Copolymer for separator and secondary battery including same

Abstract

The present invention relates to a copolymer prepared by copolymerizing two or more monomers selected from the group consisting of acrylonitrile-based monomers, acrylate-based monomers, and acrylic acid-based monomers with a vinyl acetate-based monomer and hydrolyzing the copolymer, and to core-shell particles, a slurry composition, a separator, and a secondary battery containing the copolymer.

Description

[Technical Field]

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

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

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

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

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

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

[0007] To ensure excellent battery characteristics, the coating layer must be uniformly coated and must have strong adhesive strength to the substrate.

[0008] Furthermore, in order to meet the recent trend toward higher capacity and higher output, it is necessary to further improve the heat resistance of conventional separation membranes. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Korean Patent No. 10-1430975 [Patent Document 2] Korean Patent Publication No. 10-2006-0072065 Summary of the Invention [Problem to be solved by the invention]

[0010] Therefore, the present invention aims to provide a slurry composition having excellent adhesive strength by using a copolymer.

[0011] The present invention also provides a separator having excellent heat resistance by applying the slurry composition, and a battery having excellent performance using the separator.

[0012] This reduces the defective rate during battery manufacturing and allows for the realization of a battery with excellent battery resistance and life characteristics.

[0013] However, the problems to be solved by the present invention are not limited to those mentioned above, and other problems not mentioned will be clearly understood by those skilled in the art from the following description. [Means for solving the problem]

[0014] One aspect of the present invention is a copolymer of two or more monomers selected from the group consisting of acrylonitrile-based monomers, acrylate-based monomers, and acrylic acid-based monomers with a vinyl acetate-based monomer, followed by hydrolysis. A copolymer is provided.

[0015] Another aspect of the invention is a core; and a shell surrounding the core; the shell comprises the copolymer; Core-shell particles are provided.

[0016] Another aspect of the present invention is a method for producing the copolymer; and Inorganic particles; A slurry composition is provided.

[0017] Yet another aspect of the present invention includes the slurry composition: A separation membrane is provided.

[0018] Another aspect of the present invention includes the separation membrane, A secondary battery is provided. [Effects of the Invention]

[0019] The copolymer of the present invention can increase the adhesive strength with the polyolefin film that is the substrate of the electrode and / or separator, and can improve the heat resistance of the separator.

[0020] In addition, the defective rate during battery manufacturing can be reduced, and a battery with excellent battery resistance and life characteristics can be realized. DETAILED DESCRIPTION OF THE INVENTION

[0021] The functions and effects of the present invention will be described in more detail below through specific examples of the present invention, however, these examples are presented only as examples of the present invention and do not define the scope of the invention.

[0022] Prior to this, the terms and words used in this specification and claims should not be interpreted in a limited way to their ordinary or dictionary meanings, but should be interpreted in a way that is consistent with the technical idea of ​​the present invention, in accordance with the principle that an inventor can appropriately define the concept of a term in order to best explain his or her invention.

[0023] Therefore, it should be understood that the configurations of the embodiments described in this specification are merely the most preferred embodiments of the present invention and do not represent the technical ideas of the present invention, and that at the time of filing this application, there may be various equivalents and modifications that can replace them.

[0024] In this specification, the singular expression includes the plural expression unless the context clearly dictates otherwise. In this specification, the terms "comprise," "comprise," "have," and the like are intended to specify the presence of embodied features, numbers, steps, components, or combinations thereof, and should be understood as not precluding the presence or additional possibility of one or more other features, numbers, steps, components, or combinations thereof.

[0025] In the present specification, when numerical ranges are indicated as "a to b" and "a to b," "to" and "to" are defined as ≧a and ≦b.

[0026] The copolymer according to one embodiment of the present invention may be prepared by copolymerizing two or more monomers selected from the group consisting of an acrylonitrile-based monomer, an acrylate-based monomer, and an acrylic acid-based monomer with a vinyl acetate-based monomer, followed by hydrolysis.

[0027] The hydrolysis may be alkaline hydrolysis.

[0028] In one embodiment, the copolymer may be prepared by copolymerizing and hydrolyzing 35% to 75% by weight of the acrylonitrile-based monomer, 20% to 55% by weight of an acrylate-based monomer, 1% to 10% by weight of an acrylic acid-based monomer, and 1% to 15% by weight of a vinyl acetate-based monomer.

[0029] In one embodiment, the copolymer may contain, based on 100 wt% of the total weight of the copolymer, 35 wt% to 75 wt% of acrylonitrile-based monomer units, 20 wt% to 55 wt% of acrylate-based monomer units, 1 wt% to 10 wt% of acrylic acid-based monomer units, and 1 wt% to 15 wt% of vinyl acetate-based monomer units and vinyl alcohol-based monomer units.

