Secondary battery coating composition and secondary battery using same

Abstract

The secondary battery coating composition according to the present invention is a composition for coating an electrode and / or a separator, and contains a flame retardant, a dispersant, and an aqueous solvent. The flame retardant comprises at least one of a hydroxyl-containing inorganic flame retardant, a phosphorus-based flame retardant, a halogen-based flame retardant and a melamine-based flame retardant.

Description

Technical Field

[0001] This application is based on and claims the benefit of priority from Korean Patent Applications No. 10-2023-0033531 and No. 10-2023-0186249 filed on March 14, 2023, and December 19, 2023, respectively, in the Korean Intellectual Property Office, the disclosures of which are incorporated herein in their entirety by reference.

[0002] The present invention relates to a positive electrode active material, a positive electrode slurry containing the positive electrode active material, a preparation method thereof, and a positive electrode and a lithium secondary battery containing the positive electrode active material. Background Art

[0003] With recent technological developments and the increasing demand for mobile devices, the demand for batteries as energy sources has rapidly increased. Consequently, various studies are underway to develop batteries that can meet these needs. For example, lithium secondary batteries, which have high energy density and excellent lifespan and cycle characteristics, are being actively researched as power sources for devices.

[0004] Lithium secondary batteries include a positive electrode containing a positive electrode active material capable of intercalating and deintercalating lithium ions, a negative electrode containing a negative electrode active material capable of intercalating and deintercalating lithium ions, a separator disposed between the positive and negative electrodes, and an electrolyte. The positive and negative electrodes have a structure in which an electrode active material layer is formed on one or both surfaces of an electrode current collector.

[0005] Meanwhile, in order to improve the safety of secondary batteries, improvements are being made to the characteristics of each of a positive electrode, a negative electrode, an electrolyte, and a separator. Summary of the Invention

[0006] [Technical Issues]

[0007] The present invention provides a secondary battery coating composition capable of improving the dispersibility of a flame retardant in an aqueous solvent and a secondary battery including a coating layer formed using the composition.

[0008] [Technical solution]

[0009] One embodiment of the present invention provides a secondary battery coating composition comprising a flame retardant, a dispersant, and an aqueous solvent. The flame retardant comprises at least one of an inorganic flame retardant containing a hydroxyl group, a phosphorus-based flame retardant, a halogen-based flame retardant, and a melamine-based flame retardant.

[0010] According to one embodiment of the present invention, the inorganic flame retardant comprises one or more selected from the group consisting of boehmite, pseudo-boehmite, aluminum hydroxide and magnesium hydroxide. 50 It is about 0.1 μm to 5.0 μm.

[0011] According to one embodiment of the present invention, the dispersant is a compound containing one or more carboxyl groups, and includes one or more selected from citric acid, malic acid, oxalic acid, glutamic acid, aspartic acid, amino acids, malonic acid, and fatty acids.

[0012] According to one embodiment of the present invention, the dispersant and the flame retardant are included in a weight ratio of about 1:2 to 1:150.

[0013] According to one embodiment of the present invention, the aqueous solvent may be water.

[0014] In the coating composition of one embodiment of the present invention, the solid content is about 10 wt % to 70 wt %.

[0015] The secondary battery coating composition of one embodiment further comprises an alkaline additive. The alkaline additive comprises one or more selected from lithium carbonate, sodium carbonate, potassium carbonate, magnesium carbonate, calcium carbonate, ethylenediamine, diethylenetriamine, tris(2-aminoethyl)amine, vinylene carbonate, vinyl ethylene carbonate, fluoroethylene carbonate, methyl propargyl carbonate and allyl methyl carbonate. Based on 100 parts by weight of the secondary battery coating composition, the content of the alkaline additive is about 1 to 10 parts by weight.

[0016] One embodiment of the present invention provides a secondary battery electrode comprising a current collector, an electrode active material layer, and a coating. The electrode active material layer and the coating are disposed on the current collector, and the coating is formed from the secondary battery coating composition described above. In the electrode of this embodiment of the present invention, the coating has a thickness of approximately 2 μm to 30 μm.

[0017] One embodiment of the present invention provides a lithium secondary battery, which includes an electrode coated with the secondary battery coating composition. One embodiment of the present invention provides a sodium secondary battery, which includes an electrode coated with the secondary battery coating composition.

[0018] Another embodiment of the present invention provides a secondary battery separator, comprising a porous polymer substrate and a coating layer, wherein the coating layer is disposed on one surface of the porous polymer substrate and is formed from the secondary battery coating composition.

[0019] Another embodiment of the present invention provides a method for producing a secondary battery coating composition. The secondary battery coating composition includes a flame retardant, a dispersant, and an aqueous solvent, wherein the flame retardant includes at least one of an inorganic flame retardant containing a hydroxyl group, a phosphorus flame retardant, a halogen flame retardant, and a melamine flame retardant.

[0020] Average particle size D of inorganic flame retardant 50 It is about 0.1 μm to 5.0 μm.

[0021] The dispersant comprises a compound containing one or more carboxyl groups.

[0022] [Beneficial effects]

[0023] By making the secondary battery coating composition contain at least one of a hydroxyl-containing inorganic flame retardant, a phosphorus-based flame retardant, a halogen-based flame retardant and a melamine-based flame retardant, the secondary battery of the present invention has relatively improved coating properties and heat resistance because the flame retardant can be easily dispersed even in an aqueous solvent environment.

[0024] Therefore, provided is a secondary battery including the secondary battery coating composition including a flame retardant that can be easily dispersed even in an aqueous solvent environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is an optical microscope image taken at a magnification of 300 times after the electrode coating composition prepared in Example 1 was applied to a glass slide.

[0026] Figure 2 This is an optical microscope image taken at a magnification of 300 times after the electrode coating composition prepared in Example 2 was applied to a glass slide.

[0027] Figure 3 This is an optical microscope image taken at a magnification of 300 times after the electrode coating composition prepared in Example 3 was applied to a glass slide.

[0028] Figure 4 This is an optical microscope image taken at a magnification of 300 times after the electrode coating composition prepared in Example 4 was applied to a glass slide.

[0029] Figure 5 This is an optical microscope image taken at a magnification of 300 times after the electrode coating composition prepared in Example 5 was applied to a glass slide.

