Copolymer particles for separator and secondary battery comprising same

Abstract

The present invention relates to: copolymer particles including a first copolymer including an acrylate-based monomer unit containing a C1-20 alkyl group, an acrylic acid-based monomer unit, and a monomer unit containing at least one substituted or unsubstituted aromatic ring; and a slurry composition, a separator, and a secondary battery that include the copolymer particles.

Description

Copolymer particles for separators and secondary batteries containing the same

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

[0002]

[0003] Due to their high energy density, lithium-ion batteries are widely used in the electrical, electronic, telecommunications, and computer industries. Following small lithium-ion batteries for portable electronic devices, their applications are expanding to include high-capacity batteries for hybrid and electric vehicles.

[0004] Although lithium-ion rechargeable batteries are insulated by a separator, ensuring the thermal and chemical safety of the separator is crucial, as internal or external battery malfunctions or impacts can cause a short circuit between the positive and negative electrodes, potentially leading to overheating and explosion.

[0005] Currently, polyolefin-based films are widely used as separators, but polyolefins have the disadvantage of severe thermal shrinkage at high temperatures and poor mechanical properties.

[0006] To improve the stability of such polyolefin-based separation membranes, a porous separation membrane has been developed in which a mixture of inorganic particles and a binder is coated onto a polyolefin porous substrate film.

[0007] That is, in order to suppress thermal shrinkage caused by high temperature of polyolefin-based separators and battery instability caused by dendrites, inorganic particles are coated together with a binder on one or both sides of a porous separator substrate, thereby providing the inorganic particles with the function of suppressing the shrinkage rate of the substrate, and at the same time, a safer separator can be manufactured through the coating layer.

[0008] However, there is still a need to devise measures to improve the thermal stability of separators and overcome the decrease in energy density of secondary batteries caused by the use of inorganic particles.

[0009] [Prior Art Literature]

[0010] [Patent Literature]

[0011] (Patent Document 1) Republic of Korea Published Patent Application No. 10-2024-0110791

[0012]

[0013] Accordingly, the present invention aims to improve compatibility with organic binders and organic electrolytes by using copolymer particles that replace inorganic particles used in membrane coating and a slurry composition containing the same.

[0014] Meanwhile, the aim is to provide a separator with excellent thermal stability that can reduce the risk of fire or explosion in the event of overheating or internal short circuit of a secondary battery by applying the above-mentioned slurry composition.

[0015] In addition, by applying the above slurry composition, we aim to provide a separator with excellent low permeability characteristics that improves ion conductivity, reaction stability, and battery life characteristics within the electrolyte.

[0016] In addition to this, we aim to provide a lightweight secondary battery with excellent performance (high energy density, low resistance, etc.) using the above-mentioned separator.

[0017]

[0018] However, the problems that this invention seeks to solve are not limited to those mentioned above, and other unmentioned problems will be clearly understood by those skilled in the art from the description below.

[0019]

[0020] One aspect of the present invention comprises an acrylate-based monomer unit comprising an alkyl group having 1 to 20 carbon atoms;

[0021] Acrylic acid-based monomer units; and

[0022] A first copolymer comprising monomer units comprising one or more substituted or unsubstituted aromatic rings,

[0023] Provides copolymer particles.

[0024] Another aspect of the present invention is,

[0025] The above copolymer particles; and

[0026] including a binder polymer;

[0027] Provides a slurry composition.

[0028] Another aspect of the present invention comprises a porous layer substrate comprising a coating layer to which the slurry composition is applied,

[0029] Provides a separation membrane.

[0030] Another aspect of the present invention is that the separation membrane comprises,

[0031] Provides a secondary battery.

[0032]

[0033] Since the copolymer particles of the present invention have high compatibility and stability with organic binders and organic electrolytes, they can be used in separation membranes to replace conventional inorganic particles, thereby increasing the heat resistance of the separation membrane and reducing its permeability, which can improve the performance of the separation membrane.

[0034] In addition, the weight of a secondary battery including a separator to which the copolymer particles of the present invention, which replace inorganic particles, are applied can be reduced to increase energy density, and the performance of the secondary battery can be improved by lowering resistance.

[0035]

[0036] Figure 1 is a scanning electron microscope (SEM) image of a core-shell particle prepared according to Example 1 of the present invention.

[0037]

[0038] The operation and effects of the invention will be described in more detail below through specific embodiments. However, these embodiments are merely examples of the invention and do not define the scope of the invention.

[0039] Prior to this, terms and words used in this specification and claims should not be interpreted as being limited to their ordinary or dictionary meanings, but should be interpreted in a meaning and concept consistent with the technical spirit of the invention, based on the principle that the inventor can appropriately define the concept of the terms to best describe his invention.

[0040] Therefore, it should be understood that the configuration of the embodiments described in this specification is merely one of the most preferred embodiments of the present invention and does not represent all of the technical ideas of the present invention, and that various equivalents and modifications that can replace them may exist at the time of filing this application.