[0030] Meanwhile, the vinyl acetate-based monomer unit and the vinyl alcohol-based monomer unit may be 1 wt % or more and 15 wt % or less, and the vinyl alcohol-based monomer unit may exceed 0 wt %.

[0031] That is, the acrylonitrile-based monomer, the acrylate-based monomer, the acrylic acid-based monomer, and the vinyl acetate-based monomer may be copolymerized to form an acrylonitrile-based monomer unit, an acrylate-based monomer unit, an acrylic acid-based monomer unit, and a vinyl acetate-based monomer unit, respectively.

[0032] In one embodiment, the acrylonitrile-based monomer may be formed by polymerizing at least one selected from the group consisting of methacrylonitrile and methyl acrylonitrile.

[0033] The acrylate monomer units include methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, propyl acrylate, propyl methacrylate, isopropyl acrylate, isopropyl methacrylate, butyl acrylate, butyl methacrylate, sec-butyl acrylate, sec-butyl methacrylate, tert-butyl acrylate, tert-butyl methacrylate, ethylhexyl acrylate, ethylhexyl methacrylate, lauryl acrylate, and lauryl methacrylate. The copolymer may be formed by polymerizing one or more selected from the group consisting of stearyl acrylate, stearyl acrylate, and stearyl methacrylate.

[0034] The acrylic acid-based monomer unit may be formed by polymerizing at least one selected from the group consisting of acrylic acid and methacrylic acid, and the vinyl acetate-based monomer unit may be formed by polymerizing vinyl acetate.

[0035] Meanwhile, some of the vinyl acetate-based monomer units may be converted into vinyl alcohol-based monomer units through the Singer degradation.

[0036] The degree of hydrolysis may be adjusted to, for example, 70% or more, 75% or more, 80% or more, 85% or more, 90% or more, or 95% or more.

[0037] This means that 70% or more, 75% or more, 80% or more, 85% or more, 90% or more, or 95% or more of the vinyl acetate-based monomer units can be changed to the vinyl alcohol-based monomer units.

[0038] If the content of the acrylonitrile-based monomer unit is above or below the range of the present invention, the dispersibility of the polymer particles and the inorganic slurry may be reduced, or the adhesive strength may be reduced.

[0039] If the content of the acrylate-based monomer unit is above or below the range of the present invention, the adhesive strength may be reduced.

[0040] If the content of the acrylic acid-based monomer unit is above or below the range of the present invention, aggregation and precipitation of the polymer or a decrease in adhesive strength may occur.

[0041] If the content of the vinyl acetate monomer unit is above or below the range of the present invention, safety issues such as storage safety may occur.

[0042] If the content of the vinyl alcohol-based monomer unit is above or below the range of the present invention, it may cause a decrease in adhesive strength, an increase in viscosity, an increase in particle size, and the like.

[0043] In one embodiment, the acrylic acid-based monomer units may be combined with an alkali metal, a hydroxide containing an alkali metal, or a combination thereof.

[0044] That is, the carboxylate group of the acrylic acid-based monomer unit may be bonded to an alkali metal, a hydroxide containing an alkali metal, or a combination thereof.

[0045] On the other hand, the weight ratio of the alkali metal, hydroxide containing an alkali metal, or combination thereof to the copolymer (weight of the alkali metal, hydroxide containing an alkali metal, or combination thereof:weight of the copolymer) may be 0.8 to 6.5:100.

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

[0047] The adhesive strength of a separator containing an alkali metal, an alkali metal-containing hydroxide, or a combination thereof may be determined by the strength of cohesive force and repulsive force between elements, and the adhesive strength may change depending on the content due to the difference in the strength of cohesive force, adhesive force, and repulsive force.

[0048] Meanwhile, improvement in adhesive strength of the inorganic material means an increase in adhesive strength between the inorganic material and the substrate, which may mean that the heat resistance of the separator can be improved by increasing the amount of inorganic material.

[0049] The electrode adhesive strength of the separator can reduce the defect rate caused by stacking electrodes during battery assembly, minimize void formation, and improve ionic conductivity in the electrolyte.

[0050] In addition, when a binder layer is coated separately on an inorganic coating layer, the electrode adhesion can be maximized, which ultimately minimizes the battery defect rate and further improves battery performance.

[0051] The copolymer of the present invention can improve wettability of the copolymer by bonding with an alkali metal, a hydroxide containing an alkali metal, or a combination thereof and generating an alcohol functional group, thereby inducing an anchoring effect and maximizing adhesive strength.

