Carbon nanotube dispersion and method for producing same

Abstract

The present invention relates to a carbon nanotube dispersion liquid containing carbon nanotubes, a dispersant, and a dispersion medium, wherein the dispersant contains a first dispersant and a second dispersant in a weight ratio of 100:10 to 100:90, the first dispersant being a dispersant containing a cyclic amide group, and the second dispersant being a polymeric compound containing both a sulfone group and styrene, and the weight ratio of the carbon nanotubes to the dispersant is 100:50 to 100:500, and the carbon nanotube dispersion liquid has low viscosity and contains small particles.

Description

[Technical Field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2023-0024184, filed on February 23, 2023, the entire contents of which are incorporated herein by reference.

[0002] The present invention relates to a carbon nanotube dispersion and a method for producing the same, and more particularly to a carbon nanotube dispersion having a low viscosity and a small particle size, and a method for producing the same. [Background technology]

[0003]

[0003] Along with technological development and increasing demand for mobile devices, the demand for secondary batteries as an energy source is rapidly increasing. Among these secondary batteries, lithium secondary batteries, which have high energy density and voltage, long cycle life, and low self-discharge rate, have been commercialized and widely used. In addition, research into methods for improving electrode density and manufacturing electrodes with higher energy density per unit volume for such high-capacity lithium secondary batteries is actively being conducted.

[0004] In general, high-density electrodes are formed by molding electrode active material particles having a size of several μm to several tens of μm using a high-pressure press. However, during the molding process, the particles are deformed and the spaces between the particles can be reduced, which can lead to a decrease in electrolyte permeability.

[0005] To solve the above problems, conductive materials with excellent electrical conductivity and strength are used during electrode manufacturing. The conductive material is located between the electrode active materials, maintaining micropores between the active material particles even after the molding process, facilitating electrolyte penetration. The excellent electrical conductivity of the conductive material reduces the resistance within the electrode. Among such conductive materials, carbon nanotubes, a fibrous carbon-based conductive material, are increasingly being used, which can further reduce electrode resistance by forming an electrical conductive path within the electrode.

[0006] Carbon nanotubes, a type of fine carbon fiber, are tubular carbon fibers with a diameter of less than 1 μm. Their unique structure gives them high electrical conductivity, tensile strength, and heat resistance, making them promising for practical application in a variety of fields. However, carbon nanotubes have a problem in that they are poorly dispersible due to the strong van der Waals attractive forces between them, which leads to aggregation.

[0007] To solve this problem, a method has been proposed in which carbon nanotubes are dispersed in a dispersion medium by mechanical dispersion treatment such as ultrasonic treatment, but the problem with mechanical dispersion treatment is that the carbon nanotubes aggregate as soon as the ultrasonic irradiation is stopped.

[0008] Therefore, there is a need to develop a method for producing a carbon nanotube dispersion liquid that can improve the dispersibility of carbon nanotubes while having low viscosity and containing small particles. Summary of the Invention [Problem to be solved by the invention]

[0009] The present invention is intended to solve the problems of the above-mentioned conventional technology, and aims to provide a carbon nanotube dispersion liquid that has excellent dispersibility and contains small particles with small particle size by containing a dispersant containing a cyclic amide group and a polymer compound containing both a sulfone group and styrene.

[0010] Another object of the present invention is to provide a negative electrode slurry composition for a lithium secondary battery, which contains the carbon nanotube dispersion liquid.

[0011] Another object of the present invention is to provide a method for producing the carbon nanotube dispersion liquid. [Means for solving the problem]

[0012] In order to solve the above problems, the present invention provides a carbon nanotube dispersion liquid.

[0013] [1] The present invention provides a carbon nanotube dispersion comprising carbon nanotubes (CNTs), a dispersant, and a dispersion medium, wherein the dispersant comprises a first dispersant and a second dispersant in a weight ratio of 100:10 to 100:90, the first dispersant is a dispersant containing a cyclic amide group, and the second dispersant is a polymer compound containing both a sulfone group and a styrene, and the weight ratio of the carbon nanotubes to the dispersant is 100:50 to 100:500.

