Copolymer for separator and secondary battery including same

Abstract

The present invention relates to a copolymer containing 3 wt % or more and 30 wt % or less of a monomer unit containing a sulfide group, a monomer unit containing a sulfonate group, a monomer unit containing a sulfone group, a monomer unit containing a fluoro group, a monomer unit containing a perfluoroalkyl group, or a combination thereof, based on 100 wt % of the total weight of the copolymer, and a slurry composition, separator, and secondary battery containing the copolymer.

Description

[Technical Field]

[0001] The present invention relates to a copolymer, a slurry composition containing the copolymer, a separator, and a secondary battery. [Background technology]

[0002] Lithium secondary batteries have a high energy density and are widely used in the electrical, electronic, communication and computer industries. Following small lithium secondary batteries for portable electronic devices, their application is expanding to include large-capacity secondary batteries for hybrid and electric vehicles.

[0003] Lithium secondary batteries are insulated by a separator, but internal or external abnormalities or impacts to the battery can cause a short circuit between the anode and cathode, which can lead to heat generation and explosion, so ensuring the thermal and chemical safety of the separator is extremely important.

[0004] Currently, polyolefin films are widely used as separators, but polyolefins have drawbacks such as severe heat shrinkage at high temperatures and poor mechanical properties.

[0005] In order to improve the safety of such polyolefin-based separators, porous separators have been developed in which a polyolefin porous substrate film is coated with a mixture of inorganic particles and a binder.

[0006] That is, in order to suppress thermal shrinkage of polyolefin-based separators due to high temperatures and battery instability due to dendrites, inorganic particles are coated on one or both sides of a porous separator substrate together with a binder. This allows the inorganic particles to suppress the shrinkage rate of the substrate, and the coating layer also makes it possible to produce a safer separator.

[0007] To ensure excellent battery characteristics, the coating layer must be uniformly coated and must have strong adhesion to the substrate, which in turn improves the performance and safety of secondary batteries. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Korean Patent No. 10-1430975 [Patent Document 2] Korean Patent Publication No. 10-2006-0072065 Summary of the Invention

[0009] Therefore, the present invention aims to provide a slurry composition using a copolymer, which has excellent adhesive strength between inorganic materials and electrodes on a porous substrate.

[0010] The present invention also provides a separator having excellent adhesive strength and electrical properties by applying the slurry composition, and a battery having excellent performance using the separator.

[0011] However, the problems to be solved by the present application are not limited to those mentioned above, and other problems not mentioned will be clearly understood by those skilled in the art from the following description. [Means for solving the problem]

[0012] In one aspect of the present application, the copolymer contains 3 wt % or more and 30 wt % or less of a monomer unit containing a sulfide group, a monomer unit containing a sulfonate group, a monomer unit containing a sulfone group, a monomer unit containing a fluoro group, a monomer unit containing a perfluoroalkyl group, or a combination thereof, based on 100 wt % of the total weight of the copolymer. A copolymer is provided.

[0013] Another aspect of the present application is a method for producing the copolymer; Inorganic particles; A slurry composition is provided.

[0014] Another aspect of the present application includes the slurry composition, A separation membrane is provided.

[0015] Another aspect of the present invention is a membrane comprising the separation membrane. A secondary battery is provided. [Effects of the Invention]

[0016] The copolymer of the present invention can enhance the adhesive strength of the inorganic material and electrodes to the separator substrate, and the high adhesive strength can increase the inorganic material content, thereby improving the heat resistance of the separator.

[0017] Furthermore, by improving the adhesive strength, it is possible to minimize the defect rate and void formation that may occur during battery assembly.

[0018] In addition, it can impart excellent air permeability and electrical resistance properties, thereby improving ion conductivity in the electrolyte of the battery, reaction safety, and life characteristics. DETAILED DESCRIPTION OF THE INVENTION

[0019] The functions and effects of the present invention will be described in more detail below through specific examples of the present invention, however, these examples are presented only as examples of the present invention and do not limit the scope of the invention.

[0020] Prior to this, the terms and words used in this specification and claims should not be interpreted in a limited manner based on their ordinary or dictionary meanings, but should be interpreted in a meaning and concept that is consistent with the technical idea of ​​the invention, in accordance with the principle that an inventor can appropriately define the concept of a term in order to best explain his or her invention.

