Polymer composition for separator and secondary battery containing same

Abstract

The present invention relates to a polymer composition comprising a particulate polymer containing a carboxyl group or an alcohol group; and a chain polymer containing a carboxyl group or an alcohol group; and a slurry composition, a separator, and a secondary battery containing the polymer composition (provided that when the particulate polymer contains a carboxyl group, the chain polymer contains an alcohol group, and when the particulate polymer contains an alcohol group, the chain polymer contains a carboxyl group).

Description

[Technical Field]

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

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

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

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

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

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

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

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

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

[0010] Therefore, the present invention aims to provide a slurry composition with excellent properties by using a polymer composition.

[0011] The present invention also provides a separator having excellent heat resistance to which the slurry composition is applied, and a battery having excellent performance using the separator.

[0012] However, the problems to be solved by the present application are not limited to those mentioned above, and other problems not mentioned will be clearly understood by those skilled in the art from the following description. [Means for solving the problem]

[0013] One aspect of the present invention is a particle-type polymer containing a carboxyl group or an alcohol group; and chain polymers containing carboxyl or alcohol groups; A polymer composition is provided. (However, when the particle-type polymer contains a carboxyl group, the chain-type polymer contains an alcohol group,

[0014] When the particle-type polymer contains an alcohol group, the chain-type polymer contains a carboxyl group. Another aspect of the present invention is a polymer composition as described above; and Inorganic particles; A slurry composition is provided.

[0015] Yet another aspect of the present invention includes the slurry composition: A separation membrane is provided.

[0016] Another aspect of the present invention includes the separation membrane, A secondary battery is provided.

[0017] Another aspect of the present invention is a method for producing a porous substrate by coating a slurry composition containing the polymer composition and inorganic particles onto a porous substrate and drying the slurry composition; and crosslinking at a temperature of 50°C or higher; A method for producing a separation membrane is provided. [Effects of the Invention]

[0018] The polymer composition of the present invention can improve the heat resistance of the separator and realize a battery with excellent characteristics. DETAILED DESCRIPTION OF THE INVENTION

[0019] The functions and effects of the present invention will be described in more detail below through specific examples of the present invention, but these examples are presented only as examples of the present invention and do not define the scope of the invention.

[0020] Prior to this, the terms and words used in this specification and claims should not be interpreted in a limited way to their ordinary or dictionary meanings, but should be interpreted in a meaning and concept that is consistent with the technical idea of ​​the present invention, in accordance with the principle that an inventor can appropriately define the concept of a term in order to best explain his or her invention.

[0021] Therefore, it should be understood that the configurations of the embodiments described in this specification are merely the most preferred embodiments of the present invention and do not represent the technical ideas of the present invention, and that at the time of filing this application, there may be various equivalents and modifications that can replace them.

[0022] In this specification, the singular expression includes the plural expression unless the context clearly dictates otherwise. In this specification, the terms "comprise," "comprise," "have," and the like are intended to specify the presence of embodied features, numbers, steps, components, or combinations thereof, and should be understood as not precluding the presence or additional possibility of one or more other features, numbers, steps, components, or combinations thereof.

[0023] In the present specification, when numerical ranges are indicated as "a to b" and "a to b," "to" and "to" are defined as ≧a and ≦b.

[0024] The polymer composition of one embodiment of the present invention can include a particle-type polymer containing a carboxyl group or an alcohol group; and a chain-type polymer containing a carboxyl group or an alcohol group.

[0025] However, when the particle-type polymer contains a carboxyl group, the chain-type polymer may contain an alcohol group, and when the particle-type polymer contains an alcohol group, the chain-type polymer may contain a carboxyl group.

[0026] The particulate polymer may be in the form of particles of various shapes, particularly round particles, with an average diameter of 100 nm to 2 μm.

[0027] The chain polymer may be dissolved in a solvent, and the physical form of the chain polymer may not be visually observable, i.e., it may be in a liquid form dissolved in a solvent.

