Copolymer for separator and secondary battery comprising same

Abstract

The present invention relates to: a copolymer comprising a sulfur atom-containing monomer unit, an acrylonitrile-based monomer unit, an acrylate-based monomer unit containing a linear C1-20 alkyl group, and a vinyl acetate-based monomer unit; and a slurry composition, a separator, and a secondary battery comprising same.

Description

Copolymer for separator and secondary battery containing the same

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

[0002] Due to their high energy density, lithium-ion batteries are widely used in the electrical, electronic, telecommunications, and computer industries. Following small lithium-ion batteries for portable electronic devices, their applications are expanding to include high-capacity batteries for hybrid and electric vehicles.

[0003] Although lithium-ion batteries are insulated by a separator, ensuring the thermal and chemical safety of the separator is crucial, as internal or external battery malfunctions or impacts can cause a short circuit between the positive and negative electrodes, potentially leading to overheating and explosion.

[0004] Currently, polyolefin-based films are widely used as separators, but polyolefins have the disadvantage of severe thermal shrinkage at high temperatures and poor mechanical properties.

[0005] To improve the stability of such polyolefin-based separation membranes, a porous separation membrane has been developed in which a mixture of inorganic particles and a binder is coated onto a polyolefin porous substrate film.

[0006] That is, in order to suppress thermal shrinkage caused by high temperature of polyolefin-based separators and battery instability caused by dendrites, inorganic particles are coated together with a binder on one or both sides of a porous separator substrate, thereby providing the inorganic particles with the function of suppressing the shrinkage rate of the substrate, and at the same time, a safer separator can be manufactured through the coating layer.

[0007] To ensure excellent battery characteristics, the coating layer must be uniformly coated while simultaneously requiring strong adhesion to the substrate. In particular, improvements in the performance and stability of secondary batteries are required through this.

[0008] [Prior Art Literature]

[0009] [Patent Literature]

[0010] (Patent Document 1) Republic of Korea Published Patent Application No. 10-2006-0072065

[0011] Accordingly, the present invention aims to provide a slurry composition with excellent inorganic adhesion and electrode adhesion to a porous substrate using a copolymer.

[0012] In addition, the present invention aims to provide a separator with excellent adhesion and electrical properties to which the above slurry composition is applied, and a battery with excellent performance using said separator.

[0013]

[0014] However, the problems that this invention seeks to solve are not limited to those mentioned above, and other unmentioned problems will be clearly understood by those skilled in the art from the description below.

[0015] One aspect of the present invention comprises a monomer unit containing a sulfur atom, an acrylic acid-based monomer unit, an acrylate-based monomer unit containing a linear alkyl group having 1 to 20 carbon atoms, and an acrylate-based monomer unit containing a branched alkyl group having 3 to 10 carbon atoms.

[0016] The sulfur atom of the above sulfur atom-containing monomer unit is located at the terminal of a linear alkyl group having 1 to 10 carbon atoms,

[0017] Provides a copolymer.

[0018] Another aspect of the present invention is,

[0019] A separation membrane having a coating layer containing inorganic material formed thereon, wherein the contact angle between the surface of the membrane and an aqueous copolymer solution with a solid content of 25 weight% is 90˚ or less,

[0020] Provides a copolymer.

[0021] Another aspect of the present invention is the copolymer; and

[0022] Inorganic particles; including,

[0023] A slurry composition is provided.

[0024] Another aspect of the present invention comprises a porous substrate having a coating layer formed by applying the slurry composition,

[0025] Provides a separation membrane.

[0026] Another aspect of the present invention is that the separation membrane comprises,

[0027] Provides a secondary battery.

[0028] The copolymer of the present invention can increase the adhesion of inorganic materials and electrodes to the separator substrate, and can improve the heat resistance of the separator by increasing the inorganic material content due to the high adhesion.

[0029] Furthermore, by improving adhesion, defect rates and void formation that may occur during battery assembly can be minimized, product movement between roll-to-roll processes can be facilitated, and operational stability can be enhanced. Through this, production costs can be reduced by simplifying the process and improving yield.

[0030] In addition, by increasing air permeability and lowering the battery resistance of secondary batteries, it may be possible to apply this to high-power, high-energy-density batteries where the use of current binders is limited.

[0031] The operation and effects of the invention will be described in more detail below through specific embodiments. However, these embodiments are merely examples of the invention and do not define the scope of the invention.

[0032] Prior to this, terms and words used in this specification and claims should not be interpreted as being limited to their ordinary or dictionary meanings, but should be interpreted in a meaning and concept consistent with the technical spirit of the invention, based on the principle that the inventor can appropriately define the concept of the terms to best describe his invention.

[0033] Therefore, it should be understood that the configuration of the embodiments described in this specification is merely one of the most preferred embodiments of the present invention and does not represent all of the technical ideas of the present invention, and that various equivalents and modifications that can replace them may exist at the time of filing this application.

[0034] In this specification, singular expressions include plural expressions unless the context clearly indicates otherwise. In this specification, terms such as “comprising,” “comprising,” or “having” are intended to specify the existence of the implemented features, numbers, steps, components, or combinations thereof, and should be understood as not precluding the existence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0035] In the present specification, "a to b" and "a~b" indicating numerical ranges, "to" and "~" are defined as ≥ a and ≤ b.

