High-adhesion separator for battery including pvac-pma copolymer and secondary battery including the same

Abstract

Disclosed is a high-adhesion separator for a battery, including a porous substrate and a coating layer formed on at least one surface of the porous substrate, the coating layer including an inorganic material, wherein the coating layer includes a copolymer of a moisture-hardenable phase separation polymer and vinyl acetate; and a secondary battery including the same.

Description

TECHNICAL FIELD

[0001] This application claims the priority benefit of Korean Patent Application No. 2020-0101572, filed on August 13, 2020, the disclosure of which is incorporated herein by reference in its entirety.

[0002] The present invention relates to a high adhesion separator for a battery including a PVAC-PMA copolymer and a secondary battery including the same. More particularly, the present invention relates to a high adhesion separator for a battery including a porous substrate and a coating layer formed on at least one surface of the porous substrate, the coating layer including an inorganic material, wherein the coating layer includes a copolymer of a moisture-hardenable phase separation polymer and vinyl acetate; and a secondary battery including the same. BACKGROUND

[0003] A secondary battery includes an electrode assembly having a positive electrode / separator / negative electrode structure and capable of charging and discharging. The positive electrode and the negative electrode are each manufactured by applying a slurry including an electrode active material to one surface or an opposite surface of a metal current collector and drying and calendering it. The separator is made of a porous substrate, or includes a coating layer formed on at least one surface of the porous substrate to improve the performance of the porous substrate or make up for the deficiency of the porous substrate.

[0004] The separator serves to isolate the positive electrode and the negative electrode from each other, thereby preventing an electrical short circuit from occurring between the two electrodes and allowing electrolyte and ions to pass through. The separator itself does not participate in the electrochemical reaction of the battery. However, the separator is an important factor influencing the performance and safety of the battery due to its physical properties such as electrolyte wettability and porosity. In the present specification, the "separator" is defined to include the porous substrate and the coating layer that can be applied to one surface thereof, and the "porous substrate" is defined to be only the porous substrate that does not include the coating layer.

[0005] In general, when a secondary battery is charged, lithium ions move from the positive electrode to the negative electrode via the separator. In order for the lithium ions to move smoothly, therefore, it is necessary to maintain the state in which the positive electrode, the separator, and the negative electrode are attached to each other. If the adhesion between the positive electrode and the separator and the adhesion between the negative electrode and the separator are insufficient, a phenomenon in which the positive electrode, the separator, and the negative electrode are separated from each other can occur during the process of manufacturing the secondary battery, during the use of the secondary battery, or due to external impact. This phenomenon often occurs when a plurality of positive electrodes, separators, and negative electrodes are used or a battery having a large size or a large capacity is used. In order for a high-capacity battery, therefore, it is necessary to increase the adhesion between the positive electrode and the separator and the adhesion between the negative electrode and the separator.

[0006] In the case of using a large amount of the binder, the binder charges the secondary battery, thereby the performance of the battery can be decreased. In particular, in the case that the amount of the binder added to the coating layer of the separator is too large, the binder clogs the pores of the separator, thereby the impregnability of the separator with the electrolyte is decreased and the resistance of the secondary battery is increased. In addition to this, the capacity of the battery is decreased while the life of the battery is decreased due to the increased amount of the binder.

[0007] In the case of using a binder having a high adhesion force, the amount of the binder used can be decreased. PVdF-HFP is mainly used as a conventional separator; however, the adhesion force of this binder is only 100 gf / 25 mm at 60℃ and 6.5 Mpa at the maximum. Therefore, a lot of research has been conducted on polyvinyl acetate having a low glass transition temperature and thus an adhesion force of 300 gf / 25 mm at 60℃ and 6.5 Mpa.

[0008] However, polyvinyl acetate has a lower moisture-induced phase separation property than the PVdF-based binder. In the case of applying only polyvinyl acetate to the SRS coating layer, it is thus difficult to form a binder layer on the surface of the separator.

[0009] To solve this problem, Patent Document 1 discloses mixing a moisture-induced phase separation binder and polyvinyl acetate. However, the mutual solubility between the moisture-induced phase separation binder and polyvinyl acetate is decreased under a moisture condition, thereby the phase separation effect is not great.

[0010] Patent Document 2 discloses the copolymerization of vinyl acetate and methacrylate monomers. In this document, the hardness of the methacrylate monomers is considered, however, the moisture-induced phase separation of polyvinyl acetate is not considered.

[0011] Therefore, it is necessary to construct a means for improving the moisture-induced phase separation property of polyvinyl acetate.

[0012] (Prior Art Documents)

[0013] (Patent Document 1) Korean Patent Application Publication No. 2020-0036803 (2020.04.07)

[0014] (Patent Document 2) Korean Patent Application Publication No. 2015-0106808 (2015.09.22) SUMMARY

[0015] TECHNICAL PROBLEM

[0016] The present invention has been made in view of the above problems, and an object of the present invention is to provide a high-adhesion separator for a battery configured to improve a wet phase separation property of vinyl acetate while maintaining a high adhesion force of vinyl acetate when a coating layer is formed on one surface of the separator, and a secondary battery including the same.