[0052] In one embodiment, the reaction temperature for bonding the copolymer with the alkali metal, hydroxide containing alkali metal, or a combination thereof may be 40°C or more and 70°C or less.

[0053] If the reaction temperature is below this range, the adhesive properties and reactivity of the separator may be reduced, particularly the wet electrode adhesive strength.

[0054] If the reaction temperature exceeds the above range, side reactions of the copolymer may occur.

[0055] In one embodiment, the copolymer may include a repeating monomer unit represented by the following Formula 1:

[0056] [ka] In the above formula 1, R1 to R3 are each independently hydrogen, a linear or branched hydrocarbon having 1 to 4 carbon atoms, or a combination thereof; R4 is a linear or branched hydrocarbon having 1 to 10 carbon atoms; M is hydrogen, an alkali metal, a hydroxide containing an alkali metal, or a combination thereof; and x+y+z+m+n=1.

[0057] In the above chemical formula 1, x, y, z, m, and n correspond to the weight fraction of each monomer unit, and the sum of the weight fractions of each monomer unit is 1.

[0058] In one embodiment, R1 to R3 in Formula 1 may each independently include at least one selected from the group consisting of hydrogen, methyl, and ethyl.

[0059] In addition, R4 in Chemical Formula 1 may include at least one selected from the group consisting of methyl, ethyl, n-propyl, isopropyl, n-butyl, tert-butyl, n-pentyl, n-hexyl, n-butyl, n-octyl, 2-ethylhexyl, n-nonyl, and n-decyl.

[0060] Meanwhile, M in the above Chemical Formula 1 may be Li, Na or K, but is not limited thereto.

[0061] In one embodiment, the copolymer may be a random or block copolymer depending on the synthesis process.

[0062] In one embodiment, the copolymer may have a water average molecular weight of 5,000 to 1,000,000.

[0063] If the water-average molecular weight of the copolymer is less than 5,000, the copolymer may have increased fluidity, resulting in reduced dispersibility and reduced heat resistance of the separator.If the water-average molecular weight is more than 1,000,000, the viscosity may be too high for use, which may clog the pores of the separator, resulting in reduced air permeability and resistance.

[0064] In one embodiment, the copolymer may further include 0.1 to 3 parts by weight of a cross-linking monomer, based on 100 parts by weight of the total weight of the copolymer.

[0065] The cross-linking monomer may include at least one selected from the group consisting of divinylbenzene, aliphatic difunctional methacrylate, and aromatic difunctional methacrylate.

[0066] Core-shell particles according to another embodiment of the present invention comprise a core and a shell surrounding the core, and the shell may comprise the copolymer.

[0067] Preferably, the average particle size of the core may be between 50 and 250 nm, and the average particle size of the final core-shell particles may be between 300 and 1000 nm.

[0068] If a core is not used, the particle shape may be broken down due to the absence of a hard, durable structure, and film formation may proceed, blocking the pores of the separator, resulting in reduced air permeability and resistance.

[0069] This can also cause problems in coating the electrode adhesive layer, since if the core does not provide durability, film formation may progress and block the pores of the separator.

[0070] In one embodiment, the core may be a polymer containing, but is not limited to, an acrylate-based monomer unit, an acrylic acid-based monomer unit, or a combination thereof, and the core particle may be crosslinked.

[0071] For example, the core may include a copolymer containing 90 wt% to 98 wt% of acrylate monomer units and 2 wt% to 10 wt% of acrylic acid monomer units, based on 100 wt% of the total weight of acrylate monomer units and acrylic acid monomer units.

[0072] If the content of each monomer unit in the copolymer of the core is higher or lower, the reaction safety and durability of the core may be reduced.

[0073] A slurry composition according to another embodiment of the present invention may contain the copolymer and inorganic particles.

[0074] That is, the slurry composition may include core-shell particles in which the copolymer is contained in the shell.

[0075] The inorganic particles may be any insulating particles without any limitation, and may preferably be high-dielectric insulating particles.

[0076] Specific examples of the inorganic particles include Al2O3, 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), AlOOH, or mixtures thereof.

[0077] The size of the inorganic particles is not particularly limited, and may be, for example, 0.01 μm to 30 μm, more preferably 0.1 μm to 10 μm, inclusive. If the average particle size of the inorganic particles is less than the preferred range, dispersibility may be reduced. If the average particle size of the inorganic particles is greater than the preferred range, the coating layer may become thick after coating, resulting in reduced mechanical properties.

[0078] The shape of the inorganic particles is not particularly limited, and may be, for example, spherical, elliptical, or irregular.

