Copolymer for separator and secondary battery comprising same

Abstract

The present invention relates to: a copolymer comprising an acrylonitrile-based monomer unit, an acrylate-based monomer unit containing a C1-20 linear alkyl group, an acrylate-based monomer unit containing a C3-10 branched alkyl group, an acrylic acid-based monomer unit, and a monomer unit containing a C1-20 linear or branched alkyl group including a hydroxyl group; and a slurry composition, a separator, and a secondary battery, which comprise the copolymer.

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] Lithium-ion secondary batteries are insulated by a separator, but due to internal or external battery abnormalities or impacts, a short circuit between the positive and negative electrodes may occur, which may 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] Meanwhile, the electrode adhesive layer on the separator reduces the gap between each electrode, accelerates the transfer of lithium ions, and acts as a passage.

[0008] In order to exhibit these electrode adhesive properties, a coating method is used in which a resin is dispersed in an inorganic substance and coated on a separator (A once-coated separator / OCS), and a coating method is used in which a resin is coated on top of a separator that has already been ceramic-coated (Ceramic coated separator / CCS) (A double-coated separator / DCS).

[0009] To reduce the volume of the coated separator and attached electrode and to protect the electrode, a lamination method using heat and pressure is used.

[0010] When many layers are stacked to manufacture a battery with high energy density, pressure is transmitted inside the battery, but heat is not properly transmitted, which may cause the adhesive strength of the coated separator to decrease and voids to form.

[0011] In addition, in order to secure excellent battery characteristics, the coating layer must be coated uniformly and have strong adhesion to the substrate.

[0012] In particular, in high-capacity secondary batteries, the faster the charge / discharge speed, the more densely the electrodes are stacked (staking), and thus larger and more dead spaces are created inside the secondary battery.

[0013] These voids increase the internal resistance of secondary batteries and reduce their lifespan. Applying a resin with electrode adhesion properties to the separator can significantly reduce the performance degradation caused by these voids.

[0014] [Prior Art Literature]

[0015] [Patent Document]

[0016] (Patent Document 1) Republic of Korea Patent No. 10-1430975

[0017] (Patent Document 2) Republic of Korea Patent Publication No. 10-2006-0072065

[0018] Accordingly, the present invention aims to provide a slurry composition having excellent electrode adhesion to a porous substrate by promoting a movement phenomenon using a copolymer.

[0019] In addition, the present invention seeks to provide a separator having excellent adhesive strength and breathability by applying the slurry composition, and a battery having excellent performance (electrical resistance characteristics) using the separator.

[0020]

[0021] 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.

[0022] One aspect of the present invention is a monomer unit of the acrylonitrile series;

[0023] A monomer unit of the acrylate series containing a linear alkyl group having 1 to 20 carbon atoms;

[0024] A monomer unit of the acrylate series containing a branched alkyl group having 3 to 10 carbon atoms;

[0025] Monomer units of the acrylic acid series; and

[0026] A monomer unit comprising a linear or branched alkyl group having 1 to 20 carbon atoms, including a hydroxyl group;

[0027] Provides a copolymer.

[0028] Another aspect of the original is,

[0029] The above copolymer; and

[0030] containing inorganic particles;

[0031] A slurry composition is provided.

[0032] Another aspect of the present invention is a composition comprising the slurry composition,

[0033] Provides a separation membrane.

[0034] Another aspect of the present invention is a membrane comprising:

[0035] Provides secondary batteries.

[0036] The copolymer of the present invention can promote a migration phenomenon, thereby increasing the adhesion of an electrode to a membrane substrate and improving the heat resistance and breathability of the membrane.

[0037] In addition, the copolymer of the present invention can reduce the defect rate and minimize the formation of voids that occur during the lamination process during battery assembly, and can improve ion conductivity and air permeability in the electrolyte.

[0038] Meanwhile, the adhesive strength of the separator can be maximized through the copolymer of the present invention, and ultimately, the electrical resistance characteristics and stability of the battery can be improved while minimizing battery defects.

[0039] Figure 1 is an SEM observation result according to Evaluation Example 4, which measures the movement phenomenon of the separator manufactured by Examples 1 to 3 of the present invention. Figures 1a, 1b, and 1c correspond to the SEM observation results of the separator manufactured by Examples 1, 2, and 3, respectively.

