Copolymer for a separation membrane and a secondary battery including the same

Abstract

The present invention relates to a copolymer containing, based on 100% by weight of the total weight of the copolymer, vinyl acetate monomer units of 15% by weight or less, acrylate monomer units of 10% by weight or more and 55% by weight or less, and acrylic acid monomer units bonded to one or more selected from the group consisting of alkali metals and acetate salt compounds containing alkali metals of 1% by weight or more and 10% by weight or less, a slurry composition containing the same, a separation membrane, and a secondary battery.

Description

Technical Field

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

Background Art

[0002] Lithium secondary batteries have a high energy density and are widely used in the fields of electricity, electronics, communication, and computer industries. Following small lithium secondary batteries for portable electronic devices, their application fields are also expanding to high-capacity secondary batteries such as hybrid vehicles and electric vehicles.

[0003] Although lithium-ion secondary batteries are insulated by a separation membrane, due to internal or external battery abnormal phenomena or impacts, a short circuit between the positive electrode and the negative electrode may occur, leading to heat generation and the possibility of explosion. Therefore, ensuring the thermal / chemical safety of the separation membrane is very important.

[0004] Currently, polyolefin-based films are widely used as separation membranes, but polyolefin has the disadvantages of intense heat shrinkage at high temperatures and being vulnerable to mechanical properties.

[0005] In order to improve the stability of such polyolefin-based separation membranes, porous separation membranes have been developed in which a mixture composed of inorganic particles and a binder is coated on a polyolefin porous base film.

[0006] That is, in order to suppress the heat shrinkage of the polyolefin-based separation membrane at high temperatures and the instability of the battery due to dendrites, by coating inorganic particles together with a binder on one or both sides of the porous separation membrane base material, the function of suppressing the shrinkage rate of the base material is imparted to the inorganic particles, and at the same time, a safer separation membrane can be manufactured by the coating layer.

[0007] In order to ensure excellent battery characteristics, the coating layer must be uniformly coated, and at the same time, a strong adhesive force with the base material is required.

[0008] In addition, in order to cope with recent high capacity and high output, it is necessary to further improve the heat resistance of conventional separation membranes.

Prior Art Documents

Patent Documents

[0009]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0010] Therefore, the present invention provides a slurry composition excellent in the adhesive force of an inorganic substance to a porous substrate and the adhesive force of an electrode by using a copolymer.

[0011] In addition, the present invention provides a separation membrane excellent in adhesive force and heat resistance to which the slurry composition is applied, and a battery having excellent performance using the separation membrane.

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

Means for Solving the Problems

[0013] One aspect of the present application includes 15% by weight or less of vinyl acetate monomer units, 10% by weight or more and 55% by weight or less of acrylate-based monomer units, and 1% by weight or more and 10% by weight or less of acrylic acid-based monomer units, based on 100% by weight of the total weight of the copolymer. The acrylic acid-based monomer units are combined with one or more selected from the group consisting of alkali metals and acetate salt compounds containing alkali metals. A copolymer is provided.

[0014] Another aspect of the present application is a slurry composition comprising the copolymer and inorganic particles.

[0015] Still another aspect of the present application provides a separation membrane comprising the slurry composition.

[0016] Still another aspect of the present application provides a secondary battery comprising the separation membrane.

Advantages of the Invention

[0017] The copolymer of the present invention can enhance the adhesion of the inorganic matter and the electrode to the separation membrane substrate and improve the heat resistance of the separation membrane.

[0018] Also, a battery with excellent characteristics can be realized.

Modes for Carrying Out the Invention

[0019] Hereinafter, the actions and effects of the invention will be described in more detail through specific examples of the invention. However, such examples are merely shown as examples of the invention and do not define the scope of the invention.

[0020] Prior to this, the terms and words used in this specification and the claims should not be construed as being limited to their ordinary or dictionary meanings. In accordance with the principle that the inventor can appropriately define the concept of the terms in order to explain his invention in the best possible way, they should be construed in a meaning and concept consistent with the technical idea of the present invention.