[0036]

[0037] A copolymer of one aspect of the present invention may comprise a monomer unit containing a sulfur atom, an acrylic acid-based monomer unit, an acrylate-based monomer unit containing a linear alkyl group having 1 to 20 carbon atoms, and an acrylate-based monomer unit containing a branched alkyl group having 3 to 10 carbon atoms.

[0038] In addition, the sulfur atom of the above-mentioned sulfur atom-containing monomer unit may be located at the end of a linear alkyl group having 1 to 10 carbon atoms.

[0039] The above-mentioned monomer unit containing a sulfur atom can exhibit reactive emulsifier behavior. Typically, reactive emulsifiers can perform functions and roles such as controlling the chemical structure of the polymer, controlling particle size, stabilization, and dispersion during emulsion polymerization.

[0040] The above-mentioned sulfur atom-containing monomer unit, which exhibits reactive emulsifier behavior, can surround the edges of the copolymer (water-soluble resin) of the present invention and can control the stable generation and dispersion of particles with large particle sizes compared to conventional water-soluble resins.

[0041] Therefore, the above-mentioned sulfur atom-containing monomer unit can help increase adhesion to the electrode and achieve low resistance within the secondary battery compared to particles with small particle sizes.

[0042] In addition, the monomer unit containing the sulfur atom can have a large dipole moment. Therefore, the adhesion to the inorganic material and the porous substrate or electrode can be improved through electrostatic attraction caused by the induction of polarization phenomena.

[0043] In a single covalent bond, electrons are attracted more towards the atom with higher electronegativity than the other atom. At this time, the atom with relatively higher electronegativity becomes negatively charged and the atom with lower electronegativity becomes positively charged. This is called a dipole, and its magnitude is called the dipole moment.

[0044] In one embodiment, the copolymer of the present invention may further comprise acrylonitrile-based monomer units and vinyl acetate-based monomer units or a combination thereof.

[0045] For example, the copolymer of the present invention may include a monomer unit containing a sulfur atom, an acrylic acid-based monomer unit, an acrylate-based monomer unit containing a linear alkyl group having 1 to 20 carbon atoms, an acrylate-based monomer unit containing a branched alkyl group having 3 to 10 carbon atoms, and an acrylonitrile-based monomer unit.

[0046] In one embodiment, the copolymer of the present invention may comprise, based on 100% by weight of the total weight of the copolymer, a monomer unit containing a sulfur atom in an amount of 1% or more and 20% or less by weight, a monomer unit of the acrylic acid series in an amount of 5% or more and 30% or less by weight, a monomer unit of the acrylate series in an amount of 5% or more and 30% or less by weight, a monomer unit of the acrylate series in an amount of 5% or more and 30% or less by weight, and a monomer unit of the acrylate series in an amount of 20% or more and 50% or less by weight, a monomer unit of the branched alkyl group having 3 to 10 carbon atoms.

[0047] If the content of the monomer unit containing the sulfur atom with a large dipole moment falls below the range of the present invention, the adhesive strength is reduced, and the properties of the separation membrane may be degraded.

[0048] In addition, if the content of a monomer unit containing the sulfur atom having a large dipole moment, or a combination thereof, exceeds the content range of the present invention, the reaction stability is reduced, and the characteristics of the separation membrane may be degraded.

[0049] Meanwhile, if the above acrylic acid-based monomer unit exceeds or falls below the content range of the present invention, it may cause polymer aggregation and precipitation or a decrease in adhesion.

[0050] In addition, if the content of the acrylate-based monomer unit containing a linear alkyl group having 1 to 20 carbon atoms exceeds or falls below the content range of the present invention, it may cause a decrease in adhesive strength.

[0051] In addition, if the content of the acrylate-based monomer unit containing a branched alkyl group having 3 to 10 carbon atoms exceeds or falls below the content range of the present invention, it may cause a decrease in adhesive strength.

[0052] In one embodiment, the copolymer of the present invention may further comprise, based on 100 weight% of the total weight of the copolymer, 20 weight% or more and 40 weight% or less of the acrylonitrile-based monomer units; 1 weight% or more and 20 weight% or less of the vinyl acetate-based monomer units; or a combination thereof.

[0053] If the above acrylonitrile-based monomer unit exceeds or falls below the content range of the present invention, it may cause a decrease in the dispersibility of polymer particles and inorganic slurry or a decrease in adhesion.

[0054] In addition, if the content of the vinyl acetate monomer unit exceeds or falls below the content range of the present invention, it may cause stability problems such as stability and storage stability.

[0055] In one embodiment, the copolymer of the present invention may comprise, based on 100% by weight of the total weight of the copolymer, 1% by weight or more and 10% by weight or less of the sulfur atom-containing monomer unit, 5% by weight or more and 15% by weight or less of the acrylic acid-based monomer unit, 10% by weight or more and 20% by weight or less of the acrylate-based monomer unit containing a linear alkyl group having 1 to 20 carbon atoms, 20% by weight or more and 40% by weight or less of the acrylate-based monomer unit containing a branched alkyl group having 3 to 10 carbon atoms, and 20% by weight or more and 40% by weight or less of the acrylonitrile-based monomer unit.

[0056] In one embodiment, the monomer unit containing the sulfur atom may be 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 sulfonyl ester group, a monomer unit containing a sulfonamide group, a monomer unit containing a sulfonimide group, a monomer unit containing a sulfonyl azide group, a monomer unit containing a sulfonyl hydrazide group, a monomer unit containing a sulfonyl aziridine group, a monomer unit containing a sulfonyl azitidine group, a monomer unit containing a sulfonyl carbamate group, a monomer unit containing a sulfonylurea group, a monomer unit containing a sulfonyl halide group, or a combination thereof, but is not limited thereto.