[0017] Technical Solution

[0018] To achieve the above object, the present invention provides a high-adhesion separator for a battery, the high-adhesion separator including a porous substrate and a coating layer formed on at least one surface of the porous substrate, the coating layer including an inorganic material and a binder, wherein the coating layer includes a copolymer of a wet phase separable polymer and vinyl acetate.

[0019] The wet phase separable polymer can include at least one selected from the group consisting of poly(methyl acrylate), poly(methyl methacrylate), poly(ethyl methacrylate), poly(2-hydroxyethyl methacrylate), and poly(acrylonitrile).

[0020] The wet phase separable polymer can have a glass transition temperature of 100℃ or less, and the vinyl acetate can have a glass transition temperature of 10℃ to 60℃. In the present invention, the glass transition temperature can be measured using a DSC method.

[0021] The copolymer can be a copolymer manufactured by copolymerization of the wet phase separable polymer and the vinyl acetate at a weight ratio of 80:20 to 20:80. At this time, the copolymer can have a glass transition temperature of 60℃ or less, preferably 40℃ or less.

[0022] The copolymer can be a block copolymer.

[0023] The vinyl acetate can have an adhesion force of 200 gf / 25 mm or more at 60℃ and 6.5 Mpa.

[0024] The wet phase separable polymer can undergo phase separation at a temperature of 25℃ to 80℃ and a relative humidity of 40% to 80%.

[0025] The copolymer can have a structure of Chemical Formula 1 below.

[0026] The structure of Chemical Formula 1 is described below.

[0027]

[0028] Here, m:n can be 80:20 to 20:80, and the weight average molecular weight can be 100,000 to 500,000.

[0029] The weight ratio between the inorganic material and the copolymer in the coating layer can be 60:40 to 90:10.

[0030] The present application provides a secondary battery including a positive electrode, a negative electrode, and a high adhesion separator.

[0031] The coating layer of the high adhesion separator facing the positive electrode and the coating layer of the high adhesion separator facing the negative electrode can have different components.

[0032] At this time, the copolymer can be included only in the positive electrode facing the coating layer.

[0033] In addition, the coating layer of the high adhesion separator facing the positive electrode and the coating layer of the high adhesion separator facing the negative electrode can differ from each other in terms of the composition ratio of components.

[0034] The positive electrode facing the coating layer can include a larger amount of the copolymer than the negative electrode facing the coating layer.

[0035] The adhesion between the high adhesion separator and the positive electrode at 60°C and 6.5 Mpa can be 50 gf / 25 mm or more.

[0036] In the present application, one or more constructions not conflicting with each other can be selected and combined from the above constructions.

[0037] Advantages

[0038] As is apparent from the above description, an adhesive having high adhesion is used for the separator according to the present application, thereby increasing the adhesion between the positive electrode and the separator and between the negative electrode and the separator. In addition, the phenomenon of separation between vinyl acetate and a polymer that can be separated by moisture does not occur under a humidified condition, thereby the adhesive assists in forming an asymmetric structure having high porosity in the coating layer while being uniformly distributed.

[0039] In addition, since the adhesive having high adhesion is used, the consumption of the adhesive is lower than that of a conventional adhesive, thereby improving the impregnability of the separator and increasing the capacity and life of the secondary battery.

[0040] In addition, the amount of the inorganic material in the coating layer can be increased compared to the prior art, thereby a separator having a thin coating layer while achieving the desired effect of the inorganic material can be obtained. As a result, the density of the secondary battery is also increased. BRIEF DESCRIPTION OF DRAWINGS

[0041] Figure 1 is a side view of an electrode assembly including a positive electrode, a separator, and a negative electrode according to the present application. DETAILED DESCRIPTION

[0042] Now, the preferred embodiments of the present application will be described in detail with reference to the accompanying drawings. The preferred embodiments of the present application described herein will be readily apparent to those having ordinary skill in the art of the described field of the application by reference to the drawings, detailed description, and examples that follow. While the preferred embodiments of the present application are described with particularity, various modifications can be made to the preferred embodiments of the present application. Accordingly, other embodiments are within the scope of the present application.

[0043] Where an element or layer is referred to as being "on" another element or substrate, it can be directly on the element or substrate or intervening layers can also be present. In addition, it will be understood that when a element is referred to as being "connected" to another element, it can be directly connected to the other element or intervening layers can also be present. In addition, it will be understood that when an element is referred to as being "comprising" another element, it can further include other elements not specified.

[0044] Hereinafter, the present application will be described in more detail.

[0045] The high-adhesion separator for a battery according to the present application includes a porous substrate and a coating layer formed on at least one surface of the porous substrate, the coating layer including an inorganic material and a binder. The binder includes a copolymer of a moisture-addable phase separation polymer and vinyl acetate.

