Copolymer for separator and secondary battery including same

Abstract

The present invention relates to a copolymer comprising more than 5 wt % to 70 wt % of acrylonitrile-based monomer units, 15 wt % to less than 90 wt % of acrylate-based monomer units, 1 wt % to 20 wt % of acrylamide-based monomer units, and 1 wt % to 10 wt % of acrylic acid-based monomer units, based on 100 wt % of the total weight of the copolymer, and core-shell particles, a slurry composition, a separator, and a secondary battery comprising the same.

Description

[Technical Field]

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

[0002] Lithium secondary batteries have a high energy density and are widely used in the electrical, electronic, communication, and computer industries. Following compact lithium secondary batteries for portable electronic devices, their application fields are expanding to include high-capacity secondary batteries for hybrid vehicles, electric vehicles, etc.

[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 stability of the separator is extremely important.

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

[0005] In order to improve the stability 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 at the same time, the coating layer allows for the production of a safer separator.

[0007] To ensure excellent battery characteristics, the coating layer must be uniformly coated and must also have strong adhesion 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 Registration No. 10-1430975 [Patent Document 2] Republic of Korea Patent Publication No. 10-2006-0072065 Summary of the Invention [Problem to be solved by the invention]

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

[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] This reduces the defective rate during battery production, and makes it possible to realize a battery with excellent battery resistance and life characteristics.

[0013] 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]

[0014] In one embodiment of the present application, the copolymer comprises, based on 100% by weight of the total copolymer, more than 5% but not more than 70% by weight of acrylonitrile-based monomer units, 15% or more but not more than 90% by weight of acrylate-based monomer units, 1% or more but not more than 20% by weight of acrylamide-based monomer units, and 1% or more but not more than 10% by weight of acrylic acid-based monomer units. A copolymer is provided.

[0015] Another aspect of the present application is a method for manufacturing a semiconductor device, comprising: a core; a shell surrounding the core, The shell comprises the copolymer. Core-shell particles are provided.

[0016] Yet another aspect of the present application is a polymerizable composition comprising the copolymer and and inorganic particles, A slurry composition is provided.

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

[0018] Yet another aspect of the present application includes the separation membrane, A secondary battery is provided. [Effects of the Invention]

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

[0020] Furthermore, it is possible to reduce the defective rate during battery manufacturing and to realize a battery with excellent battery resistance and life characteristics. DETAILED DESCRIPTION OF THE INVENTION

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

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

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

[0024] In this specification, the singular includes the plural unless the context clearly indicates otherwise. It should be understood that in this specification, the terms "comprise," "comprise," or "have" are intended to specify the presence of embodied features, numbers, steps, components, or combinations thereof, but do not preclude the possibility of the presence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0025] In this specification, the terms "to" and "to" in "a to b" and "a~b" that indicate numerical ranges are defined as ≧a and ≦b.

[0026] The copolymer according to one embodiment of the present application may contain, based on the total weight of the copolymer (100 wt%), more than 5 wt% but not more than 70 wt% of acrylonitrile-based monomer units, 15 wt% or more but not more than 90 wt% of acrylate-based monomer units, 1 wt% or more but not more than 20 wt% of acrylamide-based monomer units, and 1 wt% or more but not more than 10 wt% of acrylic acid-based monomer units.

[0027] As the content of the monomer unit in the acrylonitrile-based polymer increases, the electrolyte expansion rate of the separator using the copolymer increases, and the ionic conductivity and electrical resistance characteristics improve, due to the high affinity of acrylonitrile for the electrolyte.

[0028] In addition, acrylonitrile has high crystallinity and good heat resistance, so that the heat resistance of a separator using the copolymer can be improved as the content of the monomer unit of the acrylonitrile base material increases.

[0029] However, if the content of the acrylonitrile-based monomer unit exceeds 70 wt%, the excessive electrolyte expansion rate may clog the pores of the separator, resulting in a decrease in electrical resistance. In addition, the adhesive strength may decrease, causing serious problems with the separator's heat resistance.

[0030] The acrylate-based monomer unit becomes flexible and sticky when exposed to an electrolyte, which can improve adhesive strength after immersion in the electrolyte.

[0031] However, if the content of the monomer unit of the acrylate base material is 90 wt % or more, the pores of the separator may be blocked, resulting in a decrease in the air permeability and electrical resistance characteristics.