[0040] Figure 2 is an SEM observation result according to Evaluation Example 4, which measures the movement phenomenon of the separation membrane manufactured by Comparative Examples 1 to 3 of the present invention. Figures 2a, 2b, and 2c correspond to the SEM observation results of the separation membrane manufactured by Comparative Examples 1, 2, and 3, respectively.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] 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.

[0045] In this specification, “a to b” and “a~b” indicating a numerical range are defined as “a to” and “~” as ≥ a and ≤ b.

[0046]

[0047] The copolymer of one aspect of the present invention may include a monomer unit of the acrylonitrile series; a monomer unit of the acrylate series containing a linear alkyl group having 1 to 20 carbon atoms; a monomer unit of the acrylate series containing a branched alkyl group having 3 to 10 carbon atoms; a monomer unit of the acrylic acid series; and a monomer unit containing a linear or branched alkyl group having 1 to 20 carbon atoms containing a hydroxyl group.

[0048] The hydroxyl group of the monomer unit containing a linear or branched alkyl group having 1 to 20 carbon atoms including the above hydroxyl group can increase the adhesion of the electrode to the separator substrate by promoting the migration phenomenon, and can improve the heat resistance and air permeability of the separator as well as enhance the performance of the battery.

[0049] In addition, a copolymer comprising a monomer unit including a linear or branched alkyl group having 1 to 20 carbon atoms including the above hydroxyl group may be produced by an emulsion polymerization method and may exhibit a tendency for the hydrophilic group to be exposed to the outside during the reaction and structure formation.

[0050] Accordingly, after the slurry containing the copolymer and inorganic particles is applied to the membrane, coated, and dried to form a coating layer, a migration phenomenon may occur, in which the copolymer is positioned on the upper portion of the coating layer.

[0051] The copolymer positioned on the upper portion of the coating layer due to the above-mentioned movement phenomenon can contribute to an increase in the adhesion area between the separator and the adherend, thereby exhibiting high adhesion.

[0052] In addition, the above-mentioned movement phenomenon can maintain the content of the copolymer, which can act as a relatively resistance factor within the coating layer, low, thereby enabling free movement of lithium ions (Li ions), which is the main function of the separator, thereby improving the air permeability of the separator and maintaining low resistance of the battery.

[0053] In one embodiment, the copolymer may include, based on 100 wt% of the total weight of the copolymer, 1 wt% or more and 40 wt% or less of the acrylonitrile series monomer unit, 1 wt% or more and 35 wt% or less of the acrylate series monomer unit including a linear alkyl group having 1 to 20 carbon atoms, 10 wt% or more and 50 wt% or less of the acrylate series monomer unit including a branched alkyl group having 3 to 10 carbon atoms, 1 wt% or more and 20 wt% or less of the acrylic acid series monomer unit, and 1 wt% or more and 20 wt% or less of the monomer unit including a linear or branched alkyl group having 1 to 10 carbon atoms including a hydroxyl group.

[0054] For example, the copolymer may include, based on 100 wt% of the total weight of the copolymer, 10 wt% or more and 35 wt% or less of the acrylonitrile series monomer unit, 10 wt% or more and 30 wt% or less of the acrylate series monomer unit including a linear alkyl group having 1 to 20 carbon atoms, 15 wt% or more and 40 wt% or less of the acrylate series monomer unit including a branched alkyl group having 3 to 10 carbon atoms, 1 wt% or more and 15 wt% or less of the acrylic acid series monomer unit, and 1 wt% or more and 20 wt% or less of the monomer unit including a linear or branched alkyl group having 1 to 10 carbon atoms including a hydroxyl group.

[0055] If the monomer unit of the acrylonitrile series is above or 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.

[0056] If the content of the acrylate series monomer unit including the linear alkyl group having 1 to 20 carbon atoms and the acrylate series monomer unit including the branched alkyl group having 3 to 10 carbon atoms exceeds or falls below the content range of the present invention, a decrease in adhesive strength may occur.

[0057] 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.

[0058] If the monomer unit containing a linear or branched alkyl group having 1 to 10 carbon atoms including the above hydroxyl group exceeds or falls below the content range of the present invention, problems such as a decrease in adhesive strength and a decrease in the performance of the separator and battery may occur.