[0030] Figure 6 This is an optical microscope image taken at a magnification of 300 times after the electrode coating composition prepared in Example 6 was applied to a glass slide.

[0031] Figure 7 This is an optical microscope image taken at a magnification of 300 times after the electrode coating composition prepared in Example 7 was applied to a glass slide.

[0032] Figure 8 This is an optical microscope image taken at a magnification of 300 times after the electrode coating composition prepared in Comparative Example 2 was applied to a slide glass.

[0033] Figure 9This is an optical microscope image taken at a magnification of 300 times after the electrode coating composition prepared in Comparative Example 3 was applied to a slide glass.

[0034] Figure 10 Graph showing changes in battery capacity values ​​of lithium secondary batteries manufactured in Example 3 and Comparative Example 1, respectively, after operation at 25° C., as a function of the number of cycles.

[0035] In some drawings, corresponding parts are given the same reference numerals. Those skilled in the art will understand that the drawings simply and clearly illustrate the elements and are not necessarily drawn to scale. For example, to aid understanding of the various embodiments, the sizes of some elements shown in the drawings may be exaggerated compared to other elements. In addition, elements that are useful or necessary in commercially feasible embodiments but are known in the art may generally be omitted so as not to hinder understanding of the spirit of the various embodiments of the present invention. DETAILED DESCRIPTION

[0036] The advantages and features of the present invention and the methods for achieving these advantages and features will become clear with reference to the embodiments and drawings described in detail below. However, the present invention is not limited to the embodiments described below, but can be implemented in a variety of different modes. These embodiments are provided only to ensure that the present invention is fully disclosed and to fully convey the scope of the present invention to those skilled in the art. The present invention is limited only by the claims. Throughout the specification, the same reference numerals indicate the same components.

[0037] Unless otherwise defined, all terms (including technical and scientific terms) used herein may be used with the meaning that is commonly understood by one of ordinary skill in the art to which the invention belongs. In addition, unless clearly and specifically defined, terms defined in commonly used dictionaries will not be ideally or excessively interpreted.

[0038] The terms used herein are used to describe embodiments and are not intended to limit the present invention. As used herein, unless otherwise specified in a phrase, the singular also includes the plural. As used herein, "include" and / or "comprising" do not exclude the presence or addition of one or more other components in addition to the components mentioned.

[0039] When it is described herein that a certain part includes a certain component, it means that other components may be further included rather than excluded unless particularly stated otherwise.

[0040] As used herein, the expression "A and / or B" means A, or B, or A and B.

[0041] Herein, "%" means weight percent unless otherwise specifically stated.

[0042] In this paper, the average particle size D 50 It can be defined as the particle size corresponding to 50% of the cumulative volume in the particle size distribution curve. 50 For example, the measurement can be performed using the laser diffraction method, which is generally capable of measuring particle sizes ranging from submicrometers to several millimeters, and can produce results with high reproducibility and high resolution.

[0043] As used herein, the terms "about," "approximately," and "substantially" are used to indicate a numerical range or degree range or its approximate value that takes into account inherent manufacturing errors and material errors, and are used to prevent infringers from taking unfair advantage of descriptions that mention precise values ​​or absolute values ​​to aid understanding of the present invention.

[0044] To improve the safety of electrodes and separators, research is underway to develop technologies that form coatings on the outer surfaces of electrodes, active material layers, and separators. This coating protects the electrode active material layers and separators from the heat generated during secondary battery operation and improves insulation between the electrodes.

[0045] Research is underway to use insulating adhesives to form coatings for electrodes and separators. However, adhesive coatings have relatively weak heat resistance, and the adhesive strength decreases under high-temperature conditions during battery operation, which reduces battery safety.

[0046] In order to prevent this problem, the present invention provides a secondary battery in which the heat resistance of a coating layer is improved by adding a flame retardant to an electrode or separator coating composition.

[0047] When the flame retardant in the electrode or separator coating composition that improves the heat resistance of the coating of the secondary battery is unevenly dispersed, the flame retardant will settle to the bottom of the composition, which prevents the flame retardant from being evenly distributed in the coating formed by the composition, thereby reducing the effect of improving the heat resistance of the electrode. In addition, in order to prevent the above-mentioned problems, including: the flame retardant is concentrated in the lower part of the coating, the binder content in the lower part of the coating is reduced, and the coating is easily detached from the electrode, and the flame retardant particles are aggregated to form particles with a large particle size, which increases the viscosity of the composition and thus the thickness and / or surface of the coating are unevenly formed, the present invention provides a secondary battery coated with a dispersant compound containing one or more carboxyl groups, which uniformly disperses the flame retardant in the secondary battery coating composition.

[0048] The present invention provides a secondary battery coated with an aqueous solvent and / or an adhesive, wherein the content of the aqueous solvent is such that the coating composition has an appropriate viscosity, serving as a solvent for uniformly dispersing a flame retardant in the secondary battery coating composition, and is relatively inexpensive and environmentally friendly compared to secondary batteries coated with organic solvents.

[0049] Hereinafter, the present invention will be described.

[0050] Secondary battery coating composition

[0051] The secondary battery coating composition of the present invention contains a flame retardant, a dispersant and an aqueous solvent. The flame retardant comprises at least one of an inorganic flame retardant containing a hydroxyl group, a phosphorus flame retardant, a halogen flame retardant and a melamine flame retardant.

[0052] Hereinafter, each component of the secondary battery coating composition of the present invention will be described.

[0053] (1) Flame retardant

[0054] Secondary battery coating compositions contain flame retardants to improve the heat resistance of the coating layer (described later). For example, flame retardants resist softening or melting even at temperatures exceeding 900°C. Therefore, when flame retardants are included in the coating, they can maintain electrode insulation even at very high temperatures.

[0055] The flame retardant includes at least one of an inorganic flame retardant, a phosphorus flame retardant, a halogen-based flame retardant, and a melamine-based flame retardant.

[0056] Inorganic flame retardants decompose upon exposure to heat, releasing non-combustible gases such as water, carbon dioxide, sulfur dioxide, and hydrogen chloride, and inducing an endothermic reaction. This dilutes the combustible gases, preventing oxygen access, and the endothermic reaction causes cooling, reducing the formation of thermal decomposition products and thus achieving a flame retardant effect.