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

[0022] ​As used herein, the singular forms also include the plural forms unless the context clearly dictates otherwise. As used herein, terms such as "comprising," "including," or "having" are intended to specify the presence of the implemented features, numbers, steps, components, or combinations thereof, and it should be understood that they do not preclude the possibility of the presence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0023] As used herein, "from a to b" and "a~b" indicating a numerical range are defined as ≥a and ≤b.

[0024] The copolymer of one aspect of the present application contains, based on 100% by weight of the total weight of the copolymer, 15% by weight or less of vinyl acetate monomer units, 10% by weight or more and 55% by weight or less of acrylate-based monomer units, and 1% by weight or more and 10% by weight or less of acrylic acid-based monomer units. The acrylic acid-based monomer units can be combined with one or more selected from the group consisting of alkali metals and acetate salt compounds containing alkali metals.

[0025] That is, the acrylic acid-based monomer may combine with the alkali metal itself or with an acetate salt compound containing the alkali metal.

[0026] When the content range of the vinyl acetate monomer units exceeds the content range of the present application, problems of stability such as polymerization stability and storage stability may occur. When the content range of the acrylate-based monomer units exceeds or is below the content range of the present application, it may cause a decrease in adhesion. When the content range of the acrylic acid-based monomer units combined with one or more selected from the group consisting of alkali metals and acetate salt compounds containing alkali metals exceeds or is below the content range of the present application, it may cause aggregation and precipitation of polymers or a decrease in adhesion.

[0027] In the acetate salt compound containing the alkali metal, the acetate and the inorganic ions can increase their cohesive force and elastic force by means of coordinate bond, or the chemical attraction between dipoles, induced dipoles, elements with high electronegativity, etc.

[0028] Also, when drying after coating with the copolymer binder, the evaporation of water makes the distance between elements closer, and the attraction force increases further greatly, so that the effect of improving the adhesion force can be maximized.

[0029] In one embodiment, the weight ratio (weight of one or more selected from the group consisting of the alkali metal and the acetate salt compound containing the alkali metal: weight of the copolymer) of one or more selected from the group consisting of the alkali metal and the acetate salt compound containing the alkali metal to the copolymer may be 0.1 to 19:100.

[0030] For example, the weight ratio of one or more selected from the group consisting of the alkali metal and the acetate salt compound containing the alkali metal to the copolymer may be 1 to 15:100.

[0031] When the weight ratio of one or more selected from the group consisting of the alkali metal and the acetate salt compound containing the alkali metal to the copolymer exceeds or is lower than the weight ratio of the present application, the adhesion characteristics and heat resistance characteristics of the separation membrane may be reduced. In particular, the peel adhesion of the separation membrane and the adhesion of the electrode may be reduced.

[0032] The adhesion force of the separation membrane containing one or more selected from the group consisting of the alkali metal and the acetate salt compound containing the alkali metal can be determined according to the strength of the cohesive force and repulsive force between elements.

[0033] The copolymer of the present application can change the adhesion force of the inorganic substance or the adhesion force of the electrode due to the change in the superiority and inferiority of the cohesive force, adhesion force and repulsive force between elements according to the content of one or more selected from the group consisting of the alkali metal and the acetate salt compound containing the alkali metal.

[0034] When one or more selected from the group consisting of the alkali metal and acetate salt compounds containing an alkali metal are used in the production of the copolymer for binder, the overall adhesive strength is improved due to the balance between adhesion and cohesive force caused by the increase in the cohesive force between elements. However, when added in excess, the overall adhesive strength may decrease while the cohesive force decreases instead.

[0035] On the other hand, the improvement of the inorganic adhesion means an increase in the adhesion to the inorganic substance and the substrate. This can mean that, in other words, the heat resistance characteristics of the separation membrane can be improved by increasing the amount of the inorganic substance.

[0036] The electrode adhesion of the separation membrane can reduce the defect rate that occurs while loading the electrodes during battery assembly, and at the same time minimize the formation of voids and improve the ionic conductivity in the electrolyte.

[0037] Also, when the binder layer is coated alone on the inorganic coating layer, the adhesion of the electrode can be maximized. Ultimately, the adhesion of the electrode can minimize the defect rate of the battery and further improve the battery performance.