[0021] Therefore, it should be understood that the configurations of the embodiments described in this specification are merely the most preferred embodiments of the present invention and do not represent the entire technical idea of ​​the present invention, and that there may be various equivalents and modifications that can replace them at the time of filing this application.

[0022] In this specification, the singular includes the plural unless the context clearly dictates otherwise. In this specification, the terms "comprises," "includes," "has," and the like are intended to specify the presence of embodied features, numbers, steps, components, or combinations thereof, and should be understood as not precluding the presence or additional possibility of one or more other features, numbers, steps, components, or combinations thereof.

[0023] In the present specification, when numerical ranges are indicated as "a to b" and "a to b," "to" and "to" are defined as ≧a and ≦b.

[0024] The copolymer of one aspect of the present invention may contain, based on 100% by weight of the total weight of the copolymer, 3% by weight or more and 30% by weight or less of a monomer unit containing a sulfide group, a monomer unit containing a sulfonate group, a monomer unit containing a sulfone group, a monomer unit containing a fluoro group, a monomer unit containing a perfluoroalkyl group, or a combination thereof.

[0025] The monomer unit containing a sulfide group, a sulfonate group, or a sulfone group may be, for example, a monomer unit containing a sulfide group, a sulfonate group, a sulfone group, a sulfonyl ester group, a sulfonamide group, a sulfonimide group, a sulfonyl azide group, a sulfonyl hydrazide group, a sulfonyl aziridine group, a sulfonyl azitidine group, a sulfonyl carbamate group, a sulfonylurea group, or a sulfonyl halide group, but is not limited thereto.

[0026] The monomer unit containing a sulfide group, the monomer unit containing a sulfonate group, the monomer unit containing a sulfone group, the monomer unit containing a fluoro group, the monomer unit containing a perfluoroalkyl group, or a combination thereof may have a large dipole moment.

[0027] In a covalent bond, electrons are attracted more to the atom with the greater electronegativity of the two atoms. At this time, the atom with the greater electronegativity carries a (-) charge, while the atom with the lesser electronegativity carries a (+) charge. This is called a dipole, and its magnitude is called the dipole moment.

[0028] Meanwhile, a copolymer containing a monomer unit with a large dipole moment can induce polarization and exert electrostatic attraction between the inorganic material and the porous substrate or electrode, thereby increasing adhesive strength.

[0029] If the content of the sulfide group-containing monomer unit, sulfonate group-containing monomer unit, sulfone group-containing monomer unit, fluoro group-containing monomer unit, perfluoroalkyl group-containing monomer unit, or a combination thereof, which has a large dipole moment, is below the content range of the present application, the adhesive strength may decrease, and the properties of the separation membrane may be deteriorated.

[0030] If the content of the sulfide group-containing monomer unit, sulfonate group-containing monomer unit, sulfone group-containing monomer unit, fluoro group-containing monomer unit, perfluoroalkyl group-containing monomer unit, or a combination thereof, which has a large dipole moment, exceeds the content range of the present application, the reaction safety may decrease and the properties of the separation membrane may deteriorate.

[0031] In one embodiment, the copolymer may further include an acrylonitrile-based monomer unit, an acrylate-based monomer unit, an acrylic acid-based monomer unit, a vinyl acetate-based monomer unit, and a styrene-based monomer unit.

[0032] In one embodiment, the copolymer may contain, based on a total weight of the copolymer (100 wt%), 3 wt% to 15 wt% of the acrylonitrile-based monomer units, 40 wt% to 70 wt% of the acrylate-based monomer units, 1 wt% to 10 wt% of the acrylic acid-based monomer units, 1 wt% to 15 wt% of the vinyl acetate-based monomer units, and 10 wt% to 30 wt% of the styrene-based monomer units.

[0033] If the content of the acrylonitrile-based monomer unit is above or below the range of the present invention, the dispersibility of the polymer particles and the inorganic slurry may be reduced, or the adhesive strength may be reduced.

[0034] If the content of the acrylate-based monomer unit is above or below the range of the present invention, the adhesive strength may be reduced.

[0035] If the content of the acrylic acid-based monomer unit is above or below the range of the present invention, polymer aggregation and precipitation or a decrease in adhesive strength may occur.

[0036] If the content of the vinyl acetate monomer unit is above or below the range of the present invention, safety issues such as safety and storage safety may occur.

[0037] If the styrene monomer unit content is above or below the range of the present application, it may cause a decrease in wetting or adhesive strength.