[0059] In one embodiment, the acrylate series monomer unit including a linear alkyl group having 1 to 20 carbon atoms may be formed by polymerizing methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, propyl acrylate, propyl methacrylate, butyl acrylate, butyl methacrylate, lauryl acrylate, lauryl methacrylate, stearyl acrylate, stearyl methacrylate, or a combination thereof.

[0060] For example, the monomer unit of the acrylate series containing a linear alkyl group having 1 to 20 carbon atoms can be formed by polymerizing methyl methacrylate, butyl acrylate, or a combination thereof.

[0061] In addition, the acrylate series monomer unit containing a branched alkyl group having 3 to 10 carbon atoms may be formed by polymerizing isopropyl acrylate, isopropyl methacrylate, sec-butyl acrylate, sec-butyl methacrylate, tert-butyl acrylate, tert-butyl methacrylate, 2-ethyl hexyl acrylate, 2-ethyl hexyl methacrylate, or a combination thereof.

[0062] For example, a monomer unit of the acrylate series containing a branched alkyl group having 3 to 10 carbon atoms can be formed by polymerization of 2-ethylhexyl acrylate.

[0063] The above acrylic acid series monomer unit can be formed by polymerization of acrylic acid, methacrylic acid, or a combination thereof.

[0064] For example, the monomer unit of the acrylic acid series can be formed by polymerization of methacrylic acid.

[0065] Meanwhile, the monomer unit of the acrylonitrile series can be formed by polymerizing acrylonitrile, methacrylonitrile, or a combination thereof.

[0066] For example, the monomer unit of the acrylonitrile series can be formed by polymerizing acrylonitrile.

[0067] In one embodiment, the monomer unit comprising a linear or branched alkyl group having 1 to 10 carbon atoms and including a hydroxyl group may be formed by polymerizing 2-hydroxyethyl acrylate, hydroxypropyl acrylate, 4-hydroxybutyl acrylate, or a combination thereof.

[0068] A monomer that forms a monomer unit including a linear or branched alkyl group having 1 to 10 carbon atoms and including a hydroxyl group through polymerization may have the hydroxyl group positioned at the terminal of the linear or branched alkyl group.

[0069] In one embodiment, the acrylic acid series monomer unit can be combined with an alkali metal.

[0070] That is, the carboxylate group of the monomer unit of the acrylic acid series can be combined with an alkali metal, a hydroxide containing an alkali metal, or a combination thereof.

[0071] The alkali metal may be Li, K, Na or a combination thereof.

[0072] Meanwhile, the weight ratio of the alkali metal and the copolymer (weight of the alkali metal: weight of the copolymer) may be 1 to 5:100.

[0073] If the weight ratio of the alkali metal and the copolymer exceeds or falls below the weight ratio of the present invention, the adhesive properties of the separator may deteriorate. In particular, the peel adhesive strength and electrode adhesive strength of the separator may deteriorate.

[0074] 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.

[0075] 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.

[0076] 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.

[0077] Meanwhile, since the improvement in inorganic adhesion means an increase in adhesion between the inorganic material and the substrate, this may mean that the heat resistance characteristics of the separator can be improved due to the increase in inorganic material.

[0078] 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.

[0079] 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.

[0080] Meanwhile, since the improvement in inorganic adhesion means an increase in adhesion between the inorganic material and the substrate, this may mean that the heat resistance characteristics of the separator can be improved due to the increase in inorganic material.

[0081] 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.

[0082] 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.

[0083] In one embodiment, the copolymer may additionally include a vinyl acetate series monomer unit of 15 wt% or less based on 100 wt% of the total weight of the copolymer.

[0084] For example, the copolymer may additionally include a vinyl acetate series monomer unit of 10 wt% or less based on 100 wt% of the total weight of the copolymer.

[0085] If the above vinyl acetate series monomer unit exceeds the content range of the present invention, it may cause stability problems such as storage stability.

[0086] Additionally, the vinyl acetate series monomer unit can be formed by polymerizing a vinyl acetate monomer.

[0087] In one embodiment, the copolymer may include a monomer repeating unit represented by the following chemical formula 1.