[0038] In one embodiment, the copolymer may additionally include one or more selected from the group consisting of acrylonitrile-based monomer units and acrylamide-based monomer units.

[0039] Based on 100% by weight of the total weight of the copolymer, it may contain 0.1% by weight or more and 10% by weight or less of the acrylonitrile-based monomer units and 1% by weight or more and 40% by weight or less of the acrylamide-based monomer units.

[0040] If the acrylonitrile-based monomer units exceed or are below the content range of the present application, it may cause a decrease in the dispersibility of polymer particles and the slurry dispersibility of inorganic substances or a decrease in adhesion.

[0041] In addition, if the content range of the acrylamide-based monomer unit exceeds the content range of the present application, the adhesive strength may significantly decrease, and if it is below the content range of the present application, the heat resistance may decrease.

[0042] In one embodiment, the acrylate-based monomer unit may be formed by polymerizing one or more selected from the group consisting of 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, ethyl hexyl acrylate, ethyl hexyl methacrylate, lauryl acrylate, lauryl methacrylate, stearyl acrylate, and stearyl methacrylate.

[0043] In addition, the acrylic acid-based monomer unit may be formed by polymerizing one or more selected from the group consisting of acrylic acid and methacrylic acid, for example.

[0044] On the one hand, the acrylonitrile-based monomer may be formed by polymerizing one or more selected from the group consisting of, for example, acrylonitrile and methacrylonitrile.

[0045] The acrylamide-based monomer unit may be formed by polymerizing one or more selected from the group consisting of, for example, acrylamide, methacrylamide, N-ethyl acrylamide, N-ethyl methacrylamide, N-propyl acrylamide, N-isopropyl acrylamide, N-isopropyl methacrylamide, N-butyl acrylamide, N-butyl methacrylamide, N-sec-butyl acrylamide, N-sec-butyl methacrylamide, N-tert-butyl acrylamide, and N-tert-butyl methacrylamide.

[0046] In one embodiment, the copolymer may include a repeating unit of a monomer represented by the following Chemical Formula 1.

Chemical formula

[0047] In Chemical Formula 1, R1 and R2 are each independently hydrogen; a linear or branched hydrocarbon having 1 to 4 carbon atoms; or a combination thereof, and R3 is hydrogen; a linear or branched hydrocarbon having 1 to 20 carbon atoms; or a combination thereof, and M + is an alkali metal; an acetate salt containing an alkali metal; or a combination thereof, and m, n, and l may satisfy m + n + l = 1.

[0048] In the above Chemical Formula 1, m, n, and l correspond to the molar fractions of each monomer unit, and the sum of the molar fractions of each monomer unit is 1.

[0049] In one embodiment, the acetate salt compound containing an alkali metal may be represented by the following Chemical Formula 2.

Chemical Formula

[0050] In the above Chemical Formula 2, M1 + may be an alkali metal.

[0051] The alkali metal may be, but is not limited to, Li, Na, or K.

[0052] In one embodiment, each of R1 and R2 is independently any one or more selected from the group consisting of hydrogen and methyl, and R3 is hydrogen, methyl, ethyl, propyl, isopropyl, butyl, sec-butyl, tert-butyl, ethylhexyl, 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-henicosyl and iso-docosyl.

[0053] In one embodiment, the copolymer may be a random or block copolymer by a synthesis process.

[0054] In one embodiment, the number average molecular weight of the copolymer may be from 10,000 to 1,000,000.

[0055] When the number average molecular weight of the copolymer is less than 10,000, the fluidity of the copolymer may increase and the dispersibility may decrease, and the heat resistance characteristics of the separation membrane may decrease. When the number average molecular weight exceeds 1,000,000, the viscosity may be excessively high for use, and the pores of the separation membrane may be blocked, resulting in a decrease in air permeability and resistance.

[0056] The slurry composition according to another aspect of the present application may contain the copolymer and inorganic particles.

[0057] The inorganic particles can be used without limitation as long as they are insulator particles, and preferably may be insulator particles with a high dielectric constant.