[0057] That is, the sulfur atom located at the end of the linear alkyl group having 1 to 10 carbon atoms of the monomer unit containing the sulfur atom may be part of 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 sulfonylaziridine group, a sulfonylazitidine group, a sulfonyl carbamate group, a sulfonylurea group, or a sulfonyl halide group.

[0058] In one embodiment, the acrylic acid-based monomer unit may be formed by polymerizing one or more selected from the group consisting of acrylic acid and methacrylic acid.

[0059] For example, the above acrylic acid series monomer unit can be formed by polymerizing methacrylic acid.

[0060] In addition, the above acrylate series monomer unit containing a linear alkyl group having 1 to 20 carbon atoms may be formed by polymerizing one or more selected from the group consisting of methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, propyl acrylate, propyl methacrylate, butyl acrylate, butyl methacrylate, lauryl acrylate, lauryl methacrylate, stearyl acrylate, and stearyl methacrylate.

[0061] For example, the above acrylate series monomer unit containing a linear alkyl group having 1 to 20 carbon atoms can be formed by polymerizing butyl acrylate.

[0062] Meanwhile, the above-mentioned acrylate-series monomer unit containing a branched alkyl group having 3 to 10 carbon atoms may be formed by polymerizing one or more selected from the group consisting of isopropyl acrylate, isopropyl methacrylate, sec-butyl acrylate, sec-butyl methacrylate, tert-butyl acrylate, tert-butyl methacrylate, 2-ethylhexyl acrylate, and 2-ethylhexyl methacrylate.

[0063] For example, the above-mentioned acrylate series monomer unit containing a branched alkyl group having 3 to 10 carbon atoms can be formed by polymerizing 2-ethylhexyl acrylate.

[0064] In one embodiment, the sulfur atom-containing monomer unit may be formed by polymerizing one or more selected from the group consisting of 3-sulfopropyl acrylate and allyl methyl sulfide.

[0065] In one embodiment, the acrylonitrile-based monomer is formed by polymerizing one or more selected from the group consisting of acrylonitrile and methacrylonitrile, and the vinyl acetate-based monomer unit may be formed by polymerizing vinyl acetate.

[0066] In one embodiment, the acrylic acid-based monomer unit can be combined with an alkali metal.

[0067] That is, the carboxylate group of the above acrylic acid-based monomer unit can be bonded to an alkali metal.

[0068] Meanwhile, 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 the alkali metal: weight of the copolymer) may be 0.1 to 15:100.

[0069] For example, the weight ratio of the alkali metal and the copolymer may be 1 to 10:100.

[0070] If the weight ratio of the alkali metal and the copolymer exceeds or falls below the weight ratio of the present invention, the adhesive properties and heat resistance properties of the separator may be reduced. In particular, the peel adhesion and electrode adhesion of the separator may be reduced.

[0071] The adhesive strength of the separator containing the above alkali metal can be determined by the strength of the cohesive and repulsive forces between the elements.

[0072] The copolymer of the present invention may have inorganic adhesion or electrode adhesion due to changes in the relative strength of cohesive force, adhesion force, and repulsive force between elements depending on the content of the alkali metal.

[0073] When the above alkali metal is used in the manufacture of a binder copolymer, the overall adhesive strength is improved due to the harmony between adhesion and cohesion caused by the increase in cohesion between elements; however, if added in excess, the cohesion may decrease, and the overall adhesive strength may be reduced.

[0074] Meanwhile, since the improvement in the adhesion of the copolymer to inorganic materials implies an increase in adhesion between the inorganic material and the substrate, this may mean that the heat resistance properties of the separator can be improved by increasing the amount of inorganic material.

[0075] The electrode adhesion of the separator can reduce the defect rate that occurs when loading electrodes during battery assembly, minimize void formation, and improve ion conductivity within the electrolyte.

[0076] In addition, when a binder layer is coated alone on an inorganic coating layer, electrode adhesion can be maximized, and ultimately, electrode adhesion can minimize the battery failure rate and further improve battery performance.

[0077] In one embodiment, the copolymer may include a monomer repeating unit represented by the following chemical formula 1.

[0078]

[0079] [Chemical Formula 1]

[0080]

[0081]

[0082] In the above formula 1, R1, R2, and R3 are each independently hydrogen, a linear or branched hydrocarbon having 1 to 4 carbon atoms, or a combination thereof; R4 is a linear alkyl group having 1 to 20 carbon atoms; R5 is a branched alkyl group having 3 to 10 carbon atoms; R6 is hydrogen or an alkali metal; R7 is a linear alkyl group having 1 to 10 carbon atoms with a sulfur atom located at the terminal; the sulfur atom is part of 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 sulfonyliziridine group, a sulfonyliazitidine group, a sulfonyl carbamate group, a sulfonylurea group, or a sulfonyl halide group; and 0.05≤a≤0.3, 0.2≤b≤0.5, 0.05≤c≤0.3, 0≤d≤0.2, 0.01≤e≤0.2 and 0≤f≤0.4 may be possible.

[0083] However, a+b+c+d+e+f=1.