[0079] A separation membrane according to another aspect of the present invention may include the slurry composition.

[0080] The separator coating layer containing the copolymer may be used in either a single layer or a multilayer coating. For example, when used in a single layer coating together with inorganic particles, the copolymer may improve the binding strength of the inorganic particles and the electrode adhesive strength depending on the content.

[0081] When a multi-layer coating is performed by coating only a binder on an inorganic particle coating layer, the electrode adhesion can be improved.

[0082] The slurry composition may be coated on at least one surface of a porous substrate film, or the slurry composition may be formed into a film and attached to a porous substrate film to prepare a separator.

[0083] Meanwhile, the separator may be used as a separator for a secondary battery, for example, a separator for a lithium secondary battery.

[0084] An example of a method for producing a separation membrane may include the steps of: (a) dissolving or dispersing the copolymer in a solvent to prepare a polymer solution; (b) adding and mixing inorganic particles into the polymer solution of step (a); and (c) coating one or more regions selected from the group consisting of the surface of a polyolefin-based separation membrane substrate and a portion of the pores in the substrate with the mixture of step (b) and drying.

[0085] First, 1) the copolymer is prepared in the form of a polymer solution by dissolving or dispersing it in a suitable organic solvent.

[0086] The solvent preferably has a solubility index similar to that of the copolymer used as the binder and a low boiling point. This facilitates uniform mixing and subsequent solvent removal. Non-limiting examples of solvents that can be used include acetone, tetrahydrofuran, methylene chloride, chloroform, dimethylformamide, N-methyl-2-pyrrolidone (NMP), cyclohexane, water, or a mixture thereof. More preferably, the copolymer can be dispersed in water.

[0087] 2) Inorganic particles are added to and dispersed in the prepared polymer solution to prepare a mixture of inorganic particles and polymer.

[0088] It is preferable to carry out a dispersion process of the polymer solution and inorganic particles. In this case, the appropriate dispersion time may be 10 minutes to 5 hours. As a dispersion method, a conventional method may be used, and a ball mill method is particularly preferable.

[0089] The composition of the mixture consisting of inorganic particles and polymer is not particularly limited, and the thickness, pore size, and porosity of the organic / inorganic composite porous separator of the present invention can be adjusted depending on the composition.

[0090] That is, as the ratio of inorganic particles (I) to polymer (P) (ratio = I / P) increases, the porosity of the separator increases, which results in an increase in the thickness of the separator for the same solid content (weight of inorganic particles + weight of polymer).

[0091] In addition, the possibility of pore formation between inorganic particles increases, resulting in an increase in pore size. At this time, as the size (particle size) of inorganic particles increases, the interstitial distance between inorganic particles also increases, resulting in an increase in pore size.

[0092] 3) The mixture of inorganic particles and polymer thus prepared is coated on a prepared polyolefin-based separation membrane substrate, and then dried to obtain the separation membrane of the present invention.

[0093] The method for coating the mixture of inorganic particles and polymer onto the polyolefin-based separation membrane substrate can be a conventional coating method known in the art, such as bar coating, dip coating, die coating, roll coating, comma coating, gravure coating, or a combination thereof. In addition, when the mixture of inorganic particles and polymer is coated onto the polyolefin-based separation membrane substrate, coating can be performed on both sides of the separation membrane substrate, or selectively on only one side.

[0094] When the separator is used in a secondary battery, lithium ions are transferred not only through the separator substrate but also through the porous active layer, and the separator can exhibit the aforementioned improved safety when an internal short circuit occurs due to an external impact.

[0095] The secondary battery may include a positive electrode, a negative electrode, the separator interposed between the positive electrode and the negative electrode, and an electrolyte.

[0096] The secondary battery may be manufactured by a conventional method known in the art. For example, the electrodes and a separator are assembled together, and then an electrolyte is injected into the assembly.

[0097] The electrode used with the separator is not particularly limited, and the positive electrode active material may be any of the common positive electrode active materials used in the positive electrode of a secondary battery, including, but not limited to, lithium intercalation materials such as lithiated magnesium oxide, lithiated cobalt oxide, lithiated nickel oxide, or composite oxides formed by combinations thereof. The negative electrode active material may be any of the common negative electrode active materials used in the negative electrode of a conventional electrochemical device, including, but not limited to, lithium metal or a lithium alloy and lithium intercalation materials such as carbon, petroleum coke, activated carbon, graphite, or other carbons. The above-mentioned electrode active materials are bound 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, copper alloy, or a combination thereof, to form two electrodes.