[0058] 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), and mixtures thereof.

[0059] There is no special limitation on the size of the inorganic particles. For example, the average particle size may be 0.01 μm to 30 μm, and more preferably may be 0.1 μm to 10 μm. When the average particle size of the inorganic particles is less than the preferred range, the dispersibility may be low. When it exceeds the preferred range, the thickness of the coating layer after coating may become thick and the mechanical properties may deteriorate.

[0060] Also, there is no special limitation on the shape of the inorganic particles. For example, they may be spherical, plate-like, or elliptical, or may be amorphous.

[0061] The separation membrane according to another aspect of the present application can include the slurry composition.

[0062] The peel adhesion of the separation membrane may be 6 to 11 gf / mm, the adhesion of the dry electrode may be 3.5 to 5 gf / mm, and the adhesion of the wet electrode may be 11 to 16 gf / mm. The slurry composition can be coated on at least one surface of the porous substrate film, or the slurry composition can be manufactured into a film shape and laminated on the porous substrate film to manufacture the separation membrane.

[0063] On the other hand, the separation membrane can be used as a separation membrane for secondary batteries. For example, it can be used as a separation membrane for lithium secondary batteries.

[0064] As an example of manufacturing the separation membrane, it can include: (a) a step of dissolving or dispersing the copolymer in a solvent to produce a polymer solution; (b) a step of adding and mixing inorganic particles into the polymer solution of step (a); and (c) a step of coating and drying one or more regions selected from the group consisting of the surface of the polyolefin-based separation membrane substrate and a part of the pores in the substrate with the mixture of step (b).

[0065] First, 1) The copolymer is manufactured and prepared in the form of a polymer solution by dissolving or dispersing it in a suitable solvent.

[0066] As the solvent, it is preferably similar to the copolymer used as a binder in solubility index and has a low boiling point. This is to facilitate uniform mixing and subsequent removal of the solvent. 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, it can be used in a state of being water-dispersed in water.

[0067] 2) Inorganic particles are added and dispersed in the produced polymer solution to produce an inorganic particle and polymer mixture.

[0068] It is preferable to carry out the dispersion process of the polymer solution and the inorganic particles. At this time, the dispersion time is suitably 1 to 50 hours. As the dispersion method, ordinary methods can be used, and particularly the ball mill method is preferable.

[0069] The composition of the mixture composed of inorganic particles and polymers has no major restrictions, but the thickness, pore size, and porosity of the organic-inorganic composite porous separation membrane of the present invention finally produced can be adjusted thereby.

[0070] That is, as the ratio of inorganic particles (I) to polymer (P) (ratio = I / P) increases, the porosity of the separation membrane increases, which results in an increase in the thickness of the separation membrane with the same solid content (weight of inorganic particles + weight of polymer). Also, the possibility of pore formation between inorganic particles increases and the pore size increases. At this time, as the size (particle diameter) of the inorganic particles increases, the interstitial distance between the inorganics increases, so the pore size increases.

[0071] 3) By coating the prepared mixture of inorganic particles and polymer on the prepared polyolefin-based separation membrane substrate and then drying, the separation membrane of the present invention can be obtained.

[0072] At this time, as the method of coating the mixture of inorganic particles and polymer on the polyolefin-based separation membrane substrate, ordinary coating methods known in the art can be used. For example, various methods such as dip coating, die coating, roll coating, comma coating, or a mixed method thereof can be utilized. Also, when coating the mixture of inorganic particles and polymer on the polyolefin-based separation membrane substrate, it can be carried out on both sides of the separation membrane substrate, or selectively on only one side.

[0073] When the separation membrane is used in a secondary battery, not only the separation membrane substrate but also lithium ions can be transmitted through the porous active layer. When an internal short circuit occurs due to an external impact, the above-described safety improvement effect can be exhibited.

[0074] Further, the secondary battery can include a positive electrode, a negative electrode, the separator and the electrolytic solution interposed between the positive electrode and the negative electrode.

[0075] The secondary battery can be manufactured by a conventional method known in the art. For example, in one embodiment, the electrodes and the separator are assembled with each other, and then an electrolytic solution is injected into the assembly for manufacturing.