[0057] Inorganic flame retardants include compounds containing hydroxyl groups. According to one embodiment, the inorganic flame retardant comprises one or more selected from boehmite (AlO(OH)), pseudoboehmite (Al2O3·nH2O), alumina trihydrate (ATH) (Al(OH)3), and magnesium hydroxide (Mg(OH)2).

[0058] According to one embodiment, the phosphorus flame retardant exerts a flame retardant effect by forming a protective layer with polymetaphosphoric acid produced by thermal decomposition, or by blocking oxygen through a carbon film produced by dehydration during the production of polymetaphosphoric acid. The phosphorus flame retardant includes one or more selected from the following: phosphates, such as red phosphorus and ammonium phosphate; phosphine oxide, phosphine oxide diol, phosphite ester / salt, phosphonate ester / salt, triaryl phosphate, alkyl diaryl phosphate, trialkyl phosphate, and resorcinol bisdiphenyl phosphate (RDP).

[0059] According to one embodiment, the halogen-based flame retardant can exert a flame retardant effect by substantially stabilizing free radicals generated in the gas phase. The halogen-based flame retardant includes one or more selected from tribromophenoxyethane, tetrabromobisphenol-A (TBBA), octabromodiphenyl ether (OBDPE), brominated epoxy oligomers, brominated polycarbonate oligomers, chlorinated paraffins, chlorinated polyethylene, and alicyclic chlorinated flame retardants.

[0060] According to one embodiment, a melamine-based flame retardant exhibits a flame retardant effect by promoting the formation of carbonized materials, absorbing energy through melamine sublimation, and generating ammonia as a decomposition product while lowering the temperature of the burning material, thereby diluting oxygen and the combustion gas of the resin composition. For example, the melamine-based flame retardant comprises one or more selected from melamine, melamine cyanurate, and melamine phosphate.

[0061] For example, the secondary battery coating composition of the present invention includes an inorganic flame retardant. According to the present invention, the average particle size D of the inorganic flame retardant before being dissolved in the aqueous solvent is 50 The average particle size D before the inorganic flame retardant is dissolved is about 0.1 μm to 5.0 μm, and in one embodiment about 0.1 μm to 4.0 μm, or about 0.3 μm to 1.0 μm. 50 When the above range is satisfied, the occurrence of agglomeration of the inorganic flame retardant particles in the composition is minimized, thereby forming a coating layer having a uniform thickness and surface.

[0062] According to one embodiment, the content of the flame retardant is about 5 to 40 parts by weight, for example, about 15 to 30 parts by weight, or about 15 to 25 parts by weight, relative to 100 parts by weight of the secondary battery coating composition. For example, when the content of boehmite satisfies the above range, agglomeration of boehmite particles is minimized, thereby appropriately maintaining the viscosity of the secondary battery coating composition, so that a coating having a uniform thickness and surface is formed.

[0063] (2) Dispersant

[0064] The dispersant is used to improve the dispersibility of the flame retardant in the secondary battery coating composition of the present invention. According to one embodiment, the dispersant of the present invention improves the dispersibility of the flame retardant in an aqueous solvent environment.

[0065] The dispersant of the present invention includes a compound containing one or more carboxyl groups. In a secondary battery coating composition comprising an aqueous solvent and a flame retardant in one embodiment, when a compound containing one or more carboxyl groups is used as a dispersant, the dispersibility of the flame retardant in the secondary battery coating composition and the coating properties of the composition are relatively improved compared to the case where the present invention is not applied. For example, when the flame retardant is an inorganic flame retardant containing a hydroxyl group, the hydrophilic group portion of the carboxylic acid compound is bonded to the hydroxyl group on the surface of the flame retardant particles. Therefore, the dispersibility of the flame retardant is improved by electrostatic repulsion between the carboxylic acid compounds on the surface of each flame retardant particle.

[0066] The dispersant of the present invention is a compound containing one or more carboxyl groups. In one embodiment, it is a compound containing approximately 2 to 5 carboxyl groups, or a compound containing approximately 2 to 4 carboxyl groups. When the number of carboxyl groups in the dispersant satisfies the above range, the carboxylic acid compound is uniformly and densely disposed on the surface of the flame retardant particles, thereby relatively improving the dispersibility of the flame retardant.

[0067] In one embodiment of the present invention, the compound containing one or more carboxyl groups includes at least one selected from the group consisting of citric acid, malic acid, oxalic acid, glutamic acid, aspartic acid, amino acids, malonic acid, and fatty acids. For example, the compound containing one or more carboxyl groups is citric acid. Citric acid has advantages such as high solubility in aqueous solvents due to its large number of hydrophilic functional groups, excellent heat resistance due to its high melting point, and low price.

[0068] According to one embodiment, the content of the dispersant is about 0.1 to 10 parts by weight, for example, about 1 to 5 parts by weight, or about 1.9 to 2.5 parts by weight, relative to 100 parts by weight of the secondary battery coating composition. When the content of the dispersant meets the above range, the dispersibility of boehmite in the secondary battery coating composition containing an aqueous solvent is guaranteed.

[0069] At the same time, the dispersant and the flame retardant of the present invention are contained in a weight ratio of about 1:2 to 1:150, for example, about 1:4 to 1:20 or about 1:5 to 1:10. When the weight ratio of the dispersant and the flame retardant meets the above numerical range, while improving the dispersibility of the flame retardant in the aqueous solvent and improving the coating properties of the secondary battery coating composition, the thickness of the coating layer is increased by increasing the viscosity of the slurry, thereby improving the heat resistance of the secondary battery.

[0070] (3) Aqueous solvent

[0071] In the present invention, the aqueous solvent is used to ensure the coating properties of the secondary battery coating composition of the present invention by dissolving the flame retardant and the dispersant. Compared with organic solvents, the aqueous solvent used in the present invention has the advantages of low manufacturing cost, environmental friendliness and harmlessness to the human body.

[0072] As the aqueous solvent, a solvent that can dissolve the flame retardant and dispersant to a predetermined level or higher and has a non-solvent property for the electrode active material layer is used. According to one embodiment, water is used as the aqueous solvent. Alternatively, the aqueous solvent may contain an alcohol compound such as ethanol or methanol in addition to water.

