, the separator has a coating layer formed on one surface of the porous substrate, and the average value of the longitudinal shrinkage rate and the transverse shrinkage rate of the separator measured after leaving the separator at 150°C for 1 hour is less than 5%, and the difference value obtained by subtracting the air permeability value of the porous substrate from the air permeability value of the separator may be less than 20 seconds / 100cc.

[0017] In order to achieve this purpose, as another embodiment of the present disclosure, the secondary battery may include the aforementioned separator.

[0018] In one embodiment, the secondary battery may include a lithium secondary battery.

[0019] In order to achieve this purpose, as another embodiment of the present disclosure, a method for manufacturing a binder resin for coating a separator of a secondary battery comprises a polymerization step of copolymerizing a plurality of monomers; and the plurality of monomers may include methyl methacrylate, butyl acrylate, ethylhexyl acrylate, hydroxyethyl methacrylate, acrylic acid, and glycidyl methacrylate.

[0020] The means for solving the problem described above are merely exemplary and should not be interpreted as intended to limit the present disclosure. In addition to the exemplary embodiments described above, additional embodiments may exist as described in the drawings and the detailed description of the present disclosure. Effects of the invention

[0021] As described above, according to various embodiments of the present disclosure, the thermal stability of the separator is excellent because the average value of the longitudinal shrinkage rate and the transverse shrinkage rate of the separator measured after leaving a separator with a coating layer of 2 μm thickness formed on one surface at 150°C for 1 hour is less than 5%. Therefore, it is possible to manufacture a separator with excellent heat resistance while making the coating layer thin.

[0022] According to various embodiments of the present disclosure, since the difference between the air permeability value of a separator with a coating layer formed thereon and the air permeability value of a porous substrate without a coating layer formed thereon is less than 20 seconds / 100cc, even if a separator is manufactured by forming a coating layer on the surface of a porous substrate, the level of air passing through the separator is excellent, and it can contribute to the improvement of the electrical conductivity of the separator.

[0023] According to various embodiments of the present disclosure, the adhesion of the coating layer coated on the separator is excellent, so the coating layer can be prevented from separating from the separator.

[0024] The effects of the present disclosure are not limited to those mentioned above, and other unmentioned effects will be clearly understood by those skilled in the art from the description in the claims. Brief explanation of the drawing

[0025] FIG. 1 is a flowchart schematically illustrating a method for manufacturing a binder resin for coating a separator of a secondary battery according to one embodiment of the present disclosure. Specific details for implementing the invention

[0026] Preferred embodiments of the present disclosure will be described in more detail with reference to the accompanying drawings, provided that technical details that are already well known are omitted or compressed for the sake of brevity.

[0027] It should be noted that references to “one” or “one” embodiment of the present disclosure in this specification do not necessarily refer to the same embodiment, but mean at least one.

[0028] In the following embodiments, terms such as first, second, etc. are used not in a limiting sense, but for the purpose of distinguishing one component from another component.

[0029] In the following examples, singular expressions include plural expressions unless the context clearly indicates a different meaning.

[0030] In the following examples, terms such as "include" or "have" mean that the features or components described in the specification are present, and do not preclude the possibility that one or more other features or components may be added.

[0031] In the following embodiments, when a part such as a film, region, or component is described as being on or above another part, it includes not only cases where it is directly on top of another part, but also cases where another film, region, or component is interposed in between.

[0032] Throughout this specification, the term "about" used before a number is used to mean at or near that number when inherent manufacturing and material tolerances are presented in the stated meaning, and is used to prevent unscrupulous infringers from unfairly exploiting the disclosure in which precise or absolute numbers are mentioned to aid in understanding this invention.

[0033] Where an embodiment can be implemented differently, a specific process sequence may be performed differently from the order described. For example, two processes described in succession may be performed substantially simultaneously or proceed in the reverse order of the order described. That is, each step of the method described herein may be appropriately performed in any order unless otherwise stated in the specification or clearly contradicted by the context.

[0034] In the following examples, the weight-average molecular weight can be measured using gel permeation chromatography (GPC). For example, the analyte is placed in a 5 ml vial and diluted with tetrahydrofuran (THF) to a concentration of approximately 1 mg / ml. Then, the standard sample for calibration and the sample to be analyzed are filtered through a syringe filter (pore size: 0.45 μm) and measured. The analysis program used is ChemStation from Agilent Technologies, and the weight-average molecular weight (Mw) is determined by comparing the elution time of the sample with the calibration curve. The GPC measurement conditions can be set as follows.

[0035] <GPC 측정 조건>

[0036] 1. Device: Agilent Technologies 1200 Series

[0037] 2. Column: Used two PLgel mixed B columns from Polymer Laboratories

[0038] 3. Solvent: Tetrahydrofuran

[0039] 4. Column temperature: 35℃

[0040] 5. Sample concentration: 1 mg / mL, 200 μL injection

[0041] 6. Standard Sample: Polystyrene (Mp: 3900000, 723000, 316500, 52200, 31400, 7200, 3940, 485)

[0042] <Explanation of Binder Resin for Coating Separators in Secondary Batteries>

[0043] A secondary battery separator binder resin according to one embodiment is a copolymer prepared by copolymerizing a plurality of monomers. In one embodiment, the plurality of monomers may include methyl methacrylate, n-butyl acrylate, 2-ethylhexyl acrylate, 2-hydroxyethyl methacrylate, acrylic acid, glycidyl methacrylate, and a crosslinking agent. In one embodiment, the crosslinking agent may include hexanediol diacrylate (1,6-hexanediol diacrylate).

[0044] In one embodiment, based on a total amount of 100 wt% of a plurality of monomers, the content of methyl methacrylate may be applied as about 10 wt% or more to about 25 wt% or less. As a specific example, the content of methyl methacrylate may be applied as 10 wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt%, 15 wt%, 16 wt%, 17 wt%, 18 wt%, 19 wt%, 20 wt%, 21 wt%, 22 wt%, 23 wt%, 24 wt%, or 25 wt%. The content of methyl methacrylate may be in a range of one or more of the above figures and one or less of the above figures.

[0045] For example, the content range of methyl methacrylate may be set to 10% to 25% by weight, 15% to 25% by weight, 20% to 25% by weight, 11% to 25% by weight, 12% to 25% by weight, or 13% to 25% by weight. Methyl methacrylate according to one embodiment can maintain excellent film properties within the above ranges.