[0032] Meanwhile, the acrylamide-based monomer unit may play a role in suppressing electrolyte expansion, thereby helping to maintain the heat resistance of the separator.

[0033] In addition, the acrylic acid-based monomer unit can improve the influence on the stability of the copolymer and the dispersibility of the inorganic particles, thereby forming a balanced coating and improving the heat resistance of the separator.

[0034] That is, if the content of the monomer unit is outside the range, one or more of the dispersion stability of the slurry composition using the copolymer, the adhesive strength of the coating film, and the heat resistance of the separator may be reduced.

[0035] In one embodiment, the copolymer may be represented by the following Formula 1:

[0036] [ka]

[0037] In the above Chemical Formula 1, R1 is hydrogen or a linear or branched hydrocarbon having 1 to 4 carbon atoms; R2 is independently hydrogen or a linear or branched hydrocarbon having 1 to 20 carbon atoms; M is an alkali metal; m, n, x and y may be such that m+n+x+y=1.

[0038] In the above Chemical Formula 1, m, n, x, and y correspond to the weight fraction of each monomer unit, and the sum of the weight fractions of each monomer unit is 1.

[0039] In one embodiment, R1 in Formula 1 may include at least one selected from the group consisting of hydrogen, methyl, and ethyl.

[0040] In addition, R2 in the above Chemical Formula 1 can be methyl, ethyl, n-propyl, isopropyl, n-butyl, tert-butyl, n-pentyl, n-hexyl, n-heptyl, n-octyl, 2-ethylhexyl, 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, It may include any one or more selected from the group consisting of iso-pentyl, iso-heptyl, iso-octyl, iso-nonyl, iso-decyl, iso-undecyl, iso-dodecyl, iso-tridecyl, iso-tetradecyl, iso-pentadecyl, iso-cetyl, iso-hexadecyl, iso-heptadecyl, iso-stearyl, iso-octadecyl, iso-nonadecyl, iso-icosyl, iso-henicosyl, and iso-docosyl.

[0041] Meanwhile, M in the above Formula 1 may be Li, Na or K, but is not limited thereto.

[0042] In one embodiment, the copolymer may additionally include 0.005 to 3 parts by weight of a crosslinking monomer unit, based on 100 parts by weight of the total weight of the copolymer.

[0043] The cross-linking monomer unit may be any one or more selected from the group consisting of aliphatic difunctional methacrylates and aromatic difunctional methacrylates.

[0044] Preferably, the binder may be one or more of divinylbenzene and ethylene glycol dimethacrylate.

[0045] If cross-linking by the cross-linking monomer units is not performed, the adhesive strength of the copolymer is improved, but the air permeability and electrical resistance of the separator using the copolymer may be reduced.

[0046] This is because the crosslinking of the crosslinkable monomer does not provide durability, and the pores of the separator may be blocked as the film formation progresses, which may also cause problems with the coating of the electrode adhesive layer.

[0047] In one embodiment, the copolymer may be a random or block copolymer depending on the synthesis process.

[0048] In one embodiment, the number average molecular weight of the copolymer may be 5,000 or more and 1,000,000 or less.

[0049] If the number average molecular weight of the copolymer is less than 5,000, the fluidity of the copolymer increases, which may reduce dispersibility and decrease the heat resistance of the separator.If the number average molecular weight is more than 1,000,000, the viscosity may be too high for use, which may clog the pores of the separator, reducing the air permeability and resistance.

[0050] In one embodiment, the weight ratio of the acrylate-based monomer units to the acrylonitrile-based monomer units (weight % of acrylate-based monomer units / weight % of acrylonitrile-based monomer units) may be 0.2 or more and less than 18.

[0051] A smaller ratio within the above weight ratio range improves electrolyte affinity, resulting in improved electrolyte swelling and ionic conductivity, while a larger ratio within the above weight ratio range improves adhesion, resulting in more pronounced effects in the electrolyte.

[0052] Core-shell particles according to another embodiment of the present application include a core and a shell surrounding the core, and the shell can include the copolymer.

[0053] Preferably, the average particle size of the core may be 50 to 250 nm, and the average particle size of the final core-shell particles may be 300 to 1000 nm.