[0038] In one embodiment, the acrylate-based monomer unit may be methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, propyl acrylate, propyl methacrylate, isopropyl acrylate, isopropyl methacrylate, butyl acrylate, butyl methacrylate, sec-butyl acrylate, sec-butyl methacrylate, tert-butyl acrylate, tert-butyl methacrylate, ethyl hexyl acrylate, ethyl hexyl methacrylate, lauryl acrylate, or lauryl methacrylate. The polymerizable copolymer may be formed by polymerizing one or more selected from the group consisting of stearyl acrylate, stearyl acrylate, and stearyl methacrylate.

[0039] The acrylic acid-based monomer unit may be formed by polymerizing at least one selected from the group consisting of acrylic acid and methacrylic acid.

[0040] Meanwhile, the acrylonitrile-based monomer unit may be formed by polymerizing at least one selected from the group consisting of acrylonitrile and methacrylonitrile.

[0041] The vinyl acetate-based monomer unit and the styrene-based monomer unit may be formed by polymerizing vinyl acetate and styrene, respectively.

[0042] In one embodiment, the sulfonate group-containing monomer unit may be formed by polymerizing sodium vinyl sulfonate, and the perfluoroalkyl group-containing monomer unit may be formed by polymerizing one or more selected from the group consisting of 2-(perfluorooctyl)ethyl acrylate and 2-(perfluorooctyl)ethyl methacrylate.

[0043] In one embodiment, the acrylic acid-based monomer unit may be combined with an alkali metal.

[0044] That is, the carboxylate group of the acrylic acid-based monomer unit may be bonded to an alkali metal. On the other hand, the weight ratio of the alkali metal to the copolymer (weight of one or more selected from the group consisting of the alkali metal and acetate salt compounds containing an alkali metal:weight of the copolymer) may be 0.1 to 15:100.

[0045] For example, the weight ratio of the alkali metal to the copolymer may be 1 to 10:100.

[0046] If the weight ratio of the alkali metal to the copolymer is higher or lower than the weight ratio of the present invention, the adhesive properties and heat resistance of the separator may be reduced, particularly the peel adhesion strength and electrode adhesion strength of the separator may be reduced.

[0047] The adhesive strength of the separator containing the alkali metal may be determined by the strength of the cohesive force and repulsive force between elements.

[0048] The copolymer of the present invention may have different adhesive strength to inorganic materials or electrode depending on the content of the alkali metal, depending on the strength of cohesion, adhesive strength, and repulsion between elements.

[0049] When the alkali metal is used to prepare a binder copolymer, the cohesive force between elements is increased, resulting in a balance between adhesion and cohesive force, thereby improving the overall adhesive strength. However, if an excessive amount is added, the cohesive force may decrease, resulting in a decrease in the overall adhesive strength.

[0050] Meanwhile, the improvement in adhesive strength of the copolymer to inorganic materials means an increase in adhesive strength between the inorganic materials and the substrate, which means that the heat resistance of the separator can be improved by increasing the amount of inorganic materials.

[0051] The electrode adhesive strength of the separator can reduce the defect rate caused by stacking electrodes during battery assembly, minimize the formation of voids, and improve ionic conductivity in the electrolyte.

[0052] In addition, when a binder layer is coated separately on an inorganic coating layer, the electrode adhesion can be maximized, which ultimately minimizes the battery defect rate and further improves battery performance.

[0053] In one embodiment, the copolymer may include a monomer repeat unit represented by the following Formula 1: [ka] In the above Chemical Formula 1, R1 and R2 are each independently hydrogen, a linear or branched hydrocarbon having 1 to 4 carbon atoms, or a combination thereof; R3 is a linear or branched hydrocarbon having 1 to 20 carbon atoms containing one or more fluoro atoms; R4 is hydrogen, an alkali metal, or a linear or branched hydrocarbon having 1 to 20 carbon atoms; R5 is a sulfide group, a sulfonate group, a sulfone group, a sulfonyl ester group, a sulfonamide group, a sulfonimide group, a sulfonyl azide group, a sulfonyl hydrazide group, a sulfonyl aziridine group, a sulfonyl azididine group, a sulfonyl carbamate group, a sulfonylurea group, a sulfonyl halide group, or a combination thereof, and a+b+c+d+e+f may be 1.

[0054] However, a+e may be 0.03 or more and 0.3 or less.