[0084]

[0085] a, b, c, d, e, and f of the above chemical formula 1 correspond to the weight fraction of each monomer unit, and the sum of the weight fractions of each monomer unit is 1.

[0086] The above alkali metal may be Li, Na, or K, but is not limited thereto.

[0087] In one embodiment, R1, R2, and R3 are each independently one or more selected from the group consisting of hydrogen and methyl, and R4 may be one or more selected from the group consisting of methyl, ethyl, propyl, butyl, n-pentyl, n-hexyl, n-heptyl, n-octyl, n-nonyl, n-decyl, n-undecyl, lauryl, n-dodecyl, n-tridecyl, n-tetradecyl, n-pentadecyl, cetyl, n-hexadecyl, n-heptadecyl, stearyl, n-octadecyl, n-nonadecyl, n-icosyl, n-henicosyl, and n-docosyl.

[0088] In addition, the above R5 may be one or more selected from the group consisting of isopropyl, sec-butyl, tert-butyl, ethylhexyl, 2-ethylhexyl, iso-pentyl, iso-heptyl, and iso-octyl.

[0089] In one embodiment, the copolymer may be a random or block copolymer depending on the synthesis process.

[0090] In one embodiment, the number average molecular weight of the copolymer may be 10,000 to 1,000,000.

[0091] If the number average molecular weight of the copolymer is less than 10,000, the fluidity of the copolymer increases, which may reduce dispersibility and lower the heat resistance of the separator. If the number average molecular weight exceeds 1,000,000, the viscosity is too high for use and may block the pores of the separator, thereby reducing air permeability and resistance.

[0092] In one embodiment, the copolymer may be in the form of particles, and the average particle size (diameter) of the particles may be 500 nm or more and 1,500 nm or less.

[0093] For example, the average particle size (diameter) of the above particles may be 550 nm or more, 600 nm or more, or 650 nm or more, and may be 1,000 nm or less.

[0094] According to another aspect of the present invention, the contact angle between the surface of a separator with a coating layer containing inorganic material and an aqueous copolymer solution with a solid content of 25 weight% may be 90˚ or less.

[0095] The copolymer may comprise a monomer unit containing a sulfur atom according to the present invention, an acrylic acid-based monomer unit, an acrylate-based monomer unit containing a linear alkyl group having 1 to 20 carbon atoms, and an acrylate-based monomer unit containing a branched alkyl group having 3 to 10 carbon atoms, wherein the sulfur atom of the monomer unit containing a sulfur atom is located at the terminal of the linear alkyl group having 1 to 10 carbon atoms.

[0096] In one embodiment, the contact angle between the surface of a separator with a coating layer containing an inorganic material and an aqueous copolymer solution having a solid content of 25 weight% may be 50° or more, 90° or less, 55° or more, 85° or less, 60° or more, 80° or less, or 65° or more, 80° or less.

[0097] If the contact angle between the surface of a separator with a coating layer containing inorganic material and an aqueous copolymer solution with a solid content of 25% by weight exceeds or falls below the range of the present invention, the adhesion of the electrode is reduced, and the air permeability of the separator and the battery resistance of the secondary battery are increased, which may result in a decrease in the performance of the secondary battery.

[0098] In one embodiment, the separator with a coating layer containing the inorganic material may be a separator in which a slurry mixed with alumina and a polymer is coated to a thickness of 2 μm on both sides of a substrate laminated with polypropylene and polyethylene.

[0099] For example, the polymer may be an acrylamide-based, acrylate-based, vinyl-based, or a combination thereof.

[0100] A slurry composition according to another aspect of the present invention may include the copolymer and inorganic particles.

[0101] The above inorganic particles can be used without restriction if they are insulating particles.

[0102] Specific examples of the above-mentioned 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.

[0103] The above inorganic particles are not subject to any special size limitations, but for example, the average particle size may be 0.01 μm to 30 μm, and more preferably 0.1 μm to 10 μm. If the average particle size of the inorganic particles is below the above preferred range, dispersibility may be reduced, and if it exceeds the above preferred range, the thickness of the coating layer after coating may increase, and mechanical properties may be degraded.

[0104] In addition, the above-mentioned inorganic particles have no particular restrictions on shape and may be, for example, spherical, plate-shaped, elliptical, or irregular.

[0105] A separation membrane according to another aspect of the present invention may comprise a porous substrate having a coating layer formed thereon to which the slurry composition is applied.

[0106] A separator can be manufactured by coating the above slurry composition on at least one surface of a porous substrate film, or by manufacturing the above slurry composition into a film form and laminating it onto a porous substrate film.

[0107] Meanwhile, the above separator can be used as a separator for a secondary battery, for example, as a separator for a lithium secondary battery.

[0108] As an example of manufacturing a separation membrane, the method may include: (a) a step of preparing a polymer solution by dissolving or dispersing the copolymer in a solvent; (b) a step of adding and mixing inorganic particles to the polymer solution of step a); and (c) a step of coating and drying one or more regions selected from the group consisting of the surface of a polyolefin-based separation membrane substrate and a portion of the pores in the substrate with the mixture of step b).

[0109] First, 1) the copolymer is prepared and prepared in the form of a polymer solution by dissolving or dispersing it in a suitable solvent.