[0054] If a core is not used, the particle shape may be broken due to the absence of a hard, durable structure, and as film formation progresses, the pores of the separator may be blocked, resulting in reduced air permeability and resistance.

[0055] This is because if the core does not provide durability, the pores of the separator may become blocked as the film formation progresses, which may also cause problems with the coating of the electrode adhesive layer.

[0056] The core may include, but is not limited to, acrylic-based monomer units and acrylic acid-based monomer units, and the core particles may be crosslinked.

[0057] A slurry composition according to yet another aspect of the present application may include the copolymer and inorganic particles.

[0058] That is, the slurry composition may include core-shell particles in which the copolymer is included in the shell.

[0059] The inorganic particles can be used without any limitation as long as they are insulating particles, and preferably, they may be high-dielectric insulating particles.

[0060] Specific examples of the inorganic particles include Al2O3, AlO(OH) (boehmite), 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.

[0061] 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.

[0062] The shape of the inorganic particles is not particularly limited, and may be, for example, spherical, elliptical, or irregular.

[0063] A separation membrane according to yet another aspect of the present application may include the slurry composition.

[0064] The separator coating layer containing the copolymer can be used in either a single layer or a multi-layer coating. For example, when used in a single layer coating together with inorganic particles, the binding strength of the inorganic particles and the electrode adhesion strength can be improved depending on the content.

[0065] When a multi-layer coating is formed by coating a binder alone on an inorganic particle coating layer, the electrode adhesion can be improved.

[0066] The heat shrinkage rate of the separator may be 5% or less in both the MD (machine direction, longitudinal direction) and TD (transverse direction, width direction).

[0067] The slurry composition may be coated on at least one surface of a porous substrate film, or the slurry composition may be prepared into a film and then attached to a porous substrate film to prepare a separator.

[0068] Meanwhile, the separator can be used as a separator for a secondary battery, for example, a separator for a lithium secondary battery.

[0069] An example of a method for producing a separation membrane may include the steps of: (a) dissolving or dispersing the copolymer in a solvent to prepare a polymer solution; (b) adding and mixing inorganic particles into the polymer solution of step (a); and (c) coating one or more regions selected from the group consisting of the surface of a polyolefin separation membrane substrate and a portion of the pores in the substrate with the mixture of step (b) and drying.

[0070] First, 1) the copolymer is prepared in the form of a polymer solution by dissolving or dispersing it in a suitable organic solvent.

[0071] The solvent preferably has a solubility index similar to that of the copolymer used as the binder and a low boiling point. This facilitates uniform mixing and subsequent solvent removal. Non-limiting examples of solvents that can be used include acetone, tetrahydrofuran, methylene chloride, chloroform, dimethylformamide, N-methyl-2-pyrrolidone (NMP), cyclohexane, water, or a mixture thereof. More preferably, the copolymer can be dispersed in water.

[0072] 2) Inorganic particles are added to and dispersed in the prepared polymer solution to prepare a mixture of inorganic particles and polymer.

[0073] It is preferable to carry out a dispersion process of the polymer solution and inorganic particles. At this time, the dispersion time is suitably 1 to 50 hours. As a dispersion method, a conventional method can be used, and the ball mill method is particularly preferable.

[0074] The composition of the mixture consisting of inorganic particles and polymer is not limited to a large extent, and the thickness, pore size, and porosity of the organic-inorganic composite porous separator of the present invention can be adjusted depending on the composition.

[0075] In other words, as the ratio of inorganic particles (I) to polymer (P) (ratio = I / P) increases, the porosity of the separator increases, resulting 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, increasing the pore size. At this time, as the size (particle size) of the inorganic particles increases, the interstitial distance between the inorganic particles also increases, resulting in an increase in pore size.

[0076] 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.

[0077] In this case, the method for coating the mixture of inorganic particles and polymer onto the polyolefin-based separator 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 separator substrate, it can be coated on both sides of the separator substrate or selectively on only one side.

[0078] When the separator is used in a secondary battery, lithium ions can be transferred through the separator substrate as well as the porous active layer, and the separator can exhibit the aforementioned improved safety when an internal short circuit occurs due to an external impact.

[0079] The secondary battery may include a positive electrode, a negative electrode, and the separator and electrolyte interposed between the positive electrode and the negative electrode.

