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, a separator, and a secondary battery containing the copolymer.

[0002] Lithium secondary batteries have high energy density and are widely used in the electrical, electronic, communications, and computer industries. Their application areas are expanding from small lithium secondary batteries for portable electronic devices to high-capacity secondary batteries for hybrid and electric vehicles.

[0003] Although lithium secondary batteries are insulated by a separator, there is a risk of short circuiting between the positive and negative electrodes due to internal or external battery abnormalities or impacts, which can lead to overheating and explosion. Therefore, ensuring the thermal / chemical safety of the separator is very important.

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

[0005] To improve the stability of these polyolefin-based separators, a porous separator has been developed in which a mixture of inorganic particles and a binder is coated on a polyolefin porous substrate film.

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

[0007] To ensure superior battery characteristics, the coating layer must be uniformly applied and possess strong adhesion to the substrate. In particular, this requires improved performance and stability of secondary batteries.

[0008] [Prior Art Literature]

[0009] [Patent Document]

[0010] (Patent Document 1) Republic of Korea Patent No. 10-1430975

[0011] (Patent Document 2) Republic of Korea Patent Publication No. 10-2006-0072065

[0012] Accordingly, the present invention aims to provide a slurry composition having excellent inorganic adhesion and electrode adhesion to a porous substrate using a copolymer.

[0013] In addition, the present invention seeks to provide a separator having excellent adhesive strength and electrical properties by applying the slurry composition and a battery having excellent performance using the separator.

[0014]

[0015] However, the problems that the present invention seeks to solve are not limited to the problems mentioned above, and other problems not mentioned will be clearly understood by those skilled in the art from the description below.

[0016] One aspect of the present invention comprises a monomer unit including a sulfur atom, a monomer unit of the acrylonitrile series, a monomer unit of the acrylate series including a linear alkyl group having 1 to 20 carbon atoms, and a monomer unit of the vinyl acetate series.

[0017] Provides a copolymer.

[0018] Another aspect of the present invention is the copolymer; and

[0019] containing inorganic particles;

[0020] A slurry composition is provided.

[0021] Another aspect of the present invention is a composition comprising the slurry composition,

[0022] Provides a separation membrane.

[0023] Another aspect of the present invention is a membrane comprising:

[0024] Provides secondary batteries.

[0025] The copolymer of the present invention can increase the adhesion of inorganic substances and electrodes to a membrane substrate, and can improve the heat resistance properties of the membrane by increasing the inorganic substance content with high adhesion.

[0026] Additionally, by improving adhesive strength, it is possible to minimize defect rates and void formation that may occur during battery assembly.

[0027] In addition, it can improve ion conductivity, reaction stability and life characteristics in the electrolyte of the battery by imparting excellent air permeability and electrical resistance characteristics.

[0028] Hereinafter, the functions and effects of the invention will be described in more detail through specific examples. However, these examples are provided merely as examples of the invention and do not define the scope of the invention.

[0029] Prior to this, the terms or words used in this specification and claims should not be interpreted as limited to their usual or dictionary meanings, and should be interpreted as meanings and concepts that conform to the technical idea of ​​the present invention based on the principle that the inventor can appropriately define the concept of the term to explain his or her own invention in the best way.

[0030] Accordingly, the configuration of the embodiments described in this specification is only one of the most preferred embodiments of the present invention and does not represent all of the technical ideas of the present invention, so it should be understood that various equivalents and modified examples that can replace them may exist at the time of filing this application.

[0031] In this specification, singular expressions include plural expressions unless the context clearly dictates otherwise. In this specification, terms such as "comprise," "include," or "have" should be understood to indicate the presence of a feature, number, step, component, or combination thereof, but not to preclude the possibility of the presence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0032] In this specification, “a to b” and “a~b” indicating a numerical range are defined as “a to” and “~” as ≥ a and ≤ b.

[0033]

[0034] The copolymer of one aspect of the present invention may include a sulfur atom-containing monomer unit, an acrylonitrile-based monomer unit, an acrylate-based monomer unit containing a linear alkyl group having 1 to 20 carbon atoms, and a vinyl acetate-based monomer unit.

[0035] The above sulfur atom-containing monomer unit can exhibit reactive emulsifier behavior. Typically, reactive emulsifiers can perform functions and roles such as controlling the chemical structure of a polymer, controlling particle size, stabilizing, and dispersing during emulsion polymerization.

[0036] The above sulfur atom-containing monomer unit exhibiting reactive emulsifier behavior can surround the edge of the copolymer (water-soluble resin) of the present invention, and can be controlled to stably produce and disperse particles having a large particle size compared to conventional water-soluble resins.