[0073] According to one embodiment, taking into account the coating properties of the coating composition, the aqueous solvent is included in an amount that allows the composition to have an appropriate viscosity. According to one embodiment, the content of the aqueous solvent is about 20 to 90 parts by weight, for example, about 23 to 80 parts by weight, or about 65 to 78 parts by weight, relative to 100 parts by weight of the coating composition. At the same time, the solid content of the secondary battery coating composition of an embodiment of the present invention is about 10 weight % to 80 weight %, for example, about 20 weight % to 77 weight %, or about 22 weight % to 35 weight %. When the solid content meets the above range, the viscosity of the secondary battery coating composition is suitable for forming a coating using the composition while minimizing the agglomeration of the flame retardant particles.

[0074] (4) Adhesive

[0075] The secondary battery coating composition of one embodiment of the present invention further includes a binder. The binder of one embodiment further improves the adhesion between the coating layer and the current collector and / or the electrode active material layer.

[0076] The adhesive of one embodiment includes a compound that is not easily dissolved in the secondary battery electrolyte. The adhesive is a polymer adhesive, and for example, a single one or a mixture of two or more selected from polyvinylidene fluoride (PVdF), polyvinylidene fluoride-hexafluoropropylene, polyvinyl pyrrolidone, polyacrylonitrile, polyacrylimide, polyvinylidene fluoride-trichloroethylene, polyvinylidene fluoride-chlorotrifluoroethylene (PVdF-CTFE), polymethyl methacrylate, polyvinyl acetate, ethylene-vinyl acetate copolymer, polyethylene oxide, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethyl pullulan, cyanoethyl polyvinyl alcohol, cyanoethyl cellulose, cyanoethyl sucrose, pullulan, carboxymethyl cellulose (CMC), styrene butadiene rubber (SBR), acrylonitrile styrene butadiene copolymer and polyimide is used. Aqueous or non-aqueous polymer. Wherein, carboxymethyl cellulose and / or styrene butadiene rubber are easily dissolved in aqueous solvents and increase bonding strength, so that the amount of adhesive is relatively reduced.

[0077] According to one embodiment, relative to 100 parts by weight of the secondary battery coating composition of the present invention, the content of the binder is about 0.1 to 20 parts by weight, for example, about 0.1 to 10 parts by weight, or about 1 to 3 parts by weight. When the content of the binder satisfies the above range, the adhesion between the coating and the electrode is relatively improved.

[0078] (5) Alkaline additives

[0079] The secondary battery coating composition of one embodiment further includes an alkaline additive.

[0080] For example, the alkaline additive neutralizes the acidic dispersant in the composition of the present invention, i.e., the compound containing one or more carboxyl groups. Alternatively, when the alkaline additive is further included in the electrode or diaphragm coating composition of the present invention, the side reaction caused by the acid is suppressed by the acid-base neutralization reaction in the composition.

[0081] According to one embodiment, the alkaline additive comprises one or more selected from the group consisting of lithium carbonate (Li2CO3), sodium carbonate (Na2CO3), potassium carbonate (K2CO3), magnesium carbonate (MgCO3), calcium carbonate (CaCO3), ethylenediamine (EDA), diethylenetriamine (DETA), tris(2-aminoethyl)amine (TAEA), vinylene carbonate (VC), vinyl ethylene carbonate (VEC), fluoroethylene carbonate (FEC), methyl propargyl carbonate (MPC) and allyl methyl carbonate (AMC).

[0082] According to one embodiment, the content of the alkaline additive is about 0.1 to 10 parts by weight, for example, about 0.1 to 5 parts by weight, or about 0.2 to 2.3 parts by weight, relative to 100 parts by weight of the secondary battery coating composition. When the content of the alkaline additive meets the above numerical range, the dispersant contained in the composition is fully neutralized.

[0083] Meanwhile, the secondary battery coating composition according to one embodiment of the present invention is manufactured by adding and mixing a flame retardant and a dispersant in an aqueous solvent, and then performing a dispersion process.

[0084] For example, the components of the composition are mixed by adding and mixing the flame retardant and the dispersant in an aqueous solvent. In this case, mixing is performed using a mixing device such as a homomixer.

[0085] Alternatively, the composition that has undergone the mixing step can be ground and dispersed. Grinding is performed using, for example, a ball mill, a bead mill, or a basket mill. The degree of dispersion of the composition can be controlled by adjusting the grinding conditions, such as the number of times the composition passes through the ball mill, bead mill, or basket mill (hereinafter referred to as "pass number") and the rotor speed.

[0086] Meanwhile, the average particle size D of the solid particles in the composition of one embodiment of the present invention is 50It is about 0.1 μm to 10 μm, for example, about 0.3 μm to 3 μm, or about 0.3 μm to 1 μm. Here, the solid particles contain at least one of a flame retardant and a dispersant. For example, the solid particles have a form in which flame retardant particles are bonded to each other, or a form in which a dispersant is bonded to flame retardant particles. Alternatively, the solid particles have a form in which a dispersant and a binder are bonded to flame retardant particles. When the particle size of the solid particles in the composition meets the above range, the dispersibility of the flame retardant particles in the composition is improved, and the coating and adhesion of the coating are relatively improved. At the same time, the degree of dispersion of the solid particles in the composition of one embodiment is controlled by adjusting, for example, the solid content in the composition, the type and content of the dispersant, and / or the dispersion process conditions.

[0087] The viscosity of the secondary battery coating composition of one embodiment is about 10 cP to 16,000 cP, for example, about 20 cP to 4,000 cP, or about 30 cP to 600 cP. When the viscosity of the composition satisfies the above numerical range, the coating is formed at an appropriate thickness level, thereby ensuring the heat resistance of the battery while minimizing the reduction in battery life due to increased electrode resistance.

[0088] At the same time, the secondary battery coating composition of one embodiment of the present invention controls the content ratio of the flame retardant and the dispersant, making it easy to control the thickness of the coating by adjusting the viscosity of the composition, while ensuring the dispersibility of the flame retardant and the coating properties of the composition. Therefore, when manufacturing a secondary battery to ensure heat resistance, it is easy to produce a thick coating by adjusting the viscosity of the composition.

[0089] According to one embodiment, the secondary battery coating composition of the present invention is used to form a coating on an electrode. For example, the electrode coating is formed by coating the secondary battery coating composition onto a current collector and / or an electrode active material layer and then drying the composition.