[0080] The secondary battery may be manufactured by a conventional method known in the art. In one example, the electrodes and a separator are assembled together, and then an electrolyte is injected into the assembly.

[0081] The electrode used with the separator is not particularly limited, and the positive electrode active material can be any of the common positive electrode active materials used in the positive electrodes of secondary batteries, including, but not limited to, lithium intercalation materials such as lithiated magnesium oxide, lithiated cobalt oxide, lithiated nickel oxide, or composite oxides formed by combining these. The negative electrode active material can be any of the common negative electrode active materials used in the negative electrodes of conventional electrochemical devices, 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 bonded 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.

[0082] The electrolyte is a salt with the structure A+B-, where A+ is Li + , Na + , K. + and ions consisting of combinations of alkali metal cations such as PF6 - , BF4 -, Cl - , Br - , I - , ClO4 - , AsF6 - , CH3CO2 - , CF3SO3 - , N(CF3SO2)2 - , C(CF2SO2)3 - and a salt containing an anion such as the above or an ion consisting of a combination thereof is preferably dissolved and dissociated in an organic solvent consisting of propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, tetrahydrofuran, N-methyl-2-pyrrolidone (NMP), ethyl methyl carbonate (EMC), gamma butyrolactone (GBL), or a mixture thereof.

[0083] In addition to the general winding process, the separator can be applied to a battery by laminating and folding the separator and electrodes. [Example]

[0084] The present invention will be described in more detail below using examples, but the present invention is not limited thereto.

[0085] [Production Example 1] Production of copolymer Production of core particles 380 parts by weight of distilled water and 0.1 to 3 parts by weight of an emulsifier per 100 parts by weight of the monomer mixture (A) were placed in a reaction vessel and stirred, and the temperature was raised to 80°C while injecting high-purity nitrogen gas.

[0086] A decomposition initiator, ammonium persulfate, was added in an amount of 0.1 to 3 parts by weight per 100 parts by weight of the monomer mixture (A) to a reaction vessel prepared at 80°C, and a continuous emulsion polymerization reaction was carried out to produce core particles.

[0087] The monomer mixture (A) contained 90 parts by weight of a (meth)acrylate monomer and 10 parts by weight of a (meth)acrylic acid monomer, and was prepared by additionally mixing 0.1 to 1 part by weight of divinylbenzene with 100 parts by weight of the monomer mixture (A).

[0088] Fabrication of core-shell particles A reaction vessel was charged with 140 parts by weight of distilled water, 0.1 to 3 parts by weight of an emulsifier relative to 100 parts by weight of the monomer mixture (B) used to produce the shell, and 0.1 to 15 parts by weight of the produced core particles, and the mixture was stirred and heated to 70°C while injecting high-purity nitrogen gas.

[0089] A decomposition initiator, ammonium persulfate, was added to a reaction vessel prepared at 70°C in an amount of 0.05 to 3 parts by weight per 100 parts by weight of the monomer mixture (B), and a continuous emulsion polymerization reaction was carried out to produce core-shell particles.

[0090] The core-shell particles thus prepared were added with an aqueous solution of metal hydroxide (NaOH, LiOH, or KOH) to ionize the carboxylic acid moieties present in the shell.

[0091] The monomer mixture (B) was prepared by adjusting the content of acrylamide monomer (AAm), acrylonitrile monomer (AN), acrylic acid monomer (AA), and butyl acrylate (BA) in an appropriate amount, and adding 0.05 to 3 parts by weight of divinylbenzene to 100 parts by weight of the monomer mixture (B).

[0092] The produced core-shell particles were used as a binder.

[0093] [Production Example 2] Production of slurry for porous membrane coating Inorganic particles (alumina, average particle size 0.5 μm) and the core-shell particles (binder) produced in Production Example 1 were mixed at a solids weight ratio of 90:10, and then distilled water was added and mixed to a solids concentration of 35%. This mixture was thoroughly dispersed using a ball mill or a mechanical stirrer to produce a slurry.

[0094] [Production Example 3] Production of separation membrane An inorganic coating layer is formed by applying the porous membrane coating slurry prepared in Preparation Example 2 to a polyolefin porous substrate (polyethylene (PE), polypropylene (PP), etc.). Various coating methods can be used, such as dip coating, die coating, gravure coating, and comma coating.