[0041] In this specification, singular expressions include plural expressions unless the context clearly indicates otherwise. In this specification, terms such as “comprising,” “comprising,” or “having” are intended to specify the existence of the implemented features, numbers, steps, components, or combinations thereof, and should be understood as not precluding the existence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0042] In the present specification, "a to b" and "a~b" indicating numerical ranges, "to" and "~" are defined as ≥ a and ≤ b.

[0043]

[0044] The first copolymer of the copolymer particles of one aspect of the present invention may comprise an acrylate-based monomer unit comprising an alkyl group having 1 to 20 carbon atoms, an acrylic acid-based monomer unit, and a monomer unit comprising one or more substituted or unsubstituted aromatic rings.

[0045] The above copolymer particles can replace inorganic particles used for coating the separator of a secondary battery.

[0046] The average diameter of the copolymer particles may be 300 nm or more and 2 μm or less, the pH may be 5 or more and 8 or less, and the glass transition temperature may be 100°C or more and 150°C or less.

[0047] The average diameter of the above particles was measured using Malvern’s Mastersizer and Hitachi’s SU5000 FE-SEM, the pH was measured using a TOA pH meter, and the glass transition temperature was measured using TA’s DSC.

[0048] The above acrylate-based monomer unit containing an alkyl group having 1 to 20 carbon atoms can impart hydrophobicity to the copolymer particles and control the glass transition temperature of the copolymer particles.

[0049] The above acrylic acid-based monomer unit can improve the heat resistance and dispersibility of the copolymer particles.

[0050] The monomer unit comprising one or more substituted or unsubstituted aromatic rings can improve the heat resistance and electrolyte affinity of the copolymer particles.

[0051] In one embodiment, the first copolymer may additionally include an acrylonitrile-based monomer unit.

[0052] The above acrylonitrile-based monomer unit can improve the dispersibility of the copolymer particles.

[0053] In one embodiment, the first copolymer may be crosslinked with a crosslinking agent.

[0054] The above crosslinking agent can improve the electrolyte stability of the copolymer particles.

[0055] Any crosslinking agent may be used as long as it is a crosslinking agent capable of containing two or more reactive groups that can react with the monomer unit of the first copolymer.

[0056] For example, the crosslinking agent may include two or more vinyl groups, two or more methacryloyl groups, or two or more acryloyl groups.

[0057] For example, the crosslinking agent may be divinylbenzene (DVB), ethylene diacrylate (EDA), ethylene glycol dimethacrylate (EGDMA), trimethylolpropane trimethacrylate (TMPTMA), butanediol diacrylate (BDDA), pentaerythritol tetraacrylate (PETA), hexanediol diacrylate (HDDA), or a combination thereof.

[0058] The above crosslinking agent may be included in an amount of 0.01% or more and 5% or less based on 100% by weight of the total weight of the first copolymer.

[0059] If the content of the crosslinking agent exceeds the range of the present invention, not only is the polymerization stability of the copolymer particles reduced, but the copolymer particles also become hard and can easily break upon external impact.

[0060] In addition, if the crosslinking agent is below the content range of the present invention, the mechanical strength, thermal stability, and solvent resistance of the copolymer particles may be reduced.

[0061] In one embodiment, the first copolymer may comprise, based on 100 weight% of the total weight of the first copolymer, 1 weight% or more and 20 weight% or less of an acrylate-based monomer unit comprising an alkyl group having 1 to 20 carbon atoms, 1 weight% or more and 20 weight% or less of an acrylic acid-based monomer unit, and 60 weight% or more and 90 weight% or less of a monomer unit comprising one or more substituted or unsubstituted aromatic rings.

[0062] For example, the first copolymer may comprise, based on 100% by weight of the total weight of the first copolymer, 2% by weight or more and 5% by weight or less of an acrylate-based monomer unit comprising an alkyl group having 1 to 20 carbon atoms, 10% by weight or more and 20% by weight or less of an acrylic acid-based monomer unit, and 70% by weight or more and 85% by weight or less of a monomer unit comprising one or more substituted or unsubstituted aromatic rings.

[0063] If the content of the acrylate-based monomer unit containing the alkyl group having 1 to 20 carbon atoms exceeds or falls below the content range of the present invention, it may cause a decrease in adhesive strength.

[0064] If the above acrylic acid-based monomer unit exceeds the content range of the present invention, the polymerization stability of the copolymer particles is reduced, and if it falls below the content range of the present invention, the dispersibility of the copolymer particles may be reduced.

[0065] If the monomer unit containing one or more substituted or unsubstituted aromatic rings exceeds the content range of the present invention, the polymerization stability of the copolymer particles is reduced, and if it falls below the content range of the present invention, the heat resistance of the copolymer particles may be reduced.

[0066] In one embodiment, the first copolymer may additionally include 1% or more and 15% or less of acrylonitrile-based monomer units based on 100% by weight of the total weight of the first copolymer.