[0110] As for the solvent, it is preferable to have a solubility index similar to that of the copolymer used as a binder and a low boiling point. This is to facilitate uniform mixing and subsequent solvent removal. Non-limiting examples of usable solvents include acetone, tetrahydrofuran, methylene chloride, chloroform, dimethylformamide, N-methyl-2-pyrrolidone (NMP), cyclohexane, water, or mixtures thereof. More preferably, it can be used in a water-dispersed state.

[0111] 2) Inorganic particles are added and dispersed in the prepared polymer solution to prepare a mixture of inorganic particles and polymer.

[0112] It is desirable to carry out a dispersion process of the polymer solution and inorganic particles. At this time, a dispersion time of 0.1 to 24 hours may be appropriate. Conventional methods can be used as the dispersion method, and the ball mill method is particularly preferred.

[0113] The composition of the mixture consisting of inorganic particles and polymers is not significantly restricted, but accordingly, the thickness, pore size, and porosity of the organic / inorganic composite porous separation membrane of the present invention finally manufactured can be controlled.

[0114] In other words, as the ratio of inorganic particles (I) to polymers (P) (ratio = I / P) increases, the porosity of the membrane increases, which results in an increase in the thickness of the membrane at the same solid content (weight of inorganic particles + weight of polymers). Additionally, the possibility of pore formation between inorganic particles increases, leading to an increase in pore size. At this time, as the size (particle diameter) of the inorganic particles increases, the interstitial distance between the inorganic particles increases, thus increasing the pore size.

[0115] 3) A mixture of manufactured inorganic particles and polymers can be coated onto a prepared polyolefin-based separator substrate and subsequently dried to obtain the separator of the present invention.

[0116] At this time, the method of coating the mixture of inorganic particles and polymers onto a polyolefin-based separator substrate may use conventional coating methods known in the art, and various methods such as dip coating, die coating, roll coating, comma coating, or a combination thereof may be used. In addition, when coating the mixture of inorganic particles and polymers onto a polyolefin-based separator substrate, the coating may be applied to both sides of the separator substrate or selectively applied to only one side.

[0117] The air permeability of the above membrane may be 150 sec / 100 ml or less.

[0118] For example, it may be 80 sec / 100 ml or more, and 120 sec / 100 ml or less.

[0119] When the above 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 in the event of an internal short circuit caused by external impact, the aforementioned safety enhancement effect can be exhibited.

[0120] In addition, the secondary battery may include a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte.

[0121] The above secondary battery can be manufactured according to conventional methods known in the industry, and as an example thereof, the electrode and the separator are assembled and then an electrolyte is injected into the assembly to manufacture it.

[0122] There are no significant limitations on the electrodes to be applied together with the above-mentioned separator; however, the cathode active material may be any conventional cathode active material that can be used for the cathode of a secondary battery. Non-limiting examples include lithium intercalation materials such as lithium manganese oxide (lithiated magnesium oxide), lithium cobalt oxide, lithium nickel oxide, or composite oxides formed by combinations thereof. Additionally, the anode active material may be any conventional anode active material that can be used for the anode of a conventional electrochemical device. Non-limiting examples include lithium metal or lithium alloys, as well as lithium intercalation materials such as carbon, petroleum coke, activated carbon, graphite, or other carbons. The anode and cathode are configured by attaching the aforementioned electrode active materials to an anode current collector, i.e., a foil manufactured from aluminum, nickel, or a combination thereof, and a cathode current collector, i.e., a foil manufactured from copper, gold, nickel, or a copper alloy, or a combination thereof, respectively.

[0123] The above electrolyte is a salt having a structure such as A+B-, where A+ comprises ions composed of alkali metal cations such as Li+, Na+, and K+ or combinations thereof, and B- comprises anions composed of anions such as PF6-, BF4-, Cl-, Br-, I-, ClO4-, AsF6-, CH3CO2-, CF3SO3-, N(CF3SO2)2-, and C(CF2SO2)3- or combinations thereof, and is a salt comprising propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, and tetrahydrofuran It is preferable that it be dissolved and dissociated in an organic solvent composed of tetrahydrofuran, N-methyl-2-pyrrolidone (NMP), ethyl methyl carbonate (EMC), gamma butyrolactone (GBL), or a mixture thereof.

[0124] In addition to the general winding process, the process of applying the above separator to a battery may include stacking and folding of the separator and electrode.

[0125] Meanwhile, the adhesion strength between the electrode and the separator may be 1.00 gf / 20mm or more.

[0126] For example, the adhesion strength between the electrode and the separator may be 1.00 gf / 20mm or more and 1.50 gf / 20mm or less.

[0127] In addition, the battery resistance of the above secondary battery may be 4% or less.

[0128] For example, the battery resistance of the above secondary battery may be 2% or more and 3% or less.

[0129] The present invention will be explained in more detail below using examples, but the present invention is not limited thereto.

[0130]

[0131] [Preparation Example 1] Preparation of a copolymer

[0132] 0.5 parts by weight of an emulsifier (sodium lauryl sulfate (SLS)) was added to a mixture of 200 parts by weight of distilled water, 5 parts by weight of acrylonitrile, 5 parts by weight of butyl acrylate, 1 part by weight of methacrylic acid, and 5 parts by weight of 2-ethylhexyl acrylate in a 4-neck flask reactor and stirred, and the temperature was raised to 70°C while purging with nitrogen gas.

[0133] Subsequently, 0.15 parts by weight of ammonium persulfate, a pyrolytic radical initiator, was mixed with 35 parts by weight of distilled water and added dropwise over 1 hour to a reactor prepared at 70°C. At the same time, the content of a monomer containing sulfur atoms was adjusted and added dropwise over 1 hour.