[0037] Therefore, the above sulfur atom-containing monomer unit can help large-diameter particles increase adhesion to an electrode compared to small-diameter particles and achieve low resistance in a secondary battery.

[0038] In addition, the monomer unit containing the sulfur atom may have a large dipole moment. Therefore, the adhesion to inorganic materials and porous substrates or electrodes may be improved by electrostatic attraction resulting from the induction of polarization.

[0039] Within a covalent bond, electrons are more attracted to the atom with a higher electronegativity among the two atoms. At this time, the atom with a relatively higher electronegativity acquires a (-) charge, and the atom with a relatively lower electronegativity acquires a (+) charge. This is called a dipole, and its size is called the dipole moment.

[0040] In one embodiment, the copolymer of the present invention may additionally include an acrylic acid series monomer unit, an acrylate series monomer unit including a branched alkyl group having 3 to 10 carbon atoms, or a combination thereof.

[0041] Meanwhile, the copolymer of the present invention may not include a styrene series monomer unit formed by polymerization of a styrene monomer.

[0042] For example, the copolymer of the present invention includes a sulfur atom-containing monomer unit, an acrylonitrile series monomer unit, an acrylate series monomer unit containing a linear alkyl group having 1 to 20 carbon atoms, and a vinyl acetate series monomer unit, or includes a sulfur atom-containing monomer unit, an acrylonitrile series monomer unit, an acrylate series monomer unit containing a linear alkyl group having 1 to 20 carbon atoms, a vinyl acetate series monomer unit, and an acrylic acid series monomer unit, or includes a sulfur atom-containing monomer unit, an acrylonitrile series monomer unit, an acrylate series monomer unit containing a linear alkyl group having 1 to 20 carbon atoms, a vinyl acetate series monomer unit, and an acrylate series monomer unit containing a branched alkyl group having 3 to 10 carbon atoms, or includes a sulfur atom-containing monomer unit, an acrylonitrile series monomer unit, a carbon 1 to 20 It may include a monomer unit of the acrylate series containing a linear alkyl group, a monomer unit of the vinyl acetate series, a monomer unit of the acrylic acid series, and a monomer unit of the acrylate series containing a branched alkyl group having 3 to 10 carbon atoms.

[0043] In one embodiment, the copolymer of the present invention may include 0.1 wt% or more and 30 wt% or less of the sulfur atom-containing monomer unit, 1 wt% or more and 40 wt% or less of the acrylonitrile-based monomer unit, 1 wt% or more and 65 wt% or less of the acrylate-based monomer unit containing a linear alkyl group having 1 to 20 carbon atoms, and 1 wt% or more and 30 wt% or less of the vinyl acetate-based monomer unit, based on 100 wt% of the total weight of the copolymer.

[0044] For example, the copolymer of the present invention may include, based on 100 wt% of the total weight of the copolymer, 0.5 wt% or more and 30 wt% or less of the sulfur atom-containing monomer unit, 20 wt% or more and 35 wt% or less of the acrylonitrile-based monomer unit, 10 wt% or more and 65 wt% or less of the acrylate-based monomer unit containing a linear alkyl group having 1 to 20 carbon atoms, and 5 wt% or more and 15 wt% or less of the vinyl acetate-based monomer unit.

[0045] If the monomer unit containing the sulfur atom having a large dipole moment or a combination thereof is below the content range of the present invention, the adhesive strength may decrease, and the properties of the separation membrane may deteriorate.

[0046] If the 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 may be reduced, and the characteristics of the separation membrane may be deteriorated.

[0047] If the above acrylonitrile series 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 the dispersibility of inorganic slurry or a decrease in adhesive strength.

[0048] If the content of the acrylate series monomer unit containing the 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.

[0049] If the above vinyl acetate monomer unit exceeds or falls below the content range of the present invention, stability problems such as stability and storage stability may occur.

[0050] In one embodiment, based on 100 wt% of the total weight of the copolymer of the present invention, the copolymer may further include 0.1 wt% or more and 20 wt% or less of the acrylic acid series monomer unit, 0.1 wt% or more and 35 wt% or less of the acrylate series monomer unit including a branched alkyl group having 3 to 10 carbon atoms, or a combination thereof.

[0051] For example, based on 100 wt% of the total weight of the copolymer of the present invention, it may additionally include 0.5 wt% or more and 10 wt% or less of an acrylic acid series monomer unit, 10 wt% or more and 35 wt% or less of an acrylate series monomer unit including a branched alkyl group having 3 to 10 carbon atoms, or a combination thereof.

[0052] If the monomer unit of the acrylic acid series is above or below the content range of the present invention, it may cause polymer aggregation and precipitation or reduced adhesive strength.