[0046] If the methyl methacrylate content is less than 10 weight%, gelation may occur during the copolymerization process of the binder resin, making it difficult to produce a product as a binder resin, and if the methyl methacrylate content exceeds 25 weight%, it may have a negative effect on the physical properties of the coating layer made of the binder composition, such as adhesion, heat resistance, and air permeability.

[0047] In one embodiment, based on a total amount of 100 wt% of a plurality of monomers, the content of butyl acrylate may be applied as about 13 wt% or more to about 25 wt% or less. As a specific example, the content of butyl acrylate may be applied as 13 wt%, 14 wt%, 15 wt%, 16 wt%, 17 wt%, 18 wt%, 19 wt%, 20 wt%, 21 wt%, 22 wt%, 23 wt%, 24 wt%, or 25 wt%. The content of butyl acrylate may be in a range of one or more of the above figures and one or less of the above figures.

[0048] For example, the content range of butyl acrylate can be set to 13% to 25% by weight, 18% to 25% by weight, 20% to 25% by weight, or 15% to 25% by weight. The butyl acrylate according to one embodiment can maintain excellent film properties within the above ranges.

[0049] If butyl acrylate is less than 13 weight%, the adhesion or heat resistance of the coating layer made of the binder composition may decrease, or the time it takes for air to pass through the coating layer may increase, which may have a negative effect on electrical conductivity and cell efficiency, and if it exceeds 25 weight%, there is a risk that the physical properties of the coating layer made of the binder composition may deteriorate.

[0050] In one embodiment, based on a total amount of 100 wt% of a plurality of monomers, the content of ethylhexyl acrylate may be applied as about 13 wt% or more to about 25 wt% or less. As a specific example, the content of ethylhexyl acrylate may be applied as 13 wt%, 14 wt%, 15 wt%, 16 wt%, 17 wt%, 18 wt%, 19 wt%, 20 wt%, 21 wt%, 22 wt%, 23 wt%, 24 wt%, or 25 wt%. The content of ethylhexyl acrylate may be in a range of one or more of the above figures and one or less of the above figures.

[0051] For example, the content range of ethylhexyl acrylate may be set to 13% to 25% by weight, 18% to 25% by weight, 20% to 25% by weight, or 15% to 25% by weight. The ethylhexyl acrylate according to one embodiment can maintain excellent film properties within the above ranges.

[0052] If the ethylhexyl acrylate content is less than 13 weight%, the heat resistance of the coating layer made of the binder composition may decrease, or the time it takes for air to pass through the coating layer may increase, which may have a negative effect on electrical conductivity and cell efficiency, and if it exceeds 25 weight%, there is a risk that the physical properties of the coating layer made of the binder composition may deteriorate.

[0053] In one embodiment, based on a total amount of 100% by weight of a plurality of monomers, the content of hydroxyethyl methacrylate may be applied as about 5% by weight or more to about 20% by weight or less. As a specific example, the content of hydroxyethyl methacrylate may be applied as 5% by weight, 6% by weight, 7% by weight, 8% by weight, 9% by weight, 10% by weight, 11% by weight, 12% by weight, 13% by weight, 14% by weight, 15% by weight, 16% by weight, 17% by weight, 18% by weight, 19% by weight, or 20% by weight. The content of hydroxyethyl methacrylate may be in a range of one or more of the above figures and one or less of the above figures.

[0054] For example, the content range of hydroxyethyl methacrylate may be set to 5% to 20% by weight, 10% to 20% by weight, 15% to 20% by weight, or 11% to 20% by weight. Hydroxyethyl methacrylate according to one embodiment can maintain excellent film properties within the above ranges.

[0055] If hydroxyethyl methacrylate is less than 5 weight%, the heat resistance of the coating layer made of the binder composition may decrease, or the time it takes for air to pass through the coating layer may increase, which may have a negative effect on electrical conductivity and cell efficiency, and if it exceeds 20 weight%, the physical properties of the coating layer made of the binder composition may decrease.

[0056] In one embodiment, based on a total amount of 100% by weight of a plurality of monomers, the content of acrylic acid may be applied as about 1% by weight or more to about 5% by weight or less. As a specific example, the content of acrylic acid may be applied as 1% by weight, 2% by weight, 3% by weight, 4% by weight, or 5% by weight. The content of acrylic acid may be in a range of one or more of the above values ​​and one or less of the above values.

[0057] For example, the content range of acrylic acid may be set to 1 wt% to 5 wt%, 2 wt% to 5 wt%, 3 wt% to 5 wt%, or 4 wt% to 5 wt%. The acrylic acid according to one embodiment can maintain excellent film properties within the above ranges.

[0058] If the acrylic acid content is less than 1 weight%, the adhesion or heat resistance of the coating layer made from the binder composition may decrease, or the time it takes for air to pass through the coating layer may be prolonged, which may have a negative effect on electrical conductivity and cell efficiency, and there is a risk of gelation occurring during the copolymerization of the binder resin as the content of other components becomes relatively high. If the acrylic acid content exceeds 5 weight%, gelation may occur during the copolymerization process of the binder resin, making it difficult to commercialize the product as a binder resin.

[0059] In one embodiment, based on a total amount of 100 wt% of a plurality of monomers, the content of glycidyl methacrylate may be applied as about 5 wt% or more to about 25 wt% or less. As a specific example, the content of glycidyl methacrylate may be applied as 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt%, 15 wt%, 16 wt%, 17 wt%, 18 wt%, 19 wt%, 20 wt%, 21 wt%, 22 wt%, 23 wt%, 24 wt%, or 25 wt%. The content of glycidyl methacrylate may be in a range of one or more of the above figures and one or less of the above figures.

[0060] For example, the content range of glycidyl methacrylate may be set to 5 wt% to 25 wt%, 10 wt% to 25 wt%, 15 wt% to 25 wt%, 20 wt% to 25 wt%, 11 wt% to 25 wt%, 12 wt% to 25 wt%, or 13 wt% to 25 wt%. Glycidyl methacrylate according to one embodiment can maintain excellent film properties within the above ranges.