[0067] For example, the first copolymer may additionally include 5% or more and 15% or less of acrylonitrile-based monomer units based on 100% by weight of the total weight of the first copolymer.

[0068] If the acrylonitrile-based monomer unit exceeds the content range of the present invention, the polymerization stability of the copolymer particles is reduced, and if it falls below the content range of the present invention, the dispersibility and coating properties of the copolymer particles may be reduced.

[0069] In one embodiment, the acrylate-series monomer unit comprising 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.

[0070] For example, the acrylate series monomer unit containing a linear alkyl group having 1 to 20 carbon atoms may be formed by polymerizing methyl methacrylate, butyl acrylate, or a combination thereof.

[0071] In addition, the above acrylic acid series monomer unit may be formed by polymerizing acrylic acid, methacrylic acid, or a combination thereof.

[0072] For example, the above acrylic acid series monomer unit can be formed by polymerizing acrylic acid.

[0073] Meanwhile, the monomer unit containing one or more substituted or unsubstituted aromatic rings can be formed by polymerizing styrene.

[0074] In addition, the above-mentioned acrylonitrile-based monomer unit may be formed by polymerizing acrylonitrile, methacrylonitrile, or a combination thereof.

[0075] For example, the above acrylonitrile-based monomer unit can be formed by polymerizing acrylonitrile.

[0076] In one embodiment, the acrylic acid-based monomer unit may be combined with an alkali metal, an alkali metal-containing hydroxide, ammonium (NH4), or a combination thereof.

[0077] That is, the carboxylate group of the above acrylic acid series monomer unit can be combined with an alkali metal, a hydroxide containing an alkali metal, ammonium (NH4), or a combination thereof.

[0078] The above alkali metal may be Li, K, Na, or a combination thereof.

[0079] Meanwhile, the weight ratio of the alkali metal and the first copolymer (weight of the alkali metal: weight of the first copolymer) may be 1 to 5:100.

[0080] If the weight ratio of the alkali metal and the first copolymer exceeds or falls below the weight ratio of the present invention, the storage stability of the copolymer particles and the slurry stability may be reduced.

[0081] In one embodiment, the first copolymer may include a monomer repeating unit represented by the following chemical formula 1.

[0082]

[0083] [Chemical Formula 1]

[0084]

[0085]

[0086] In the above Chemical Formula 1, R1 and R3 are each independently hydrogen, a linear or branched hydrocarbon having 1 to 4 carbon atoms, or a combination thereof; R2 is hydrogen, an alkali metal, ammonium (NH4), a linear or branched hydrocarbon having 1 to 20 carbon atoms, or a combination thereof; and R4 is hydrogen, a linear or branched hydrocarbon having 1 to 4 carbon atoms, a halogen element, ethylene, ethylene oxide, ethyl alcohol, an allyl group, a primary amine group, a secondary amine group, a tertiary amine group, a quaternary ammonium group, a sulfide group, a sulfonate group, a sulfone group, a sulfonyl ester group, a sulfonamide group, a sulfonimide group, a sulfonyl azide group, a sulfonyl hydrazide group, a sulfonyl aziridine group, a sulfonyl azitidine group, a sulfonyl carbamate group, a sulfonylurea group, a sulfonyl halide group, or It could be a combination of these.

[0087] In addition, 0.02≤a≤0.40 and 0.60≤b≤0.90 may be possible.

[0088] a and b of the above chemical formula 1 correspond to the weight ratio of each monomer unit in the first copolymer.

[0089] In one embodiment, R1 and R3 of the above formula 1 may each independently include one or more selected from the group consisting of hydrogen, methyl, and ethyl.

[0090] Additionally, R2 may be Li, K, Na, ammonium (NH4), hydrogen, 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 may 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.

[0091] In one embodiment, the first copolymer may be a random or block copolymer depending on the synthesis process.

[0092] In one embodiment, the number average molecular weight of the first copolymer may be 10,000 to 1,000,000.

[0093] If the number average molecular weight of the first copolymer is less than 10,000, the fluidity of the copolymer increases, which may reduce dispersibility and lower the heat resistance of the separator. If the number average molecular weight exceeds 1,000,000, the viscosity is too high for use and may block the pores of the separator, thereby reducing air permeability and resistance.

[0094] In one embodiment, the copolymer particles may be core-shell type particles, and the first copolymer may be included in the shell of the core-shell type particles.

[0095] Meanwhile, the core of the copolymer particle may include a second copolymer having a weight ratio of acrylate-based monomer units to acrylic acid-based monomer units (weight of acrylate-based monomer units: weight of acrylic acid-based monomer units) of 80 to 99: 1 to 20.

[0096] In addition, the second copolymer of the core can be crosslinked with 0.1 to 1 weight part of a crosslinking agent based on 100 weight parts of the second copolymer.

[0097] A slurry composition according to another aspect of the present invention may include the copolymer particles and the binder polymer.