[0095] After coating, the coating was dried using warm air, hot air, vacuum drying, infrared drying, or other methods, and the drying temperature range was 60 to 85°C.

[0096] The thickness of the inorganic coating layer is 0.5 to 6 μm on one or both sides. If the thickness is less than 0.5 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.

[0097] [Examples 1 to 4 and Comparative Examples 1 to 6] Examples 1 to 4 and Comparative Examples 1 to 6 were prepared according to Preparation Example 1 by adjusting the monomer composition ratio in the monomer mixture (B) used for preparing the shell, the use of crosslinking monomers, and the use of core particles, as shown in Table 1 below.

[0098] Using the binder copolymers prepared in Examples 1 to 4 and Comparative Examples 1 to 6, a slurry for coating a porous membrane and a separator were prepared in Preparation Example 2 and Preparation Example 3, respectively.

[0099] [Table 1]

[0100] In Table 1, "O" indicates that crosslinking and core particles were applied, and "X" indicates that crosslinking and core particles were not applied.

[0101] As shown in Table 1 above, Comparative Example 5 did not use a crosslinking monomer in the shell manufacturing step, and Comparative Example 6 did not use core particles.

[0102] [Evaluation Example 1] Electrolyte expansion rate of binder film The core-shell particles (binder) of Examples 1 to 4 and Comparative Examples 1 to 6 were dried at 60°C for 6 hours to prepare binder films. 0.2 g of the dried binder film was weighed and placed in 30 g of electrolyte, followed by immersion at 60°C for 72 hours. The swollen binder film was taken out, the electrolyte on the surface was removed, and the weight was measured to calculate the degree of expansion rate in response to the electrolyte.

[0103] [Evaluation Example 2] Adhesion strength of slurry for porous membrane coating The separator and electrode prepared in Preparation Example 3 using the core-shell particles (binder) of Examples 1 to 4 and Comparative Examples 1 to 6 were cut into a size of 25 mm in width and 100 mm in length.

[0104] A double-sided tape measuring 20 mm in width and 40 mm in length was attached to an acrylic plate measuring 40 mm in width and 100 mm in length. The prepared separator was attached to the double-sided tape and then gently pressed five times with a hand roller.

[0105] The prepared test specimen was attached to a UTM (20 kgf Load Cell), one side of the separator was attached to the upper clip of the tensile strength tester, and the tape attached to one side of the separator was attached to the lower clip, and the 180° peel strength was measured at a speed of 100 mm / min. At least five test specimens were prepared per sample and the average value was calculated.

[0106] [Evaluation Example 3] Heat shrinkage rate of separation membrane The separator prepared in Preparation Example 3 using the core-shell particles (binder) of Examples 1 to 4 and Comparative Examples 1 to 6 was prepared as a sample measuring 5 cm x 5 cm in width and length. The sample was left in an oven at 150°C for 1 hour, and then the shrinkage rate was measured.

[0107] [Evaluation Example 4] Adhesion strength of separation membrane to dry electrode The separator and electrode prepared in Preparation Example 3 using the core-shell particles (binder) of Examples 1 to 4 and Comparative Examples 1 to 6 were cut into a size of 25 mm in width and 100 mm in length. The cut separator and the electrode were pressed together at 70° C. and 500 kg pressure for 30 seconds using a hot press device.

[0108] The prepared test specimen was attached to a UTM (20 kgf Load Cell), one side of the separator was attached to the upper clip of the tensile strength tester, and the tape attached to one side of the separator was attached to the lower clip, and the 180° peel strength was measured at a speed of 100 mm / min. At least five test specimens were prepared per sample and the average value was calculated.

[0109] [Evaluation Example 5] Adhesion strength of wet electrode of separation membrane The separator and electrode prepared in Preparation Example 3 using the core-shell particles (binder) of Examples 1 to 4 and Comparative Examples 1 to 6 were cut into a size of 25 mm in width and 100 mm in length.

[0110] The cut separator and the electrode were pressed together at 70° C. and 500 kg pressure for 30 seconds using a hot press device.

[0111] The test piece produced by pressing was placed in an aluminum pouch and immersed in an electrolyte for 1 hour, and then pressed again using a hot press device at 70° C. and a pressure of 500 kg for 10 seconds.