[0061] If the glycidyl methacrylate content is less than 5 weight%, it may have a negative effect on the physical properties of the coating layer made of the binder composition, such as heat resistance and air permeability, and if the glycidyl methacrylate content exceeds 25 weight%, gelation may occur during the copolymerization process of the binder resin, making it difficult to produce the product as a binder resin.

[0062] In one embodiment, based on a total amount of 100% by weight of a plurality of monomers, the content of the crosslinking agent may be applied as about 0.1% by weight or more to about 1% by weight or less. As a specific example, the content of the crosslinking agent may be applied as 0.1% by weight, 0.2% by weight, 0.3% by weight, 0.4% by weight, 0.5% by weight, 0.6% by weight, 0.7% by weight, 0.8% by weight, 0.9% by weight, or 1% by weight. The content of the crosslinking agent may be in a range of one or more of the above values ​​and one or less of the above values.

[0063] For example, the content range of the crosslinking agent may be set to 0.1 wt% to 1 wt%, 0.2 wt% to 1 wt%, 0.3 wt% to 1 wt%, or 0.5 wt% to 1 wt%. The crosslinking agent according to one embodiment can maintain excellent film properties within the above ranges.

[0064] If the crosslinking agent is less than 0.1 weight%, the effect of improving the degree of crosslinking due to the crosslinking agent is negligible, and if the crosslinking agent exceeds 1 weight%, gelation may occur during the copolymerization process of the binder resin.

[0065] In one embodiment, the binder resin for coating the separator of a secondary battery may have a non-volatile content of about 10% or more to about 50% or less. As a specific example, the non-volatile content of the binder resin may be applied as 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, or 50%. The non-volatile content of the binder resin may be in a range of one or more of the above values ​​and one or less of the above values.

[0066] For example, the non-volatile content range of the binder resin can be set to a range of 10% to 50%, 20% to 50%, 30% to 50%, 40% to 50%, or 10% to 40%.

[0067] In one embodiment, the non-volatile content of the binder resin is a ratio derived by comparing the weight of the binder resin measured after being withdrawn and heated for 3 hours in a dryer at a temperature of 100°C or higher to 110°C or lower with the weight of the binder resin before heating, and can be calculated by the following mathematical formula 1.

[0068] [Mathematical Formula 1]

[0069] Non-volatile content of binder resin (%) = Weight of binder resin after heating / Weight of binder resin before heating × 100

[0070] According to one embodiment, a binder resin for coating a separator of a secondary battery can be implemented as a copolymer of methyl methacrylate, butyl acrylate, ethylhexyl acrylate, hydroxyethyl methacrylate, acrylic acid, and glycidyl methacrylate. The copolymerization reaction of the binder resin for coating a separator of a secondary battery can be represented by Reaction Scheme 1 below. In the copolymerization process of the binder resin, a solvent (e.g., water), a polymerization initiator (e.g., potassium persulfate (KPS)), an emulsifier, and ammonia water may be used. In the copolymerization process of the binder resin, the amounts of the solvent, polymerization initiator, emulsifier, and ammonia water can be appropriately set as needed.

[0071] [Reaction Equation 1]

[0072]

[0073] In one embodiment, the binder resin for coating the separator of a secondary battery is a copolymer of methyl methacrylate, butyl acrylate, ethylhexyl acrylate, hydroxyethyl methacrylate, acrylic acid, and glycidyl methacrylate, and can be represented by the following chemical formula 1.

[0074] [Chemical Formula 1]

[0075]

[0076] In the above chemical formula 1, a is a rational number (or integer or natural number) from 129 to 12984, b is a rational number (or integer or natural number) from 97 to 9753, c is a rational number (or integer or natural number) from 67 to 6784, d is a rational number (or integer or natural number) from 38 to 3842, e is a rational number (or integer or natural number) from 20 to 2082, and f is a rational number (or integer or natural number) from 35 to 3517.

[0077] The copolymer according to Chemical Formula 1 may have a weight-average molecular weight of about 50,000 g / mol or more to about 5,000,000 g / mol or less. As a specific example, the weight-average molecular weight of the copolymer according to Formula 1 is 50,000 g / mol, 60,000 g / mol, 70,000 g / mol, 80,000 g / mol, 90,000 g / mol, 100,000 g / mol, 200,000 g / mol, 300,000 g / mol, 400,000 g / mol, 500,000 g / mol, 600,000 g / mol, 700,000 g / mol, 800,000 g / mol, 900,000 g / mol, 1,000,000 g / mol, 2,000,000 g / mol, 3,000,000 g / mol, 4,000,000 g / mol, or It can be applied at 5,000,000 g / mol. The weight-average molecular weight of the copolymer according to Chemical Formula 1 may be in the range of one or more of the above values ​​and one or less of the above values.

[0078] For example, the weight-average molecular weight range of the copolymer according to Formula 1 is 50,000 g / mol to 5,000,000 g / mol, 60,000 g / mol to 5,000,000 g / mol, 70,000 g / mol to 5,000,000 g / mol, 80,000 g / mol to 5,000,000 g / mol, 100,000 g / mol to 5,000,000 g / mol, 200,000 g / mol to 5,000,000 g / mol, 1,000,000 g / mol to 5,000,000 g / mol, 2,000,000 g / mol to 5,000,000 g / mol, and 3,000,000 g / mol to It can be prepared in the range of 5,000,000 g / mol or 4,000,000 g / mol to 5,000,000 g / mol.

[0079] <Description of Binder Composition for Coating Separator Membranes of Secondary Batteries>

[0080] A binder composition for coating a separator of a secondary battery according to one embodiment may include particles and the aforementioned binder resin. According to one embodiment, the binder resin may be applied in an amount of about 1 part by weight or more to about 10 parts by weight or less. As a specific example, the content of the binder resin may be applied as 1 part by weight, 1.1 parts by weight, 1.2 parts by weight, 1.3 parts by weight, 1.4 parts by weight, 1.5 parts by weight, 1.6 parts by weight, 1.7 parts by weight, 1.8 parts by weight, 1.9 parts by weight, 2 parts by weight, 3 parts by weight, 4 parts by weight, 5 parts by weight, 6 parts by weight, 7 parts by weight, 8 parts by weight, 9 parts by weight, or 10 parts by weight. The content of the binder resin may be in a range of one or more of the above values ​​and one or less of the above values.