[0076] There is no major limitation on the electrodes applied together with the separator. As the positive electrode active material, a conventional positive electrode active material used for the positive electrode of a secondary battery can be used. Non-limiting examples thereof include lithium intercalation materials such as lithiated magnesium oxide, lithiated cobalt oxide, lithiated nickel oxide, or composite oxides formed by combinations thereof. Also, as the negative electrode active material, a conventional negative electrode active material used for the negative electrode of a conventional electrochemical device can be used. Non-limiting examples thereof include lithium metal, or lithium adsorption materials such as lithium alloys and carbon, petroleum coke, activated carbon, graphite or other carbons. The two electrode active materials described above are each 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 or a copper alloy, or a combination thereof, to form the two electrodes.

[0077] The electrolyte is a salt having a structure such as A+B−, where A+ includes alkali metal cations such as Li+, Na+, K+ and ions composed of combinations thereof, and B− includes anions such as PF6−, BF4−, Cl−, Br−, I−, ClO4−, AsF6−, CH3CO2−, CF3SO3−, N(CF3SO2)2−, C(CF2SO2)3− and ions composed of combinations thereof. A salt dissolved and dissociated in an organic solvent composed 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 is preferred.

[0078] As a process of applying the separation membrane to a battery, in addition to winding which is a general process, processes such as stacking and folding of the separation membrane and the electrode are possible.

Examples

[0079] Hereinafter, the present application will be described more specifically using examples, but the present application is not limited thereto.

[0080] [Production Example 1] Production of Copolymer 200 parts by weight of distilled water and 0.1 to 3 parts by weight of an emulsifier based on 100 parts by weight of the monomer mixture were charged into a reaction vessel, and the temperature was raised to 70 °C and stirred while injecting high-purity nitrogen gas. Potassium persulfate, a decomposition-type initiator, and the monomer mixture were respectively added to the reaction vessel prepared at 60 °C in amounts of 0.1 to 0.5 parts by weight based on 100 parts by weight of the monomer mixture, and a continuous polymerization reaction was allowed to proceed to produce a copolymer.

[0081] An aqueous solution of a metal hydroxide (NaOH, LiOH, KOH) was added to the copolymer produced by the polymerization reaction (emulsion polymerization reaction) to produce a neutralized copolymer.

[0082] An acetate salt compound containing an alkali metal in a regulated content was added to the neutralized copolymer in an amount of 100 parts by weight of the copolymer and reacted to produce a copolymer for binder.

[0083] [Production Example 2] Production of Slurry for Porous Membrane Coating Inorganic particles (alumina, average particle size 0.5 μm) and the copolymer for binder produced in Production Example 1 were mixed so that the solid content weight ratio was 80:20, and then distilled water was added to adjust the solid content concentration to 35% and mixed. This mixture was sufficiently dispersed by the ball mill method or a mechanical stirrer to produce a slurry.

[0084] [Production Example 3] Production of Separation Membrane The slurry for porous membrane coating produced in Production Example 2 was applied to a polyolefin porous substrate (such as polyethylene (PE), polypropylene (PP)) to form an inorganic coating layer. As the coating method, various methods such as dip coating, die coating, gravure coating, and comma coating can be used.

[0085] After coating, it was dried by methods such as hot air, hot wind, vacuum drying, and infrared drying, and the drying temperature range was 40 to 80 °C.

[0086] The thickness of the inorganic coating layer is 1 to 6 μm on one or both sides. When the thickness is less than 1 μm, there is a problem that the heat resistance of the separation membrane is significantly reduced. When the thickness exceeds 6 μm, the thickness of the separation membrane may be excessively thick, reducing the energy density of the battery and increasing the resistance.

[0087] [Examples and Comparative Examples] Examples 1 to 5 and Comparative Examples 1 and 2 were produced according to Production Example 1 by adjusting the content of the acetate salt compound containing an alkali metal as shown in Table 1 below.

[0088] The monomers used in the examples and comparative examples were vinyl acetate (10% by weight), acrylonitrile 35% by weight, butyl acrylate (50% by weight), and acrylic acid (5% by weight).