[0046] Porous substrate

[0047] The porous substrate electrically insulates the positive electrode and the negative electrode from each other, thereby preventing a short circuit, and provides a movement path of lithium ions. A porous film having high resistance to an electrolyte solution as an organic solvent and having a very small pore diameter can be used. The porous substrate is not particularly limited as long as the porous substrate can be generally used as a material for a separator of a secondary battery. For example, the porous substrate can include a resin such as a polyolefin-based resin (polyethylene, polypropylene, polybutylene, polyisobutylene, or polymethylpentene), polyvinyl chloride, or a mixture or copolymer thereof, or can include a resin such as polyethylene terephthalate, polycycloolefin, polyethersulfone, polyamide, polyimide, polyamide-imide, polyaramid, nylon, or polytetrafluoroethylene. Among them, it is preferable to use a polyolefin-based resin because the applicability of a slurry for a porous coating layer is high and the thickness of a separator for a secondary battery is reduced, thereby increasing the percentage of an electrode active material layer in a battery and thus increasing the capacity per unit volume thereof.

[0048] The thickness of the porous substrate can be 1 μm to 100 μm, particularly 1 μm to 30 μm.

[0049] Both a dry-type porous substrate and a wet-type porous substrate can be used as the porous substrate. The wet-type porous substrate is advantageous in that the mechanical strength of the wet-type porous substrate is high, thereby less frequently causing a short circuit even if the wet-type porous substrate is formed to be thin.

[0050] Coating

[0051] Although the thickness of the coating layer is not particularly limited, the thickness of the coating layer can be 1 to 2 μm in consideration of improving the density of the battery and improving the properties of the separator. If the thickness of the coating layer is less than 1 μm, it is difficult to obtain the desired effect as the coating layer, which is not desirable. If the thickness of the coating layer is more than 2 μm, the performance of the battery is suddenly reduced compared to the effect as the coating layer, which is also not desirable.

[0052] The density of the coating layer of the separator according to the present application can be 2 g / m 3 or less. If the density of the coating layer is more than 2 g / m 3 , the electrolyte impregnation rate is suddenly reduced, which is not desirable.

[0053] The coating layer can be formed on the surface of the porous substrate facing the positive electrode, the surface of the porous substrate facing the negative electrode, or both the surface of the porous substrate facing the positive electrode and the surface of the porous substrate facing the negative electrode. In consideration of the adhesion between the separator and the positive electrode and between the separator and the negative electrode, it is preferable that the coating layer be formed on the opposite surfaces of the porous substrate.

[0054] Although various methods can be used to form the coating layer, the coating layer can be formed using a wet phase separation method, which is advantageous for high porosity and asymmetric structure formation. A method in which the porous substrate is impregnated with a slurry obtained by adding a coating composition including an inorganic material and a binder to a solvent or the slurry is applied to the porous substrate can be used. Any ordinary coating method well known in the art to which the present application pertains can be used as the application or coating method. For example, dip coating, die coating, roll coating, comma coating, or a combination thereof can be used.

[0055] After the coating layer is formed on the porous substrate, a step of drying the coating layer is performed. The drying step can be performed using an oven or a heating type chamber set at a temperature range in consideration of the vapor pressure of the solvent, or the porous substrate having the coating layer formed thereon can be exposed to room temperature so that the solvent volatilizes. At this time, conditions such as a temperature range of 25 to 100°C and a relative humidity of 40% or more can be considered.

[0056] Any ordinary solvent known in the art to which the present application pertains can be used without limitation as the solvent required for manufacturing the separator according to the present application. Preferably, acetone, tetrahydrofuran, acetonitrile, dimethylformamide, dimethylsulfoxide, dimethylacetamide, N-methylpyrrole, or water is used. A mixture of two or more thereof can also be used.

[0057] Inorganic material

[0058] The inorganic material added to the coating layer functions to increase the mechanical strength of the separator. The inorganic material is not particularly limited, as long as the inorganic material provides uniform thickness to the coating layer and does not undergo oxidation and / or reduction within the operating voltage range in which the secondary battery of the present application is applied. Particularly, in the case where inorganic particles having ion transport ability are used, the ion conductivity of the electrochemical device can be improved, thereby improving the performance of the battery. Further, in the case where inorganic particles having high dielectric constant are used as the inorganic particles, the degree of dissociation of an electrolyte salt, such as a lithium salt, in the liquid electrolyte can be increased, thereby improving the ion conductivity of the electrolyte.

[0059] In recent years, although alumina (Al203) has been mainly used as the inorganic material, a metal, a metal oxide, or a metal hydroxide has been used as the inorganic material in order to improve the flame retardancy of the battery. In the separator according to the present application, any one of alumina, a metal, a metal oxide, and a metal hydroxide can be used as the inorganic material, or a mixture of two or more materials regardless of their kinds can be used as the inorganic material.

[0060] The metal hydroxide or the metal hydrate can be any one or a combination of two or more selected from the group consisting of aluminum hydroxide (Al(OH)3), magnesium hydroxide (Mg(OH)2), aluminum oxide hydroxide (AIO(OH)), CaO AI2O3 6H2O, calcium hydroxide, chromium hydroxide, nickel hydroxide, and boron hydroxide.

[0061] The kind of the metal oxide is not particularly limited. For example, at least one selected from the group consisting of a metal oxide having a dielectric constant of 5 or more, a metal oxide having piezoelectricity, and a metal oxide having lithium ion transport ability can be used.

[0062] The metal oxide having a dielectric constant of 5 or more can be SrTiO3, SnO2, CeO2, MgO, NiO, CaO, ZnO, ZrO2, Y2O3, AI2O3, or TiO2.