[0081] For example, the content range of the binder resin may be provided in the range of 1 to 10 parts by weight, 2 to 10 parts by weight, 3 to 10 parts by weight, or 4 to 10 parts by weight. The binder resin according to one embodiment can maintain excellent film properties within the above ranges.

[0082] If the binder resin is less than 1 part by weight, there is a risk that the coating layer will easily peel off, and if the binder resin exceeds 10 parts by weight, the heat resistance of the coating layer formed by applying the binder composition may decrease, or the thermal shrinkage rate of the coating layer may increase, and the time it takes for air to pass through the coating layer may be prolonged, which may have a negative effect on electrical conductivity and cell efficiency.

[0083] According to one embodiment, the particles may be applied in an amount of about 80 parts by weight or more to about 97 parts by weight or less. As a specific example, the content of the particles may be applied as 80 parts by weight, 81 parts by weight, 82 parts by weight, 83 parts by weight, 84 parts by weight, 85 parts by weight, 86 parts by weight, 87 parts by weight, 88 parts by weight, 89 parts by weight, 90 parts by weight, 91 parts by weight, 92 parts by weight, 93 parts by weight, 94 parts by weight, 95 parts by weight, 96 parts by weight, or 97 parts by weight. The content of the particles may be in a range of one or more of the above figures and one or less of the above figures.

[0084] For example, the particle content range may be provided in the range of 80 to 97 parts by weight, 80 to 95 parts by weight, 85 to 97 parts by weight, 90 to 97 parts by weight, or 85 to 90 parts by weight.

[0085] According to one embodiment, the particles may comprise any one of inorganic particles, organic particles, and mixtures thereof. In one embodiment, the inorganic particles may comprise at least one selected from metal oxides and metalloid oxides. For example, the inorganic particles may comprise at least one selected from boehmite, alumina, barium sulfate, magnesium oxide, magnesium hydroxide, clay, silica, and titanium dioxide. According to one embodiment, the inorganic particles may be in the form of spheres, plates, fibers, etc.

[0086] In one embodiment, the organic particles may include at least one selected from polystyrene, polyvinylidene fluoride, polymethyl methacrylate, polyacrylonitrile, polyvinylidene, and polyethylene oxide.

[0087] In one embodiment, the binder composition for coating a separator of a secondary battery may further include at least one of a dispersant, an adhesive, a thickener, and a wetting agent. According to one embodiment, the dispersant may be applied in an amount of about 0.1 parts by weight or more to about 5 parts by weight or less. As a specific example, the content of the dispersant may be applied as 0.1 parts by weight, 0.2 parts by weight, 0.3 parts by weight, 0.4 parts by weight, 0.5 parts by weight, 0.6 parts by weight, 0.7 parts by weight, 0.8 parts by weight, 0.9 parts by weight, 1 part by weight, 2 parts by weight, 3 parts by weight, 4 parts by weight, or 5 parts by weight. The content of the dispersant may be in the range of one or more of the above values ​​and one or less of the above values.

[0088] For example, the content range of the dispersant may be provided in the range of 0.1 to 5 parts by weight, 0.5 to 5 parts by weight, 1 to 5 parts by weight, or 1 to 3 parts by weight.

[0089] According to one embodiment, the adhesive may be applied in an amount of about 0.1 parts by weight or more to about 5 parts by weight or less. As a specific example, the content of the adhesive may be applied as 0.1 parts by weight, 0.2 parts by weight, 0.3 parts by weight, 0.4 parts by weight, 0.5 parts by weight, 0.6 parts by weight, 0.7 parts by weight, 0.8 parts by weight, 0.9 parts by weight, 1 part by weight, 2 parts by weight, 3 parts by weight, 4 parts by weight, or 5 parts by weight. The content of the adhesive may be in a range of one or more of the above values ​​and one or less of the above values.

[0090] For example, the content range of the adhesive may be provided in the range of 0.1 to 5 parts by weight, 0.5 to 5 parts by weight, 1 to 5 parts by weight, or 1 to 3 parts by weight.

[0091] According to one embodiment, the thickener may be applied in an amount of about 0.1 parts by weight or more to about 0.5 parts by weight or less. As a specific example, the content of the thickener may be applied as 0.1 parts by weight, 0.2 parts by weight, 0.3 parts by weight, 0.4 parts by weight, or 0.5 parts by weight. The content of the thickener may be in a range of one or more of the above values ​​and one or less of the above values.

[0092] For example, the content range of the thickener can be set to a range of 0.1 to 0.5 parts by weight, 0.1 to 0.4 parts by weight, 0.1 to 0.3 parts by weight, or 0.1 to 0.2 parts by weight.

[0093] According to one embodiment, a wetting agent may be applied in an amount of about 0.1 parts by weight or more to about 1 part by weight or less. As a specific example, the content of the wetting agent may be applied as 0.1 parts by weight, 0.2 parts by weight, 0.3 parts by weight, 0.4 parts by weight, 0.5 parts by weight, 0.6 parts by weight, 0.7 parts by weight, 0.8 parts by weight, 0.9 parts by weight, or 1 part by weight. The content of the wetting agent may be in a range of one or more of the above values ​​and one or less of the above values.

[0094] For example, the content range of the wetting agent may be provided in the range of 0.1 to 1 part by weight, 0.1 to 0.5 parts by weight, 0.1 to 0.4 parts by weight, 0.1 to 0.3 parts by weight, or 0.1 to 0.2 parts by weight.

[0095] Explanation of secondary battery separators

[0096] A separator according to one embodiment may include a porous substrate and a coating layer formed by applying the aforementioned binder composition to one or both sides of the porous substrate. For example, the coating layer may be formed only on the upper or lower surface of the porous substrate, or the coating layer may be formed on both the upper and lower surfaces, respectively.

[0097] According to one embodiment, the thickness of the coating layer formed on one surface of a porous substrate may be about 1.5 μm or more to about 2 μm or less. As a specific example, the thickness of the coating layer may be applied as 1.5 μm, 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm, or 2 μm. The thickness of the coating layer may be a range of one or more of the above values ​​and one or less of the above values. For example, the thickness range of the coating layer may be provided as a range of 1.5 μm to 2 μm, 1.6 μm to 2 μm, 1.7 μm to 2 μm, 1.8 μm to 2 μm, or 1.9 μm to 2 μm.