[0055] In the above Chemical Formula 1, a, b, c, d, e, and f correspond to the weight fraction of each monomer unit, and the sum of the weight fractions of each monomer unit is 1.

[0056] The alkali metal may be, but is not limited to, Li, Na or K.

[0057] In one embodiment, R1 and R2 are each independently at least one selected from the group consisting of hydrogen and methyl, and R4 is selected from the group consisting of hydrogen, methyl, ethyl, propyl, isopropyl, butyl, sec-butyl, tert-butyl, ethylhexyl, n-pentyl, n-hexyl, n-heptyl, n-octyl, 2-ethylhexyl, n-nonyl, n-decyl, n-undecyl, lauryl, n-dodecyl, n-tridecyl, n-tetradecyl, n-pentadecyl, cetyl, n-hexadecyl, n-heptadecyl, stearyl, and n-octadecyl. and may be any one or more selected from the group consisting of decyl, n-nonadecyl, n-icosyl, n-heneicosyl, n-docosyl, iso-pentyl, iso-heptyl, iso-octyl, iso-nonyl, iso-decyl, iso-undecyl, iso-dodecyl, iso-tridecyl, iso-tetradecyl, iso-pentadecyl, iso-cetyl, iso-hexadecyl, iso-heptadecyl, iso-stearyl, iso-octadecyl, iso-nonadecyl, iso-icosyl, iso-heneicosyl, and iso-docosyl.

[0058] In one embodiment, the copolymer may be a random or block copolymer depending on the synthesis process.

[0059] In one embodiment, the copolymer may have a water-average molecular weight of 10,000 to 1,000,000.

[0060] If the water-average molecular weight of the copolymer is less than 10,000, the fluidity of the copolymer may increase, resulting in poor dispersibility and poor heat resistance of the separator.If the water-average molecular weight exceeds 1,000,000, the viscosity may be too high for use, which may clog the pores of the separator, resulting in poor air permeability and resistance.

[0061] A slurry composition according to another aspect of the present application may include the copolymer and inorganic particles.

[0062] The inorganic particles can be used without any limitation as long as they are insulating particles.

[0063] Specific examples of the inorganic particles include Al2O3, AlOOH, SiO2, TiO2, ZrO2, ZnO, NiO, CaO, SnO2, Y2O3, MgO, BaTiO3, CaTiO3, SrTiO3, SiC, Li3PO4, Pb(Zr,Ti)O3 (PZT), (Pb,La)(Zr,Ti)O3 (PLZT), and mixtures thereof.

[0064] The size of the inorganic particles is not particularly limited, and may be, for example, 0.01 μm to 30 μm, more preferably 0.1 μm to 10 μm, inclusive. If the average particle size of the inorganic particles is less than the preferred range, dispersibility may be reduced. If the average particle size of the inorganic particles is greater than the preferred range, the coating layer may become thick after coating, resulting in reduced mechanical properties.

[0065] The shape of the inorganic particles is not particularly limited, and may be, for example, spherical, plate-like, elliptical, or irregular.

[0066] A separation membrane according to another aspect of the present application may include the slurry composition.

[0067] The slurry composition may be coated on at least one surface of a porous substrate film, or the slurry composition may be formed into a film and attached to a porous substrate film to prepare a separator.

[0068] Meanwhile, the separator can be used as a separator for a secondary battery, for example, a separator for a lithium secondary battery.

[0069] An example of a method for producing a separation membrane may include the steps of: (a) dissolving or dispersing the copolymer in a solvent to prepare a polymer solution; (b) adding and mixing inorganic particles into the polymer solution of step (a); and (c) coating one or more regions selected from the group consisting of the surface of a polyolefin separation membrane substrate and a portion of the pores in the substrate with the mixture of step (b) and drying.

[0070] First, 1) the copolymer is prepared in the form of a polymer solution by dissolving or dispersing it in a suitable solvent.

[0071] The solvent preferably has a solubility index similar to that of the copolymer used as the binder and a low boiling point. This facilitates uniform mixing and subsequent solvent removal. Non-limiting examples of solvents that can be used include acetone, tetrahydrofuran, methylene chloride, chloroform, dimethylformamide, N-methyl-2-pyrrolidone (NMP), cyclohexane, water, or a mixture thereof. More preferably, the copolymer can be dispersed in water.