[0090] According to one embodiment, the composition of the present invention is also used to form a coating on a separator. For example, the composition of the present invention is applied to a separator coated with an aqueous binder slurry and then dried to form a separator coating.

[0091] electrode

[0092] The electrode of the embodiment of the present invention is described. The electrode of the present invention includes a current collector, an electrode active material layer and a coating. The electrode active material layer and the coating are arranged on the current collector, and the coating is formed by the above-mentioned secondary battery coating composition. In this case, the secondary battery coating composition is the same as described above.

[0093] For example, the current collector is conductive and does not cause chemical changes in the battery. Alternatively, as the current collector, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with, for example, carbon, nickel, titanium, or silver can be used.

[0094] As the electrode active material layer in the secondary battery of the present invention, a positive electrode active material layer containing a positive electrode active material or a negative electrode active material layer containing a negative electrode active material is used. As the positive electrode active material, for example, lithium cobalt-based oxide, lithium nickel-based oxide, lithium manganese-based oxide, lithium iron phosphate, lithium nickel manganese cobalt-based oxide or a combination thereof is used. Alternatively, as the positive electrode active material, for example, LiCoO2, LiNiO2, LiMn2O4, LiCoPO4, LiFePO4, LiNi a Mn b Co c O2 (where 0 < a, b, c < 1). Examples of the negative electrode active material include one or more negative electrode active materials selected from the following: natural graphite, artificial graphite, and carbonaceous materials; lithium-containing titanium composite oxide (LTO), and a metal (Me) such as Si, Sn, Li, Zn, Mg, Cd, Ce, Ni, or Fe; an alloy composed of the metal (Me); an oxide (MeOx) of the metal (Me); and a composite of the metal (Me) and carbon.

[0095] The electrode active material layer of one embodiment includes a conductive material and a binder in addition to active materials such as a positive electrode active material and a negative electrode active material.

[0096] The conductive material of one embodiment is a material that does not cause chemical changes in the battery and has conductivity, and the following are used as the conductive material, for example: graphite; carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal process black; conductive fibers such as carbon fibers and metal fibers; fluorinated carbon powders; metal powders such as aluminum powder and nickel powder; conductive whiskers such as zinc oxide whiskers and potassium titanate whiskers; conductive metal oxides such as titanium oxide; or conductive materials such as polyphenylene derivatives. Examples of commercially available conductive materials include various acetylene black products (available from Chevron Chemical Company, Denka Singapore Private Limited, and Gulf Oil Company), Ketjen black EC series (available from Armak Company), Vulcan XC-72 (available from Cabot Company), and Super P (available from Timcal Company).

[0097] The binder is a component that helps to bind the active material to the conductive material and to the current collector. According to one embodiment, the binder is added in an amount of about 1% to 30% by weight relative to the total weight of the mixture containing the positive electrode active material. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluororubber, and various copolymers thereof.

[0098] Meanwhile, the coating of one embodiment of the present invention is formed by applying the above-mentioned secondary battery coating composition to a current collector and then drying the coating composition. For example, a coating is formed on an uncoated area on the current collector where no electrode active material layer is formed. In this case, the coating is formed to partially overlap with the end of the electrode active material layer. A coating of a certain thickness is formed on the current collector and the electrode active material layer. In this case, the thickness of the coating is about 2 μm to 30 μm, for example, about 2 μm to 20 μm, or about 5 μm to 13 μm. When the thickness of the coating satisfies the above range, the adhesion of the coating to the current collector and / or the electrode active material layer is relatively high.

[0099] The coating of one embodiment of the present invention has relatively superior coating properties compared to conventional coatings. For example, the coating thickness and / or surface are relatively uniform. Alternatively, the flame retardant particles are evenly dispersed throughout the coating. As a result, the heat resistance and lifespan of the secondary battery are relatively improved.

[0100] secondary batteries

[0101] A lithium secondary battery according to one embodiment of the present invention will be described.

[0102] The lithium secondary battery of the present invention is a lithium secondary battery having the above-mentioned electrodes. In this case, the electrodes are as described above. For example, the electrodes are positive electrodes and / or negative electrodes. A lithium secondary battery according to one embodiment of the present invention includes a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and an electrolyte.

[0103] The separator of one embodiment of the present invention has low resistance to the transfer of ions in the electrolyte and has relatively excellent electrolyte impregnation ability. For example, the porous polymer film composed of a polyolefin polymer (such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, ethylene / methacrylate copolymer) is used alone or in a laminated structure of more than two layers. Alternatively, a porous non-woven fabric can be used, such as a non-woven fabric made of high melting point glass fiber or polyethylene terephthalate fiber.

[0104] An electrolyte according to one embodiment includes an organic solvent and a lithium salt.

[0105] As an organic solvent of an embodiment, a solvent that can act as a medium through which ions participating in the electrochemical reaction of the battery can move is used. As an organic solvent, for example, an ester solvent such as methyl acetate, ethyl acetate, γ-butyrolactone or ε-caprolactone; an ether solvent such as dibutyl ether or tetrahydrofuran; a ketone solvent such as cyclohexanone; an aromatic hydrocarbon solvent such as benzene or fluorobenzene; or a carbonate solvent such as dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC) or propylene carbonate (PC) can be used. For example, a carbonate solvent can be used, and a mixture of a cyclic carbonate (such as ethylene carbonate or propylene carbonate) having high ionic conductivity and high dielectric constant and a linear carbonate compound (such as ethyl methyl carbonate, dimethyl carbonate or diethyl carbonate) having low viscosity, which can improve the charge and discharge performance of the battery, can be used.

[0106] As a lithium salt of one embodiment, for example, LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF)3SO2)2, LiCl, LiI, or LiB(C2O4)2 can be used. For example, the lithium salt is included in the electrolyte at a concentration of about 0.6 mol% to about 2 mol%.

[0107] In addition to the above-mentioned electrolyte components, the electrolyte of one embodiment of the present invention may further include at least one additive such as pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, n-glyme dimethyl ether, hexanoic acid triamide, nitrobenzene derivatives, sulfur, quinone imine dye, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol or aluminum chloride for the purpose of improving battery life characteristics, inhibiting battery capacity reduction, and increasing battery discharge capacity.