[0098] According to one embodiment, the separator may have a coating layer formed on one surface of a porous substrate (e.g., the upper or lower surface of the porous substrate). In one embodiment, after leaving the separator, on which a coating layer is formed on one surface of a porous substrate, at 150°C for 1 hour, the longitudinal shrinkage rate and transverse shrinkage rate of the separator are measured, and the average value of the measured longitudinal shrinkage rate and transverse shrinkage rate may be less than 5%. Here, the average value of the longitudinal shrinkage rate and transverse shrinkage rate refers to the value obtained by adding the longitudinal shrinkage rate and the transverse shrinkage rate and dividing by 2.

[0099] In one embodiment, the longitudinal shrinkage rate value (%) of the separator can be calculated by the following mathematical formula 2.

[0100] [Mathematical Formula 2]

[0101]

[0102] In one embodiment, the transverse shrinkage rate value (%) of the separator can be calculated by the following mathematical formula 3.

[0103] [Mathematical Formula 3]

[0104]

[0105] In one embodiment, the longitudinal direction of the separator is the direction in which the separator is manufactured, and refers to the direction of travel of the machine for forming the separator (i.e., the MD (Machine Direction) direction) or the length direction of the separator. In one embodiment, the transverse direction of the separator refers to a direction perpendicular to the direction of travel of the machine (i.e., the TD (Transverse Direction) direction) or the width direction of the separator. The transverse direction of the separator may be a direction perpendicular to the longitudinal direction of the separator.

[0106] According to one embodiment, a separator with a coating layer formed on one surface of a porous substrate is left at 150°C for 1 hour, and then the longitudinal shrinkage rate and transverse shrinkage rate values ​​of the separator are measured, and the average value of the measured longitudinal shrinkage rate and transverse shrinkage rate values ​​is less than about 5%, about 4.9% or less, about 4.8% or less, about 4.7% or less, about 4.6% or less, about 4.5% or less, about 4.4% or less, about 4.3% or less, about 4.2% or less, about 4.1% or less, about 4% or less, about 3.9% or less, about 3.8% or less, about 3.7% or less, about 3.6% or less, about 3.5% or less, about 3.4% or less, about 3.3% or less, about 3.2% or less, about 3.1% or less, about 3% or less, about 2.9% or less, about 2.8% It may be less than, about 2.7% or less, about 2.6% or less, about 2.5% or less, about 2.4% or less, about 2.3% or less, about 2.2% or less, about 2.1% or less, about 2% or less, about 1.9% or less, about 1.8% or less, about 1.7% or less, about 1.6% or less, about 1.5% or less, about 1.4% or less, about 1.3% or less, about 1.2% or less, about 1.1% or less, about 1% or less, about 0.9% or less, about 0.8% or less, about 0.7% or less, about 0.6% or less, or about 0.5% or less.

[0107] After leaving a separator with a coating layer formed on one side of a porous substrate at 150°C for 1 hour, the longitudinal shrinkage rate and transverse shrinkage rate of the separator are measured, and the lower limit of the average value obtained by adding the measured longitudinal shrinkage rate and transverse shrinkage rate and dividing by 2 is not specifically limited, but, for example, it may be about 0.1% or more, about 0.2% or more, about 0.3% or more, or about 0.4% or more.

[0108] After leaving a separator with a coating layer formed on one side of a porous substrate at 150°C for 1 hour, the longitudinal shrinkage rate and transverse shrinkage rate values ​​of the separator are measured, and the average value of the measured longitudinal shrinkage rate and transverse shrinkage rate values ​​may be in the range of one or more of the above values ​​and one or less of the above values.

[0109] For example, after leaving a separator with a coating layer formed on one side of a porous substrate at 150°C for 1 hour, the longitudinal shrinkage rate and transverse shrinkage rate values ​​of the separator are measured, and the range of the average value obtained by adding the measured longitudinal shrinkage rate and transverse shrinkage rate values ​​and dividing by 2 is 0.1% or more to less than 5%, 0.1% or more to 4.9% or less, 0.1% or more to 4.8% or less, 0.1% or more to 4.7% or less, 0.1% or more to 4.6% or less, 0.1% or more to 4.5% or less, 0.1% or more to 4.4% or less, 0.1% or more to 4.3% or less, 0.1% or more to 4.2% or less, 0.1% or more to 4.1% or less, 0.1% or more to 4% or less, 0.1% or more to 3.9% or less, and 0.5% or more to It may be 3.8% or less, 1% or more to 3.7% or less, 1.2% or more to 3.8% or less, 1.3% or more to 3.8% or less, or 1.4% or more to 3.8% or less.

[0110] According to one embodiment, the difference obtained by subtracting the air permeability value of the porous substrate from the air permeability value of the separator may be less than 20 seconds / 100cc. Here, the air permeability value of the porous substrate refers to the value measured for the air permeability of the porous substrate without forming a coating layer on the surface of the porous substrate (e.g., both sides of the porous substrate). In this specification, air permeability refers to the air permeability of 100cc of air to 1 inch 2 It refers to the time it takes to pass through a membrane of an area.

[0111] According to one embodiment, the difference obtained by subtracting the air permeability value of the porous substrate from the air permeability value of the separator is less than about 20 sec / 100cc, about 19.9 sec / 100cc or less, about 19.8 sec / 100cc or less, about 19.7 sec / 100cc or less, about 19.6 sec / 100cc or less, about 19.5 sec / 100cc or less, about 19.4 sec / 100cc or less, about 19.3 sec / 100cc or less, about 19.2 sec / 100cc or less, about 19.1 sec / 100cc or less, about 19 sec / 100cc or less, about 18 sec / 100cc or less, about 17 sec / 100cc or less, about 16 sec / 100cc or less, about 15 sec / 100cc or less, about 14 sec / 100cc or less, about It may be 13 seconds / 100cc or less, about 12 seconds / 100cc or less, about 11 seconds / 100cc or less, or about 10 seconds / 100cc or less.