[0053] If the content of the acrylate series 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.

[0054] In one embodiment, the monomer unit containing the sulfur atom may be, but is not limited to, 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.

[0055] In one embodiment, the acrylate series monomer unit including a linear alkyl group having 1 to 20 carbon atoms may be formed by polymerizing at least one 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.

[0056] Meanwhile, the acrylonitrile series monomer unit can be formed by polymerizing at least one selected from the group consisting of acrylonitrile and methacrylonitrile.

[0057] Additionally, the above vinyl acetate series monomer unit can be formed by polymerization of vinyl acetate.

[0058] In one embodiment, the monomer unit containing the sulfur atom can be formed by polymerizing sodium vinyl sulfonate.

[0059] In one embodiment, the acrylic acid series monomer unit may be formed by polymerizing at least one selected from the group consisting of, for example, acrylic acid and methacrylic acid.

[0060] In addition, the acrylate series monomer unit containing a branched alkyl group having 3 to 10 carbon atoms may be formed by polymerizing at least one selected from the group consisting of isopropyl acrylate, isopropyl methacrylate, sec-butyl acrylate, sec-butyl methacrylate, tert-butyl acrylate, tert-butyl methacrylate, 2-ethyl hexyl acrylate, and 2-ethyl hexyl methacrylate.

[0061] In one embodiment, the acrylic acid series monomer unit can be combined with an alkali metal.

[0062] That is, the carboxylate group of the monomer unit of the acrylic acid series can be combined with an alkali metal.

[0063] Meanwhile, the weight ratio of the alkali metal and the copolymer (weight of at least one selected from the group consisting of the alkali metal and an acetate salt compound containing the alkali metal: weight of the copolymer) may be 0.1 to 15:100.

[0064] For example, the weight ratio of the alkali metal and the copolymer may be 1 to 10:100.

[0065] When 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 of the separator may deteriorate. In particular, the peel adhesion and electrode adhesion of the separator may deteriorate.

[0066] The adhesive strength of the separation membrane containing the above alkali metal can be determined according to the strength of the cohesive force and repulsive force between the elements.

[0067] The copolymer of the present invention may have changes in the inorganic adhesion or electrode adhesion due to changes in the cohesion, adhesion, and repulsion between elements depending on the content of the alkali metal.

[0068] When the above alkali metal is used in the production of a copolymer for a binder, the overall adhesive strength is improved through the harmony of adhesion and cohesion due to the increase in cohesion between elements, but if added in excessive amounts, the cohesion strength may decrease, thereby lowering the overall adhesive strength.

[0069] Meanwhile, since the improvement in the inorganic adhesion of the copolymer means an increase in the adhesion between the inorganic material and the substrate, this may mean that the heat resistance characteristics of the separation membrane can be improved due to the increase in the amount of inorganic material.

[0070] The electrode adhesion of the separator can reduce the defect rate that occurs when loading electrodes during battery assembly, minimize the formation of voids, and improve ion conductivity within the electrolyte.

[0071] In addition, when a binder layer is coated solely on an inorganic coating layer, electrode adhesion can be maximized, and ultimately, electrode adhesion can minimize battery failure rate and further improve battery performance.

[0072] In one embodiment, the copolymer may include a monomer repeating unit represented by the following chemical formula 1.

[0073]

[0074] [Chemical Formula 1]

[0075]

[0076]

[0077] 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, 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 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, and 0.01≤a≤0.65, 0≤b≤0.35, 0≤c≤0.2, 0.01≤d≤0.3, 0.001≤e≤0.3 and 0.01≤f≤0.4 may be true.

[0078] However, a+b+c+d+e+f=1.

[0079]

[0080] In the above chemical formula 1, a, b, c, d, e and f correspond to the weight fractions of each monomer unit, and the sum of the weight fractions of each monomer unit is 1.

[0081] The alkali metal may be, but is not limited to, Li, Na or K.

[0082] In one embodiment, R1, R2 and R3 are each independently at least one selected from the group consisting of hydrogen and methyl, and R4 may be at least one 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.

[0083] Additionally, the R5 may be at least one selected from the group consisting of isopropyl, sec-butyl, tert-butyl, ethylhexyl, 2-ethylhexyl, iso-pentyl, iso-heptyl, and iso-octyl.

[0084] In one embodiment, the copolymer may be a random or block copolymer depending on the synthesis process.

[0085] In one embodiment, the number average molecular weight of the copolymer may be 10,000 to 1,000,000.

[0086] If the number average molecular weight of the copolymer is less than 10,000, the fluidity of the copolymer may increase, which may reduce dispersibility and deteriorate the heat resistance of the membrane. If the number average molecular weight exceeds 1,000,000, the viscosity may be too high for use and may block the pores of the membrane, which may reduce the air permeability and resistance.