[0088]

[0089] [Chemical Formula 1]

[0090]

[0091]

[0092] In the above chemical formula 1, R1 to R3 is 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, and R5 is A branched alkyl group having 3 to 10 carbon atoms, R6 is a linear or branched alkyl group having 1 to 10 carbon atoms containing a hydroxyl group, R7 is COOM, M is hydrogen, an alkali metal, or a combination thereof, 0.01≤a≤0.35, 0.1≤b≤0.5, 0.01≤c≤0.2, 0≤d≤0.15, 0.01≤e≤0.2, and 0.01≤f≤0.4, and a+b+c+d+e+f=1.

[0093] 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.

[0094] In one embodiment, R1 to R3 of the above chemical formula 1 may each independently include at least one selected from the group consisting of hydrogen, methyl, and ethyl.

[0095] Additionally, R4 can be methyl, ethyl, n-propyl, n-butyl, tert-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, n-docosyl or a combination thereof, and R5 can be iso-propyl, tert-butyl, sec-butyl, 2-ethylhexyl, n-nonyl, n-decyl, iso-pentyl, iso-heptyl, iso-octyl, iso-nonyl, iso-decyl or a combination thereof.

[0096] Meanwhile, R6 in the above chemical formula 1 may be 2-hydroxyethyl, hydroxypropyl, 4-hydroxybutyl or a combination thereof.

[0097] In one embodiment, the copolymer may be a random or block copolymer depending on the synthesis process.

[0098] In one embodiment, the number average molecular weight of the copolymer may be 10,000 to 1,000,000.

[0099] 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.

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

[0101] The above inorganic particles can be used without limitation as long as they are insulating particles, and preferably, they can be high-dielectric-constant insulating particles.

[0102] 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.

[0103] 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.

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

[0105] A separation membrane according to another aspect of the present invention may comprise the slurry composition.

[0106] 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.

[0107] 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.

[0108] 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).

[0109] 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.

[0110] 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.

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

[0112] It is desirable to perform a dispersion process of the polymer solution and inorganic particles. The dispersion time may be 1 to 50 hours. Conventional methods can be used for dispersion, with the ball mill method being particularly preferred.

[0113] 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.

[0114] 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 pore formation between inorganic particles increases, which increases the pore size. At this time, as the size (particle diameter) of the inorganic particles increases, the interval between inorganic particles (interstitial distance) increases, which increases the pore size.

[0115] 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.

[0116] 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.

[0117] In one embodiment, the separator may have an area of ​​the copolymer of 60% or more with respect to the total area of ​​the slurry composition coating layer on the surface of the separator as measured by a scanning electron microscope.

[0118] For example, the area of ​​the copolymer relative to the total area of ​​the slurry composition coating layer on the surface of the separation membrane may be 65% or more or 70% or more.

[0119] When the above separator is used in a secondary battery, lithium ions can be transferred not only through the separator substrate but also through the porous active layer, and the aforementioned safety improvement effect can be exhibited when an internal short circuit occurs due to an external impact.

[0120] 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.

[0121] 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.

[0122] 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.

[0123] 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.

[0124] 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.

[0125] Hereinafter, the present invention will be described in more detail using examples, but the present invention is not limited thereto.

[0126]

[0127] [Manufacturing Example 1] Manufacturing of copolymer

[0128] In a four-necked flask reactor, a mixture of 200 parts by weight of distilled water, 5 parts by weight of acrylonitrile (AN), 5 parts by weight of butyl acrylate (BA), 1 part by weight of methacylic acid (MAA), and 5 parts by weight of 2-ethylhexyl acrylate (2-EHA) was added 0.1 to 1 part by weight of an emulsifier, stirred, and heated to 70°C while purging nitrogen gas.

[0129] In a reactor prepared at 70°C, 0.15 parts by weight of ammonium persulfate, a thermally decomposable radical initiator, was mixed with 35 parts by weight of distilled water and added dropwise over 1 hour. At the same time, a monomer mixture of 25 parts by weight of acrylonitrile, 10 parts by weight of butylacrylate, 10 parts by weight of methacrylic acid, 10 parts by weight of methyl methacrylate (MMA), 25 parts by weight of 2-ethylhexyl acrylate, and 10 parts by weight of a monomer containing a linear or branched alkyl group having 1 to 20 carbon atoms and a hydroxyl group was added dropwise over 2 hours to produce a copolymer through an emulsion polymerization reaction.