[0072] 2) Inorganic particles are added to and dispersed in the prepared polymer solution to prepare a mixture of inorganic particles and polymer.

[0073] It is preferable to carry out a dispersion process of the polymer solution and inorganic particles. In this case, the dispersion time may be 0.1 to 24 hours. As a dispersion method, a conventional method may be used, and a ball mill method is particularly preferable.

[0074] The composition of the mixture consisting of inorganic particles and polymer is not particularly limited, and the thickness, pore size, and porosity of the organic / inorganic composite porous separator of the present invention can be adjusted depending on the composition.

[0075] That is, as the ratio of inorganic particles (I) to polymer (P) (ratio = I / P) increases, the porosity of the separator increases, resulting in an increase in the thickness of the separator for the same solid content (inorganic particle weight + polymer weight). Also, the possibility of voids forming between inorganic particles increases, increasing the size of the voids. However, as the size (particle size) of the inorganic particles increases, the interstitial distance between the inorganic particles also increases, resulting in an increase in the size of the voids.

[0076] 3) The mixture of inorganic particles and polymer thus prepared is coated on a prepared polyolefin-based separation membrane substrate, and then dried to obtain the separation membrane of the present invention.

[0077] The method for coating the mixture of inorganic particles and polymer onto the polyolefin-based separation membrane substrate can be a conventional coating method known in the art, such as dip coating, die coating, roll coating, comma coating, or a combination thereof. Furthermore, when the mixture of inorganic particles and polymer is coated onto the polyolefin-based separation membrane substrate, it can be applied to both sides of the separation membrane substrate or selectively to only one side.

[0078] When the separator is used in a secondary battery, lithium ions can be transferred not only through the separator substrate but also through the porous active layer, and the above-mentioned safety improvement effect can be exhibited when an internal short circuit occurs due to an external impact.

[0079] The secondary battery may include an anode, a cathode, the separator interposed between the anode and the cathode, and an electrolyte.

[0080] The secondary battery can be manufactured by a conventional method known in the art. For example, the electrodes and a separator are assembled together, and then an electrolyte is injected into the assembly.

[0081] The electrode used with the separator is not particularly limited, but the positive electrode active material may be any of the common positive electrode active materials that can be used in the positive electrode of a secondary battery, including, but not limited to, lithium intercalation materials such as lithium manganese oxide, lithium cobalt oxide, lithium nickel oxide, or composite oxides formed by combining these. The negative electrode active material may be any of the common negative electrode active materials that can be used in the negative electrode of a conventional electrochemical device, including, but not limited to, lithium metal or a lithium alloy and lithium intercalation materials such as carbon, petroleum coke, activated carbon, graphite, or other carbons. The above-mentioned active materials for both electrodes are attached to an anode current collector, i.e., a foil made of aluminum, nickel, or a combination thereof, and a cathode current collector, i.e., a foil made of copper, gold, nickel, copper alloy, or a combination thereof, to form two electrodes.

[0082] The electrolyte is a salt having a structure such as A+B-, where A+ includes an alkali metal cation such as Li+, Na+, or K+, or a combination thereof, and B- includes an anion such as PF6-, BF4-, Cl-, Br-, I-, ClO4-, AsF6-, CH3CO2-, CF3SO3-, N(CF3SO2)2-, or C(CF2SO2)3-, or a combination thereof. Preferably, the compound is dissolved and dissociated in an organic solvent such as N-methyl-2-pyrrolidone (NMP), ethyl methyl carbonate (EMC), gamma butyrolactone (GBL), or a mixture thereof.

[0083] In applying the separator to a battery, in addition to the general winding process, processes such as stacking and folding of the separator and electrodes are possible. [Example]

[0084] The present invention will be described in more detail below using examples, but the present invention is not limited thereto.

[0085] [Production Example 1] Production of copolymer 260 parts by weight of distilled water, a portion of the monomer mixture, and 0.1 to 5 parts by weight of an emulsifier per 100 parts by weight of the monomer mixture were added to a reaction vessel, and the mixture was heated to 70°C and stirred while injecting high-purity nitrogen gas. The remaining part by weight of the monomer mixture and 0.15 parts by weight of ammonium persulfate, a decomposition initiator per 100 parts by weight of the monomer mixture, were successively added to the reaction vessel at 70°C to carry out a polymerization reaction to produce a copolymer.