[0087] 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.

[0088] For example, the average particle size (diameter) of the particles may be 550 nm or more, 600 nm or more, or 650 nm or more, and may be 1,000 nm or less.

[0089] A slurry composition according to another aspect of the present invention may include the copolymer and inorganic particles.

[0090] The above inorganic particles can be used without limitation as long as they are insulating particles.

[0091] Specific examples of the above 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.

[0092] The above inorganic particles have no particular limitations on size, but may have, for example, an average particle diameter of 0.01 μm to 30 μm, more preferably 0.1 μm to 10 μm. If the average particle diameter of the inorganic particles is less than 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 become thicker, resulting in deterioration of mechanical properties.

[0093] In addition, the above-mentioned inorganic particles have no particular limitation on shape, and may be, for example, spherical, plate-shaped, elliptical, or irregular.

[0094] A separation membrane according to another aspect of the present invention may comprise the slurry composition.

[0095] A separator can be manufactured by coating the above slurry composition on at least one side of a porous substrate film, or by manufacturing the above slurry composition in a film form and laminating it to a porous substrate film.

[0096] Meanwhile, the above separator can be used as a separator for a secondary battery, and for example, can be used as a separator for a lithium secondary battery.

[0097] As an example of manufacturing a separation membrane, the method may include: (a) preparing a polymer solution by dissolving or dispersing the copolymer in a solvent; (b) adding and mixing inorganic particles into the polymer solution of step a); and (c) 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 a porous portion of the substrate with the mixture of step b).

[0098] First, 1) the above copolymer is prepared and manufactured in the form of a polymer solution by dissolving or dispersing it in an appropriate solvent.

[0099]

[0100] The solvent preferably has a solubility index similar to that of the copolymer used as the 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 state dispersed in water.

[0101] 2) Inorganic particles are added and dispersed in the manufactured polymer solution to manufacture a mixture of inorganic particles and polymer.

[0102] It is desirable to perform a dispersion process of the polymer solution and inorganic particles. The dispersion time may be between 0.1 and 24 hours. Conventional methods can be used for dispersion, with the ball mill method being particularly preferred.

[0103] There is no significant restriction on the composition of the mixture composed of inorganic particles and polymers, but the thickness, pore size, and porosity of the organic / inorganic composite porous separation membrane of the present invention can be controlled accordingly.

[0104] That is, as the ratio of inorganic particles (I) to polymer (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 polymer). In addition, the possibility of forming pores between inorganic particles increases, which increases the pore size. At this time, as the size (diameter) of the inorganic particles increases, the interval between inorganic particles (interstitial distance) increases, which increases the pore size.

[0105] 3) The separation membrane of the present invention can be obtained by coating the mixture of manufactured inorganic particles and polymers on a prepared polyolefin-based separation membrane substrate and then drying it.

[0106] At this time, the method of coating the mixture of inorganic particles and polymers on the polyolefin-based membrane substrate can use a conventional coating method known in the art, and various methods such as dip coating, die coating, roll coating, comma coating, or a mixed method thereof can be used. In addition, when coating the mixture of inorganic particles and polymers on the polyolefin-based membrane substrate, it can be performed on both sides of the membrane substrate or selectively on only one side.

[0107] When the above separator is used in a secondary battery, not only can lithium ions be transferred through the separator substrate but also through the porous active layer, it can exhibit the aforementioned safety improvement effect when an internal short circuit occurs due to an external impact.

[0108] Additionally, 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.

[0109] The above secondary battery can be manufactured according to a conventional method known in the art. For example, the secondary battery is manufactured by assembling the electrode and separator interposed therebetween, and then injecting an electrolyte into the assembly.

[0110] There is no particular limitation on the electrode to be applied together with the above separator, but the cathode active material can be a typical cathode active material that can be used for the cathode of a secondary battery, and non-limiting examples thereof include lithium intercalation materials such as lithium manganese oxide (lithiated magnesium oxide), lithium cobalt oxide (lithiated cobalt oxide), lithium nickel oxide (lithiated nickel oxide), or a composite oxide formed by a combination thereof. In addition, the anode active material can be a typical cathode active material that can be used for the cathode of a conventional electrochemical device, and non-limiting examples thereof include lithium metal, or a lithium alloy, and a lithium adsorption material such as carbon, petroleum coke, activated carbon, graphite, or other carbons. The positive electrode and negative electrode are formed by bonding the above-described positive electrode active material and negative electrode active material to a positive electrode current collector, i.e., a foil made of aluminum, nickel, or a combination thereof, and a negative electrode current collector, i.e., a foil made of copper, gold, nickel, or a copper alloy, or a combination thereof, respectively.