[0028] On the other hand, the particle-type polymer may be dispersed in a solvent, and the chain-type polymer may be dissolved in the solvent, or they may be mixed together.

[0029] As the solvent, any solvent may be used as long as it can disperse the particulate polymer and disperse or dissolve the chain polymer, and for example, water may be used.

[0030] In one embodiment, the particle-type polymer and the chain-type polymer may include at least one monomer unit selected from the group consisting of an acrylate-based monomer unit and an acrylic acid-based monomer unit.

[0031] Examples of the acrylate monomer unit include methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, propyl acrylate, propyl methacrylate, isopropyl acrylate, isopropyl methacrylate, butyl acrylate, butyl methacrylate, sec-butyl acrylate, sec-butyl methacrylate, tert-butyl acrylate, tert-butyl methacrylate, hexyl acrylate, 2-ethylhexyl acrylate, lauryl acrylate, and lauryl methacrylate. The copolymer may be formed by polymerizing one or more selected from the group consisting of stearyl acrylate, stearyl acrylate, and stearyl methacrylate.

[0032] That is, the acrylate-based monomer unit may be formed by copolymerizing two or more or three or more types of acrylate-based monomers.

[0033] For example, the acrylate-based monomer unit may be formed by copolymerizing two or more selected from the group consisting of butyl acrylate, methyl methacrylate, and butyl methacrylate.

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

[0035] In one embodiment, the particle-type polymer may further include a hydroxyacrylate-based monomer unit.

[0036] For example, the particulate polymer may be a copolymer containing an acrylate-based monomer unit and an acrylic acid-based monomer unit, or a copolymer containing an acrylate-based monomer unit and a hydroxyacrylate-based monomer unit.

[0037] When the particulate polymer is a copolymer containing an acrylate-based monomer unit and an acrylic acid-based monomer unit, the copolymer may contain 70 wt% to 95 wt% of the acrylate-based monomer unit and 5 wt% to 30 wt% of the acrylic acid-based monomer unit, based on 100 wt% of the total weight of the copolymer.

[0038] Meanwhile, when the particulate polymer is a copolymer containing an acrylate monomer and a hydroxyacrylate monomer unit, the copolymer may contain 70 wt% to 95 wt% of the acrylate monomer unit and 5 wt% to 30 wt% of the hydroxyacrylate monomer unit, based on 100 wt% of the total weight of the copolymer.

[0039] The chain polymer may further include a vinyl alcohol-based monomer unit.

[0040] For example, the chain polymer may be a polymer consisting of only acrylic acid monomer units, a copolymer containing an acrylate-based monomer and a vinyl alcohol-based monomer unit, or a copolymer containing an acrylate-based monomer unit and an acrylic acid-based monomer unit.

[0041] When the chain polymer is a copolymer containing acrylate-based monomer units and vinyl alcohol-based monomer units, it may contain 40 wt% or less of acrylate-based monomer units and 60 wt% or more of vinyl alcohol-based monomer units, based on 100 wt% of the total weight of the copolymer.

[0042] Meanwhile, when the chain polymer contains an acrylate-based monomer and an acrylic acid-based monomer unit, the chain polymer may contain 30 wt% or less of the acrylate-based monomer unit and 70 wt% or more of the acrylic acid-based monomer unit, based on 100 wt% of the total weight of the chain polymer.

[0043] Meanwhile, the hydroxyacrylate-based monomer unit of the particle-type polymer may be formed by polymerizing one or more selected from the group consisting of 2-hydroxyethyl acrylate and 2-hydroxyethyl methacrylate.

[0044] In one embodiment, the particulate polymer may further include 5 wt % to 10 wt % of acrylonitrile monomer units, acrylamide monomer units, or a combination thereof, based on 100 wt % of the total weight of the particulate polymer.