[0130] A metal hydroxide (NaOH, LiOH, KOH) aqueous solution was added to the manufactured copolymer to neutralize the copolymer, thereby producing a final copolymer for a secondary battery separator binder.

[0131]

[0132] [Manufacturing Example 2] Manufacturing of slurry for porous film coating

[0133] Inorganic particles (boehmite (average particle size: 0.5 ㎛)) and the copolymer for membrane binder manufactured by Manufacturing Example 1 were mixed at a solid weight ratio of 80:20, and then additional distilled water was added to a solid concentration of 35 wt% and mixed. This mixture was sufficiently dispersed using a ball mill method or a rotating / rotating mixer to prepare a slurry.

[0134]

[0135] [Manufacturing Example 3] Manufacturing of a membrane

[0136] 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 can be used, such as bar coating, dip coating, slot die coating, gravure coating, and comma coating.

[0137] In addition, after coating, drying was performed using hot air drying methods such as jet blow, counter blow, vacuum drying, and windless drying methods such as infrared, and the drying temperature range was 50 to 80°C.

[0138] 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.

[0139]

[0140] Example 1

[0141] A copolymer for a membrane binder was prepared according to Manufacturing Example 1 using 2-hydroxyethyl acrylate (2-HEA) as a monomer containing a linear or branched alkyl group having 1 to 20 carbon atoms and including a hydroxyl group, and a slurry for a porous membrane coating and a membrane were prepared according to Manufacturing Examples 2 and 3, respectively, using the copolymer.

[0142]

[0143] Example 2

[0144] A copolymer for a membrane binder was prepared according to Manufacturing Example 1 using hydroxypropyl acrylate (HPA) as a monomer containing a linear or branched alkyl group having 1 to 20 carbon atoms and including a hydroxyl group, and a slurry for a porous membrane coating and a membrane were prepared according to Manufacturing Examples 2 and 3, respectively, using the copolymer.

[0145]

[0146] Example 3

[0147] A copolymer for a membrane binder was prepared according to Manufacturing Example 1 using 4-hydroxybutyl acrylate (4-HBA) as a monomer containing a linear or branched alkyl group having 1 to 20 carbon atoms and including a hydroxyl group, and a slurry for a porous membrane coating and a membrane were prepared according to Manufacturing Examples 2 and 3, respectively, using the copolymer.

[0148]

[0149] Comparative Example 1

[0150] A copolymer for a membrane binder, a slurry for a porous membrane coating, and a membrane were prepared in the same manner as in Example 1, except that 10 parts by weight of butyl acrylate was additionally added instead of a monomer containing a linear or branched alkyl group having 1 to 20 carbon atoms and including a hydroxyl group.

[0151]

[0152] Comparative Example 2

[0153] A copolymer for a membrane binder, a slurry for a porous membrane coating, and a membrane were prepared in the same manner as in Example 1, except that 10 parts by weight of 2-ethylhexyl acrylate was additionally added instead of a monomer containing a linear or branched alkyl group having 1 to 20 carbon atoms and including a hydroxyl group.

[0154]

[0155] Comparative Example 3

[0156] A copolymer for a membrane binder, a slurry for a porous membrane coating, and a membrane were prepared in the same manner as in Example 1, except that 10 parts by weight of methyl methacrylate was additionally added instead of a monomer containing a linear or branched alkyl group having 1 to 20 carbon atoms and including a hydroxyl group.

[0157] The monomer content of the copolymer for the membrane binder of Examples 1 to 3 and Comparative Examples 1 to 3 is shown in Table 1 below.

[0158]

[0159] Monomer content (parts by weight) Monomer containing a linear or branched alkyl group having 1 to 20 carbon atoms containing a hydroxyl group ANBAMAA2-EHAMMA Example 110 (2-HEA) 30 15 11 30 10 Example 210 (HPA) 30 15 11 30 10 Example 310 (4-HBA) 30 15 11 30 10 Comparative Examples 1-30 25 11 30 10 Comparative Examples 2-30 15 11 40 10 Comparative Example 3-30 15 11 30 20

[0160]

[0161] AN, BA, MAA, 2-EHA, MMA, 2-HEA, HPA and 4-HBA in Table 1 above represent acrylonitrile, butyl acrylate, methacylic acid, 2-ethylhexyl acrylate, methyl methacrylate, 2-hydroxyethyl acrylate, hydroxypropyl acrylate and 4-hydroxybutyl acrylate, respectively.