[0134] After the dropwise loading of the monomer containing the initiator and sulfur atoms was completed, a monomer mixture of 25 parts by weight of acrylonitrile, 10 parts by weight of butyl acrylate, 10 parts by weight of methacrylic acid, 10 parts by weight of methyl methacrylate, and 25 parts by weight of 2-ethylhexyl acrylate was added dropwise for 2 hours to prepare a copolymer through an emulsion polymerization reaction.

[0135] A copolymer subjected to a neutralization reaction was prepared by adding an aqueous solution of metal hydroxide (NaOH) to the copolymer prepared by the above polymerization reaction (emulsion polymerization reaction).

[0136]

[0137] [Preparation Example 2] Preparation of a slurry for porous membrane coating

[0138] Inorganic particles [boehmite (average particle size 0.5 μm)] and the binder copolymer prepared according to Preparation Example 1 were mixed in a solid weight ratio of 80:20, and then distilled water was added and mixed to achieve a solid concentration of 35%. This mixture was sufficiently dispersed using a ball mill or a mechanical stirrer to prepare a slurry.

[0139]

[0140] [Preparation Example 3] Preparation of a separation membrane with a coating layer containing inorganic material

[0141] An inorganic coating layer was formed by applying the porous membrane coating slurry prepared according to 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.

[0142] In addition, after coating, it was dried using methods such as hot air, hot air, vacuum drying, and infrared drying, and the drying temperature range was 50 to 80℃.

[0143] The thickness of the above inorganic coating layer was 1 to 6 μm on one side or both sides, and if the thickness was less than 1 μm, there was a problem that the heat resistance of the separator was significantly reduced, and if the thickness exceeded 6 μm, the thickness of the separator was too thick, which could reduce the energy density of the battery and increase the resistance.

[0144] In the present manufacturing example, a porous substrate laminated with polyethylene and polypropylene was used, a comma coating was used, vacuum drying was performed at a drying temperature of 60°C, and the thickness of the inorganic coating layer was 2 μm on both sides.

[0145]

[0146] [Preparation Example 4] Preparation of a coated separator for electrode adhesion

[0147] An aqueous solution of the copolymer of Preparation Example 1 (solid content 25 wt%) was coated to a thickness of 2 μm on the surface of a separator having a coating layer containing an inorganic material prepared according to Preparation Example 3.

[0148]

[0149] [Examples and Comparative Examples]

[0150] Examples 1 to 4 and Comparative Examples 1 to 3 were prepared according to Preparation Example 1 by adjusting the monomer content as shown in Table 1 below, and the prepared copolymer was used to prepare a porous membrane coating slurry according to Preparation Example 2 and a separation membrane according to Preparation Example 3.

[0151]

[0152] Copolymer monomer and content (parts by weight) ANBAMAAEHAMMASAM Example 1 30 15 11 30 10 5 Example 2 30 15 11 30 10 3 Example 3 30 15 11 30 10 5 Example 4 30 15 11 30 10 3 Comparative Example 1 30 20 11 30 10 0 Comparative Example 2 30 25 11 30 10 0 Comparative Example 3 30 15 11 35 10 0

[0153]

[0154] In Table 1 above, AN represents acrylonitrile, BA represents butyl acrylate, MAA represents methacrylic acid, EHA represents 2-ethylhexyl acrylate, MMA represents methylmethacrylate, and SAM represents a monomer containing a sulfur atom.

[0155] In Examples 1 and 2, 3-sulfopropyl acrylate was used as the sulfur atom-containing monomer, and in Examples 3 and 4, allyl methyl sulfide was used as the sulfur atom-containing monomer.

[0156]

[0157] [Evaluation Example 1] Dry electrode adhesion of the separator

[0158] An electrode-adhesive coated separator was prepared by coating a separator prepared according to Preparation Example 3 using the binder copolymers of Examples 1 to 4 and Comparative Examples 1 to 3 with an aqueous solution (solid content 25 wt%) of the binder copolymers of Examples 1 to 4 and Comparative Examples 1 to 3 to a thickness of 2 μm according to Preparation Example 4.

[0159] The prepared electrode adhesive coating separator was cut to a size of 25 mm in width and 70 mm in length.

[0160] Cut an anode to a width of 25 mm and a length of 40 mm onto the prepared separator, position it so that the anode coating surface meets the separator coating surface, and apply a hot press at 65°C and 65 kg / cm² 2 The temperature and pressure were applied for 30 seconds.

[0161] The prepared specimens were mounted on a UTM (1kgf Load cell), one side of the separator was fixed to the upper clip of the tensile strength tester, and the cathode was fixed to the lower clip. The 180° peel strength was measured at a speed of 100 mm / min. At least 5 specimens were prepared and measured per sample, and the average value was calculated.

[0162]

[0163] [Evaluation Example 2] Air permeability of the separator

[0164] The electrode adhesive coating separator prepared as in Evaluation Example 1 was cut into a circular shape with a diameter of 30 mm, left in a dry room with a temperature of 20°C and a humidity of 0-5% for 24 hours, and then placed in the measuring section of an air permeability meter of Ilshin Autoclave Co., Ltd.

[0165] Afterwards, 100 ml of air per second was sprayed onto the membrane to check the amount of gas that passed through for 5 seconds.