[0045] The acrylonitrile monomer unit may be formed by polymerizing one or more selected from the group consisting of acrylonitrile and methacrylonitrile, and the acrylamide monomer unit may be formed by polymerizing one or more selected from the group consisting of acrylamide and methacrylamide.

[0046] In one embodiment, the particle-type polymer may include a monomer repeating unit represented by the following Formula 1 or Formula 2:

[0047] [ka]

[0048] [ka]

[0049] The a, b, c, and d in the above chemical formulas 1 and 2 can represent the weight fraction of each repeating unit.

[0050] In one embodiment, the chain polymer may include a monomer repeat unit represented by Formula 3 or Formula 4:

[0051] [ka]

[0052] [ka]

[0053] The e, f, g, and h in the above chemical formulas 3 and 4 can represent the weight fraction of each repeating unit.

[0054] In one embodiment, the weight ratio of the particle-type polymer to the chain-type polymer (weight of particle-type polymer:weight of chain-type polymer) may be 1:9 to 9:1.

[0055] For example, the weight ratio of the particle-type polymer to the chain-type polymer (particle-type polymer weight: chain-type polymer weight) may be 7:3 to 3:7, 4:6 to 6:4, or 5:5.

[0056] In one embodiment, the particle-type polymer and the chain-type polymer may be linked to each other by an ester bond.

[0057] The particle-type polymer and the chain-type polymer can be connected to each other by hydrogen bonds.

[0058] The linkage (bond) between the particle-type polymer and the chain-type polymer through the ester bond and / or hydrogen bond may be formed by a reaction between a carboxyl group and an alcohol group contained in the particle-type polymer and the chain-type polymer.

[0059] The bond between the particle-type polymer and the chain-type polymer can improve the heat resistance of the separator to which the polymer composition of the present invention is applied.

[0060] In one embodiment, the particle-type polymer may be synthesized by emulsion polymerization, and the chain-type polymer may be synthesized by hydrolyzing a prepolymer synthesized by emulsion polymerization, or by solution polymerization.

[0061] That is, the vinyl acetate monomer unit may be converted into a vinyl alcohol-based monomer unit by hydrolysis.

[0062] The degree of hydrolysis may be 70% or more.

[0063] For example, the degree of hydrolysis may be 70% or more, 80% or more, or 90% or more.

[0064] For the hydrolysis reaction, an aqueous solution of a metal hydroxide, such as NaOH, KOH, or LiOH, may be used.

[0065] In one embodiment, the particle-type polymer may have a water-average molecular weight of 5,000 to 10,000,000, and the chain-type polymer may have a water-average molecular weight of 5,000 to 10,000,000.

[0066] If the water-average molecular weight of the particulate polymer and chain polymer is less than 5,000, the fluidity of the composition may increase, reducing dispersibility and the heat resistance of the separation membrane may decrease.If the water-average molecular weight of the particulate polymer and chain polymer is more than 10,000,000, the viscosity may be too high for use, blocking the pores of the separation membrane and reducing the air permeability and resistance.

[0067] A slurry composition according to another embodiment of the present invention may contain the polymer composition and inorganic particles.

[0068] The inorganic particles may be any insulating particles without any limitation, and may preferably be high-dielectric insulating particles.

[0069] Specific examples of the 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), or mixtures thereof.

[0070] The size of the inorganic particles is not particularly limited, and may be, for example, an average particle size of 0.01 μm to 30 μm, more preferably 0.1 μm to 10 μm. If the average particle size of the inorganic particles is less than the preferred range, dispersibility may be reduced, and if it exceeds the preferred range, the thickness of the coating layer after coating may be increased, resulting in reduced mechanical properties.

[0071] Furthermore, the shape of the inorganic particles is not particularly limited, and may be, for example, spherical, elliptical, plate-like, or irregular.

[0072] A separation membrane according to another aspect of the present invention may include the slurry composition.