[0098] The above copolymer particles do not change shape even in a separation membrane formed by applying the above slurry composition to a porous layer substrate to form a coating layer, and the shape of the particles can be maintained.

[0099] For example, the binder polymer may include an acrylic polymer or copolymer, an acrylamide polymer or copolymer, an acrylic acid polymer or copolymer, a styrene butadiene rubber (SBR) polymer or copolymer, an ethylene vinyl acetate (EVA) polymer or copolymer, a urethane polymer or copolymer, an imide polymer or copolymer, or a combination thereof.

[0100] In one embodiment, the weight ratio of the copolymer particles to the binder polymer (weight of the copolymer particles:weight of the binder polymer) may be 70 to 99:1 to 30.

[0101] For example, the weight ratio of the copolymer particles to the binder polymer may be 80 to 99:1 to 20.

[0102] If the weight ratio of the copolymer particles to the binder polymer exceeds the range of the present invention, the heat resistance of the copolymer particles may be reduced, and if it falls below the range of the present invention, the dispersibility and coating properties of the copolymer particles on the separator substrate may be reduced.

[0103] Since the copolymer particles replace the inorganic particles, the slurry composition may not contain inorganic particles.

[0104] In addition, the slurry composition may further include inorganic particles.

[0105] For example, the weight ratio of the copolymer particles to the inorganic particles (weight of the copolymer particles:weight of the inorganic particles) may be 15 to 100:0 to 85.

[0106] The above-mentioned inorganic particles can be used without limitation as long as they are insulating particles, and preferably, they can be high dielectric constant insulating particles.

[0107] Specific examples of the above-mentioned inorganic particles include Al2O3, AlOOH, SiO2, TiO2, ZrO2, ZnO, NiO, CaO, SnO2, Y2O3, MgO, BaTiO3, CaTiO3, SrTiO3, SiC, Li3PO4, Pb(Zr,Ti)O3(PZT), (Pb,La)(Zr,Ti)O3(PLZT), and mixtures thereof.

[0108] The above inorganic particles are not subject to any special size limitations, but for example, the average particle size may be 0.01 μm to 30 μm, and more preferably 0.1 μm to 10 μm. If the average particle size of the inorganic particles is below the above preferred range, dispersibility may be reduced, and if it exceeds the above preferred range, the thickness of the coating layer after coating may increase, and mechanical properties may be degraded.

[0109] In addition, the above-mentioned inorganic particles have no particular restrictions on shape and may be, for example, spherical, plate-shaped, elliptical, or irregular.

[0110] A separation membrane according to another aspect of the present invention may include a porous layer substrate comprising a coating layer to which the slurry composition is applied.

[0111] A separator can be manufactured by coating the above slurry composition on at least one surface of a porous substrate film, or by manufacturing the above slurry composition into a film form and laminating it onto a porous substrate film.

[0112] Meanwhile, the above separator can be used as a separator for a secondary battery, for example, as a separator for a lithium secondary battery.

[0113] As an example of manufacturing a separation membrane, the method may include: (a) a step of manufacturing the copolymer particles; (b) a step of preparing a mixture by adding and dispersing the copolymer particles (and optionally adding the inorganic particles) in a prepared binder polymer solution; and (c) a step of coating and drying one or more regions selected from the group consisting of the surface of a polyolefin-based separation membrane substrate and a portion of the pores in the substrate with the mixture of step b).

[0114] The above binder polymer solution can be prepared by dissolving or dispersing the binder polymer in a suitable solvent.

[0115] As for the solvent, it is preferable to have a solubility index similar to that of the binder polymer and a low boiling point. This is to facilitate uniform mixing and subsequent solvent removal. Non-limiting examples of usable solvents include acetone, tetrahydrofuran, methylene chloride, chloroform, dimethylformamide, N-methyl-2-pyrrolidone (NMP), cyclohexane, water, or mixtures thereof. More preferably, it can be used in a water-dispersed state.

[0116] It is preferable to carry out a dispersion process of the binder polymer solution and the copolymer particles (and optionally the inorganic particles). At this time, the dispersion time may be appropriately 10 minutes to 24 hours. Conventional methods may be used as the dispersion method, and the ball mill method is particularly preferred.

[0117] The thickness, pore size, and porosity of the separation membrane of the present invention, finally manufactured, can be controlled according to the composition of the mixture consisting of the copolymer particles (and optionally the inorganic particles are added) and the binder polymer.

[0118] That is, as the ratio (ratio = I / P) of the copolymer particles (and optionally the inorganic particles) (I) to the binder polymer (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 the copolymer particles (and optionally the inorganic particles) + weight of the binder polymer). In addition, the possibility of pore formation between the copolymer particles (and optionally the inorganic particles) increases, thereby increasing the pore size. At this time, as the size (particle diameter) of the copolymer particles (and optionally the inorganic particles) increases, the interstitial distance between the copolymer particles (and optionally the inorganic particles) increases, thus increasing the pore size.