[0063] The metal oxide having piezoelectricity in which a potential difference is formed due to positive and negative charges generated between opposite surfaces thereof when a predetermined pressure is applied to the particles can be selected from the group consisting of BaTiO3, Pb(Zr,Ti)O3 (PZT), Pb(Mg 1- x La x Zr 1-y Ti y O3(PLZT), Pb(Mg 1 / 3 Nb 2 / 3at least one of the group consisting of O3-PbTiO3(PMN-PT), hafnium oxide (HfO2), and mixtures thereof.

[0064] The metal oxide having lithium ion transport capability including lithium element but moving lithium ions without storing lithium can be at least one selected from the group consisting of lithium phosphate (Li3PO4); lithium titanium phosphate (Li x Ti y (PO4)3, 0 < x < 2, 0 < y < 3); lithium titanium aluminum phosphate (Li x Al y Ti z (PO4)3, 0 < x < 2, 0 < y < 1, 0 < z < 3); (LiAlTiP) x O y based glass (0 < x < 4, 0 < y < 13), such as 14Li2O-9Al2O3-38TiO2-39P2O5; lithium lanthanum titanate (Li x La y TiO3, 0 < x < 2, 0 < y < 3); lithium germanium thiophosphate (Li x Ge y P z S w , 0 < x < 4, 0 < y < 1, 0 < z < 1, 0 < w < 5), such as Li 3.25 Ge 0.25 P 0.75 S4; and mixtures thereof.

[0065] Further, in addition to the metal oxide, at least one selected from the group consisting of lithium nitride (Li x N y , 0 < x < 4, 0 < y < 2), such as Li3N; SiS2-based glass (Li x Si y S z , 0 < x < 3, 0 < y < 2, 0 < z < 4), such as Li3PO4-Li2S-SiS2; P2S5-based glass (Li x P y S z , 0 < x < 3, 0 < y < 3, 0 < z < 7), such as LiI-Li2S-P2S5; and mixtures thereof can be further included.

[0066] Although the particle size of the inorganic material is not particularly limited, the D50 can have a range of 20 nm to 10 µm, specifically 100 nm to 1 µm, in consideration of the purpose of forming a coating layer having a uniform thickness and providing proper porosity.

[0067] In the particle size distribution curve of the particles, D50 means the particle size of the particles equal to 50% of the cumulative number of the particles, and the average particle size of the inorganic particles can be measured using a Particle Size Analyzer (product name: MASTERSIZER 3000; manufacturer: Malvern).

[0068] The content of the inorganic material can be 1 to 99% by weight, preferably 50 to 99% by weight, based on the entire solid content of the coating excluding additives such as a dispersant. If the content of the inorganic material is less than 1% by weight based on the entire solid content of the coating excluding additives such as a dispersant, it is difficult to obtain the desired effect, and the number of empty spaces formed between the inorganic particles is reduced by the binder. As a result, the pore size and porosity of the coating can be reduced, and thus the performance of the battery can be reduced. If the content of the inorganic material is greater than 99% by weight based on the entire solid content of the coating excluding additives such as a dispersant, the content of the binder is too small, whereby the adhesion between the inorganic particles can be reduced, and thus the inorganic coating can be separated from the porous substrate or uncoated areas can be generated at the time of coating, which is also not desirable.

[0069] Dispersant

[0070] The coating can further include a dispersant to further improve the dispersibility of the inorganic material. The dispersant serves to maintain the state in which the inorganic material is uniformly dispersed in the binder at the time of manufacturing the coating slurry. For example, an anionic surfactant can be used in order to maintain uniform dispersion while increasing the dispersibility.

[0071] An anionic component including at least one selected from the group consisting of carboxylate, phosphate, sulfonate, and sulfate can constitute the head of the anionic surfactant. Among them, an anionic surfactant including sulfonate can be used.

[0072] A material having nonionic surfactant properties can be used as the tail of the anionic surfactant. Although the material having nonionic surfactant properties is not particularly limited, a material including an alkyl group can be used. The material including an alkyl group can be a polyoxyalkylene having 5 to 200 oxyalkylene repeating units. At this time, the polyoxyalkylene can be at least one selected from the group consisting of polyethylene oxide, polypropylene oxide, and polyethylene oxide-polypropylene oxide copolymer.

[0073] A typical example of the anionic surfactant is carboxyl methyl cellulose (CMC).

[0074] In addition, at least one selected from the group consisting of an oil-soluble polyamine, an oil-soluble amine compound, a fatty acid, a fatty alcohol, a sorbitol fatty acid ester, tannin, and pyrogallic acid can be used as the dispersant.

[0075] The content of the dispersant can be 0.2 parts by weight to 10 parts by weight based on 100 parts by weight of the inorganic material. If the dispersant is included in an amount of less than 0.2 parts by weight based on 100 parts by weight of the inorganic material, the inorganic material can be easily precipitated. In contrast, if the dispersant is included in an amount of more than 10 parts by weight based on 100 parts by weight of the inorganic material, the adhesion of the coating layer to the porous substrate can be reduced or impurities can be generated as a result of a reaction with an electrolyte solution when a secondary battery is manufactured.