[0098] The electrolyte is a salt having the structure A+B-, where A+ includes alkali metal cations such as Li+, Na+, K+, or a combination thereof, and B- is PF6 - , BF4 - , Cl - , Br - , I - , ClO4 - , AsF6 - , CH3CO2 - , CF3SO3 - , N(CF3SO2)2 - , C(CF2SO2)3 - It is preferable that a salt containing an anion such as the above or an ion consisting of a combination thereof is dissolved and dissociated in an organic solvent consisting of propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, tetrahydrofuran, N-methyl-2-pyrrolidone (NMP), ethyl methyl carbonate (EMC), gamma butyrolactone (GBL), or a mixture thereof.

[0099] In applying the separator to a battery, in addition to the general winding process, lamination and folding processes of the separator and electrodes are possible. [Mode for carrying out the invention]

[0100] The present invention will be described in more detail below using examples, but the present invention is not limited thereto.

[0101] [Production Example 1] Production of copolymer Production of core particles 370 parts by weight of distilled water and 0.1 to 3 parts by weight of a nonionic emulsifier per 100 parts by weight of the monomer mixture (A) were placed in a reaction vessel and stirred, and the mixture was heated to 83°C while injecting high-purity nitrogen gas.

[0102] A decomposition initiator, ammonium persulfate, was added in an amount of 0.1 to 3 parts by weight per 100 parts by weight of the monomer mixture (A) to a reaction vessel prepared at 83°C, and a crosslinking monomer was added to carry out a continuous emulsion polymerization reaction to produce core particles.

[0103] The monomer mixture (A) contained acrylic acid monomer (AA) and methylmethacrylate (MMA).

[0104] Meanwhile, the contents of acrylic acid monomer (AA), methyl methacrylate (MMA) and crosslinking monomer were adjusted to 96.5 wt%, 2.5 wt%, and 1 wt%, respectively, based on 100 wt% of the total weight of acrylic acid monomer (AA), methyl methacrylate (MMA) and crosslinking monomer.

[0105] Fabrication of core-shell particles A reaction vessel was charged with 235 parts by weight of distilled water, 0.05 to 2 parts by weight of emulsifier per 100 parts by weight of monomer mixture (B), and 2.0 parts by weight of the produced core particles, and the mixture was stirred and heated to 65°C while injecting high-purity nitrogen gas. 0.15 parts by weight of ammonium persulfate, a decomposition initiator, per 100 parts by weight of monomer mixture (B), was added to the reaction vessel prepared at 65°C, and a continuous emulsion polymerization reaction was carried out to produce core-shell particles.

[0106] Meanwhile, the core particles may be used in an amount of 0.1 to 10 parts by weight based on 100 parts by weight of the monomer mixture.

[0107] Then, a metal hydroxide (NaOH, LiOH, or KOH) was added at a controlled temperature and for a certain period of time to modify the surface functional groups of the shell. That is, the carboxylic acid moieties present in the shell were ionized.

[0108] The monomer mixture (B) was adjusted to contain 42 wt %, 8 wt %, 40 wt % and 10 wt % of acrylonitrile monomer (AN), acrylic acid monomer (AA), butyl acrylate (BA) and vinyl acetate (VAc), respectively.

[0109] In addition, the monomer mixture (B) further contained 2.0 parts by weight of a cross-linking monomer (divinylbenzene) based on 100 parts by weight of the total weight of the monomer mixture (B).

[0110] The produced core-shell particles were used as a binder.

[0111] [Production Example 2] Production of slurry for porous membrane coating Inorganic particles (alumina, average particle size 0.4 μm) and the core-shell particles (binder) prepared in Preparation Example 1 were mixed in a solid powder weight ratio of 80:20, and then additives such as a dispersant and a surface tension reducing agent and additional distilled water were added and mixed to a solid powder concentration of 35 wt %. This mixture was thoroughly dispersed using a ball mill or a mechanical stirrer to prepare a slurry.

[0112] [Production Example 3] Production of separation membrane An inorganic coating layer is formed by applying the porous membrane coating slurry prepared in Preparation Example 2 to a polyolefin (thickness: 11 μm) porous substrate (polyethylene (PE), polypropylene (PP), etc.). Various coating methods can be used, such as dip coating, die coating, gravure coating, and comma coating.

[0113] After coating, the coating was dried using warm air, hot air, vacuum drying, infrared drying, or other methods, and the drying temperature range was 50 to 80°C.

[0114] The thickness of the inorganic coating layer is 1 to 6 μm on one or both sides. If the thickness is less than 1 μm, the heat resistance of the separator is significantly reduced. If the thickness is more than 6 μm, the separator is too thick, which reduces the energy density of the battery and increases the resistance.