[0111] The above electrolyte is a salt having a structure such as A+B-, where A+ contains an ion formed by an alkali metal cation such as Li+, Na+, K+ or a combination thereof, and B- contains an anion such as PF6-, BF4-, Cl-, Br-, I-, ClO4-, AsF6-, CH3CO2-, CF3SO3-, N(CF3SO2)2-, C(CF2SO2)3- or a salt formed by a combination thereof, such as propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, tetrahydrofuran. It is preferable that it is dissolved and dissociated in an organic solvent consisting of tetrahydrofuran, N-methyl-2-pyrrolidone (NMP), ethyl methyl carbonate (EMC), gamma butyrolactone (GBL), or a mixture thereof.

[0112] In addition to the general process of winding, processes for applying the above separator to a battery include stacking and folding of the separator and electrode.

[0113] Hereinafter, the present invention will be described in more detail using examples, but the present invention is not limited thereto.

[0114]

[0115] [Manufacturing Example 1] Manufacturing of copolymer

[0116] In a reaction vessel, 245 parts by weight of distilled water, some part by weight of a monomer mixture (A), and 0.1 to 5 parts by weight of an emulsifier were added to 100 parts by weight of the monomer mixture, and the temperature was raised to 70°C and stirred while injecting high-purity nitrogen gas.

[0117] Ammonium persulfate, a decomposition initiator, was prepared in an amount of 0.15 parts by weight per 100 parts by weight of the monomer mixture, and some part (B) by weight of the remaining monomer mixture was prepared, and these were continuously added to a reaction vessel heated to 70°C to initiate emulsion polymerization.

[0118] Immediately after the end of adding a portion (B) of the remaining monomer mixture, the remaining portion (C) of the remaining monomer mixture was continuously added to produce a copolymer.

[0119] A neutralized copolymer was prepared by adding an aqueous solution of metal hydroxide (NaOH, LiOH, KOH) to the copolymer prepared by the above polymerization reaction (emulsion polymerization reaction).

[0120]

[0121] [Manufacturing Example 2] Manufacturing of slurry for porous film coating

[0122] Inorganic particles [alumina (average particle size: 0.5 ㎛) or boehmite (average particle size: 0.7 ㎛)] and the copolymer for binder manufactured according to Manufacturing Example 1 were mixed at a solid weight ratio of 80:20, and then distilled water was added to a solid concentration of 35% and mixed. This mixture was sufficiently dispersed using a ball mill method or a mechanical stirrer to manufacture a slurry.

[0123]

[0124] [Manufacturing Example 3] Manufacturing of a membrane

[0125] The porous film coating slurry manufactured by Manufacturing Example 2 was applied to a polyolefin porous substrate (polyethylene (PE), polypropylene (PP), etc.) to form an inorganic coating layer. Various coating methods, such as dip coating, die coating, gravure coating, and comma coating, can be used.

[0126] In addition, after coating, it was dried using methods such as warm air, hot air, vacuum drying, and infrared drying, and the drying temperature range was 50 to 80°C.

[0127] The thickness of the above-mentioned inorganic coating layer was 1 to 6 ㎛ on one side or both sides. If the thickness was less than 1 ㎛, there was a problem that the heat resistance of the separator was significantly reduced, and if the thickness exceeded 6 ㎛, the separator was too thick, which could reduce the energy density of the battery and increase the resistance.

[0128]

[0129] [Examples and Comparative Examples]

[0130] Examples 1 to 10 and Comparative Examples 1 and 4 were prepared by adjusting the content of monomers as shown in Table 1 below, producing a copolymer according to Manufacturing Example 1, and using the prepared copolymer, producing a slurry for a porous film coating according to Manufacturing Example 2 and a separation membrane according to Manufacturing Example 3.

[0131] In addition, the average particle size (diameter) of the copolymers of Examples 1 to 10 and Comparative Examples 1 and 4 analyzed by Particle Sizer NICOMP 380 is shown in Table 1 below.

[0132]

[0133] Copolymer monomer and content (wt%)Average particle size (nm)ANBAEHAMAAVAcNa-VSExample 12430305101650Example 22460-5101650Example 32428285105750Example 42456-5105750Example 52461--105750Example 625252551010750Example 72550-51010750Example 82555--1010750Example 9251515510301000Example 102530-510301000Comparative Example 12530305100450Comparative Example 22560-5100450Comparative Example 36112125100450Comparative Example 46124-5100450

[0134]

[0135] In the above Table 1, the monomer AN represents acrylonitrile, BA represents butylacrylate, EHA represents 2-ethylhexyl acrylate, MAA represents methacrylic acid, VAc represents vinylacetate, and Na-VS represents sodium vinyl sulfonate.