[0076] Binder

[0077] The coating layer can further include a binder. The binder can include a copolymer of a moisture phase-separable polymer and vinyl acetate.

[0078] Vinyl acetate can have an adhesion of 200 gf / 25 mm or more at 60°C and 6.5 MPa.

[0079] The moisture phase-separable polymer is not particularly limited, as long as the moisture phase-separable polymer is used to stably fix the coating layer to the surface of the porous substrate while having a moisture phase-separation effect. For example, the moisture phase-separable polymer can be at least one selected from the group consisting of poly(methyl acrylate), poly(methyl methacrylate), poly(ethyl methacrylate), poly(2-hydroxyethyl methacrylate), and poly(acrylonitrile). The acrylate-based binder can be manufactured by copolymerization of a soft monomer having a low glass transition temperature Tg and a hard monomer having a high glass transition temperature in a predetermined ratio.

[0080] At this time, the moisture phase-separable polymer can undergo phase separation at a temperature of 25°C to 80°C and a relative humidity of 40% to 80%.

[0081] The conditions of the temperature range and the relative humidity range must be satisfied in order for the copolymer of the moisture phase-separable polymer and vinyl acetate to have a phase separation property.

[0082] In addition, the moisture phase-separable polymer can have a glass transition temperature of 100°C or less, and vinyl acetate can have a glass transition temperature of 10°C to 60°C. As the copolymer of the moisture phase-separable polymer and vinyl acetate having different glass transition temperatures is used, as described above, a binder having increased adhesion can be obtained.

[0083] The copolymer can be manufactured by copolymerization of the moisture-permeable phase-separating polymer and vinyl acetate in a weight ratio of 80:20 to 20:80. The vinyl acetate can include vinyl acetate monomers and polyvinyl acetate. As a result, the vinyl acetate monomers or the polyvinyl acetate can be copolymerized with the moisture-permeable phase-separating polymer into the copolymer.

[0084] The copolymer can have a glass transition temperature of 60℃ or less, specifically 40℃ or less. If the percentage difference between the moisture-permeable phase-separating polymer and the vinyl acetate in the copolymer is too large, certain performances of the adhesive such as adhesion, strength, and moisture-permeable phase-separation characteristics of the adhesive can be reduced.

[0085] The copolymer can be manufactured using various methods such as emulsion polymerization and solution polymerization, and the manufacturing method is not particularly limited. In addition, the reaction conditions used in the method can be appropriately adjusted by those skilled in the art.

[0086] The copolymer can be a block copolymer. The block copolymer can form a periodically arranged structure such as a sphere, a cylinder, a gyroid, an inverse structure, or a lamella by phase separation.

[0087] The copolymer can have a structure of the following Chemical Formula 1.

[0088] (Chemical Formula 1)

[0089]

[0090] In Chemical Formula 1, m:n can be 80:20 to 20:80, and the weight average molecular weight can be 100,000 to 500,000.

[0091] The weight ratio between the inorganic material and the copolymer each as a solid content constituting the coating layer can be 60:40 to 95:5. If the content of the copolymer is less than 10% by weight based on the solid content of the coating layer, sufficient adhesion can not be obtained. If the content of the copolymer is greater than or equal to 40% by weight based on the solid content of the coating layer, the copolymer can act as a resistance of the separator, thereby possibly reducing the performance of the battery.

[0092] The content of the copolymer is merely illustrative, and the content of the copolymer that can be adjusted is presented as an illustration in order to obtain a high-performance secondary battery desired in the present application.

[0093] The coating layer of the separator can be configured to have a single-layer structure or a multi-layer structure. In the case where the coating layer of the separator has a multi-layer structure, the copolymer can be provided at the outermost layer of the coating layer, i.e., the coating layer facing the positive electrode or the negative electrode.

[0094] The present application provides a secondary battery including the separator.

[0095] Figure 1 is a side view of an electrode assembly including a cathode, a separator, and an anode according to the present application.

[0096] A secondary battery according to the present application can include a cathode 100, a separator 200, and an anode 300.

[0097] Positive electrode

[0098] For example, the cathode 100 can be manufactured by applying a cathode mixture of a cathode active material, a conductive agent, and a binder to the cathode current collector 110 to form a cathode active material layer 120 on at least one surface of the cathode current collector 110. If necessary, a filler can be further added to the cathode mixture.

[0099] In general, the cathode current collector 110 is manufactured to have a thickness of 3 μm to 500 μm. The cathode current collector 110 is not particularly limited as long as the cathode current collector exhibits high conductivity while the cathode current collector does not induce any chemical change in a battery to which the cathode current collector is applied. For example, the cathode current collector can be made of stainless steel, aluminum, nickel, or titanium. Alternatively, the cathode current collector can be made of aluminum or stainless steel whose surface is treated with carbon, nickel, titanium, or silver. In particular, aluminum can be used. The cathode current collector 110 can have a micro-scale uneven pattern formed on its surface to increase adhesion to the cathode active material layer 120. For example, the cathode current collector can be configured in various forms such as a film, a sheet, a foil, a mesh, a porous body, a foam body, and a non-woven fabric body.