[0119] A separation membrane of the present invention can be obtained by coating a mixture of the manufactured copolymer particles (and optionally the inorganic particles) and the binder polymer onto a prepared polyolefin-based separation membrane substrate and then drying it.

[0120] At this time, the method of coating the mixture of the copolymer particles (and optionally the inorganic particles) and the binder polymer onto the polyolefin-based separator substrate may use conventional coating methods known in the art, such as dip coating, die coating, roll coating, comma coating, or a combination thereof. In addition, when coating the mixture of the copolymer particles (and optionally the inorganic particles) and the binder polymer onto the polyolefin-based separator substrate, the coating may be applied to both sides of the separator substrate or may be selectively applied to only one side.

[0121] In one embodiment, when the separator is left at 120°C for 1 hour, the thermal shrinkage rate in the MD (Machine Direction, length direction) and TD (Transverse Direction, width direction) directions may be 1.5% or less, respectively.

[0122] For example, when the above separator is left at 120°C for 1 hour, the thermal shrinkage rate in the MD (Machine Direction, length direction) direction may be 0% or more and 1.3% or less, and the thermal shrinkage rate in the TD (Transverse Direction, width direction) direction may be 0% or more and 1.2% or less.

[0123] In addition, when the above separator is left at 150°C for 1 hour, the thermal shrinkage rate in the MD (Machine Direction, length direction) and TD (Transverse Direction, width direction) directions may be 5% or less, respectively.

[0124] For example, when the above separator is left at 150°C for 1 hour, the thermal shrinkage rate in the MD (Machine Direction, length direction) direction may be 3.0% or more and 4.7% or less, and the thermal shrinkage rate in the TD (Transverse Direction, width direction) direction may be 3.0% or more and 4.6% or less.

[0125] In one embodiment, the air permeability of the separator may be less than 125 sec / 100cc.

[0126] For example, the air permeability of the above membrane may be 95 sec / 100cc or more, less than 124 sec / 100cc, 100 sec / 100cc or more, less than 124 sec / 100cc, or 100 sec / 100cc or more, 124 sec / 100cc or less.

[0127]

[0128] In addition, the secondary battery may include a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte.

[0129] The above secondary battery can be manufactured according to conventional methods known in the art, and as an example thereof, the electrode and the separator are assembled and then an electrolyte is injected into the assembly to manufacture it.

[0130] There are no significant limitations on the electrodes to be applied together with the above-mentioned separator; however, the cathode active material may be any conventional cathode active material that can be used for the cathode of a secondary battery. Non-limiting examples include lithium intercalation materials such as lithium manganese oxide (lithiated magnesium oxide), lithium cobalt oxide, lithium nickel oxide, or composite oxides formed by combinations thereof. Additionally, the anode active material may be any conventional anode active material that can be used for the anode of a conventional electrochemical device. Non-limiting examples include silicon, lithium metal, or lithium alloys, as well as lithium intercalation materials such as carbon, petroleum coke, activated carbon, graphite, or other carbons. The anode and cathode are configured by attaching the aforementioned anode and cathode active materials to an anode current collector, i.e., a foil manufactured from aluminum, nickel, or a combination thereof, and a cathode current collector, i.e., a foil manufactured from copper, gold, nickel, or a copper alloy, or a combination thereof, respectively.

[0131] The above electrolyte is a salt having a structure such as A+B-, where A+ comprises ions composed of alkali metal cations such as Li+, Na+, and K+ or combinations thereof, and B- comprises anions composed of anions such as PF6-, BF4-, Cl-, Br-, I-, ClO4-, AsF6-, CH3CO2-, CF3SO3-, N(CF3SO2)2-, and C(CF2SO2)3- or combinations thereof, and is a salt comprising propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, and tetrahydrofuran It is preferable that it be dissolved and dissociated in an organic solvent composed of tetrahydrofuran, N-methyl-2-pyrrolidone (NMP), ethyl methyl carbonate (EMC), gamma butyrolactone (GBL), or a mixture thereof.

[0132] In addition to the general winding process, the process of applying the above separator to a battery may include stacking and folding of the separator and electrode.

[0133] In one embodiment, the resistance of the secondary battery may be 1.05 Ω or less.

[0134] For example, the resistance of the above secondary battery may be 0.80 Ω or more and 1.03 Ω or less.

[0135]

[0136] The present invention will be explained in more detail below using examples, but the present invention is not limited thereto.

[0137]

[0138] [Preparation Example 1] Preparation of copolymer particles

[0139] Core particle manufacturing

[0140] 0.1 to 3 parts by weight of a sulfate-based emulsifier were added to 400 parts by weight of distilled water and 100 parts by weight of monomer mixture (A) in a reaction vessel and stirred, and the temperature was raised to 83°C while injecting high-purity nitrogen gas.

[0141] Core particles were prepared by carrying out a continuous emulsion polymerization reaction by adding 0.1 to 3 parts by weight of ammonium persulfate, a decomposition initiator, to a reaction vessel prepared at 83°C and a monomer mixture (A) to 100 parts by weight of the monomer mixture (A).