[0108] The lithium secondary battery of one embodiment of the present invention is manufactured by placing a separator between a positive electrode and a negative electrode to form an electrode assembly, then introducing the electrode assembly into a cylindrical or prismatic battery case, and then injecting an electrolyte into the battery case. Alternatively, the lithium secondary battery is manufactured by stacking the electrode assemblies, then impregnating the electrodes with an electrolyte, and placing the resulting product into a bag and sealing it.

[0109] When manufacturing a lithium secondary battery according to an embodiment of the present invention, the electrode assembly is dried to remove one or more organic solvents selected from the group consisting of N-methyl-2-pyrrolidone (NMP), acetone, ethanol, propylene carbonate, ethyl methyl carbonate, ethylene carbonate, and dimethyl carbonate and used in manufacturing the positive electrode. Alternatively, if an electrolyte having the same composition as the above-mentioned organic solvent is used in manufacturing the positive electrode, the drying process of the electrode assembly is omitted.

[0110] Meanwhile, in the description above, the coating composition has been described in conjunction with a lithium secondary battery, but the coating composition of the embodiment of the present invention can be similarly applied to a sodium secondary battery using sodium instead of lithium. For example, the coating composition of the present invention can be similarly applied to a sodium ion secondary battery manufactured using a sodium-containing material rather than a lithium-containing material as a positive electrode active material.

[0111] Furthermore, unlike the above-described lithium secondary battery, a lithium secondary battery according to another embodiment of the present invention is an all-solid-state battery.

[0112] The battery case of the embodiment of the present invention can be easily applied according to the outer shape corresponding to the use of the battery, and can be manufactured in a cylindrical shape using a can, a square shape, a pouch shape, or a coin shape, for example.

[0113] The lithium secondary battery of one embodiment of the present invention stably exhibits relatively improved discharge capacity, relatively improved output characteristics, and relatively improved excellent capacity retention, so that the lithium secondary battery can be used in portable devices such as mobile phones, laptop computers, digital cameras, and energy storage systems (ESS), such as electric vehicles such as hybrid electric vehicles (HEVs).

[0114] Hereinafter, the present invention will be described in more detail by way of examples. However, the following examples are only examples to help understand the present invention and do not limit the scope of the invention. It is obvious to those skilled in the art that various changes and modifications can be made within the scope and technical spirit of this specification, and these changes and modifications naturally fall within the scope of the appended claims.

[0115] In the following examples and comparative examples, the coating composition of the present invention is described as being applied to secondary battery electrodes. However, as described above, the coating composition of the present invention can also be applied to other electrode component structures besides electrodes, such as separators.

[0116] Examples and Comparative Examples

[0117] Example 1

[0118] (1) Preparation of electrode coating composition

[0119] 40 g of deionized water as a solvent, 10 g of boehmite (average particle size D 50 : 0.2 μm) and 0.1 g of citric acid used as a dispersant were roughly mixed, and then mixed for 10 minutes using a Homo mixer (available under the product name "Dispermat LC" from VMA).

[0120] (2) Manufacturing of lithium secondary batteries

[0121] Artificial graphite, carbon black, carboxymethyl cellulose (CMC) and styrene butadiene rubber (SBR) were mixed in a weight ratio of 94.3:2.0:1.2:2.5 and distilled water was added to produce a negative electrode slurry. The negative electrode slurry was applied to one surface of a 10 μm thick copper (Cu) metal film and then dried in a vacuum. The dried negative electrode slurry was then rolled, dried in a vacuum oven at 130 ° C for 12 hours, and punched to produce a negative electrode active material layer. The electrode coating composition produced as described above was applied to the negative electrode active material layer, and the electrode coating composition was then dried in a vacuum to produce a negative electrode having a 12.4 μm thick coating formed thereon.

[0122] As the positive electrode active material, Li[Ni 0.83 Co 0.11 Mn 0.06 ]O2, carbon nanotubes (CNTs), polyvinylidene fluoride (PVdF), and hydrogenated nitrile rubber (H-NBR) were added to an N-methylpyrrolidone (NMP) solvent at a weight ratio of 97.0:1.0:1.5:0.5 and stirred to produce a positive electrode slurry. The positive electrode slurry was coated on one surface of a 15μm thick aluminum film and then vacuum dried at 130°C for 10 hours. The dried positive electrode slurry was roll-pressed, dried in a vacuum oven at 130°C for 12 hours, and punched to produce a positive electrode.

[0123] The negative electrode and positive electrode manufactured as described above were assembled with a 10 μm thick porous polyethylene separator using a stacking method, thereby manufacturing an electrode assembly.

[0124] LiPF 6 was dissolved in a solvent obtained by mixing ethylene carbonate (EC) and ethyl methyl carbonate (EMC) at a weight ratio of 20:80 to a concentration of 1.2 M, thereby preparing an electrolyte.

[0125] The electrode assembly is housed in a pouch-type battery case, an electrolyte is injected, and the battery case is sealed to manufacture a lithium secondary battery.

[0126] Example 2

[0127] An electrode coating composition was manufactured in the same manner as in Example 1, except that, in the electrode coating composition of Example 1, 0.5 g of citric acid was mixed instead of 0.1 g of citric acid.

[0128] A lithium secondary battery was manufactured in the same manner as in Example 1 except that the above-mentioned electrode coating composition was used.

[0129] Example 3

[0130] An electrode coating composition was manufactured in the same manner as in Example 1, except that, in the electrode coating composition of Example 1, 1.0 g of citric acid was mixed instead of 0.1 g of citric acid.

[0131] A lithium secondary battery was manufactured in the same manner as in Example 1 except that the above-mentioned electrode coating composition was used.

[0132] Example 4

[0133] An electrode coating composition was manufactured in the same manner as in Example 1, except that, in the electrode coating composition of Example 1, 2.0 g of citric acid was mixed instead of 0.1 g of citric acid.

[0134] A lithium secondary battery was manufactured in the same manner as in Example 1 except that the above-mentioned electrode coating composition was used.

[0135] Example 5

[0136] An electrode coating composition was manufactured in the same manner as in Example 1, except that, in the electrode coating composition of Example 1, 4.0 g of citric acid was mixed instead of 0.1 g of citric acid.

[0137] A lithium secondary battery was manufactured in the same manner as in Example 1 except that the above-mentioned electrode coating composition was used.