[0100] The cathode active material included in the cathode active material layer 120 can be composed of, for example, a layered compound such as lithium nickel oxide (LiNiO2) or a compound substituted with one or more transition metals; a lithium manganese oxide represented by the chemical formula LiMnO4 (wherein x = 0 ~ 0.33), or a lithium manganese oxide such as LiMnO3, LiMn2O3, LiMnO2; a lithium copper oxide (Li2CuO2); a vanadium oxide such as LiV3O8, V2O5, and Cu2V2O7; a Ni-site type lithium nickel oxide represented by the chemical formula LiNi 1+x Mn 2-x O4 (wherein x = 0 ~ 0.33), or a lithium manganese oxide such as LiMnO3, LiMn2O3, LiMnO2; a lithium copper oxide (Li2CuO2); a vanadium oxide such as LiV3O8, V2O5, and Cu2V2O7; a Ni-site type lithium nickel oxide represented by the chemical formula LiNi 1-x MxO2 (wherein M = Co, Mn, Al, Cu, Fe, Mg, B, or Ga, x = 0.01 ~ 0.3); a Li-site type lithium nickel oxide represented by the chemical formula LiMn 2-x M xLi2Mn3MO8 (wherein M = Fe, Co, Ni, Cu, or Zn); LiMn2O4 in which part of Li in the chemical formula is substituted with an alkaline earth metal ion; a disulfide compound; and Fe2(MoO4)3. However, the present application is not limited thereto.

[0101] The conductive agent is generally added so that the conductive agent occupies 0.1 to 30% by weight based on the total weight of the mixture including the positive electrode active material. The conductive agent is not particularly limited as long as the conductive agent has high conductivity without inducing any chemical change in the battery to which the conductive agent is applied. For example, graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, or thermal black; conductive fibers such as carbon fibers or metal fibers; metal powders such as carbon fluoride powder, aluminum powder, or nickel powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; or conductive materials such as polyaniline or polypyrrole can be used as the conductive agent.

[0102] The binder included in the positive electrode 100 is a component that assists in the binding between the positive electrode active material and the conductive agent and the binding with the current collector. The binder is generally added in an amount of 0.1 to 30% by weight based on the total weight of the mixture including the positive electrode active material. As examples of the binder, polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butadiene rubber, fluoro rubber, and various copolymers can be used.

[0103] <negative electrode>

[0104] The negative electrode 300 can be formed by applying a negative electrode mixture including a negative electrode active material to at least one surface of the negative electrode current collector 310 and drying to form a negative electrode active material layer 320 on the negative electrode current collector 310, or can be composed only of the negative electrode current collector 310. When necessary, a binder or a conductive agent can be selectively further added.

[0105] The negative current collector 310 is generally manufactured to have a thickness of 3 μm to 500 μm. The negative current collector 310 is not particularly limited as long as the negative current collector exhibits high electrical conductivity while the negative current collector does not induce any chemical change in a battery to which the negative current collector is applied. For example, the negative current collector can be made of copper, stainless steel, aluminum, nickel, titanium, or calcined carbon. Alternatively, the negative current collector can be made of copper or stainless steel, or aluminum cadmium alloy, the surface of which is treated with carbon, nickel, titanium, or silver. In addition thereto, in the same manner as the positive current collector 110, the negative current collector can have a micro-scale uneven pattern formed on the surface thereof to increase the binding force with the negative active material layer 320. The negative current collector can be configured in various forms such as a film, a sheet, a foil, a mesh, a porous body, a foam body, and a non-woven fabric body.

[0106] The negative active material layer 320 includes a negative active material. As the negative active material, for example, carbon such as non-graphitized carbon and graphite-based carbon; lithium transition metal composite oxides such as LiCoO2, LiMnO2, LiNiO2, LiFeO2, LiCo1-xMnxO2(0≤x≤1), LiNi1-xMnxO2(0≤x≤1), LiCo1-xMnO2(0≤x≤1), LiFe1-xMnxO2(0≤x≤1), Fe2O3(0≤x≤1), Li x Fe2O3(0≤x≤1), Li x WO2(0≤x≤1), Sn x Me 1-x Me’ y O z a metal composite oxide such as (Me: Mn, Fe, Pb, Ge; Me’: Al, B, P, Si, a Group 1, 2, or 3 element of the periodic table, a halogen; 0 < x ≤ 1; 1 ≤ y ≤ 3; 1 ≤ z ≤ 8); lithium metal; a lithium alloy; a silicon-based alloy; a tin-based alloy; a metal oxide such as SnO, SnO2, PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4, and Bi2O5; an electrically conductive polymer such as polyacetylene; or a Li-Co-Ni-based material.

[0107] Separator

[0108] The separator 200 according to the present application can have the same configuration as the separator described above. The separator 200 can have the coating layers 220 and 230 formed on at least one surface of the porous substrate 210. At this time, it is preferable that the coating layers 220 are formed on the surface of the porous substrate 210 facing the positive electrode and the surface of the porous substrate 210 facing the negative electrode, respectively, so as to increase the binding force with the positive electrode 100 and the negative electrode 300.