[0073] After applying the slurry composition to the separator, the crosslinking step (heat treatment) is performed, and the heat shrinkage measured immediately thereafter may be 1 to 2% in both the MD (machine direction) and TD (transverse direction).

[0074] After the crosslinking step, the heat shrinkage measured after leaving the film at 150° C. for 1 hour may be within 5% in both the MD and TD directions.

[0075] The slurry composition may be coated on at least one surface of a porous substrate film, or the slurry composition may be prepared in the form of a film and then attached to a porous substrate film to prepare a separator.

[0076] Meanwhile, the separator may be used as a separator for a secondary battery, for example, a separator for a lithium secondary battery.

[0077] A method for producing a separation membrane according to another embodiment of the present invention may include the steps of coating a porous substrate with a slurry composition containing the polymer composition of the present invention and inorganic particles, drying the slurry, and crosslinking the slurry at a temperature of 50°C or higher.

[0078] The drying temperature of the coating and drying steps may be 40°C or higher and 80°C or lower.

[0079] For example, it may be 40°C or higher, 50°C or higher, 60°C or higher, or 70°C or higher.

[0080] The reaction time for the coating and drying steps may be from 1 minute to 30 minutes.

[0081] For example, it may be 5 minutes or less, 10 minutes or less, 15 minutes or less, 20 minutes or less, or 25 minutes or less.

[0082] On the other hand, the temperature of the crosslinking step may be 50° C. or higher and 100° C. or lower, for example, 50° C. or higher, 60° C. or higher, 70° C. or higher, or 80° C. or higher.

[0083] The reaction time for the crosslinking step may be 30 minutes or more and 5 hours or less.

[0084] For example, it may be 1 hour or more, 2 hours or more, or 3 hours or more.

[0085] An example of a method for producing a separation membrane may include the steps of: (a) dissolving or dispersing the polymer composition in a solvent to prepare a polymer solution; (b) adding and mixing inorganic particles into the polymer solution of step (a); and (c) coating one or more regions selected from the group consisting of the surface of a polyolefin-based separation membrane substrate and a portion of the pores in the substrate with the mixture of step (b) and drying.

[0086] First, 1) the polymer composition is prepared in the form of a polymer solution by dissolving or dispersing it in a suitable solvent.

[0087] The solvent preferably has a low boiling point, which allows for easy removal of the solvent after uniform mixing. Non-limiting examples of solvents that can be used include acetone, tetrahydrofuran, methylene chloride, chloroform, dimethylformamide, N-methyl-2-pyrrolidone (NMP), cyclohexane, water, and mixtures thereof. More preferably, the solvent can be dispersed in water.

[0088] 2) Inorganic particles are added to and dispersed in the prepared polymer solution to prepare a mixture of inorganic particles and polymer.

[0089] It is preferable to carry out a dispersion process of the polymer solution and the inorganic particles. As a dispersion method, a conventional method can be used, and a ball mill method is particularly preferable.

[0090] There are no major limitations on the composition of the mixture of inorganic particles and polymer, and the thickness, pore size, and porosity of the organic / inorganic composite porous separator of the present invention can be adjusted accordingly.

[0091] That is, as the ratio of inorganic particles (I) to polymer (P) (ratio = I / P) increases, the porosity of the separator increases, which results in an increase in the thickness of the separator for the same solid content (weight of inorganic particles + weight of polymer). In addition, the possibility of pore formation between inorganic particles increases, resulting in an increase in pore size. However, as the size (particle size) of inorganic particles increases, the interstitial distance between inorganic particles also increases, resulting in an increase in pore size.

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

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

[0094] When the separator is used in a secondary battery, lithium ions can be transferred not only through the separator substrate but also through the porous active layer, and the above-mentioned safety improvement effect can be achieved in the event of an internal short circuit caused by an external impact.