[0142] A monomer mixture (A) comprises 98 parts by weight of a methyl acrylate-based monomer (MMA) and 1 part by weight of an acrylic acid monomer (AA), and is prepared by additionally mixing 0.5 parts by weight of divinyl benzene with respect to 100 parts by weight of the monomer mixture (A).

[0143] The above monomer mixture (A) corresponds to a monomer mixture for preparing the second copolymer of the present invention.

[0144]

[0145] Core-shell particle manufacturing

[0146] 0.6 parts by weight of a sulfate-based emulsifier and 1 part by weight of the prepared core particles were added to 245 parts by weight of distilled water and 100 parts by weight of a monomer mixture (B) used to manufacture the shell in a 4-neck flask reactor and stirred, and the temperature was raised to 60°C while injecting high-purity nitrogen gas.

[0147] A monomer mixture (B) and 0.15 parts by weight of ammonium persulfate, a decomposition initiator, were added to a reaction vessel prepared at 60°C to carry out a continuous emulsion polymerization reaction with respect to 100 parts by weight of the monomer mixture (B). After all the additions were finished, the temperature of the reactor was raised to 80°C and aged to produce copolymer particles.

[0148] The manufactured copolymer particles were neutralized with an aqueous solution of metal hydroxide (NaOH).

[0149] The above monomer mixture (B) corresponds to a monomer mixture for preparing the first copolymer of the present invention.

[0150]

[0151] [Preparation Example 2] Preparation of a slurry for porous membrane coating

[0152] The copolymer particles prepared according to Preparation Example 1, inorganic particles (alumina (average diameter: 300 nm)) and binder polymer (acrylamide-based solution binder (number average molecular weight measured by GPC: 200,000) and / or acrylic-based emulsion binder (number average molecular weight measured by GPC: 70,000)) were mixed in a solid weight ratio (weight of copolymer particles: weight of inorganic particles: weight of binder polymer) of 48.5:48.5:3, and then additional distilled water was added and mixed to achieve a solid concentration of 35 wt%. This mixture was sufficiently dispersed using a ball mill or a rotary / rotating mixer to prepare a slurry.

[0153]

[0154] [Preparation Example 3] Preparation of a separation membrane

[0155] A coating layer was formed by applying the porous membrane coating slurry prepared according to Preparation Example 2 to a polyolefin porous substrate (polyethylene (PE) and / or polypropylene (PP)). Various coating methods can be used, such as bar coating, dip coating, slot die coating, gravure coating, and comma coating.

[0156] In addition, after coating, drying was performed using hot air drying methods such as Jet blow and Counter blow, and windless drying methods such as vacuum drying and infrared, and the drying temperature range was 50~80℃.

[0157] The thickness of the above inorganic coating layer was 1 to 6 μm on one side or both sides, and if the thickness was less than 1 μm, there was a problem that the heat resistance of the separator was significantly reduced, and if the thickness exceeded 6 μm, the thickness of the separator was too thick, which could reduce the energy density of the battery and increase the resistance.

[0158] In this manufacturing example, the drying temperature was set to 60°C, and the porous substrate was coated with a thickness of 4 μm on both sides by bar coating.

[0159]

[0160] Examples 1 to 5 and Comparative Examples 1 to 4

[0161] As shown in Table 1 below, the weight ratio of the monomers in the monomer mixture (B) was adjusted to prepare a shell of a copolymer core-shell particle for a separation membrane binder (including the first copolymer of the present invention) according to Preparation Example 1, and a slurry for porous membrane coating and a separation membrane were prepared, respectively, according to Preparation Examples 2 and 3 using the shell.

[0162]

[0163] Classification Copolymer Monomer Weight Ratio SMAAANBADVB Example 18 210 52.5 0.5 Example 2 77 15 52.5 0.5 Example 3 72 20 52.5 0.5 Example 4 77 10 10 2.5 0.5 Example 5 72 10 15 2.5 0.5 Comparative Example 1 50 25 15 100 Comparative Example 2 45 20 15 200 Comparative Example 3 40 25 20 150 Comparative Example 4 Coated separator containing inorganic particles

[0164]

[0165] SM, AA, AN, BA, and DVB in Table 1 above represent styrene, acylic acid, acrylonitrile, butyl acrylate, and divinyl benzene, respectively.

[0166] Meanwhile, Comparative Example 4 used a purchased conventional alumina-coated separator.

[0167]

[0168] [Evaluation Example 1] Thermal shrinkage rate of the separator

[0169] The separators of Examples 1 to 5 and Comparative Examples 1 to 4 were prepared by punching a width and length of 5 x 5 cm and marking a dot at a 4 x 4 cm point. Afterward, they were placed in ovens at 120°C and 150°C for 1 hour each, and the thermal shrinkage rate was measured by calculating the shrinkage ratio by measuring the distance between the dots before and after the placement.