[0112] The lower limit of the difference value obtained by subtracting the air permeability value of the porous substrate from the air permeability value of the separator is not specifically limited, but, for example, it may be about 0.1 sec / 100cc or more, about 0.5 sec / 100cc or more, about 1 sec / 100cc or more, about 2 sec / 100cc or more, about 3 sec / 100cc or more, about 4 sec / 100cc or more, about 5 sec / 100cc or more, about 6 sec / 100cc or more, about 7 sec / 100cc or more, about 8 sec / 100cc or more, or about 9 sec / 100cc or more.

[0113] According to one embodiment, the difference value obtained by subtracting the air permeability value of the porous substrate from the air permeability value of the separation membrane may be in the range of one or more of the above values ​​and one or less of the above values.

[0114] For example, according to one embodiment, the range of the difference value obtained by subtracting the air permeability value of the porous substrate from the air permeability value of the separator is 0.1 sec / 100cc or more to less than 20 sec / 100cc, 0.1 sec / 100cc or more to about 19.9 sec / 100cc or less, 0.1 sec / 100cc or more to about 19.8 sec / 100cc or less, 0.1 sec / 100cc or more to about 19.7 sec / 100cc or less, 0.1 sec / 100cc or more to about 19.6 sec / 100cc or less, 0.1 sec / 100cc or more to about 19.5 sec / 100cc or less, 0.1 sec / 100cc or more to about 19.4 sec / 100cc or less, 0.1 sec / 100cc or more to about 19.3 sec / 100cc or less, It may be 0.1 second / 100cc or more to about 19.2 seconds / 100cc or less, 0.1 second / 100cc or more to about 19.1 seconds / 100cc or less, 0.1 second / 100cc or more to about 19 seconds / 100cc or less, 1 second / 100cc or more to about 18 seconds / 100cc or less, 10 seconds / 100cc or more to about 17 seconds / 100cc or less, 1 second / 100cc or more to about 16 seconds / 100cc or less, 1 second / 100cc or more to about 15 seconds / 100cc or less, or 1 second / 100cc or more to about 14 seconds / 100cc or less.

[0115] <Explanation of secondary batteries>

[0116] A secondary battery according to one embodiment may include a separator, a positive electrode, a negative electrode, and an electrolyte. A separator according to one embodiment may be manufactured by applying a coating binder composition to one or both sides of a porous substrate and drying it to form a coating layer.

[0117] In one embodiment, the method of forming a coating layer by applying a coating binder composition to a porous substrate is not particularly limited. For example, a coating layer can be formed using a dip coating method, a die coating method, a roll coating method, a comma coating method, etc. When forming a coating layer by applying a coating binder composition to a porous substrate, different coating methods may be mixed and used.

[0118] In one embodiment, the porous substrate is a membrane having a plurality of pores formed therein. The material of the porous substrate may include at least one of polypropylene, polyethylene, polyolefin, mixtures thereof, and copolymers thereof.

[0119] According to one embodiment, a secondary battery can be manufactured by installing a positive electrode, a negative electrode, and a separator inside a battery case and introducing an electrolyte into the battery case.

[0120] In one embodiment, the secondary battery may include a lithium secondary battery. For example, the secondary battery may include at least one of a lithium-ion battery and a lithium-ion polymer battery.

[0121] <Description of the method for manufacturing binder resin for coating separators of secondary batteries>

[0122] FIG. 1 is a flowchart schematically illustrating a method for manufacturing a binder resin for coating a separator of a secondary battery according to one embodiment of the present disclosure. Referring to FIG. 1, the method for manufacturing a binder resin for coating a separator of a secondary battery according to one embodiment may include a polymerization step (S101).

[0123] In step S101, a plurality of monomers can be copolymerized. For example, in this step, methyl methacrylate, butyl acrylate, ethylhexyl acrylate, hydroxyethyl methacrylate, acrylic acid, glycidyl methacrylate, and a crosslinking agent can be copolymerized.

[0124] According to one embodiment, in step S101, a binder resin can be prepared using various known polymerization methods. For example, the binder resin can be prepared by emulsion polymerization, suspension polymerization, dispersion polymerization, a two-step polymerization method using a seed, etc. In step S101, the polymerization temperature and polymerization time may be changed depending on the polymerization method or the type of polymerization initiator used. For example, in step S101, the polymerization temperature may be about 30°C or higher to about 100°C or lower, and the polymerization time may be about 30 minutes or higher to about 20 hours or lower.

[0125] When applying a two-step polymerization method using a seed in step S101, acrylic acid is added to a solvent and stirred to form a pre-emulsion, and then methyl methacrylate, butyl acrylate, ethylhexyl acrylate, hydroxyethyl methacrylate, glycidyl methacrylate, and a crosslinking agent are added to the pre-emulsion to polymerize.

[0126] In step S101, when copolymerizing a plurality of monomers, additional components such as a polymerization initiator, solvent, and emulsifier may be added. In one embodiment, the polymerization initiator is not limited to a specific type as long as it can cause radical generation. For example, the polymerization initiator may include at least one selected from ammonium persulfate, potassium persulfate, sodium persulfate, benzoyl peroxide, butyl hydroperoxide, cumene hydroperoxide, azobisisobutyronitrile, and mixtures thereof.

[0127] In one embodiment, the solvent may include water. For copolymerization, it is also possible to use other known types of solvents or to use a mixture of different types of solvents.

[0128] In one embodiment, the emulsifier may include at least one of anionic emulsifiers, nonionic emulsifiers, and mixtures thereof. The anionic emulsifier may include at least one of phosphate-based, carboxylate-based, sulfate-based, succinate-based, sulfosuccinate-based, sulfonate-based, and disulfonate-based emulsifiers.

[0129] According to one embodiment, the anionic emulsifier may include at least one of sodium alkyl sulfate, sodium polyoxyethylene sulfate, sodium lauryl ether sulfate, sodium polyoxyethylene lauryl ether sulfate, sodium lauryl sulfate, sodium alkyl sulfonate, sodium alkyl ether sulfonate, and sodium alkylbenzene sulfonate.

[0130] In one embodiment, the nonionic emulsifier may include at least one of polyoxyethylene glycol, polyoxyethylene glycol methyl ether, polyoxyethylene monoallyl ether, polypropylene glycol, polyoxyethylene stearyl ether, and polyoxyethylene octyl ether.

[0131] The present disclosure is described in more detail below through specific embodiments and experimental examples. The following embodiments and experimental examples are merely illustrative to aid in understanding the present disclosure, and therefore the scope of the rights of the present disclosure is not limited thereto.