[0162]

[0163] [Evaluation Example 1] Dry electrode adhesion of the separator (Dry feel test)

[0164] The membranes manufactured according to Examples 1 to 3 and Comparative Examples 1 to 3 were prepared by cutting them into pieces having a width of 25 mm and a length of 70 mm.

[0165] An anode was cut to a width of 25 mm and a length of 40 mm on the prepared separator, positioned so that the anode coating surface met the separator coating surface, and pressed with a hot press at a temperature of 65°C and a pressure of 500 kg for 10 seconds.

[0166] The manufactured specimens were mounted on a Universal Testing Machine (UTM) (1 kgf load cell), with the cathode fixed at the top and the separator fixed at the bottom, 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.

[0167]

[0168] [Evaluation Example 2] Air permeability of the membrane (Gurley test)

[0169] The membranes manufactured according to Examples 1 to 3 and Comparative Examples 1 to 3 were cut into circles with a diameter of 30 mm and prepared. The prepared membranes were left in a dry room at a temperature of 20°C and a humidity of 0 to 5% for 24 hours, and then placed in the measuring section of an air permeability measuring device (Ilshin Autoclave Co., Ltd.).

[0170] Afterwards, 100 ml of air per second was sprayed onto the membrane and the amount of gas that passed through for 5 seconds was measured.

[0171]

[0172] [Evaluation Example 3] Battery resistance of the separator

[0173] The membranes manufactured according to Examples 1 to 3 and Comparative Examples 1 to 3 were prepared by cutting them into circles with a diameter of 18 mm.

[0174] The prepared separator was dried again in a vacuum oven at 60°C for 12 hours, and then a coin cell was manufactured using an anode containing graphite-silicon oxide and an anode containing nickel-cobalt-manganese in a dry room at 20°C and 0-5% humidity.

[0175] The battery resistance of the manufactured coin cell was measured using an impedance device from BioLogics.

[0176] The increased resistance value (Ω) was calculated as a percentage by comparing the slurry for porous membrane coating with that of an uncoated membrane.

[0177]

[0178] The dry electrode adhesion, air permeability and battery resistance of the separators of Examples 1 to 3 and Comparative Examples 1 to 3 measured by Evaluation Examples 1 to 3 are shown in Table 2 below.

[0179]

[0180] [Evaluation Example 4] Membrane migration phenomenon

[0181] The membranes manufactured according to Examples 1 to 3 and Comparative Examples 1 to 3 were prepared by cutting them into squares with a length of 20 mm.

[0182] The coating surface of the porous membrane coating slurry of the prepared membrane was positioned upward, and after platinum (Pt) coating, the movement phenomenon of the membrane was confirmed by measuring the area of ​​the binder copolymer and inorganic particles (boehmite) distributed on the surface using a scanning electron microscope (SEM), as shown in Figures 1 and 2.

[0183] Figures 1a, 1b and 1c correspond to SEM observation results of the separator manufactured by Examples 1, 2 and 3, respectively, and Figures 2a, 2b and 2c correspond to SEM observation results of the separator manufactured by Comparative Examples 1, 2 and 3, respectively.

[0184] In FIGS. 1 and 2, the spherical particles correspond to the binder copolymer, and the non-spherical plate-shaped particles correspond to inorganic particles (boehmite).

[0185] The degree of migration was quantified as the ratio of the area occupied by the binder copolymer to the total area of ​​the coating surface of the membrane confirmed by SEM.

[0186] That is, the degree of the migration phenomenon was calculated as (area occupied by the binder copolymer / total area of ​​the coating surface of the membrane) * 100.

[0187]

[0188] The results measured by Evaluation Examples 1 to 4 are shown in Table 2 below.