[0136]

[0137] [Evaluation Example 1] Adhesion of slurry for porous film coating (Peel strength test)

[0138] A tape having a width of 18 mm and a length of 30 mm or more was attached to a separator manufactured according to Manufacturing Example 3 using the copolymers for binders of Examples 1 to 10 and Comparative Examples 1 and 4, and then lightly pressed five times with a hand roller to prepare a specimen.

[0139] The manufactured specimens were mounted on a UTM (1 kgf Load cell), one side of the separator was fixed to the upper clip of the tensile strength tester, and the tape attached to one side of the separator was fixed to the lower clip. The 180° peel strength was measured at a speed of 100 mm / min. At least five specimens were manufactured for each sample, measured, and the average value was calculated.

[0140]

[0141] [Evaluation Example 2] Dry electrode adhesion of the separator

[0142] A separation membrane manufactured according to Manufacturing Example 3 using the copolymers for binders of Examples 1 to 10 and Comparative Examples 1 to 4 was prepared by cutting it into a width of 20 mm and a length of 70 mm.

[0143] An electrode cut to 25 mm in width and 70 mm in length was placed on the prepared separator, and a specimen was manufactured by applying a temperature and pressure of 65°C and 500 kg for 10 seconds using a hot press.

[0144] The manufactured specimens were mounted on a UTM (1 kgf load cell), one side of the separator was fixed to the upper clip of the tensile strength tester, and the electrode was fixed to the lower clip, and the 180° peel strength was measured at a speed of 100 mm / min. At least five specimens were manufactured for each sample, measured, and the average value was calculated.

[0145]

[0146] [Evaluation Example 3] Wet electrode adhesion of the separator

[0147] A separation membrane manufactured according to Manufacturing Example 3 using the copolymers for binders of Examples 1 to 10 and Comparative Examples 1 to 4 was cut to a size of 20 mm in width and 70 mm in length.

[0148] An electrode cut to 25 mm in width and 70 mm in length was placed on the prepared separator, then enclosed in an aluminum pouch and immersed in the electrolyte for 12 hours at room temperature, and then hot-pressed at 65°C and 65 kg / cm 2The temperature and pressure were applied for 30 seconds.

[0149] The prepared specimens were mounted on a UTM (1 kgf load cell), one side of the separator was fixed to the upper clip of the tensile strength tester, and the electrode was fixed to the lower clip. The 180° peel strength was measured at a speed of 100 mm / min. At least five specimens were prepared for each sample, measured, and the average value was calculated.

[0150]

[0151] [Evaluation Example 4] Membrane permeability

[0152] The time (in seconds) required for 100 cc of air to permeate through a membrane manufactured according to Manufacturing Example 3 using the copolymers for binders of Examples 1 to 10 and Comparative Examples 1 to 4 was measured using an air permeability measuring device. The change in air permeability was calculated based on the air permeability of an uncoated membrane.

[0153]

[0154] [Evaluation Example 5] Electrical resistance of the membrane

[0155] A separator manufactured according to Manufacturing Example 3 using the copolymers for binders of Examples 1 to 10 and Comparative Examples 1 to 4 was punched to a diameter of 18 mm, and a CR2032 coin cell composed of a graphite negative electrode and an NCM622 positive electrode was assembled.

[0156] The assembled coin cells were formed in an impedance device from Biologics and their resistance was measured at SOC 50. The resistance values ​​of each coated membrane were compared and calculated as a percentage compared to the uncoated membrane as a reference.

[0157]

[0158] Peel adhesion, dry electrode adhesion, and wet electrode adhesion of the separator manufactured according to Manufacturing Example 3 using the copolymers for binders of Examples 1 to 10 and Comparative Examples 1 to 4 evaluated by Evaluation Examples 1 to 3 are shown in Table 2 below.

[0159]

[0160] Copolymer Peel Adhesion (gf / mm) Dry Electrode Adhesion (gf / mm) Wet Electrode Adhesion (gf / mm) Example 14.98 3.31 7.01 Example 25.22 2.90 8.01 Example 36.89 4.81 12.01 Example 47.01 4.30 15.11 Example 57.13 4.44 15.41 Example 67.12 5.32 11.51 Example 77.22 4.77 13.56 Example 87.23 4.89 13.99 Example 94.85 3.95 6.99 Example 103.98 3.01 8.61 Comparative Example 13.54 2.86 4.10 Comparative Example 23.662.316.96Comparative example 33.221.864.11Comparative example 43.450.886.21

[0161]

[0162] As shown in Table 2 above, the peel adhesion of the separator to which the copolymer for binder of Examples 1 to 10 was applied was within the range of 3.5 gf / mm or more and 9.0 gf / mm or less, the dry electrode adhesion was within the range of 2.5 gf / mm or more and 7.0 gf / mm or less, and the wet electrode adhesion was within the range of 5.5 gf / mm or more and 20.0 gf / mm or less.