[0132] Manufacture of binder resin

[0133] <Examples 1–22 and Comparative Examples 1–12>

[0134] Copolymer binder resins for each example and comparative example were prepared by adding a polymerization initiator (potassium persulfate), 25 v / v% ammonia water, and an emulsifier (sodium lauryl sulfate) to water along with methyl methacrylate (MMA), butyl acrylate (BA), ethylhexyl acrylate (2-EHA), hydroxyethyl methacrylate (2-HEMA), acrylic acid (AA), a crosslinking agent (hexanediol diacrylate (HDDA)), and glycidyl methacrylate (GMA), which were weighed according to the input amounts (units are weight%) of each component listed in Tables 1 to 6 below, maintaining the temperature at 80°C for 4 hours under a nitrogen atmosphere, and carrying out a polymerization reaction.

[0135] division MMA BA 2-EHA 2-HEMA AA HDDA GMA Example 1 10 25 25 15 3 1 21 Example 2 15 25 25 10 3 1 21 Example 3 20 25 20 10 3 1 21 Example 4 25 20 20 10 3 1 21 Comparative Example 1 5 25 25 20 3 1 21 Comparative Example 2 30 20 20 5 3 1 21

[0136] division MMA BA 2-EHA 2-HEMA AA HDDA GMA Example 5 17 13 25 20 3 1 21 Example 6 11 19 25 20 3 1 21 Example 7 11 25 20 19 3 1 21 Comparative Example 3 18 7 25 25 3 1 21 Comparative Example 4 11 31 20 13 3 1 21

[0137] division MMA BA 2-EHA 2-HEMA AA HDDA GMA Example 8 17 25 13 20 3 1 21 Example 9 11 25 19 20 3 1 21 Example 10 11 20 25 19 3 1 21 Comparative Example 5 18 25 7 25 3 1 21 Comparative Example 6 11 20 31 13 3 1 21

[0138] division MMA BA 2-EHA 2-HEMA AA HDDA GMA Example 11 20 25 25 5 3 1 21 Example 12 15 25 25 10 3 1 21 Example 13 10 25 25 15 3 1 21 Example 14 10 25 20 20 3 1 21 Comparative Example 7 25 25 25 0 3 1 21 Comparative Example 8 10 20 20 25 3 1 21

[0139] division MMA BA 2-EHA 2-HEMA AA HDDA GMA Example 15 15 25 20 17 1 1 21 Example 16 15 25 20 15 3 1 21 Example 17 15 25 20 13 5 1 21 Comparative Example 9 15 25 20 18 0 1 21 Comparative Example 10 15 25 20 11 7 1 21

[0140] division MMA BA 2-EHA 2-HEMA AA HDDA GMA Example 18 21 25 25 20 3 1 5 Example 19 16 25 25 20 3 1 10 Example 20 16 25 25 15 3 1 15 Example 21 16 25 25 10 3 1 20 Example 22 16 25 25 5 3 1 25 Comparative Example 11 25 25 25 20 4 1 0 Comparative Example 12 16 25 20 5 3 1 30

[0141] Preparation of binder compositions according to each example and comparative example

[0142] A binder composition was prepared by combining 1.3 parts by weight of binder resin, 97 parts by weight of boehmite, 1 part by weight of dispersant, 0.5 parts by weight of adhesive, 0.5 parts by weight of wetting agent, and 0.2 parts by weight of thickener according to each example and comparative example.

[0143] Preparation of specimens according to each example and comparative example

[0144] Polyethylene fabric with a thickness of 9 μm was prepared for each example and comparative example, and a binder composition according to each example and comparative example was applied to the upper surface of the polyethylene fabric and dried to form a coating layer with a thickness of 2 μm.

[0145] Heat resistance evaluation

[0146] After leaving specimens for each example and comparative example at 150°C for 1 hour, the longitudinal shrinkage rate and transverse shrinkage rate of the specimens were measured using Equation 2 and Equation 3. If the average value of the measured longitudinal shrinkage rate and transverse shrinkage rate was less than 5%, the heat resistance was evaluated as good, and if it was 5% or more, the heat resistance was evaluated as poor. The results are listed in Tables 7, 8, 9, 10, 11, and 12 below.

[0147] Air permeability evaluation

[0148] The air permeability of the specimens for each example and comparative example was measured in accordance with JIS P8117, and a Gurley tester was used as the measuring device. The air permeability of the polyethylene fabric was measured without forming a coating layer on the surface of the polyethylene fabric with a thickness of 9 μm. After measuring the air permeability of the specimens for each example and comparative example, if the difference between the air permeability value of the specimen and the air permeability value of the polyethylene fabric was less than 20 seconds / 100cc, the air permeability was evaluated as good, and if the difference was 20 seconds / 100cc or more, the air permeability was evaluated as poor, and the results are listed in Tables 7, 8, 9, 10, 11, and 12 below.

[0149] Adhesion strength evaluation

[0150] The adhesive strength (unit is gf / 15mm) was measured when the coating layer was peeled off from the polyethylene fabric at a speed of 200 m / min using a tensile testing machine (TA.XTplusC Texture Analyser) at room temperature (20~25℃). If the measured adhesive strength was 10 gf / 15mm or higher, the adhesive strength was evaluated as good, and if the measured adhesive strength was less than 10 gf / 15mm, the adhesive strength was evaluated as poor. The results are listed in Tables 7, 8, 9, 10, 11, and 12 below.

[0151] division heat resistance Air permeability Adhesion Example 1 Good Good Good Example 2 Good Good Good Example 3 Good Good Good Example 4 Good Good Good Comparative Example 1 - - - Comparative Example 2 error error error

[0152] Referring to the results in Table 7, it was confirmed that the heat resistance, air permeability, and adhesion of the examples were generally good. Comparative Example 1, in which the methyl methacrylate content was less than 10 wt%, could not be prepared as a binder composition because gelation occurred during the copolymerization process of the binder resin, and the physical properties of the specimen could not be evaluated. Comparative Example 2, in which the methyl methacrylate content exceeded 25 wt%, was confirmed to have poor heat resistance, air permeability, and adhesion of the specimen.