[0115] [Examples 1 to 4 and Comparative Examples 1 to 3] Examples 1 to 4 and Comparative Examples 1 to 3 were prepared according to Preparation Example 1 by adjusting the content of metal hydroxide used and the reaction temperature with the metal hydroxide as shown in Table 1 below to change the surface functional groups of the shell of the core-shell particles of Preparation Example 1.

[0116] Using the binder copolymers prepared in Examples 1 to 4 and Comparative Examples 1 to 3, a slurry for coating a porous membrane and a separator were prepared in Preparation Examples 2 and 3, respectively.

[0117] [Table 1] The weight ratio of the metal hydroxide in Table 1 above indicates the weight parts of the metal hydroxide added to 100 weight parts of the copolymer forming the shell of the core-shell particle in order to change the surface functional groups of the core-shell particle.

[0118] For example, the weight ratio in Example 1 indicates that 2 parts by weight of a metal hydroxide was added to 100 parts by weight of the copolymer forming the shell of the core-shell particles to change the surface functional groups of the core-shell particles.

[0119] [Evaluation Example 1] Average diameter and glass transition temperature of core-shell particles The average diameters of the core-shell particles of Examples 1 to 4 and Comparative Examples 1 to 3 were analyzed using a particle size analyzer (product name: Z3000, manufacturer: Nicomp).

[0120] 10 to 20 mg of the core-shell particles of Examples 1 to 4 and Comparative Examples 1 to 3 were placed in a 40 μl aluminum pan, and the glass transition temperature was analyzed by checking the thermal behavior using a DSC (Differential Scanning Calorimeter).

[0121] [Evaluation Example 2] Adhesion strength of slurry for porous membrane coating A tape having a width of 18 mm and a length of 30 mm or more was attached to the separator prepared in Preparation Example 3 using the core-shell particles (binder) of Examples 1 to 4 and Comparative Examples 1 to 3, and then gently pressed five times with a hand roller.

[0122] The prepared specimen was attached to a UTM (1 kgf Load cell), one side of the separator was attached to the upper clip of the tensile tester, and a tape attached to one side of the separator was attached to the lower clip, and the 180° peel strength was measured at a speed of 100 mm / min. At least five specimens were prepared per sample and measured, and the average value was calculated.

[0123] [Evaluation Example 3] Dry electrode adhesion of separation membrane The separator prepared in Preparation Example 3 using the core-shell particles (binder) of Examples 1 to 4 and Comparative Examples 1 to 3 was cut into a size of 20 mm in width and 70 mm in length.

[0124] An electrode cut to a width of 25 mm and a length of 70 mm was placed on the prepared separator, and then hot-pressed at 65°C and 65 kg / cm 2 The temperature and pressure were applied for 30 seconds.

[0125] The prepared specimen was attached to a UTM (1 kgf Load cell), one side of the separator was attached to the upper clip of the tensile tester, and a tape attached to one side of the separator was attached to the lower clip, and the 180° peel strength was measured at a speed of 100 mm / min. At least five specimens were prepared per sample and measured, and the average value was calculated.

[0126] [Evaluation Example 4] Wet electrode adhesion of separation membrane The separator prepared in Preparation Example 3 using the core-shell particles (binder) of Examples 1 to 4 and Comparative Examples 1 to 3 was cut into a size of 20 mm in width and 70 mm in length.

[0127] An electrode cut to a width of 25 mm and a length of 70 mm was placed on the prepared separator, and then sealed and left at room temperature for 12 hours to impregnate the electrolyte. After that, the separator was heated at 65°C and 65 kg / cm2 in a hot press. 2 The temperature and pressure were applied for 30 seconds.

[0128] The prepared specimen was attached to a UTM (1 kgf Load cell), one side of the separator was attached to the upper clip of the tensile tester, and a tape attached to one side of the separator was attached to the lower clip, and the 180° peel strength was measured at a speed of 100 mm / min. At least five specimens were prepared per sample and measured, and the average value was calculated.

[0129] [Evaluation Example 5] Change in air permeability of separation membrane The separator prepared according to Preparation Example 3 using the core-shell particles (binders) of Examples 1 to 4 and Comparative Examples 1 to 3 was used to measure the time (time) required for 100 cc of air to pass through using an air permeability tester.

[0130] Meanwhile, the change in air permeability is the value obtained by subtracting the air permeability of an uncoated polyolefin separator from the air permeability of the separator prepared in Preparation Example 3 using the core-shell particles (binder) of Examples 1 to 4 and Comparative Examples 1 to 3.