[0163] Specifically, the peel adhesion of the separator to which the copolymer for binder of Examples 1 to 10 was applied was within the range of 3.90 gf / mm or more and 8.0 gf / mm or less, the dry electrode adhesion was within the range of 3.0 gf / mm or more and 6.0 gf / mm or less, and the wet electrode adhesion was within the range of 6.99 gf / mm or more and 16.0 gf / mm or less.

[0164] Meanwhile, it was confirmed that the separator to which the binder copolymers of Examples 1 to 10, which used sodium vinylsulfonate containing an atom with high electronegativity as a monomer, were applied had higher peel adhesion than the separator to which the binder copolymers of Comparative Examples 1 to 4, which did not use sodium vinylsulfonate as a monomer, were applied.

[0165] Meanwhile, it was confirmed that the separator to which the binder copolymers of Examples 1 to 10 using sodium vinylsulfonate as a monomer were applied generally had higher dry electrode adhesion and wet electrode adhesion than the separator to which the binder copolymers of Comparative Examples 1 to 4 were applied.

[0166] In addition, it was confirmed that peel adhesion, dry electrode adhesion, and wet electrode adhesion were the best when the content of sodium vinylsulfonate was 5 to 10 wt% based on 100 wt% of the total weight of the copolymer for the binder.

[0167] In addition, when 2-ethylhexyl acrylate was included, the dry adhesive strength tended to increase and the wet adhesive strength tended to decrease.

[0168]

[0169] The change in the air permeability of the separation membrane manufactured according to Manufacturing Example 3 using the copolymers for binders of Examples 1 to 10 and Comparative Examples 1 to 4 evaluated by Evaluation Example 4 is shown in Table 3 below.

[0170]

[0171] Copolymer air permeability (sec / 100cc) Example 1△53 Example 2△53 Example 3△47 Example 4△48 Example 5△49 Example 6△42 Example 7△42 Example 8△45 Example 9△40 Example 10△40 Comparative Example 1△65 Comparative Example 2△63 Comparative Example 3△33 Comparative Example 4△35

[0172]

[0173] As shown in Table 3 above, the change in air permeability of the separation membrane to which the copolymer for binder of Examples 1 to 10 was applied was included in the range of △36 sec / 100cc or more and △60 sec / 100c or less.

[0174] Specifically, the change in air permeability of the separation membrane to which the copolymer for binder of Examples 1 to 10 was applied was included in the range of △38 sec / 100cc or more and △55 sec / 100c or less.

[0175] Meanwhile, it was confirmed that as the content of sodium vinyl sulfonate in the copolymer for binder increased, the change in air permeability tended to decrease compared to the uncoated membrane.

[0176] This is because as the content of sodium vinyl sulfonate increases, the glass transition temperature of the copolymer increases, which reduces the film formation phenomenon of the copolymer when coating the membrane, preventing the pores of the membrane from being blocked.

[0177]

[0178] The resistance of the cell to which the separator manufactured according to Manufacturing Example 3 was applied using the copolymers for binders of Examples 1 to 10 and Comparative Examples 1 to 4 evaluated by Evaluation Example 5 is shown in Table 4 below.

[0179]

[0180] Copolymer Resistance (%) Example 1 - 0.363 Example 2 - 0.501 Example 3 - 1.952 Example 4 - 2.139 Example 5 - 2.151 Example 6 - 1.877 Example 7 - 1.949 Example 8 - 1.955 Example 9 - 0.942 Example 10 + 0.801 Comparative Example 1 + 1.222 Comparative Example 2 + 1.422 Comparative Example 3 + 2.030 Comparative Example 4 + 2.531

[0181]

[0182] As shown in Table 4 above, the electrical resistance of the cell using the separator to which the copolymer for binder of Examples 1 to 10 was applied was within the range of -2.5% or more and -0.1% or less.

[0183] Specifically, the electrical resistance of the cell using the separator to which the copolymer for binder of Examples 1 to 10 was applied was within the range of -2.3% or more and -0.3% or less.

[0184] That is, the electrical resistance of the cell to which the separator to which the copolymer for binder of Comparative Examples 1 to 4 was applied was lowered compared to the cell to which the separator to which the copolymer for binder of Comparative Examples 1 to 4 was applied.