[0153] division heat resistance Air permeability Adhesion Example 5 Good Good Good Example 6 Good Good Good Example 7 Good Good Good Comparative Example 3 error error error Comparative Example 4 error error Good

[0154] Referring to the results in Table 8, it was confirmed that the heat resistance, air permeability, and adhesion of the examples were generally good. Comparative Example 3, which had a butyl acrylate content of less than 13 wt%, had poor heat resistance, air permeability, and adhesion, and Comparative Example 4, which had a butyl acrylate content exceeding 25 wt%, had poor heat resistance and air permeability.

[0155] division heat resistance Air permeability Adhesion Example 8 Good Good Good Example 9 Good Good Good Example 10 Good Good Good Comparative Example 5 error error Good Comparative Example 6 error error Good

[0156] Referring to the results in Table 9, it was confirmed that the heat resistance, air permeability, and adhesion of the examples were generally good. Comparative Example 5, which had an ethylhexyl acrylate content of less than 13 wt%, had poor heat resistance and air permeability, and Comparative Example 6, which had an ethylhexyl acrylate content of more than 25 wt%, had poor heat resistance and air permeability.

[0157] division heat resistance Air permeability Adhesion Example 11 Good Good Good Example 12 Good Good Good Example 13 Good Good Good Example 14 Good Good Good Comparative Example 7 error error Good Comparative Example 8 error error Good

[0158] Referring to the results in Table 10, it was confirmed that the heat resistance, air permeability, and adhesion of the examples were generally good. Comparative Example 7, in which the content of hydroxyethyl methacrylate was less than 5 wt%, had poor heat resistance and air permeability, and Comparative Example 8, in which the content of hydroxyethyl methacrylate exceeded 20 wt%, had poor heat resistance and air permeability.

[0159] division heat resistance Air permeability Adhesion Example 15 Good Good Good Example 16 Good Good Good Example 17 Good Good Good Comparative Example 9 - - - Comparative Example 10 - - -

[0160] Referring to the results in Table 11, it was confirmed that the heat resistance, air permeability, and adhesion of the examples were generally good. Comparative Examples 9 and 10, in which the acrylic acid content fell outside the aforementioned numerical range, could not be manufactured into a binder composition because gelation occurred during the copolymerization process of the binder resin, and the physical properties of the specimens could not be evaluated.

[0161] division heat resistance Air permeability Adhesion Example 18 Good Good Good Example 19 Good Good Good Example 20 Good Good Good Example 21 Good Good Good Example 22 Good Good Good Comparative Example 11 error error Good Comparative Example 12 - - -

[0162] Referring to the results in Table 12, it was confirmed that the heat resistance, air permeability, and adhesion of the examples were generally good. Comparative Example 11, which had a glycidyl methacrylate content of less than 5 wt%, had poor heat resistance and air permeability, and Comparative Example 12, which had a glycidyl methacrylate content exceeding 25 wt%, could not be manufactured into a binder composition because gelation occurred during the copolymerization process of the binder resin, and the physical properties of the specimen could not be evaluated.

[0163] As described above, according to various embodiments of the present disclosure, the average value of the longitudinal shrinkage rate and the transverse shrinkage rate of the membrane measured after leaving the membrane at 150°C for 1 hour is less than 5%, so the thermal stability of the membrane is excellent.

[0164] According to various embodiments of the present disclosure, the difference between the air permeability value of a separator with a coating layer formed thereon and the air permeability value of a porous substrate without a coating layer formed thereon is less than 20 seconds / 100cc. That is, even if a separator is manufactured by forming a coating layer on the surface of a porous substrate, the level of air passing through the separator is excellent, so there is little possibility that the coating layer will have a negative effect on the electrical conductivity of the secondary battery.

[0165] According to various embodiments of the present disclosure, the adhesion of the coating layer coated on the separator is excellent, so the coating layer can be prevented from separating from the separator.

[0166] As explained above, the specific description of the present disclosure has been provided through embodiments, but since the above-described embodiments are merely preferred examples of the present disclosure, the present disclosure should not be understood as being limited only to the above embodiments, and the scope of the rights of the present disclosure should be understood as the claims set forth below and their equivalents.

Claims

Claim 1 A binder resin for coating a separator of a secondary battery, wherein the resin is a copolymer formed by copolymerizing a plurality of monomers, and the plurality of monomers comprises 10 to 25 wt% methyl methacrylate, 13 to 25 wt% butyl acrylate, 13 to 25 wt% ethylhexyl acrylate, 5 to 20 wt% hydroxyethyl methacrylate, 1 to 5 wt% acrylic acid, 5 to 25 wt% glycidyl methacrylate, and 0.1 to 1 wt% crosslinking agent. Claim 2 delete Claim 3 A binder resin for coating a separator of a secondary battery, characterized in that, in claim 1, the crosslinking agent comprises hexanediol diacrylate. Claim 4 delete Claim 5 A binder composition for coating a separator of a secondary battery, comprising a binder resin according to any one of claims 1 and 3; and particles; wherein the particles comprise at least one of inorganic particles and organic particles. Claim 6 A separation membrane characterized by comprising: a porous substrate; and a coating layer formed by applying a binder composition according to claim 5 to one or both sides of the porous substrate. Claim 7 A separator according to claim 6, wherein the separator has a coating layer formed on one surface of the porous substrate, and the average value of the longitudinal shrinkage rate and the transverse shrinkage rate of the separator measured after leaving the separator at 150°C for 1 hour is less than 5%, and the difference value obtained by subtracting the air permeability value of the porous substrate from the air permeability value of the separator is less than 20 sec / 100cc. Claim 8 A secondary battery characterized by including a separator according to claim 6. Claim 9 In claim 8, the secondary battery is characterized in that the secondary battery includes a lithium secondary battery. Claim 10 A method for manufacturing a binder resin for coating a separator of a secondary battery, comprising a polymerization step of copolymerizing a plurality of monomers; wherein the plurality of monomers comprise 10 to 25 wt% methyl methacrylate, 13 to 25 wt% butyl acrylate, 13 to 25 wt% ethylhexyl acrylate, 5 to 20 wt% hydroxyethyl methacrylate, 1 to 5 wt% acrylic acid, 5 to 25 wt% glycidyl methacrylate, and 0.1 to 1 wt% crosslinking agent.

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