[0166]

[0167] [Evaluation Example 3] Battery resistance of the separator

[0168] A coating separator for electrode adhesion prepared as in Evaluation Example 1 was cut to a diameter of 18 mm, dried once again in a vacuum oven at 60°C for 12 hours, and then a CR2032 coin cell was assembled in a dry room with a temperature of 20°C and a humidity of 0-5% using an anode containing graphite-silicon oxide and an anode containing nickel-cobalt-manganese (NCM622).

[0169] After forming the assembled coin cell in the impedance device of Biologics, the resistance was measured at SOC 50.

[0170] The above formation was charged and discharged three times at a voltage of 2.75 to 4.20 V with rate limits of 0.1C, 0.2C, and 0.5C, respectively.

[0171] The resistance values ​​of each coated separator were compared and calculated as a percentage when an uncoated separator substrate was used as a reference.

[0172]

[0173] [Evaluation Example 4] Contact Angle Measurement

[0174] A separator with a coating layer containing inorganic material was prepared and cut into a square with sides of 50 mm.

[0175] The separator with the coating layer containing the above-mentioned inorganic material was a separator in which a mixed coating layer of alumina and a polymer was formed with a thickness of 2 μm on both sides of a substrate laminated with polypropylene and polyethylene.

[0176] After positioning the substrate of the contact angle measuring device so that the coating layer containing the inorganic material of the separator membrane is positioned upward, an aqueous solution (solid content 25 wt%) of the binder copolymer of Examples 1 to 4 and Comparative Examples 1 to 3 was dropped onto the coating layer containing the inorganic material of the separator membrane in an amount of 50 μl through the needle of the contact angle measuring device.

[0177] Subsequently, the contact angles of the left and right sides were verified using a contact angle measuring instrument (Surface Tech Co., Ltd., GSA), and the average value was calculated.

[0178]

[0179] The measurement results according to Evaluation Examples 1 to 4 are shown in Table 2 below.

[0180]

[0181] Copolymer Dry Electrode Adhesion (gf / 20mm) Air Permeability (sec / 100ml) Battery Resistance (%) Contact Angle (Degree (˚)) Example 1 1.3 288 2.3 26 7.6 Example 2 1.3 091 2.2 16 9.3 Example 3 1.2 1109 2.7 87 6.0 Example 4 1.1 898 2.9 57 2.5 Comparative Example 10.6 2322 6.4 49 7.1 Comparative Example 20.8 4498 6.5 211 2.4 Comparative Example 30.7 221 6.9 89 9.0

[0182]

[0183] As shown in Table 2 above, when the binder copolymers of Examples 1 to 4 were applied, the dry electrode adhesion strength was measured to be 1.18 gf / 20mm or more and 1.32 gf / 20mm or less, the air permeability was 88 sec / 100 ml or more and 109 sec / 100 ml or less, the cell resistance was 2.21% or more and 2.95% or less, and the contact angle was 67.6˚ or more and 76.0˚ or less.

[0184] Meanwhile, when the binder copolymers of Comparative Examples 1 to 3 were applied, the dry electrode adhesion strength was measured to be less than 1.00 gf / 20 mm, the air permeability was greater than 150 sec / 100 ml, the cell resistance was greater than 4%, and the contact angle was greater than 90˚.

[0185] That is, when the binder copolymer of Comparative Examples 1 to 3 was applied, compared to when the binder copolymer of Examples 1 to 4 was applied, the dry electrode adhesion was lowered, and the air permeability and battery resistance were higher, so it was confirmed that the performance of the secondary battery was degraded.

[0186] In addition, it was confirmed that the performance degradation of these secondary batteries can be predicted based on the magnitude of the measured contact angle.

[0187] When a monomer containing sulfur atoms was added, the material affinity between the emulsion-type copolymer and the inorganic coating separator and electrode was improved through the enhancement of the dipole moment, and it was confirmed that the dry adhesion strength was improved.

[0188] This improvement in affinity could be predicted through a low contact angle. A lower contact angle implies improved wetting with the substrate, and this result may mean that a stable surface and adhesive surface can be formed.

[0189] In addition, the improvement in wettability provided coating uniformity of the polymer material acting as a relative resistance factor across the entire coating surface and enabled the free movement of lithium ions (Li ions), which is the main function of the separator, so it appeared that the low contact angle copolymer brought about improvements in air permeability and battery resistance.

[0190]

[0191] In other words, it was confirmed that a separator with excellent substrate and electrode adhesion can be manufactured by using a copolymer containing monomer units containing sulfur atoms within the content range of the present invention as a binder.

[0192] In addition, it was found that the performance of a secondary battery can be improved by using a separator with excellent air permeability and electrical resistance characteristics, which utilizes a copolymer containing monomer units containing sulfur atoms of the present invention.

[0193]

[0194] The scope of the present invention is defined by the claims set forth below rather than by the detailed description above, and all modifications or variations derived from the meaning and scope of the claims and equivalent concepts thereof should be interpreted as being included within the scope of the present invention.

[0195] The copolymer of the present invention can increase the adhesion of inorganic materials and electrodes to the separator substrate, and can improve the heat resistance of the separator by increasing the inorganic material content due to the high adhesion.

[0196] Furthermore, by improving adhesion, defect rates and void formation that may occur during battery assembly can be minimized, product movement between roll-to-roll processes can be facilitated, and operational stability can be enhanced. Through this, production costs can be reduced by simplifying the process and improving yield.