[0086] A metal hydroxide (NaOH, LiOH, KOH) aqueous solution was added to the copolymer produced by the polymerization reaction (emulsion polymerization reaction) to carry out a neutralization reaction to produce a copolymer.

[0087] [Production Example 2] Production of slurry for porous membrane coating Inorganic particles [alumina (average particle size 0.5 μm) or boehmite (average particle size 0.7 μm)] and the binder copolymer prepared in Preparation Example 1 were mixed in a solid powder weight ratio of 80:20, and then distilled water was added to a solid powder concentration of 35% and mixed. This mixture was thoroughly dispersed using a ball mill or a mechanical stirrer to prepare a slurry.

[0088] [Production Example 3] Production of separation membrane An inorganic coating layer is formed by applying the porous membrane coating slurry prepared in Preparation Example 2 to a polyolefin porous substrate (polyethylene (PE), polypropylene (PP), etc.). Various coating methods can be used, such as dip coating, die coating, gravure coating, and comma coating.

[0089] After coating, the coating was dried using warm air, hot air, vacuum drying, infrared drying, or other methods, and the drying temperature range was 50 to 80°C.

[0090] The thickness of the inorganic coating layer is 1 to 6 μm on one or both sides. If the thickness is less than 1 μm, the heat resistance of the separator is significantly reduced. If the thickness is more than 6 μm, the separator is too thick, which reduces the energy density of the battery and increases the resistance.

[0091] [Examples and Comparative Examples] In Examples 1 to 5 and Comparative Examples 1 and 2, copolymers were prepared according to Preparation Example 1 by adjusting the monomer contents as shown in Table 1 below, and a porous membrane coating slurry according to Preparation Example 2 and a separator according to Preparation Example 3 were prepared using the prepared copolymers.

[0092] [Table 1] In Table 1, the monomer AN represents acrylonitrile, BA represents butyl acrylate, ST represents styrene, MAA represents methacrylic acid, VAc represents vinyl acetate, Na-VS represents sodium vinyl sulfonate, and FA represents 2-(perfluorooctyl)ethyl acrylate.

[0093] Na-VS and FA contain atoms with high electronegativity and correspond to monomers with large dipole moments.

[0094] [Evaluation Example 1] Adhesion strength (peel adhesion strength) of slurry for porous membrane coating A tape measuring 18 mm in width and 30 mm in length was attached to the separator prepared according to Preparation Example 3 using the binder copolymers of Examples 1 to 5 and Comparative Examples 1 and 2, and then gently pressed five times with a hand roller to prepare a test specimen.

[0095] The prepared specimen was attached to a UTM (1 kgf Load cell), one side of the separator was attached to the upper clip of the tensile strength tester, and a tape attached to one side of the separator was attached to the lower clip, and the 180° peel strength was measured at a speed of 100 mm / min. Five or more specimens were prepared for each sample and measured, and the average value was calculated.

[0096] [Evaluation Example 2] Dry electrode adhesion strength of separation membrane Separator membranes prepared according to Preparation Example 3 using the binder copolymers of Examples 1 to 5 and Comparative Examples 1 and 2 were cut into a width of 20 mm and a length of 70 mm.

[0097] An electrode cut to a width of 25 mm and a length of 70 mm was placed on the prepared separator, and then a test specimen was manufactured by applying a temperature of 65°C and a pressure of 500 kg for 10 seconds in a hot press.

[0098] The prepared specimen was attached to a UTM (1 kgf Load Cell), one side of the separator was attached to the upper clip of the tensile strength machine, and the electrode was attached to the lower clip, and the 180° peel strength was measured at a speed of 100 mm / min. At least five specimens were prepared per sample and measured, and the average value was calculated.

[0099] [Evaluation Example 3] Air permeability of separation membrane The time (seconds) required for 100 cc of air to pass through the separators prepared according to Preparation Example 3 using the binder copolymers of Examples 1 to 5 was measured using an air permeability tester. The change in air permeability was calculated based on the air permeability of an uncoated separator.

[0100] That is, the change in air permeability is the value obtained by subtracting the air permeability of an uncoated polyolefin separator from the air permeability of a separator prepared according to Preparation Example 3 using the binder copolymers of Examples 1 to 5.

[0101] [Evaluation Example 4] Electrical resistance of separation membrane The separators prepared according to Preparation Example 3 using the binder copolymers of Examples 1 to 5 and Comparative Examples 1 and 2 were punched to a diameter of 18 mm, and a CR2032 coin cell consisting of a black smoke cathode and an NCM622 anode was assembled.