[0112] The prepared test specimen was attached to a UTM (20 kgf Load cell), and one side of the separator was attached to the upper clip of the tensile strength tester, while a tape attached to one side of the separator was attached to the lower clip. The 180° peel strength was measured at a speed of 100 mm / min.

[0113] Five or more test pieces were prepared for each sample and measured, and the average value was calculated.

[0114] [Evaluation Example 6] Air permeability of separation membrane Using the core-shell particles (binders) of Examples 1 to 4 and Comparative Examples 1 to 6 and the separation membrane prepared in Preparation Example 3, the time (seconds) required for 100 cc of air to permeate was measured using an air permeability measuring device.

[0115] [Evaluation Example 7] Electrical resistance of separation membrane Using the core-shell particles (binders) of Examples 1 to 4 and Comparative Examples 1 to 6, the separator prepared in Preparation Example 3, lithium metal, and a SUS plate were interposed between them to prepare coin cell-type electrode assemblies.

[0116] The prepared electrode assembly was filled with an electrolyte solution containing a lithium salt and sealed to manufacture a lithium secondary battery.

[0117] The impedance of the manufactured battery was measured using an impedance analyzer, and the results are shown in Table 2 below.

[0118] [Evaluation Example 8] Ion conductivity of separation membrane The ionic conductivity of the separator prepared in Preparation Example 3 using the core-shell particles (binders) of Examples 1 to 4 and Comparative Examples 1 to 6 was calculated using the electrical resistance measured by the method of Evaluation Example 7 according to the following Equation 1.

[0119] Number 1 Ionic conductivity = sample thickness / (electrical resistance x sample area)

[0120] The evaluation results of Evaluation Examples 1 to 8 are shown in Table 2 below.

[0121] [Table 2]

[0122] The "△" in the air permeability in Table 2 indicates the difference in air permeability before and after coating a polyolefin porous substrate (polyethylene (PE), polypropylene (PP), etc.) with the slurry for coating a porous membrane prepared in Preparation Example 2.

[0123] For example, in the case of Example 1, after coating with the slurry for coating a porous membrane, the air permeability was increased by 12 sec / 100 cc compared to before coating with the slurry for coating a porous membrane.

[0124] When the core-shell particles (binders) of Examples 1 to 4 were used, it was confirmed that the higher the acrylonitrile content of the shell, the higher the electrolyte expansion coefficient, the higher the ionic conductivity, and the lower the electrical resistance.

[0125] Meanwhile, it can be seen that the adhesive strength (inorganic, dry and wet) improves as the content of butyl acrylate in the shell increases.

[0126] It was confirmed that when the core-shell particles (binder) of Comparative Example 1, in which the acrylonitrile content of the shell was more than 70 wt % and the butyl acrylate content of the shell was less than 15 wt %, were used, the electrolyte expansion rate was significantly increased.

[0127] That is, although the ionic conductivity is excellent due to the increased content of acrylonitrile in the shell, the high affinity for the electrolyte causes excessive electrolyte expansion, which clogs the pores of the separator, resulting in high electrical resistance.

[0128] In addition, the hardness of the acrylonitrile shell and excessive electrolyte expansion reduce adhesive strength, which ultimately can cause serious problems in the performance of the separator's heat resistance.

[0129] When the core-shell particles (binder) of Comparative Example 2, in which the acrylonitrile content of the shell is 5 wt% or less and the butyl acrylate content of the shell is 90 wt% or more, are used, it can be confirmed that the adhesive strength and ionic conductivity are improved.

[0130] However, due to its soft and sticky nature on the electrolyte, it clogs the pores of the separator, significantly reducing its air permeability and resistance.

[0131] When the core-shell particles (binder) of Comparative Example 3, which did not contain acrylamide in the shell, were used, it was confirmed that the electrolyte expansion coefficient was higher and the thermal shrinkage coefficient was higher, resulting in a decrease in heat resistance, compared to the core-shell particles (binder) of Example 3, which contained the same amount of acrylonitrile and acrylate in the shell but also contained acrylamide.

[0132] It was confirmed that when the core-shell particles (binder) of Comparative Example 4, which did not contain acrylic acid in the shell, were used, the thermal shrinkage rate was larger and the heat resistance properties were reduced compared to the core-shell particles (binder) of Example 3, which contained the same amount of acrylonitrile in the shell but also contained acrylic acid.