[0109] The coating layer 220 facing the positive electrode and the coating layer 230 facing the negative electrode can have different components. The reason for this is that the binding force between the positive electrode 100 and the separator 200 is lower than the binding force between the negative electrode 300 and the separator 200. In order to increase the binding force between the positive electrode 100 and the separator 200, therefore, the copolymer according to the present application can be added to the coating layer 220 facing the positive electrode, whereby the adhesion of the coating layer 220 facing the positive electrode can be increased.

[0110] Furthermore, in the separator 200, the coating layer 220 facing the positive electrode and the coating layer 230 facing the negative electrode can differ from each other in terms of the composition ratio of components. At this time, the copolymer is used in each of the coating layer 220 facing the positive electrode and the coating layer 230 facing the negative electrode, however the percentage of the copolymer used in the coating layer 220 facing the positive electrode and the coating layer 230 facing the negative electrode can differ from each other. Since the copolymer has a high adhesion, the amount of the copolymer used in the coating layer 230 facing the negative electrode can be less than the amount of the copolymer used in the coating layer 220 facing the positive electrode.

[0111] In the above construction, the adhesion between the separator 200 and the positive electrode 100 under the condition of 60°C and 6.5Mpa can be 50gf / 25mm or more.

[0112] Furthermore, in the present application, the adhesion of the separator can be easily adjusted using the copolymer, whereby the adhesion between the positive electrode 100 and the separator 200 and the adhesion between the negative electrode 300 and the separator 200 can be adjusted so as to be similar to each other.

[0113] Hereinafter, the present application will be described with reference to the following examples. These examples are provided only to more easily understand the present application, and should not be construed as limiting the scope of the present application.

[0114] <Example 1>

[0115] Vinyl acetate and poly(methyl acrylate) were copolymerized at a weight ratio of 80:20 to form a first copolymer having a weight average molecular weight of 300,000. 6.5 wt% of the first copolymer, 91 wt% of alumina, and 2.5 wt% of a dispersant were dispersed in acetone to form a slurry. A porous substrate made of a polyolefin material, having a thickness of 14.0 μm, was prepared, and the slurry was applied to the surface of the porous substrate facing the electrode to form a coating layer. Finally, a separator having a coating layer formed thereon, while having a thickness of 15.5 μm, was manufactured, and was used as Example 1.

[0116] <Example 2>

[0117] In Example 2, a separator having a coating formed thereon, while having a thickness of 15.6 μm, was manufactured in the same manner as in Example 1, except that, in comparison with the separator according to Comparative Example 1, vinyl acetate and poly(methyl acrylate) were copolymerized in a weight ratio of 60:40 to form a second copolymer, and 6.8 wt% of the second copolymer, 90.7 wt% of alumina, and 2.5 wt% of a dispersant were dispersed in acetone to form a slurry.

[0118] <Example 3>

[0119] In Example 3, a separator having a coating formed thereon, while having a thickness of 15.4 μm, was manufactured in the same manner as in Example 1, except that, in comparison with the separator according to Comparative Example 1, vinyl acetate and poly(methyl acrylate) were copolymerized in a weight ratio of 40:60 to form a third copolymer.

[0120] <Comparative Example 1>

[0121] In Comparative Example 1, polyvinyl acetate having a weight average molecular weight of 500,000 was used alone instead of the first copolymer according to Example 1. At this time, a separator having a coating formed thereon, while having a thickness of 14.9 μm, was manufactured in the same manner as in Example 1, except that 7.5 wt% of polyvinyl acetate, 90 wt% of alumina, and 2.5 wt% of a dispersant were dispersed in acetone to form a slurry.

[0122] <Comparative Example 2>

[0123] In Comparative Example 2, a separator having a coating formed thereon, while having a thickness of 15.1 μm, was manufactured in the same manner as in Example 1, except that the weight average molecular weight of polyvinyl acetate was 300,000, and 7.4 wt% of polyvinyl acetate, 90.1 wt% of alumina, and 2.5 wt% of a dispersant were dispersed in acetone to form a slurry.

[0124] <Comparative Example 3>

[0125] In Comparative Example 3, a separator having a coating formed thereon, while having a thickness of 15.5 μm, was manufactured in the same manner as in Example 1, except that polyvinyl acetate having a weight average molecular weight of 500,000 and PVdF-HFP were mixed in a ratio of 8:2 to form a binder, and 6.4 wt% of the binder, 91.1 wt% of alumina, and 2.5 wt% of a dispersant were dispersed in acetone to form a slurry.

[0126] <Comparative Example 4>

[0127] In Comparative Example 4, a separator having a coating formed thereon, while having a thickness of 15.7 μm, was manufactured in the same manner as in Example 1, except that polyvinyl acetate having a weight average molecular weight of 300,000 and PVdF-HFP were mixed in a ratio of 8:2 to form a binder, and 6.2 wt% of the binder, 91.3 wt% of alumina, and 2.5 wt% of a dispersant dispersed in acetone to form a slurry.