[0170]

[0171] [Evaluation Example 2] Air permeability of the separator

[0172] After leaving the separator membranes of Examples 1 to 5 and Comparative Examples 1 to 4 in a dry room overnight, the time (in seconds) required for 100cc of air to pass through was measured using an air permeator (Asahi Seiko EG series).

[0173]

[0174] [Evaluation Example 3] Battery Resistance

[0175] The separator prepared according to Examples 1 to 5 and Comparative Examples 1 to 4 was dried once again in a vacuum oven in a drying room at 40°C for 4 hours, and then cut into a circular shape with a diameter of 18 mm.

[0176] A coin cell was fabricated in a dry room using the prepared separator, with a graphite-containing anode and a nickel-cobalt-manganese (NCM622)-containing anode.

[0177] The cell resistance value of the fabricated coin cell was measured at SOC 50 after formation using an impedance device from Biologics.

[0178]

[0179] The thermal shrinkage rate, air permeability, and battery resistance of the separators of Examples 1 to 5 and Comparative Examples 1 to 4, measured by Evaluation Examples 1 to 3, are shown in Table 2 below.

[0180]

[0181] Thermal Shrinkage Rate [%, (MD / TD)] Air Permeability (sec / 100cc) Resistance (Ω) 120℃ 150℃ Example 1 0.1 / 0 3.6 / 3.5 10 7 0.85 Example 2 0.1 / 0.1 3.7 / 3.5 10 5 0.85 Example 3 0.3 / 0.4 3.8 / 3.8 12 1 1.01 Example 4 0.3 / 0.2 3.8 / 3.7 10 0 0.78 Example 5 0.5 / 0.5 4.0 / 4.0 12 4 1.03 Comparative Example 1 1.4 / 1.5 5.8 / 5.8 14 0 1.21 Comparative Example 2 1.6 / 1.6 6.0 / 5.9 13 2 1.10 Comparative Example 3 2.0 / 2.1 6.4 / 6.5 14 4 1.23 Comparative Example 40.4 / 0.43.9 / 4.01291.18

[0182]

[0183] As shown in Table 2 above, when the separator membranes of Examples 1 to 5 were left at 120°C for 1 hour, the thermal shrinkage rate in the MD (Machine Direction, length direction) direction was 0.1% or more and 0.5% or less, and the thermal shrinkage rate in the TD (Transverse Direction, width direction) direction was 0% or more and 0.5% or less.

[0184] In addition, when the separator membranes of Examples 1 to 5 were left at 150°C for 1 hour, the thermal shrinkage rate in the MD (Machine Direction, length direction) direction was 3.6% or more and 4.0% or less, and the thermal shrinkage rate in the TD (Transverse Direction, width direction) direction was 3.5% or more and 4.0% or less.

[0185] In contrast, when the membranes of Comparative Examples 1 to 3, which do not contain crosslinking monomers (DVB) and are not crosslinked and have a styrene content below the content range of the present invention, were left at 120°C for 1 hour, the thermal shrinkage rate in the MD (Machine Direction, length direction) direction was 1.4% or more and 2.0% or less, and the thermal shrinkage rate in the TD (Transverse Direction, width direction) direction was 1.5% or more and 2.1% or less.

[0186] In addition, when the separator membranes of Comparative Examples 1 to 3 were left at 150°C for 1 hour, the thermal shrinkage rate in the MD (Machine Direction, length direction) direction was 5.8% or more and 6.4% or less, and the thermal shrinkage rate in the TD (Transverse Direction, width direction) direction was 5.8% or more and 6.5% or less, and it was confirmed that the thermal shrinkage rate characteristics were degraded.

[0187] In addition, the inorganic coated separator of Comparative Example 4 had a thermal shrinkage rate of 0.4% in the MD (Machine Direction, length direction) direction and 0.4% in the TD (Transverse Direction, width direction) direction when left at 120°C for 1 hour, and a thermal shrinkage rate of 3.9% in the MD (Machine Direction, length direction) direction and 4.0% in the TD (Transverse Direction, width direction) direction when left at 150°C for 1 hour.

[0188] Thus, the separators of Examples 1 to 5 exhibited a thermal shrinkage rate that was improved or equivalent (or similar) compared to conventional inorganic particle coated separators, despite not containing inorganic particles.

[0189] In terms of air permeability, the membranes of Examples 1 to 5 exhibited an air permeability of 100 sec / 100cc or more and 124 sec / 115cc or less.

[0190] The membranes of Comparative Examples 1 to 4 exhibited a high air permeability of 129 sec / 100cc or more and 144 sec / 100cc or less compared to the separation of Examples 1 to 5, confirming that the air permeability characteristics of the membranes were degraded.

[0191] In terms of the electrical resistance of the battery, the electrical resistance of the secondary batteries of Examples 1 to 5 was 0.78 Ω or more and 1.03 Ω or less.