[0102] The assembled coin cells were formed using an impedance analyzer manufactured by Biologics, and the resistance was measured at SOC 50. The resistance values ​​of each coated separator were calculated as a percentage, relative to the uncoated separator as a reference.

[0103] The peel adhesion strength and dry electrode adhesion strength of the separators prepared according to Preparation Example 3 using the binder copolymers of Examples 1 to 5 and Comparative Examples 1 and 2 evaluated in Evaluation Examples 1 and 2 are shown in Table 2 below.

[0104] [Table 2] As shown in Table 2 above, the peel adhesive strength of the separators to which the binder copolymers of Examples 1 to 5 were applied was in the range of 6.5 to 11 gf / mm, and the dry electrode adhesive strength was in the range of 1.5 to 5.0 gf / mm.

[0105] Meanwhile, it was confirmed that the separators employing the binder copolymers of Examples 1 to 5, which use sodium vinyl sulfonate or 2-(perfluorooctyl)ethyl acrylate as monomers containing atoms with high electronegativity, have higher peel adhesion strength and dry electrode adhesion strength than the separators employing the binder copolymers of Comparative Examples 1 and 2, which do not use sodium vinyl sulfonate or 2-(perfluorooctyl)ethyl acrylate as monomers.

[0106] It was also confirmed that the peel adhesive strength tends to decrease slightly as the content of sodium vinyl sulfonate or 2-(perfluorooctyl)ethyl acrylate in the binder copolymer increases.

[0107] The change in air permeability of the separators prepared according to Preparation Example 3 using the binder copolymers of Examples 1 to 5 evaluated in Evaluation Example 3 is shown in Table 3 below.

[0108] [Table 3] As shown in Table 3 above, the change in air permeability of the separators to which the binder copolymers of Examples 1 to 5 were applied was within the range of △30 sec / 100cc to △65 sec / 100cc.

[0109] On the other hand, it was confirmed that the change in air permeability compared to an uncoated separator tends to decrease as the content of sodium vinyl sulfonate or 2-(perfluorooctyl)ethyl acrylate in the binder copolymer increases.

[0110] This is because the higher the content of sodium vinyl sulfonate or 2-(perfluorooctyl)ethyl acrylate, the higher the glass transition temperature of the copolymer, which reduces the film formation phenomenon of the copolymer during coating of the separator, making it impossible to block the pores of the separator.

[0111] The resistances of the cells in which the separators prepared according to Preparation Example 3 using the binder copolymers of Examples 1 to 5 and Comparative Examples 1 and 2 were applied, as evaluated in Evaluation Example 4, are shown in Table 4 below.

[0112] [Table 4] As shown in Table 4 above, the electrical resistance of the cells using the separators to which the binder copolymers of Examples 1 to 5 were applied was within the range of -1.0% to 0.9%.

[0113] That is, compared to the cells using an uncoated separator, the electrical resistance of the cells using the separators with the binder copolymers of Examples 1 to 5 was lower or slightly increased.

[0114] Meanwhile, it was confirmed that the cells employing the separators prepared using the binder copolymers of Examples 1 to 5, which contain highly electronegative atoms, such as sodium vinyl sulfonate or 2-(perfluorooctyl)ethyl acrylate, as monomers, had lower electrical resistance than the cells employing the separators prepared using the binder copolymers of Comparative Examples 1 and 2, which do not use sodium vinyl sulfonate or 2-(perfluorooctyl)ethyl acrylate as monomers.

[0115] It was also confirmed that the electrical resistance of the cell tends to decrease as the content of sodium vinyl sulfonate or 2-(perfluorooctyl)ethyl acrylate in the binder copolymer increases.

[0116] Such a decrease in electrical resistance is due to the high electronegativity of sodium vinyl sulfonate or 2-(perfluorooctyl)ethyl acrylate, which improves ionic conductivity in the electrolyte.

[0117] That is, it was confirmed that a separator with excellent adhesive strength can be manufactured by using a copolymer containing a monomer unit with a large dipole moment within the content range of the present invention as a binder.

[0118] In addition, it has been found that the performance of secondary batteries can be improved by using a separator with excellent air permeability, heat resistance, and electrical resistance properties, which uses a copolymer containing a monomer unit with a large dipole moment within the content range of the present invention.