[0014] [2] The present invention relates to a method for manufacturing a carbon nanotube having a specific surface area (BET) of 800 m 2 / g or more.

[0015] [3] The present invention provides the carbon nanotube dispersion liquid according to [1] or [2] above, wherein the carbon nanotubes are single-walled carbon nanotubes.

[0016] [4] The present invention provides the carbon nanotube dispersion liquid according to any one of [1] to [3], wherein the carbon nanotubes are contained in an amount of 0.1 to 5 parts by weight per 100 parts by weight of the carbon nanotube dispersion liquid.

[0017] [5] The present invention provides the carbon nanotube dispersion liquid according to any one of [1] to [4] above, wherein the first dispersant is one or more selected from the group consisting of polyvinylpyrrolidone, poly-N-vinyl-5-methoxazolidone, polyvinylaziridinone, polyvinylazetidinone, polyvinylpiperidone, polyvinylcaprolactam, polymethylenepyrrolidone (poly(3-methylene-2-pyrrolidone)), polymethylmethylenepyrrolidone (poly(N-methyl-3-methylene-2-pyrrolidone)), and polyvinylphthalimide.

[0018] [6] The present invention provides a carbon nanotube dispersion liquid according to any one of [1] to [5], wherein the second dispersant is one or more selected from the group consisting of polystyrene sulfonic acid, a salt of polystyrene sulfonic acid, and a sulfonate styrene-maleic acid copolymer.

[0019] [7] The present invention provides the carbon nanotube dispersion liquid according to any one of [1] to [6], wherein the second dispersant is one or more selected from the group consisting of sulfonated polystyrene, sulfonated styrene-maleic acid copolymer, sodium polystyrene sulfonate, polystyrene sulfonic acid, and ammonium polystyrene sulfonate.

[0020] [8] The present invention provides a carbon nanotube dispersion liquid according to any one of [1] to [7], wherein the dispersant contains a first dispersant and a second dispersant in a weight ratio of 100:20 to 100:80.

[0021] [9] The present invention provides the carbon nanotube dispersion liquid according to any one of [1] to [8] above, wherein the weight ratio of the carbon nanotubes to the dispersant is 100:100 to 100:250.

[0022]

[10] The present invention provides a carbon nanotube dispersion liquid according to any one of [1] to [9] above, wherein the dispersion medium is one or more selected from the group consisting of amide-based polar organic solvents, alcohol-based solvents, glycol-based solvents, glycol ether-based solvents, ketone-based solvents, ester-based solvents, and aqueous solvents.

[0023]

[11] The present invention provides a carbon nanotube dispersion liquid according to any one of [1] to

[10] , wherein the carbon nanotube dispersion liquid exhibits a viscosity increase rate of 20% or less when left at 25°C for one week.

[0024]

[12] The present invention provides a carbon nanotube dispersion liquid according to any one of [1] to

[11] , wherein the carbon nanotube dispersion liquid contains carbon nanotube aggregate particles having an average particle size (D50) of 0.5 μm to 5.4 μm.

[0025]

[13] The present invention provides a carbon nanotube dispersion liquid according to any one of [1] to

[12] , wherein the carbon nanotube dispersion liquid contains carbon nanotube aggregate particles having an average particle size (D90) of 1.5 μm to 15.0 μm.

[0026] In order to solve the above-mentioned other problems, the present invention also provides an electrode slurry composition for a lithium secondary battery.

[0027]

[14] The present invention provides an electrode slurry composition for a lithium secondary battery, comprising the carbon nanotube dispersion liquid according to any one of [1] to

[13] above and an electrode active material.

[0028] In order to solve the above-mentioned other problems, the present invention also provides a method for producing a carbon nanotube dispersion liquid.