[0089] That is, after emulsion polymerization of the vinyl acetate, butyl acrylate, and acrylic acid, NaOH was added and reacted. Next, an acetate salt compound containing an alkali metal (sodium acetate) was added with the content adjusted and reacted to produce a copolymer for a binder.

[0090] Using the binder copolymers produced in Examples 1 to 5 and Comparative Examples 1 and 2, a slurry for porous membrane coating and a separation membrane were produced according to Production Example 2 and Production Example 3, respectively.

[0091]

Table 1

[0092] [Evaluation Example 1] Adhesion of the slurry for porous membrane coating (Peel adhesion) Using the binder copolymers of Examples 1 to 5 and Comparative Examples 1 and 2, the separation membranes produced according to Production Example 3 were cut into pieces with a width of 18 mm and a length of 100 mm.

[0093] An acrylic plate with an area of 40 mm in width and 100 mm in length was pasted with a double-sided tape with an area of 20 mm in width and 40 mm in length. After pasting the prepared separation membrane onto the double-sided tape, it was gently pressed 5 times with a hand roller.

[0094] The manufactured test piece was mounted on a UTM (1 kgf Load cell). One part of the separation membrane was fixed to the upper clip of the tensile strength machine, and the tape pasted on one side of the separation membrane was fixed to the lower clip. The 180° peel strength was measured at a speed of 100 mm / min. More than 5 test pieces per sample were prepared and measured, and the average value was calculated.

[0095] [Evaluation Example 2] Adhesion of the Dry Electrode of the Separation Membrane Using the binder copolymers of Examples 1 to 5 and Comparative Examples 1 and 2, the separation membranes produced according to Production Example 3 were cut into pieces with a width of 20 mm and a length of 70 mm for preparation.

[0096] After placing the electrodes cut into a width of 25 mm and a length of 70 mm on the prepared separation membrane, the temperature and pressure of 65 °C and 500 kg were applied for 30 seconds with a Hot-press to produce test pieces.

[0097] The manufactured test piece was mounted on a UTM (3 kgf Load cell). One part of the separation membrane was fixed to the upper clip of the tensile strength machine, and the tape pasted on one side of the separation membrane was fixed to the lower clip. The 180° peel strength was measured at a speed of 100 mm / min. More than 5 test pieces per sample were prepared and measured, and the average value was calculated.

[0098] [Evaluation Example 3] Adhesion of the Wet Electrode of the Separation Membrane Using the binder copolymers of Examples 1 to 5 and Comparative Examples 1 and 2, the separation membranes produced according to Production Example 3 were cut into pieces with a width of 20 mm and a length of 70 mm for preparation.

[0099] After placing an electrode cut to a width of 25 mm and a length of 70 mm on the prepared separation membrane, it was enclosed in an aluminum pouch and impregnated with an electrolytic solution at room temperature for 12 hours. Then, a test piece was manufactured by applying a temperature of 65 °C and a pressure of 500 kgf with a Hot-press.

[0100] The manufactured test piece was attached to a UTM (3 kgf Load cell). One part of the separation membrane was fixed to the upper clip of the tensile strength machine, and the tape attached to one side of the separation membrane was fixed to the lower clip. The 180° peel strength was measured at a speed of 100 mm / min. More than 5 test pieces per sample were prepared and measured, and the average value was calculated.

[0101] The evaluation results of Evaluation Examples 1 to 3 are shown in Table 2 below.

[0102]

Table 2

[0103] Through the measurement results in Table 2 above, it was confirmed that the content of the acetate salt compound affects the peel adhesion and the adhesion of the electrode.

[0104] That is, it was confirmed that the separation membranes using the binder copolymers of Examples 1 to 5 manufactured by adding an acetate salt compound had improved peel adhesion, adhesion of the dry electrode, and adhesion of the wet electrode compared to the separation membrane using the binder copolymer of Comparative Example 1 manufactured without using an acetate salt compound.