[0128] <Experimental Example 1: Measurement of Adhesion between Negative Electrode and Separator>

[0129] To measure the adhesion between each of the separators and the negative electrode manufactured according to Comparative Examples 1 to 3 and Examples 1 to 3, the separator and the negative electrode were adhered to each other at 60°C and 6.5 MPa to manufacture a half battery, and an end portion of the half battery was mounted to a UTM device (LLOYD Instrument LF Plus). The UTM device was used to apply a force of 180° at a measurement speed of 300 mm / min to the half battery to measure a force required to separate the negative electrode and the separator from each other.

[0130] <Experimental Example 2: Evaluation of Air Permeability>

[0131] The air permeability was measured according to ASTM D726-94. The Gurley value used herein, which is air flow resistance, was measured using a Gurley densometer. The air permeability value described herein is shown as a time (sec) required for 100 cc of air to pass through a 1 in 2 cross section of each of the separators manufactured according to the Comparative Examples and Examples at a pressure of 12.2 in water column, i.e., air permeation time.

[0132] The results measured according to Experimental Examples 1 and 2 are shown in Table 1 below.

[0133] [Table 1]

[0134]

[0135] As can be seen from the above Table 1, the adhesion is higher in the case where the copolymer according to the present application is used than in the case where the non-copolymerized polyvinyl acetate or the mixture of polyvinyl acetate and PVdF-HFP is used.

[0136] In addition, it can be seen that the adhesion to the electrode increases in proportion to the percentage of the poly(methyl acrylate) in the copolymer.

[0137] In addition, it can be seen that, in the case where the copolymer according to the present application is used, the air permeability is higher than in the case where a mixture of polyvinyl acetate and PVdF-HFP is used, whereby the performance of the secondary battery can be improved in the case where the separator according to the present application is used.

[0138] Those skilled in the art to which the present application pertains will appreciate that, based on the above description, various applications and modifications can be made within the scope of the present application.

[0139] [Reference Signs]

[0140] 100: positive electrode

[0141] 110: positive electrode current collector

[0142] 120: positive electrode active material layer

[0143] 200: separator

[0144] 210: porous substrate

[0145] 220: positive electrode-facing coating layer

[0146] 230: negative electrode-facing coating layer

[0147] 300: negative electrode

[0148] 310: negative electrode current collector

[0149] 320: negative electrode active material layer

[0150] Industrial applicability

[0151] As is apparent from the above description, an adhesive having high adhesion is used for the separator according to the present application, whereby the adhesion between the positive electrode and the separator and between the negative electrode and the separator is increased. In addition, the phenomenon of separation between the vinyl acetate and the polymer that can be separated by humidification does not occur under humidification conditions, whereby the adhesive assists in forming an asymmetric structure having high porosity in the coating layer while being uniformly distributed.

[0152] In addition, since the adhesive having high adhesion is used, the consumption of the adhesive is lower than that of a conventional adhesive, whereby the impregnability of the separator is improved and the capacity and life of the secondary battery are increased.

[0153] In addition, the amount of the inorganic material in the coating layer can be increased compared to the prior art, whereby a separator having a thin coating layer while achieving the desired effects of the inorganic material can be obtained. As a result, the density of the secondary battery is also increased.

Claims

1. A separator for a battery, the separator comprising: a porous substrate; and a coating layer formed on at least one surface of the porous substrate, the coating layer comprising an inorganic material and a binder, wherein the binder is a copolymer of a moisture-induced phase-separable polymer and vinyl acetate, wherein the moisture-induced phase-separable polymer is poly(methyl acrylate), wherein the copolymer is a block copolymer and has a structure of Chemical Formula 1: Chemical Formula 1 wherein m:n is 80:20 to 20:

80. 2.The separator of claim 1, wherein the moisture-induced phase-separable polymer has a glass transition temperature of 100℃ or less, and wherein the vinyl acetate has a glass transition temperature of 10℃ to 60℃. 3.The separator of claim 1, wherein the copolymer is manufactured by copolymerization of the moisture-induced phase-separable polymer and the vinyl acetate in a weight ratio of 80:20 to 20:

80. 4.The separator of claim 1, wherein the vinyl acetate has an adhesion of 200 gf / 25 mm or more at a condition of 60℃ and 6.5 Mpa. 5.The separator of claim 1, wherein the moisture-induced phase-separable polymer undergoes phase separation at a temperature of 25℃ to 80℃ and a relative humidity of 40% to 80%. 6.The separator of claim 1, wherein a weight ratio between the inorganic material and the copolymer in the coating layer is 60:40 to 90:

10. 7.A secondary battery comprising: a positive electrode; a negative electrode; and the separator of any one of claims 1 to 6. 8.The secondary battery of claim 7, wherein the coating layer of the separator facing the positive electrode and the coating layer of the separator facing the negative electrode have different compositions. 9.The secondary battery of claim 8, wherein the copolymer is included only in the coating layer facing the positive electrode. 10.The secondary battery of claim 7, wherein the coating layer of the separator facing the positive electrode and the coating layer of the separator facing the negative electrode differ from each other in a composition ratio of the components. 11.The secondary battery of claim 10, wherein the coating layer facing the positive electrode includes a greater amount of the copolymer than the coating layer facing the negative electrode. 12.The secondary battery of claim 7, wherein an adhesion between the separator and the positive electrode is 50 gf / 25 mm or more at a condition of 60℃ and 6.5 Mpa.

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