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

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

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

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

[0099] In applying the separator to a battery, in addition to the general winding process, processes such as stacking and folding of the separator and electrodes are possible. [Example]

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

[0101] [Production Example 1] Production of particle-type polymers A1 and A2 A reaction vessel was charged with 370 parts by weight of distilled water and 0.1 to 3.0 parts by weight of an emulsifier per 100 parts by weight of the monomer mixture, and the mixture was stirred and heated to 75°C while injecting high-purity nitrogen gas. 0.15 parts by weight of ammonium persulfate, a decomposition initiator, per 100 parts by weight of the monomer mixture and the monomer mixture were added to the reaction vessel at 75°C, and a continuous emulsion polymerization reaction was carried out.

[0102] Meanwhile, a particulate polymer A1 was prepared by using a monomer mixture containing butyl acrylate monomer, methacrylate monomer, butyl methacrylate, and acrylic acid (AA) monomer in a weight ratio of 10:25:55:10, and a particulate polymer A2 was prepared by using a monomer mixture containing butyl acrylate monomer, methacrylate monomer, butyl methacrylate, and 2-hydroxyethyl acrylate (HEA) monomer in a weight ratio of 10:25:55:10.

[0103] [Production Example 2] Production of Chain Polymer B1 A reaction vessel was charged with 250 parts by weight of distilled water and 0.1 to 3.0 parts by weight of an emulsifier per 100 parts by weight of the monomer mixture, and the mixture was stirred and heated to 65°C while injecting high-purity nitrogen gas. 0.35 parts by weight of potassium persulfate, a decomposition initiator, per 100 parts by weight of the monomer mixture and the monomer mixture were added to the reaction vessel heated to 65°C, and a continuous emulsion polymerization reaction was carried out to prepare a prepolymer.

[0104] On the other hand, a monomer mixture containing vinyl acetate and methacrylate in a weight ratio of 65:35 was used.

[0105] The copolymer prepolymer prepared by emulsion polymerization was heated at 60°C in 2 to 5 times the alcohol solvent to swell or dissolve.

[0106] Thereafter, a metal hydroxide (NaOH) aqueous solution was added to hydrolyze the polymer, thereby producing a polymer B1 having an alcohol functional group.

[0107] [Production Example 3] Production of Chain Polymer B2 A reactor was heated to 65°C while injecting high-purity nitrogen gas into 250 parts by weight of distilled water and 100 parts by weight of acrylic acid (AA) monomer. 0.3% of ammonium persulfate, a decomposition initiator, was added to the reactor at 65°C to carry out a continuous solution polymerization reaction.

[0108] [Production Example 4] Production of binder polymer compositions C1 and C2 The particle-type polymer A1 prepared in Preparation Example 1 and Preparation Example 2 was mixed with the chain-type polymer B1 to prepare a polymer composition C1 for a separator binder.

[0109] Meanwhile, the particle-type polymer A2 prepared in Preparation Example 1 and Preparation Example 3 was mixed with the chain-type polymer B2 to prepare a polymer composition C2 for a separator binder.

[0110] [Production Example 5] Production of slurry for porous membrane coating Inorganic particles (alumina, average particle size 0.5 μm) and polymer composition C1 or C2 for a separator binder prepared in Preparation Example 4 were mixed at a solids weight ratio of 8:2, and then distilled water was added and mixed to a solids concentration of 35 wt %.

[0111] This mixture was thoroughly dispersed using a ball mill or a mechanical stirrer to produce a slurry.

[0112] [Production Example 6] Production of separation membrane The porous membrane coating slurry prepared in Preparation Example 5 was applied to a polyolefin porous substrate (polyethylene (PE), polypropylene (PP), etc.) to form an inorganic coating layer.

[0113] As the coating method, various methods such as dip coating, die coating, gravure coating, and comma coating can be used.

[0114] After coating, the coating was dried using warm air, hot air, vacuum drying, infrared drying, or the like, and the drying temperature range was 40 to 80°C.