[0138] Example 6

[0139] An electrode coating composition was manufactured in the same manner as in Example 1, except that 0.1 g of ethylenediamine was additionally mixed into the electrode coating composition of Example 1 as a basic additive.

[0140] A lithium secondary battery was manufactured in the same manner as in Example 1 except that the above-mentioned electrode coating composition was used.

[0141] Example 7

[0142] When preparing the electrode coating composition, 40 g of deionized water as a solvent, 10 g of aluminum hydroxide (average particle size D 50 : 0.6 μm) and 3 g of melamine (average particle size D 50: 1 μm), 0.3 g of citric acid as a dispersant and 0.3 g of ethylenediamine as an alkaline additive were roughly mixed and then mixed for 10 minutes using a Homo mixer (available under the product name "Dispermat LC" from VMA).

[0143] Comparative Example 1

[0144] A lithium secondary battery was manufactured in the same manner as in Example 1, except that no coating layer was formed on the negative electrode of the lithium secondary battery.

[0145] Comparative Example 2

[0146] An electrode coating composition was manufactured in the same manner as in Example 1, except that citric acid was not mixed as a dispersant when the electrode coating composition was manufactured.

[0147] A lithium secondary battery was manufactured in the same manner as in Example 1 except that the above-mentioned electrode coating composition was used.

[0148] Comparative Example 3

[0149] An electrode coating composition was manufactured in the same manner as in Example 1, except that silicon monoxide (SiO), which is not a flame retardant, was used instead of boehmite.

[0150] A lithium secondary battery was manufactured in the same manner as in Example 1 except that the above-mentioned electrode coating composition was used.

[0151] [Table 1]

[0152]

[0153] Experimental Example 1: Determination of Viscosity of Electrode Coating Composition

[0154] The viscosity of each electrode coating composition prepared in Examples 1 to 7 and Comparative Examples 2 to 3 was measured, and the measurement results are shown in Table 2 below.

[0155] The viscosity of the composition was measured using a viscometer (available under the product name "DV2T" from Brookfield) under the conditions of 25°C and 12 rpm.

[0156] Experimental Example 2: Evaluation of the Dispersibility of Inorganic Particles in Electrode Coating Compositions

[0157] Each electrode coating composition prepared in Examples 1 to 7 and Comparative Examples 2 to 3 was applied to a glass slide, and then the degree of dispersion of the inorganic particles in the composition was evaluated using an optical microscope as follows. The results of the dispersion evaluation are shown in Tables 2 and 3 below. Figures 1 to 9 middle.

[0158] O: Good dispersibility (no agglomeration of inorganic particles)

[0159] X: Poor dispersibility (agglomeration of inorganic particles)

[0160] Figure 1 This is an optical microscope image taken at a magnification of 300 times after the electrode coating composition prepared in Example 1 was applied to a glass slide.

[0161] Figure 2 This is an optical microscope image taken at a magnification of 300 times after the electrode coating composition prepared in Example 2 was applied to a glass slide.

[0162] Figure 3 This is an optical microscope image taken at a magnification of 300 times after the electrode coating composition prepared in Example 3 was applied to a glass slide.

[0163] Figure 4 This is an optical microscope image taken at a magnification of 300 times after the electrode coating composition prepared in Example 4 was applied to a glass slide.

[0164] Figure 5 This is an optical microscope image taken at a magnification of 300 times after the electrode coating composition prepared in Example 5 was applied to a glass slide.

[0165] Figure 6 This is an optical microscope image taken at a magnification of 300 times after the electrode coating composition prepared in Example 6 was applied to a glass slide.

[0166] Figure 7 This is an optical microscope image taken at a magnification of 300 times after the electrode coating composition prepared in Example 7 was applied to a glass slide.

[0167] Figure 8 This is an optical microscope image taken at a magnification of 300 times after the electrode coating composition prepared in Comparative Example 2 was applied to a slide glass.

[0168] Figure 9 This is an optical microscope image taken at a magnification of 300 times after the electrode coating composition prepared in Comparative Example 3 was applied to a slide glass.

[0169] [Table 2]

[0170]

[0171] Experimental Example 3: Evaluation of Heat Resistance Characteristics of Secondary Batteries

[0172] The lithium secondary batteries manufactured in Examples 3 and 7 and Comparative Examples 1 and 3 were subjected to a hot box test in a fully charged state with an SOC of 100% (4.45 V) while changing the temperature under the following conditions.

[0173] 1) Raise the temperature from 25°C to 130°C at a rate of 5°C / min, and then maintain the temperature for 30 minutes.

[0174] 2) Raise the temperature from 130°C to 200°C at a rate of 2°C / min, and then maintain the temperature for 30 minutes.

[0175] 3) Raise the temperature from 200°C to 260°C at a rate of 2°C / min, and then maintain the temperature for 30 minutes.

[0176] At this time, a thermocouple installed in the center of the lithium secondary battery pouch was used to measure the rapid temperature rise start temperature and the maximum temperature of each secondary battery. In addition, a hot box test was conducted to confirm whether the secondary battery ignited. The results are shown in Table 3 below.

[0177] -O: Lithium secondary battery fire

[0178] -X: Lithium secondary battery did not catch fire

[0179] [Table 3]

[0180]

[0181] Experimental Example 4: Evaluation of Room-Temperature Life Performance of Secondary Batteries

[0182] The lithium secondary batteries manufactured in Example 3 and Comparative Example 1 were charged and discharged at 25° C. under the following conditions, and the battery capacity (unit: Ah) corresponding to the number of cycles was measured, and the capacity retention (%) was calculated.

[0183] -Charging conditions: Charge at a rate of 0.2C in CC (constant current) / CV (constant voltage) mode, with a cutoff of 4.25V and 0.05C

[0184] -Discharge conditions: Discharge at a rate of 0.2C in CC mode and cut off at 3.0V

[0185] At this time, the battery capacity and the capacity retention rate at 100 cycles were measured using IL-2C-525S obtained from JEIO TECH Co., Ltd. The measurement results are shown in Figure 9 and Table 4.

[0186] Figure 10 Graph showing changes in battery capacity values ​​of lithium secondary batteries manufactured in Example 3 and Comparative Example 1, respectively, after operation at 25° C., as a function of the number of cycles.