[0119] The scope of the present invention is indicated by the claims that follow rather than by the above detailed description, and all modifications or variations that fall within the meaning and scope of the claims and their equivalent concepts should be interpreted as being included within the scope of the present invention. [Industrial Applicability]

[0120] The copolymer of the present invention can enhance the adhesive strength of the inorganic material and electrodes to the separator substrate, and the high adhesive strength can increase the inorganic material content, thereby improving the heat resistance of the separator.

[0121] Furthermore, by improving the adhesive strength, it is possible to minimize the defect rate and void formation that may occur during battery assembly.

[0122] In addition, it can impart excellent air permeability and electrical resistance properties, thereby improving ion conductivity in the electrolyte of the battery, reaction safety, and life characteristics.

Claims

1. The copolymer contains 3% by weight or more and 30% by weight or less of a monomer unit containing a sulfide group, a monomer unit containing a sulfonate group, a monomer unit containing a sulfone group, a monomer unit containing a fluoro group, a monomer unit containing a perfluoroalkyl group, or a combination thereof, based on 100% by weight of the total weight of the copolymer. Copolymer.

2. Further containing acrylonitrile-based monomer units, acrylate-based monomer units, acrylic acid-based monomer units, vinyl acetate-based monomer units and styrene-based monomer units, The copolymer of claim 1.

3. The copolymer contains, based on 100% by weight of the total weight of the copolymer, 3% by weight or more and 15% by weight or less of the acrylonitrile-based monomer units, 40% by weight or more and 70% by weight or less of the acrylate-based monomer units, 1% by weight or more and 10% by weight or less of the acrylic acid-based monomer units, 1% by weight or more and 15% by weight or less of the vinyl acetate-based monomer units, and 10% by weight or more and 30% by weight or less of the styrene-based monomer units. The copolymer of claim 2.

4. The acrylate monomer units include methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, propyl acrylate, propyl methacrylate, isopropyl acrylate, isopropyl methacrylate, butyl acrylate, butyl methacrylate, and sec-butyl acrylate. acrylate, sec-butyl methacrylate, tert-butyl acrylate, tert-butyl methacrylate, ethylhexyl acrylate, ethylhexyl methacrylate, lauryl acrylate, lauryl methacrylate, stearyl acrylate, and stearyl methacrylate. is formed by polymerizing one or more selected from the group consisting of The acrylic acid-based monomer unit is formed by polymerizing at least one selected from the group consisting of acrylic acid and methacrylic acid, The acrylonitrile-based monomer is formed by polymerizing at least one selected from the group consisting of acrylonitrile and methacrylonitrile. The copolymer of claim 2.

5. The sulfonate group-containing monomer unit is formed by polymerizing sodium vinyl sulfonate, The perfluoroalkyl group-containing monomer unit is formed by polymerizing one or more monomers selected from the group consisting of 2-(perfluorooctyl)ethyl acrylate and 2-(perfluorooctyl)ethyl methacrylate. The copolymer of claim 1.

6. The acrylic acid-based monomer unit is bonded to an alkali metal. The copolymer of claim 2.

7. The monomer repeat unit is represented by the following formula 1: The copolymer of claim 1. 【Chemical 1】 In the above formula 1, R １ and R ２ are each independently hydrogen, a linear or branched hydrocarbon having 1 to 4 carbon atoms, or a combination thereof; R ３ is a linear or branched hydrocarbon having 1 to 20 carbon atoms containing one or more fluoro atoms, R ４ is hydrogen, an alkali metal, or a linear or branched hydrocarbon having 1 to 20 carbon atoms; R ５ is a sulfide group, a sulfonate group, a sulfone group, a sulfonyl ester group, a sulfonamide group, a sulfonimide group, a sulfonyl azide group, a sulfonyl hydrazide group, a sulfonyl aziridine group, a sulfonyl azitidine group, a sulfonyl carbamate group, a sulfonylurea group, a sulfonyl halide group, or a combination thereof; a+b+c+d+e+f=1. (where a+e is equal to or greater than 0.03 and equal to or less than 0.3)

8. The copolymer is a random or block copolymer. The copolymer of claim 1.

9. The copolymer according to any one of claims 1 to 8; and inorganic particles; Slurry composition.

10. The slurry composition of claim 9, Separation membrane.

11. The separation membrane according to claim 10, Secondary battery.

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