[0115] The thickness of the inorganic coating layer is 1 to 6 μm on one or both sides. If the thickness is less than 1 μm, the heat resistance of the separator is significantly reduced. If the thickness is more than 6 μm, the separator is too thick, which reduces the energy density of the battery and increases the resistance.

[0116] [Example 1] A binder polymer composition C1 was prepared according to Production Example 4 using the particle-type polymer A1 and chain-type polymer B1 produced in Production Example 1 and Production Example 2, respectively, in a solids weight ratio of 4:6.

[0117] Thereafter, a slurry for coating a porous membrane was prepared according to Preparation Example 5, and the prepared slurry for coating a porous membrane was coated and dried according to Preparation Example 6 to prepare a separation membrane.

[0118] Thereafter, a cross-linking step was carried out at 80°C for 1 hour.

[0119] [Example 2] A separation membrane was produced in the same manner as in Example 1, except that the reaction time of the crosslinking step was set to 3 hours.

[0120] [Example 3] A separation membrane was produced in the same manner as in Example 1, except that the particle-type polymer A1 and the chain-type polymer B1 were mixed in a solids weight ratio of 5:5.

[0121] [Example 4] A separation membrane was produced in the same manner as in Example 2, except that the particle-type polymer A1 and the chain-type polymer B1 were mixed in a solids weight ratio of 5:5.

[0122] [Example 5] A binder polymer composition C2 was prepared according to Production Example 4 using the particle-type polymer A2 and chain-type polymer B2 produced in Production Example 1 and Production Example 3, respectively, in a solids weight ratio of 5:5.

[0123] Thereafter, a slurry for coating a porous membrane was prepared according to Preparation Example 5, and the prepared slurry for coating a porous membrane was coated and dried according to Preparation Example 6 to prepare a separation membrane.

[0124] Thereafter, a cross-linking step was carried out at 80°C for 1 hour.

[0125] [Example 6] A separation membrane was produced in the same manner as in Example 5, except that the reaction time of the crosslinking step was set to 3 hours.

[0126] [Example 7] A separation membrane was produced in the same manner as in Example 5, except that the particle-type polymer A2 and the chain-type polymer B2 were mixed in a solids weight ratio of 6:4.

[0127] [Example 8] A separation membrane was produced in the same manner as in Example 6, except that the particle-type polymer A2 and the chain-type polymer B2 were mixed in a solids weight ratio of 6:4.

[0128] [Comparative Example 1] A separation membrane was produced in the same manner as in Example 1, except that the crosslinking step was not performed during the production of the separation membrane.

[0129] Comparative Example 2 A separation membrane was produced in the same manner as in Example 7, except that the crosslinking step was not carried out during the production of the separation membrane.

[0130] The binder polymer compositions, the solid weight ratios of the particle-type polymer and the chain-type polymer, and the crosslinking step conditions of Examples 1 to 8 and Comparative Examples 1 and 2 are shown in Table 1 below. [Table 1]

[0131] [Evaluation Example 1] Heat shrinkage rate of separation membrane Separation membrane samples of Examples 1 to 8 and Comparative Examples 1 and 2, each measuring 5 cm x 5 cm in length and width, were prepared.

[0132] Each of the prepared samples was left in an oven at 150°C for 1 hour, and then the thermal shrinkage was measured.

[0133] That is, the heat shrinkage of the separators of Examples 1 to 8 was calculated by [(length in MD and TD after the drying and crosslinking step - length in MD and TD of the separator after being left in an oven at 150°C for 1 hour) / length in MD and TD after the drying and crosslinking step] x 100.

[0134] On the other hand, the thermal shrinkage rates of the separation membranes of Comparative Examples 1 and 2 were calculated as [(lengths in MD and TD after the drying step - lengths in MD and TD of the separation membrane after being left in an oven at 150°C for 1 hour) / lengths in MD and TD after the drying step] × 100.

[0135] The calculation results are shown in Table 2 below.