[0105] On the other hand, it was confirmed that the separation membranes using the binder copolymers of Comparative Example 2 manufactured by excessively adding an acetate salt compound had lower peel adhesion, adhesion of the dry electrode, and adhesion of the wet electrode compared to the separation membranes manufactured using the binder copolymers of Examples 1 to 5.

[0106] That is, it was confirmed that a separator having excellent peel adhesion, dry electrode adhesion, and wet electrode adhesion can be produced using the copolymer for binder to which the acetate salt compound within the content range of the present application is added.

[0107] In addition, it was found that the performance of a secondary battery can be improved by using a separator having excellent heat resistance and adhesion characteristics, in which the copolymer for binder to which the acetate salt compound within the content range of the present application is added is used.

[0108] The scope of the present invention is defined by the claims hereinafter rather than the above detailed description, and it should be construed that all changes or modified forms derived from the meaning and scope of the claims and the equivalent concept thereof are included in the scope of the present invention.

Industrial Applicability

[0109] The copolymer of the present invention can enhance the adhesion of the inorganic substance and the electrode to the separator substrate and improve the heat resistance of the separator. In addition, a battery with excellent characteristics can be realized.

Claims

1. Based on 100% by weight of the total weight of the copolymer, it contains 15% by weight or less of vinyl acetate monomer units, 10% by weight or more and 55% by weight or less of acrylate-based monomer units, and 1% by weight or more and 10% by weight or less of acrylic acid-based monomer units, wherein the acrylic acid-based monomer units are combined with one or more selected from the group consisting of alkali metals and acetate salt compounds containing alkali metals, a copolymer.

2. The weight ratio of one or more selected from the group consisting of alkali metals and acetate salt compounds containing alkali metals to the copolymer (weight of one or more selected from the group consisting of alkali metals and acetate salt compounds containing alkali metals: weight of the copolymer) is 0.1 to 19:100, The copolymer according to Claim 1.

3. Additionally containing one or more selected from the group consisting of acrylonitrile-based monomer units and acrylamide-based monomer units, The copolymer according to Claim 1.

4. The acrylate monomer unit is formed by polymerizing one or more selected from the group consisting of methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, propyl acrylate, propyl methacrylate, isopropyl acrylate, isopropyl methacrylate, butyl acrylate, butyl methacrylate, sec-butyl acrylate, sec-butyl methacrylate, tert-butyl acrylate, tert-butyl methacrylate, ethylhexyl acrylate, ethylhexyl methacrylate, lauryl acrylate, lauryl methacrylate, stearyl acrylate and stearyl methacrylate. The acrylic acid monomer unit is formed by polymerizing one or more selected from the group consisting of acrylic acid and methacrylic acid. The copolymer according to claim 1.

5. Including the repeating unit of the monomer represented by the following Chemical Formula 1. The copolymer according to claim 1. 【Chemical 1】 In the Chemical Formula 1, R 1 and R 2 are each independently hydrogen; a linear or branched hydrocarbon having 1 to 4 carbon atoms; or a combination thereof, R 3 is hydrogen; a linear or branched hydrocarbon having 1 to 20 carbon atoms; or a combination thereof, M + is an alkali metal; an acetate salt containing an alkali metal; or a combination thereof, m, n and l satisfy m + n + l = 1.

6. The acetate salt compound containing the alkali metal is represented by the following Chemical Formula 2. The copolymer according to claim 5. 【Chemical Formula 2】 In the Chemical Formula 2, M 1 + is an alkali metal.

7. Said R 1 and R 2 are each independently any one or more selected from the group consisting of hydrogen and methyl, The aforementioned R 3 is any one or more selected from the group consisting of hydrogen, methyl, ethyl, propyl, isopropyl, butyl, sec-butyl, tert-butyl, ethylhexyl, 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-henicosyl and iso-docosyl, The copolymer according to claim 5.

8. The copolymer is a random or block copolymer. The copolymer according to claim 1.

9. A slurry composition comprising the copolymer according to any one of claims 1 to 8, and inorganic particles.

10. A separation membrane comprising the slurry composition according to claim 9.

11. A secondary battery comprising the separation membrane according to claim 10. ​

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