[0131] The particle sizes and glass transition temperatures (Tg) of the core-shell particles of Examples 1 to 4 and Comparative Examples 1 to 3 measured by Evaluation Example 1 are shown in Table 2 below.

[0132] [Table 2] As shown in Table 2 above, the average diameter of the core-shell particles of Examples 1 to 4 was measured to be 450-480 nm.

[0133] It was confirmed that the average diameter of the core-shell particles increased as the content of the metal hydroxide reacted to change the surface functional groups of the core-shell particles increased and the reaction temperature increased.

[0134] The glass transition temperatures of the core-shell particles of Examples 1 to 4 were measured to be 36.3 to 36.7°C.

[0135] It was observed that the glass transition temperature remained relatively constant despite changes in metal hydroxide content.

[0136] In particular, the core-shell particles (binder) of Comparative Example 3, which contained an excessive amount of metal hydroxide, had a very large average diameter. This is because when an excessive amount of metal hydroxide was contained, all of the carboxylic acids in the core-shell particles (binder) were replaced with carboxylates.

[0137] The peel adhesion strength and electrode adhesion strength (dry and wet) of the separators prepared in Preparation Example 3 using the core-shell particles of Examples 1 to 4 and Comparative Examples 1 to 3 measured in Evaluation Examples 2 to 4 are shown in Table 3 below.

[0138] [Table 3] As shown in Table 3 above, the separators prepared according to Preparation Example 3 using the core-shell particles (binders) of Examples 1 to 4 had peel adhesion strengths in the range of 0.02 to 0.2 gf / mm, dry electrode adhesion strengths in the range of 0.1 to 1 gf / mm, and wet electrode adhesion strengths in the range of 0.3 to 1.5 gf / mm.

[0139] Meanwhile, the separator prepared in Preparation Example 3 using the core-shell particles (binders) of Examples 1 to 4 showed higher peel adhesion strength than the separator prepared in Preparation Example 3 using the core-shell particles (binders) of Comparative Examples 1 and 3.

[0140] It was confirmed that the peel adhesive strength increased as the content of the metal hydroxide used increased and the reaction temperature with the metal hydroxide increased.

[0141] This is because the vinyl acetate monomers used in the production of core-shell particles (binders) have relatively low reactivity when polymerized with acrylate monomers, and are therefore mainly located on the surface of the particles. By adding a metal hydroxide, some of the functional groups of the vinyl acetate monomer units on the surface of the core-shell particles (binders) are converted to alcohols, improving adhesive strength and wettability.

[0142] However, when using the core-shell particles (binder) of Comparative Example 3, which contained an excessive amount of metal hydroxide, it was confirmed that the peel adhesive strength was actually lost. This is because when an excessive amount of metal hydroxide is contained, all of the carboxylic acids in the core-shell particles (binder) are replaced with carboxylates, causing a decrease in adhesive strength.

[0143] Similarly, it was also confirmed that the electrode adhesion (dry and wet) improved with increasing content of metal hydroxide used.

[0144] On the other hand, the separator prepared in Preparation Example 3 using the core-shell particles (binder) of Comparative Example 2, which had a low reaction temperature, was found to have a significantly lower wet electrode adhesion strength than the separator prepared in Preparation Example 3 using the core-shell particles (binder) of Examples 3 and 4, which had a high reaction temperature and reacted with the same amount of metal hydroxide.

[0145] This is because the hydrolysis reaction accelerates as the reaction temperature increases, and the hydrolyzed core-shell particles (binder) form hydrogen bonds with the oxide layer on the outermost surface of the inorganic material, providing strong adhesive strength.

[0146] The changes in air permeability of the separators prepared in Preparation Example 3 using the core-shell particles of Examples 1 to 4 and Comparative Examples 1 to 3, as measured in Evaluation Example 5, are shown in Table 4 below.

[0147] [Table 4] As shown in Table 4, the change in air permeability of the separator prepared in Preparation Example 3 using the core-shell particles (binder) of Examples 1 to 4 was in the range of Δ1 sec / 100 cc to Δ26 sec / 100 cc.

[0148] The change in air permeability tended to increase with increasing content of metal hydroxide used.

[0149] On the other hand, when the core-shell particles (binder) of Comparative Example 3 containing an excessive amount of metal hydroxide were used, the change in air permeability was significantly large, which is presumably related to the increase in the average diameter of the core-shell particles (binder) of Comparative Example 3.