[0187] [Table 4]

[0188] Capacity retention rate of secondary battery after 100 cycles (%) Example 3 99.74376 Comparative Example 1 99.66858

[0189] As shown in Tables 1 and 2, Figures 1 to 9 As shown, in the electrode coating compositions of Examples 1 to 6 of the present invention, in which boehmite and a compound containing one or more carboxyl groups are mixed in an aqueous solvent, it can be seen that the boehmite has good dispersibility and almost no agglomeration between particles occurs.

[0190] In the electrode coating composition of Example 7, a flame retardant containing aluminum hydroxide and melamine and a compound containing at least one carboxyl group are mixed in an aqueous solvent. Aluminum hydroxide exhibits high endothermic energy, but due to the generation of excess water, it may exhibit an explosive reaction with lithium, while melamine, as the above-mentioned inorganic flame retardant, has a higher endothermic effect than boehmite. Therefore, it can be predicted that the use of a flame retardant containing only melamine will exhibit the best flame retardant effect. However, in the case of an internal short circuit, inorganic flame retardants help to appropriately achieve an insulating effect by surface coating, and it is difficult to manufacture a slurry containing only melamine. Therefore, it is preferred to use a mixed flame retardant as in the above-mentioned Example 7.

[0191] Meanwhile, for the electrode coating composition of Comparative Example 2 (which does not contain a compound containing one or more carboxyl groups in the aqueous solvent of the present invention and to which the present invention is not applied), it is known that boehmite cannot be properly dispersed, resulting in agglomeration between particles and a particle shape having a particle size of about 50 μm. In addition, for the electrode coating composition of Comparative Example 3 in which boehmite is replaced by silicon monoxide (SiO), which is not applied to the present invention, it can be seen that agglomeration between particles occurs because silicon monoxide (SiO) is not fully dispersed.

[0192] As shown in Tables 1 and 3, for Comparative Example 1 in which the present invention is not applied and no coating is formed on the negative electrode, and Comparative Example 3 in which silicon monoxide (SiO) is included in the coating instead of boehmite, it can be seen that the rapid temperature rise starting temperature of the secondary battery is significantly lower than those of Examples 3 and 7, the maximum temperature of the secondary battery is significantly higher than those of Examples 3 and 7, and unlike Examples 3 and 7, the secondary battery catches fire in the hot box test.

[0193] As shown in Tables 1 and 4, Figure 10 As shown, for Example 3 (wherein a coating is formed by mixing boehmite and a compound containing one or more carboxyl groups in an aqueous solvent of the electrode coating composition of the present invention), it can be seen that the capacity retention rate (%) at room temperature is relatively better than that of Comparative Example 1 to which the present invention is not applied.

[0194] Although the present invention has been described with reference to its embodiments in the foregoing detailed description, it will be clearly understood by those skilled in the art that various modifications and changes may be made to the present invention without departing from the spirit and scope of the present invention as defined by the appended claims. Therefore, the technical scope of the present invention should not be limited to the contents described in the detailed description of the specification, but should be determined based on the claims.

Claims

1. A coating composition for a secondary battery, comprising: flame retardants; dispersants; and Aqueous solvents, in, The flame retardant includes at least one of an inorganic flame retardant containing a hydroxyl group, a phosphorus-based flame retardant, a halogen-based flame retardant, and a melamine-based flame retardant.

2. The coating composition according to claim 1, wherein The inorganic flame retardant comprises at least one selected from boehmite, pseudo-boehmite, aluminum hydroxide and magnesium hydroxide.

3. The coating composition according to claim 1, wherein The average particle size D of the inorganic flame retardant 50 It is about 0.1 μm to 5.0 μm.

4. The coating composition according to claim 1, wherein The dispersant comprises a compound containing one or more carboxyl groups.

5. The coating composition according to claim 1, wherein The dispersant comprises one or more selected from the group consisting of citric acid, malic acid, oxalic acid, glutamic acid, aspartic acid, amino acids, malonic acid and fatty acids.

6. The coating composition according to claim 1, wherein The dispersant and the flame retardant are included in a weight ratio of about 1:2 to 1:

150.

7. The coating composition according to claim 1, wherein The aqueous solvent is water.

8. The coating composition according to claim 1, wherein The coating composition has a solids content of about 10% to 70% by weight.

9. The coating composition of claim 1, further comprising a basic additive.

10. The coating composition according to claim 9, wherein The alkaline additive comprises at least one selected from the group consisting of lithium carbonate, sodium carbonate, potassium carbonate, magnesium carbonate, calcium carbonate, ethylenediamine, diethylenetriamine, tris(2-aminoethyl)amine, vinylene carbonate, vinylethylene carbonate, fluoroethylene carbonate, methyl propargyl carbonate, and allyl methyl carbonate.

11. The coating composition according to claim 9, wherein The basic additive may be present in an amount of about 1 to 10 parts by weight based on 100 parts by weight of the coating composition.

12. A secondary battery electrode, comprising: current collector; an electrode active material layer; and coating, wherein the electrode active material layer and the coating are disposed on the current collector, and The coating layer is formed from the coating composition according to claim 1.

13. The secondary battery electrode according to claim 12, wherein The coating has a thickness of about 2 μm to 30 μm. 14 . A lithium secondary battery comprising the secondary battery electrode according to claim 12 . 15 . A sodium secondary battery comprising the secondary battery electrode according to claim 12 .

16. A secondary battery separator, comprising: porous polymer substrate; and coating, wherein the coating is disposed on one surface of the porous polymer substrate, and The coating layer is formed from the coating composition according to claim 1.

17. A method for producing a coating composition for a secondary battery, wherein: The coating composition comprises a flame retardant, a dispersant and an aqueous solvent, and The flame retardant includes at least one of an inorganic flame retardant containing a hydroxyl group, a phosphorus flame retardant, a halogen flame retardant and a melamine flame retardant.

18. The method of claim 17, wherein: The inorganic flame retardant includes at least one selected from the group consisting of boehmite, pseudo-boehmite, aluminum hydroxide, and magnesium hydroxide.

19. The method of claim 17, wherein: The average particle size D of the inorganic flame retardant 50 It is about 0.1 μm to 5.0 μm.

20. The method of claim 17, wherein: The dispersant includes a compound containing one or more carboxyl groups.

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