[0136] [Table 2]

[0137] It was confirmed that the separators prepared using the polymer compositions of Examples 1 to 8 and Comparative Examples 1 and 2 that underwent a crosslinking step had a lower thermal shrinkage rate than the coated separators that did not undergo a crosslinking step.

[0138] The separators that had undergone the crosslinking step were left in an oven at 150°C for 1 hour, and the thermal shrinkage in the TD and MD directions of the separators prepared using the polymer compositions of Examples 1 to 8 and Comparative Examples 1 and 2 was measured and found to be within 5%.

[0139] In particular, when the crosslinking step was performed for 3 hours, the thermal shrinkage in the TD and MD directions was sometimes within 4% and 3%, respectively.

[0140] In contrast, the separators of Comparative Examples 1 and 2, which did not undergo a crosslinking step, had thermal shrinkage rates of 7 to 8% in the TD and MD directions measured after being left in an oven at 150°C for 1 hour.

[0141] This confirms that the separation membrane that has undergone the crosslinking step has improved heat resistance compared to a separation membrane that has not undergone the crosslinking step.

[0142] It was also confirmed that the effect of improving heat resistance was further improved when the reaction time of the crosslinking step was extended from 1 hour to 3 hours.

[0143] That is, it was found that the performance of secondary batteries can be improved by preparing a separator with excellent heat resistance using the polymer composition of the present invention.

[0144] The scope of the present invention is indicated by the claims that follow rather than by the above detailed description, and all modifications or variations that can be arrived at from the meaning and scope of the claims and their equivalents should be interpreted as being included in the scope of the present invention. [Industrial Applicability]

[0145] The polymer composition of the present invention can improve the heat resistance of the separator and realize a battery with excellent characteristics.

Claims

1. a particle-type polymer containing carboxyl or alcohol groups; and chain polymers containing carboxyl or alcohol groups; Polymer compositions. (However, when the particle-type polymer contains a carboxyl group, the chain-type polymer contains an alcohol group, When the particle-type polymer contains an alcohol group, the chain-type polymer contains a carboxyl group.

2. The particle-type polymer and the chain-type polymer each contain at least one monomer unit selected from the group consisting of an acrylate-based monomer unit and an acrylic acid-based monomer unit; The polymer composition of claim 1.

3. The particle-type polymer further contains a hydroxyacrylate-based monomer unit, The chain polymer further contains a vinyl alcohol-based monomer unit. The polymer composition of claim 2.

4. The particle-type polymer further includes an acrylonitrile monomer unit, an acrylamide monomer unit, or a combination thereof; The polymer composition of claim 3.

5. The particle-type polymer includes a monomer repeating unit represented by the following formula 1 or 2: The polymer composition of claim 1. 【Chemistry 1】 【Chemistry 2】

6. The chain polymer includes a monomer repeating unit represented by the following formula 3 or 4: The polymer composition of claim 1. 【Transformation 3】 【Chemistry 4】

7. the weight ratio of the particle-type polymer to the chain-type polymer (particle-type polymer weight:chain-type polymer weight) is 1:9 to 9:1; The polymer composition of claim 1.

8. The particle-type polymer and the chain-type polymer are connected to each other by an ester bond. The polymer composition of claim 1.

9. The particle-type polymer is synthesized by an emulsion polymerization method, The chain polymer is synthesized by hydrolyzing a prepolymer synthesized by emulsion polymerization or by solution polymerization. The polymer composition of claim 1.

10. The polymer composition according to any one of claims 1 to 9; and inorganic particles; Slurry composition.

11. The slurry composition of claim 10, Separation membrane.

12. The separation membrane according to claim 11, Secondary battery.

13. A step of coating a porous substrate with a slurry composition containing the polymer composition according to any one of claims 1 to 9 and inorganic particles, and drying the slurry composition; and crosslinking at a temperature of 50°C or higher; A method for manufacturing a separation membrane.

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