[0189]

[0190] Dry Electrode Adhesion (gf / 20 mm)Air Permeability (sec / 100 ml)Battery Resistance (%)Migration (%)Example 11.241033.1485~90Example 21.10962.8475~80Example 31.181102.9880~85Comparative Example 10.626048.6640~45Comparative Example 20.664218.4240~45Comparative Example 30.423844.4530~35

[0191]

[0192] As shown in Table 2 above, the dry electrode adhesion of the separators of Examples 1 to 3 using a monomer including a linear or branched alkyl group having 1 to 20 carbon atoms and containing a hydroxyl group was superior to the dry electrode adhesion of the separators of Comparative Examples 1 to 3 using a copolymer not including a monomer including a linear or branched alkyl group having 1 to 20 carbon atoms and containing a hydroxyl group.

[0193] Meanwhile, the dry electrode adhesion of the separators of Examples 1 to 3 was measured to be in the range of 0.90 gf / 20 mm or more and 2 gf / 20 mm or less.

[0194]

[0195] In addition, the air permeability of the membranes of Examples 1 to 3 using a monomer containing a linear or branched alkyl group having 1 to 20 carbon atoms and containing a hydroxyl group was lower than the air permeability of the membranes of Comparative Examples 1 to 3 using a copolymer not containing a monomer containing a linear or branched alkyl group having 1 to 20 carbon atoms and containing a hydroxyl group.

[0196] Meanwhile, the air permeability of the separation membranes of Examples 1 to 3 was measured to be in the range of 85 sec / 100 ml or more and 150 sec / 100 ml or less.

[0197] In addition, the battery resistance of the cell to which the separator of Examples 1 to 3 was applied using a monomer containing a linear or branched alkyl group having 1 to 20 carbon atoms and containing a hydroxyl group was lower than the battery resistance of the cell to which the separator of Comparative Examples 1 to 3 was applied using a monomer containing a linear or branched alkyl group having 1 to 20 carbon atoms and containing a hydroxyl group.

[0198] Meanwhile, the battery resistance of the cell to which the separator of Examples 1 to 3 was applied using a monomer containing a linear or branched alkyl group having 1 to 20 carbon atoms and including a hydroxyl group was measured to be in the range of 1% or more and 4% or less.

[0199] In addition, the membranes of Examples 1 to 3 using a monomer containing a linear or branched alkyl group having 1 to 20 carbon atoms and containing a hydroxyl group had a higher surface area ratio of the binder polymer than the membranes of Comparative Examples 1 to 3 using a monomer containing a linear or branched alkyl group having 1 to 20 carbon atoms and containing a hydroxyl group.

[0200] Meanwhile, the surface area ratio of the binder polymer of the separation membrane of Examples 1 to 3 using a monomer containing a linear or branched alkyl group having 1 to 20 carbon atoms and including a hydroxyl group was measured to be in the range of 60% or more and 95% or less.

[0201]

[0202] Therefore, the separators of Examples 1 to 3 using a monomer including a linear or branched alkyl group having 1 to 20 carbon atoms and containing a hydroxyl group were able to improve electrode adhesion, reduce air permeability, reduce battery resistance of a secondary battery, and further promote the movement phenomenon, compared to the separators of Comparative Examples 1 to 3 not using a monomer including a linear or branched alkyl group having 1 to 20 carbon atoms and containing a hydroxyl group.

[0203]

[0204] It was found that a separator using a copolymer for a binder, in which a monomer including a linear or branched alkyl group having 1 to 20 carbon atoms and a hydroxyl group in the content range of the present invention is used, can improve the battery resistance performance of a secondary battery by promoting the movement phenomenon and having excellent adhesive strength and air permeability.

[0205] In addition, a copolymer for a binder using a monomer containing a linear or branched alkyl group having 1 to 20 carbon atoms and including a hydroxyl group in the content range of the present invention can improve the movement of the battery and stability between operations through improved adhesive strength, reduce the defect rate during process application, and improve productivity.

[0206] Meanwhile, a copolymer for a binder using a monomer including a linear or branched alkyl group having 1 to 20 carbon atoms and a hydroxyl group in the content range of the present invention can also be applied to a secondary battery requiring high voltage and high current characteristics through reduced battery resistance.

[0207]

[0208] 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.

[0209] The copolymer of the present invention can promote a migration phenomenon, thereby increasing the adhesion of an electrode to a membrane substrate and improving the heat resistance and breathability of the membrane.