[0185] Meanwhile, it was confirmed that the cell to which the separator manufactured using the copolymer for binder using sodium vinylsulfonate as a monomer, which includes an atom with a high electronegativity of Examples 1 to 10, was applied had a lower electrical resistance than the cell to which the separator manufactured using the copolymer for binder of Comparative Examples 1 to 4, in which sodium vinylsulfonate was not used.

[0186]

[0187] That is, it was confirmed that when a monomer unit formed by polymerizing sodium vinylsulfonate was included in a copolymer for a binder, the electrical resistance of the cell tended to decrease.

[0188] This decrease in electrical resistance is due to the improved ionic conductivity within the electrolyte caused by the high electronegativity of sodium vinylsulfonate and its larger particle size than that of inorganic materials.

[0189]

[0190] That is, it was confirmed that a separator having excellent substrate and electrode adhesion can be manufactured by using a copolymer including a monomer unit containing sulfur atoms in the content range of the present invention as a binder.

[0191] In addition, it was found that the performance of a secondary battery can be improved by using a separator having excellent air permeability and electrical resistance characteristics using a copolymer including a monomer unit containing a sulfur atom of the present invention.

[0192]

[0193] The scope of the present invention is indicated by the claims described below rather than the detailed description above, and all changes or modifications derived from the meaning and scope of the claims and their equivalent concepts should be interpreted as being included in the scope of the present invention.

[0194] The copolymer of the present invention can increase the adhesion of inorganic substances and electrodes to a membrane substrate, and can improve the heat resistance properties of the membrane by increasing the inorganic substance content with high adhesion.

[0195] Additionally, by improving adhesive strength, it is possible to minimize defect rates and void formation that may occur during battery assembly.

[0196] In addition, it can improve ion conductivity, reaction stability and life characteristics in the electrolyte of the battery by imparting excellent air permeability and electrical resistance characteristics.

Claims

1. A monomer unit including a sulfur atom, a monomer unit of the acrylonitrile series, a monomer unit of the acrylate series including a linear alkyl group having 1 to 20 carbon atoms, and a monomer unit of the vinyl acetate series. Copolymer.

2. In paragraph 1, An acrylic acid series monomer unit, an acrylate series monomer unit containing a branched alkyl group having 3 to 10 carbon atoms, or a combination thereof, Copolymer.

3. In paragraph 1, Based on 100 wt% of the total weight of the copolymer, the sulfur atom-containing monomer unit is 0.1 wt% or more and 30 wt% or less; 1 wt% or more and 40 wt% or less of the above acrylonitrile series monomer unit; An acrylate series monomer unit containing a linear alkyl group having 1 to 20 carbon atoms in an amount of 1 wt% or more and 65 wt% or less; and Containing 1 wt% or more and 30 wt% or less of the above vinyl acetate series monomer unit; Copolymer.

4. In paragraph 2, Based on 100 wt% of the total weight of the copolymer, it further comprises 0.1 wt% or more and 20 wt% or less of the acrylic acid series monomer unit, 0.1 wt% or more and 35 wt% or less of the acrylate series monomer unit including a branched alkyl group having 3 to 10 carbon atoms, or a combination thereof. Copolymer.

5. In paragraph 1, The monomer unit containing the sulfur atom includes 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 monomer unit of the acrylate series containing the linear alkyl group having 1 to 20 carbon atoms is formed by polymerizing at least one 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 acrylonitrile series monomer is formed by polymerizing at least one selected from the group consisting of acrylonitrile and methacrylonitrile. Copolymer.

7. In paragraph 1, The above sulfur atom-containing monomer unit is formed by polymerization of sodium vinylsulfonate, Copolymer.

8. In paragraph 2, The above acrylic acid series monomer unit is formed by polymerizing at least one selected from the group consisting of acrylic acid and methacrylic acid. The monomer unit of the acrylate series containing a branched alkyl group having 3 to 10 carbon atoms is formed by polymerizing at least one selected from the group consisting of isopropyl acrylate, isopropyl methacrylate, sec-butyl acrylate, sec-butyl methacrylate, tert-butyl acrylate, tert-butyl methacrylate, 2-ethyl hexyl acrylate and 2-ethyl hexyl methacrylate. Copolymer.

9. In paragraph 1, Containing a monomer repeating unit represented by the following chemical formula 1, 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, 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 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, 0.01≤a≤0.65, 0≤b≤0.35, 0≤c≤0.2, 0.01≤d≤0.3, 0.001≤e≤0.3, and 0.01≤f≤0.4, a+b+c+d+e+f=1.

10. A copolymer according to any one of claims 1 to 9; and containing inorganic particles; Slurry composition.

11. Containing the slurry composition of Article 10, Membrane.

12. Including the separation membrane of Article 11, Secondary battery.

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