[0197] In addition, by increasing air permeability and lowering the battery resistance of secondary batteries, it may be possible to apply this to high-power, high-energy-density batteries where the use of current binders is limited.

Claims

1. A monomer unit containing a sulfur atom, an acrylic acid-based monomer unit, an acrylate-based monomer unit containing a linear alkyl group having 1 to 20 carbon atoms, and an acrylate-based monomer unit containing a branched alkyl group having 3 to 10 carbon atoms, and The sulfur atom of the above sulfur atom-containing monomer unit is located at the terminal of a linear alkyl group having 1 to 10 carbon atoms, Copolymer.

2. In Paragraph 1, A combination of acrylonitrile-based monomer units and vinyl acetate-based monomer units or a combination thereof, further comprising Copolymer.

3. In Paragraph 1, Based on 100% by weight of the total weight of the copolymer, the above-mentioned monomer units containing sulfur atoms in an amount of 1% or more and 20% or less by weight; 5 weight% or more and 30 weight% or less of the above acrylic acid-based monomer units; An acrylate-based monomer unit comprising a linear alkyl group having 1 to 20 carbon atoms in an amount of 5 weight% or more and 30 weight% or less; and 1. Acrylate-based monomer units comprising 20% ​​by weight or more and 50% by weight or less of the branched alkyl group having 3 to 10 carbon atoms; Copolymer.

4. In Paragraph 2, Based on 100% by weight of the total weight of the copolymer, the acrylonitrile-based monomer unit in an amount of 20% by weight or more and 40% by weight or less; the vinyl acetate-based monomer unit in an amount of 1% by weight or more and 20% by weight or less; or further comprising a combination thereof, Copolymer.

5. In Paragraph 1, The monomer unit containing the sulfur atom above comprises 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 sulfonyl ester group, a monomer unit containing a sulfonamide group, a monomer unit containing a sulfonimide group, a monomer unit containing a sulfonyl azide group, a monomer unit containing a sulfonyl hydrazide group, a monomer unit containing a sulfonyl aziridine group, a monomer unit containing a sulfonyl azitidine group, a monomer unit containing a sulfonyl carbamate group, a monomer unit containing a sulfonylurea group, a monomer unit containing a sulfonyl halide group, or a combination thereof. Copolymer.

6. In Paragraph 1, The above acrylic acid series monomer unit is formed by polymerizing one or more selected from the group consisting of acrylic acid and methacrylic acid, and The above acrylate-series monomer unit comprising a linear alkyl group having 1 to 20 carbon atoms is formed by polymerizing one or more selected from the group consisting of methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, propyl acrylate, propyl methacrylate, butyl acrylate, butyl methacrylate, lauryl acrylate, lauryl methacrylate, stearyl acrylate, and stearyl methacrylate. The above acrylate-series monomer unit containing a branched alkyl group having 3 to 10 carbon atoms is formed by polymerizing one or more selected from the group consisting of isopropyl acrylate, isopropyl methacrylate, sec-butyl acrylate, sec-butyl methacrylate, tert-butyl acrylate, tert-butyl methacrylate, 2-ethylhexyl acrylate, and 2-ethylhexyl methacrylate. Copolymer.

7. In Paragraph 1, The above sulfur atom-containing monomer unit is formed by polymerizing one or more selected from the group consisting of 3-sulfopropyl acrylate and allyl methyl sulfide, Copolymer.

8. In Paragraph 2, The above acrylonitrile-based monomer is formed by polymerizing one or more selected from the group consisting of acrylonitrile and methacrylonitrile, and The above vinyl acetate series monomer unit is formed by the polymerization of vinyl acetate, Copolymer.

9. In Paragraph 1, A monomer repeating unit represented by the following chemical formula 1, comprising Copolymer. [Chemical Formula 1] In the above chemical formula 1, R1, R2, and R3 are each independently hydrogen, a linear or branched hydrocarbon having 1 to 4 carbon atoms, or a combination thereof, and R4 is a linear alkyl group having 1 to 20 carbon atoms, and R5 is a branched alkyl group having 3 to 10 carbon atoms, and R6 is hydrogen or an alkali metal, and R7 is a linear alkyl group having 1 to 10 carbon atoms with a sulfur atom located at the terminal, and the sulfur atom is part of a sulfide group, a sulfonate group, a sulfone group, a sulfonyl ester group, a sulfonamide group, a sulfonimide group, a sulfonylazide group, a sulfonyl hydrazide group, a sulfonylaziridine group, a sulfonylazitidine group, a sulfonyla carbamate group, a sulfonylurea group, or a sulfonyl halide group, and 0.05≤a≤0.3, 0.2≤b≤0.5, 0.05≤c≤0.3, 0≤d≤0.2, 0.01≤e≤0.2 and 0≤f≤0.4, and a+b+c+d+e+f=1.

10. A separation membrane having a coating layer containing inorganic material formed thereon, wherein the contact angle between the surface of the separation membrane and an aqueous copolymer solution having a solid content of 25 wt% is 90˚ or less, Copolymer.

11. A copolymer of any one of claims 1 to 10; and Inorganic particles; including, Slurry composition.

12. A porous substrate comprising a coating layer formed by applying the slurry composition of claim 11, Separator.

13. Including the separator of Paragraph 12, Secondary battery.

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