[0210] In addition, the copolymer of the present invention can reduce the defect rate and minimize the formation of voids that occur during the lamination process during battery assembly, and can improve ion conductivity and air permeability in the electrolyte.

[0211] Meanwhile, the adhesive strength of the separator can be maximized through the copolymer of the present invention, and ultimately, the electrical resistance characteristics and stability of the battery can be improved while minimizing battery defects.

Claims

1. Acrylonitrile series monomer unit; A monomer unit of the acrylate series containing a linear alkyl group having 1 to 20 carbon atoms; A monomer unit of the acrylate series containing a branched alkyl group having 3 to 10 carbon atoms; Monomer units of the acrylic acid series; and A monomer unit comprising a linear or branched alkyl group having 1 to 20 carbon atoms, including a hydroxyl group; Copolymer.

2. In paragraph 1, Based on 100 wt% of the total weight of the above copolymer, 1 wt% or more and 40 wt% or less of the above acrylonitrile series monomer unit, A monomer unit of the acrylate series containing a linear alkyl group having 1 to 20 carbon atoms in an amount of 1 wt% or more and 35 wt% or less, A monomer unit of the acrylate series containing a branched alkyl group having 3 to 10 carbon atoms in an amount of 10 wt% or more and 50 wt% or less, 1 wt% or more and 20 wt% or less of the above acrylic acid series monomer unit, and Comprising a monomer unit comprising a linear or branched alkyl group having 1 to 10 carbon atoms, comprising 1 wt% or more and 20 wt% or less of the hydroxyl group, Copolymer.

3. In paragraph 1, The monomer unit of the acrylate series containing the linear alkyl group having 1 to 20 carbon atoms is formed by polymerization of methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, propyl acrylate, propyl methacrylate, butyl acrylate, butyl methacrylate, lauryl acrylate, lauryl methacrylate, stearyl acrylate, stearyl methacrylate or a combination thereof, The above-mentioned acrylate series monomer unit containing a branched alkyl group having 3 to 10 carbon atoms is formed by polymerization of isopropyl acrylate, isopropyl methacrylate, sec-butyl acrylate, sec-butyl methacrylate, tert-butyl acrylate, tert-butyl methacrylate, 2-ethyl hexyl acrylate, 2-ethyl hexyl methacrylate or a combination thereof. The above acrylic acid series monomer unit is formed by polymerization of acrylic acid, methacrylic acid or a combination thereof. The above acrylonitrile series monomer unit is formed by polymerization of acrylonitrile, methacrylonitrile or a combination thereof. Copolymer.

4. In paragraph 1, The monomer unit containing a linear or branched alkyl group having 1 to 10 carbon atoms including the above hydroxyl group is formed by polymerization of 2-hydroxyethyl acrylate, hydroxypropyl acrylate, 4-hydroxybutyl acrylate or a combination thereof. Copolymer.

5. In paragraph 1, The above acrylic acid series monomer unit is combined with an alkali metal, Copolymer.

6. In paragraph 1, Based on 100 wt% of the total weight of the above copolymer, it additionally contains 15 wt% or less of a vinyl acetate series monomer unit. Copolymer.

7. In paragraph 1, Comprising a monomer repeating unit represented by the following chemical formula 1, Copolymer. [Chemical Formula 1] In the above chemical formula 1, R 1 Inland 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 alkyl group having 1 to 20 carbon atoms, R 5 Is It is a branched alkyl group having 3 to 10 carbon atoms, R 6 is a linear or branched alkyl group having 1 to 10 carbon atoms containing a hydroxyl group, R 7 is COOM, M is hydrogen, an alkali metal, or a combination thereof, 0.01≤a≤0.35, 0.1≤b≤0.5, 0.01≤c≤0.2, 0≤d≤0.15, 0.01≤e≤0.2, and 0.01≤f≤0.4, a+b+c+d+e+f=1.

8. In paragraph 1, The above copolymer is a random or block copolymer, Copolymer.

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

10. Containing the slurry composition of clause 9, Membrane.

11. In paragraph 10, The area of ​​the copolymer is 60% or more of the total area of ​​the slurry composition coating layer on the surface of the separation membrane as measured by a scanning electron microscope. Membrane.

12. Containing the separation membrane of Article 10, Secondary battery.

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