[0192] In contrast, the secondary batteries of Comparative Examples 1 to 4 exhibited high electrical resistance of 1.10 Ω or more and 1.23 Ω or less, confirming that the electrical resistance characteristics of the secondary batteries were degraded.

[0193]

[0194] Therefore, when using copolymer particles of the specific components and composition of the present invention, it was possible to manufacture a separation membrane of excellent performance having a low thermal shrinkage rate and low air permeability.

[0195] In addition, when using the copolymer particles of the present invention, it was possible to manufacture a secondary battery with excellent performance and low electrical resistance.

[0196] Due to the aforementioned characteristics, the copolymer particles of the present invention can also be applied to secondary batteries requiring high voltage and high current characteristics.

[0197]

[0198] The scope of the present invention is defined by the claims set forth below rather than by the detailed description above, and all modifications or variations derived from the meaning and scope of the claims and equivalent concepts thereof should be interpreted as being included within the scope of the present invention.

[0199]

[0200] Since the copolymer particles of the present invention have high compatibility and stability with organic binders and organic electrolytes, they can be used in separation membranes to replace conventional inorganic particles, thereby increasing the heat resistance of the separation membrane and reducing its permeability, which can improve the performance of the separation membrane.

[0201] In addition, the weight of a secondary battery including a separator to which the copolymer particles of the present invention, which replace inorganic particles, are applied can be reduced to increase energy density, and the performance of the secondary battery can be improved by lowering resistance.

Claims

1. An acrylate-based monomer unit comprising an alkyl group having 1 to 20 carbon atoms; Acrylic acid-based monomer units; and A first copolymer comprising monomer units comprising one or more substituted or unsubstituted aromatic rings, Copolymer particles.

2. In Paragraph 1, The first copolymer further comprises acrylonitrile-based monomer units, Copolymer particles.

3. In Paragraph 1, The above first copolymer is crosslinked with a crosslinking agent, Copolymer particles.

4. In Paragraph 3, The above crosslinking agent comprises 0.01 weight% or more and 5 weight% or less, based on 100 weight% of the total weight of the first copolymer. Copolymer particles.

5. In Paragraph 1, The first copolymer is based on 100% by weight of the total weight of the first copolymer, Acrylate-based monomer units comprising 1 weight% or more and 20 weight% or less of the above alkyl group having 1 to 20 carbon atoms, 1 weight% or more and 20 weight% or less of the above acrylic acid-based monomer units, and A monomer unit comprising one or more substituted or unsubstituted aromatic rings in an amount of 60 weight% or more and 90 weight% or less, Copolymer particles.

6. In Paragraph 2, The first copolymer is based on 100% by weight of the total weight of the first copolymer, A further comprising 1 weight% or more and 15 weight% or less of acrylonitrile-based monomer units, Copolymer particles.

7. In Paragraph 2, The above acrylate-series monomer unit comprising a linear alkyl group having 1 to 20 carbon atoms is 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, and The above acrylic acid-based monomer unit is formed by polymerizing acrylic acid, methacrylic acid, or a combination thereof, and The monomer unit comprising one or more substituted or unsubstituted aromatic rings is formed by the polymerization of styrene, and The above acrylonitrile-based monomer unit is formed by polymerizing acrylonitrile, methacrylonitrile, or a combination thereof. Copolymer particles.

8. In Paragraph 1, The above acrylic acid-based monomer unit is combined with an alkali metal, an alkali metal-containing hydroxide, ammonium (NH4), or a combination thereof, Copolymer particles.

9. In Paragraph 1, The first copolymer comprises a monomer repeating unit represented by the following chemical formula 1, Copolymer particles. [Chemical Formula 1] In the above chemical formula 1, R1 and R3 are each independently hydrogen, a linear or branched hydrocarbon having 1 to 4 carbon atoms, or a combination thereof, and R2 is hydrogen, an alkali metal, ammonium (NH4), a linear or branched hydrocarbon having 1 to 20 carbon atoms, or a combination thereof, and R4 is hydrogen, a linear or branched hydrocarbon having 1 to 4 carbon atoms, a halogen element, ethylene, ethylene oxide, ethyl alcohol, an allyl group, a primary amine group, a secondary amine group, a tertiary amine group, a quaternary ammonium group, a sulfide group, a sulfonate group, a sulfone group, a sulfonyl ester group, a sulfonamide group, a sulfonimide group, a sulfonyl azide group, a sulfonyl hydrazide group, a sulfonyl aziridine group, a sulfonyl azitidine group, a sulfonyl carbamate group, a sulfonyl urea group, a sulfonyl halide group, or a combination thereof, and 0.02≤a≤0.40 and 0.60≤b≤0.

90.

10. A copolymer particle of any one of claims 1 to 9; and including a binder polymer; Slurry composition.

11. A porous layer substrate comprising a coating layer to which the slurry composition of claim 10 is applied, Separator.

12. Including the separator of paragraph 11, Secondary battery.

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