[0150] In addition, it was confirmed that the separation membrane prepared in Preparation Example 3 using the core-shell particles (binder) of Comparative Example 2, which had a low reaction temperature, had a larger change in air permeability than the separation membranes prepared in Preparation Example 3 using the core-shell particles (binder) of Examples 3 and 4, which had a high reaction temperature and reacted with the same amount of metal hydroxide.

[0151] As a result, the separators prepared using the core-shell particles (binder) of the examples had excellent substrate and / or electrode adhesion and air permeability control capabilities.

[0152] In addition, it can be confirmed that the excellent adhesive strength and heat resistance of the core-shell particles (binder) of the present invention can reduce the defective rate during battery manufacturing and realize separator properties that are advantageous for maintaining battery resistance and lifespan.

[0153] The scope of the present invention is indicated by the claims that follow rather than by the above detailed description, and all modifications and variations that fall within the meaning and scope of the claims and their equivalents should be interpreted as being included within the scope of the present invention. [Industrial Applicability]

[0154] The copolymer of the present invention can increase the adhesive strength with the polyolefin film that is the substrate of the electrode and / or separator, and can improve the heat resistance of the separator.

[0155] In addition, the defective rate during battery manufacturing can be reduced, and a battery with excellent battery resistance and life characteristics can be realized.

Claims

1. It is produced by copolymerizing two or more monomers selected from the group consisting of acrylonitrile-based monomers, acrylate-based monomers, and acrylic acid-based monomers with vinyl acetate-based monomers, followed by hydrolysis. Copolymer.

2. The copolymer is produced by copolymerizing and hydrolyzing 35% by weight or more and 75% by weight or less of the acrylonitrile-based monomer, 20% by weight or more and 55% by weight or less of the acrylate-based monomer, 1% by weight or more and 10% by weight or less of the acrylic acid-based monomer, and 1% by weight or more and 15% by weight or less of the vinyl acetate-based monomer, The copolymer of claim 1.

3. The copolymer contains, based on 100% by weight of the total weight of the copolymer, 35% by weight or more and 75% by weight or less of acrylonitrile-based monomer units, 20% by weight or more and 55% by weight or less of acrylate-based monomer units, 1% by weight or more and 10% by weight or less of acrylic acid-based monomer units, and 1% by weight or more and 15% by weight or less of vinyl acetate-based monomer units and vinyl alcohol-based monomer units, The copolymer of claim 1. (However, the content of the vinyl alcohol-based monomer unit exceeds 0% by weight.)

4. The acrylic acid-based monomer unit is bonded to an alkali metal, a hydroxide containing an alkali metal, or a combination thereof. The copolymer according to claim 3.

5. the weight ratio of the alkali metal, the hydroxide containing an alkali metal, or the combination thereof to the copolymer (weight of the alkali metal, the hydroxide containing an alkali metal, or the combination thereof:weight of the copolymer) is 0.8 to 6.5:100; The copolymer according to claim 4.

6. The reaction temperature for bonding the copolymer with the alkali metal, hydroxide containing an alkali metal, or a combination thereof is 40° C. or more and 70° C. or less. The copolymer according to claim 4.

7. The monomer repeat unit is represented by the following formula 1: The copolymer of claim 1. 【Chemical 1】 In the above formula 1, R １ Or R ３ are each independently hydrogen, a linear or branched hydrocarbon having 1 to 4 carbon atoms, or a combination thereof; R ４ is a linear or branched hydrocarbon having 1 to 10 carbon atoms, M is hydrogen, an alkali metal, a hydroxide containing an alkali metal, or a combination thereof; x+y+z+m+n=1.

8. R in the above-mentioned Chemical Formula 1 １ Or R ３ each independently contains one or more selected from the group consisting of hydrogen, methyl, and ethyl, R in the above-mentioned Chemical Formula 1 ４ includes at least one selected from the group consisting of methyl, ethyl, n-propyl, isopropyl, n-butyl, tert-butyl, n-pentyl, n-hexyl, n-butyl, n-octyl, 2-ethylhexyl, n-nonyl, and n-decyl; The copolymer according to claim 7.

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

10. Based on 100 parts by weight of the total weight of the copolymer, Further containing 0.1 parts by weight or more and 3 parts by weight or less of a crosslinking monomer, The copolymer of claim 1.

11. core; a shell surrounding the core; The shell comprises a copolymer according to any one of claims 1 to 10. Core-shell particles.

12. the core comprises a polymer comprising acrylate-based monomer units and acrylic acid-based monomer units or a combination thereof; The core-shell particle according to claim 11.

13. The copolymer according to any one of claims 1 to 10; and inorganic particles; Slurry composition.

14. The slurry composition of claim 13, Separation membrane.

15. The separation membrane according to claim 14, Secondary battery.

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