[0133] When the core-shell particles (binder) of Comparative Example 5, in which the shell was not cross-linked, were used, it was confirmed that the air permeability and electrical resistance properties were lower than those of the core-shell particles (binder) of Example 1, in which the shell contained the same amount of monomer and was cross-linked.

[0134] When the particles (binder) of Comparative Example 6, which did not contain core particles, were used, it was confirmed that the air permeability and electrical resistance properties were lower than those of the core-shell particles (binder) of Example 1, which contained core particles but had the same content of monomer in the shell.

[0135] As a result, the separator produced using the core-shell particles (binder) of the example had excellent substrate adhesion and excellent heat resistance within 5% at 150°C.

[0136] In addition, it has been confirmed that the excellent electrode adhesion can reduce the defective rate during battery manufacturing and achieve separator characteristics that are advantageous for maintaining battery resistance and lifespan.

[0137] The scope of the present invention is indicated by the claims set forth below rather than by the above detailed description, and all modifications and variations derived from the meaning and scope of the claims and their equivalents should be construed as being included within the scope of the present invention. [Industrial Applicability]

[0138] The copolymer of the present invention can improve the dispersion stability of the slurry composition, increase the adhesive strength with the polyolefin film that is the separator substrate and / or with the electrodes, and improve the heat resistance of the separator.

[0139] Furthermore, it is possible to reduce the defective rate during battery manufacturing and to realize a battery with excellent battery resistance and life characteristics.

Claims

1. A copolymer comprising acrylonitrile monomer units, acrylate monomer units, acrylamide monomer units, acrylic acid monomer units, and crosslinking monomer units, Based on 100% by weight of the total weight of the copolymer, the copolymer contains more than 5% by weight but not more than 70% by weight of acrylonitrile monomer units, 15% by weight or more but not more than 90% by weight of acrylate monomer units, 1% by weight or more but not more than 20% by weight of acrylamide monomer units, and 1% by weight or more but not more than 10% by weight of acrylic acid monomer units; Based on 100 parts by weight of the total weight of the copolymer, the copolymer additionally contains 0.005 to 3 parts by weight of a crosslinking monomer unit. Copolymer.

2. The copolymer contains a chemical structure represented by the following chemical formula 1: The copolymer of claim 1. 【Chemistry 1】 In the above Chemical Formula 1, R 1 is hydrogen, a linear or branched hydrocarbon having 1 to 4 carbon atoms, R 2 are each independently a linear or branched hydrocarbon having 1 to 20 carbon atoms; M is hydrogen or an alkali metal; m, n, x and y are such that m+n+x+y=1.

3. R of Formula 1 1 contains at least one selected from the group consisting of hydrogen, methyl, and ethyl, R of Formula 1 2 is methyl, ethyl, n-propyl, isopropyl, n-butyl, tert-butyl, n-pentyl, n-hexyl, n-heptyl, n-octyl, 2-ethylhexyl, 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, iso -pentyl, iso-heptyl, iso-octyl, iso-nonyl, iso-decyl, iso-undecyl, iso-dodecyl, iso-tridecyl, iso-tetradecyl, iso-pentadecyl, iso-cetyl, iso-hexadecyl, iso-heptadecyl, iso-stearyl, iso-octadecyl, iso-nonadecyl, iso-icosyl, iso-heneicosyl, and iso-docosyl; The copolymer of claim 2.

4. The crosslinking monomer unit is at least one selected from the group consisting of an aliphatic difunctional methacrylate and an aromatic difunctional methacrylate; The copolymer of claim 1.

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

6. The number average molecular weight of the copolymer is 5,000 or more and 1,000,000 or less. The copolymer of claim 1.

7. a weight ratio of the acrylate monomer units to the acrylonitrile monomer units (weight % of acrylate monomer units / weight % of acrylonitrile monomer units) of 0.2 or more and less than 18; The copolymer of claim 1.

8. The core and a shell surrounding the core, The shell comprises the copolymer of claim 1. Core-shell particles.

9. The copolymer according to any one of claims 1 to 7, and inorganic particles, Slurry composition.

10. The slurry composition of claim 9, Separation membrane.

11. The separation membrane according to claim 10, Secondary battery.

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