[0029]

[15] The present invention provides a method for producing a carbon nanotube dispersion liquid according to any one of [1] to

[13] above, which includes the steps of (1) mixing carbon nanotubes, a dispersant, and a dispersion medium to produce a mixture, and (2) dispersing the mixture, wherein the dispersant contains a first dispersant and a second dispersant in a weight ratio of 100:10 to 100:90, the first dispersant is a dispersant containing a cyclic amide group, and the second dispersant is a polymeric compound containing both a sulfone group and a styrene, and the weight ratio of the carbon nanotubes to the dispersant is 100:50 to 100:500. [Effects of the Invention]

[0030] The carbon nanotube dispersion of the present invention contains both a dispersant containing a cyclic amide group and a polymeric compound containing both a sulfone group and styrene, thereby providing excellent carbon nanotube dispersibility and low viscosity, and allowing the carbon nanotubes contained in the dispersion to have a small particle size, thereby providing advantageous effects in terms of storage and use of the carbon nanotube dispersion and realizing a coating layer of uniform thickness. DETAILED DESCRIPTION OF THE INVENTION

[0031] The terms and words used in this specification and claims should not be interpreted in a limited way to their ordinary or dictionary meanings, but should be interpreted in a way that is consistent with the technical idea of ​​the present invention, based on the principle that the inventors can appropriately define the concepts of terms in order to best explain their inventions.

[0032] The terms used in this specification are used only to describe exemplary embodiments and are not intended to limit the present invention. The singular expressions include the plural expressions unless the context clearly indicates otherwise.

[0033] As used herein, the terms "comprises," "comprises," or "having" are intended to specify the presence of embodied features, numbers, steps, components, or combinations thereof, and should be understood as not precluding the presence or possible addition of one or more other features, numbers, steps, components, or combinations thereof.

[0034] In this specification, "%" means % by weight unless expressly indicated otherwise.

[0035] In this specification, the average particle size "D50" refers to the particle size corresponding to 50% of the cumulative volume, and "D90" refers to the particle size corresponding to 90% of the cumulative volume. The D50 and D90 can be measured, for example, by the laser diffraction method. The laser diffraction method generally can measure particle sizes from the submicron range to several mm, and can provide results with high reproducibility and high resolution.

[0036] In this specification, the "specific surface area" is measured by the BET method, and specifically, can be calculated from the amount of nitrogen gas adsorbed at liquid nitrogen temperature (77 K) using a BELSORP-mino II manufactured by BEL Japan.

[0037] The present invention will be specifically described below.

[0038] The carbon nanotube dispersion liquid of the present invention is a carbon nanotube dispersion liquid containing carbon nanotubes (CNTs), a dispersant, and a dispersion medium, wherein the dispersant contains a first dispersant and a second dispersant in a weight ratio of 100:10 to 100:90, the first dispersant is a dispersant containing a cyclic amide group, and the second dispersant is a polymer compound containing both a sulfone group and styrene, and the weight ratio of the carbon nanotubes to the dispersant is 100:50 to 100:500.

[0039] Carbon nanotube dispersion Each component of the carbon nanotube dispersion liquid of the present invention will be specifically described below.

[0040] (1) Carbon nanotubes The term "carbon nanotube" used in the present invention refers to a secondary structure formed by the assembly of carbon nanotube units to form a bundle, either entirely or partially. The carbon nanotube units have a cylindrical graphite sheet with a nano-sized diameter, and are arranged in a sp 2 Carbon nanotubes have a bond structure. Depending on the angle and structure of the graphite sheets, they can exhibit conductive or semiconductive properties. Carbon nanotube units can be classified into single-walled carbon nanotubes (SWCNTs), double-walled carbon nanotubes (DWCNTs), and multi-walled carbon nanotubes (MWCNTs) depending on the number of bonds that make up the walls.

[0041] The term "bundle type" as used herein, unless otherwise specified, refers to a secondary shape in which multiple carbon nanotube units are arranged side by side with their longitudinal axes oriented in substantially the same direction, or are arranged and then twisted or entangled, like a bundle or rope. The term "non-bundle type or entangled type" refers to a form in which carbon nanotube units are entangled without having a fixed shape like a bundle or rope.

[0042] Carbon nanotubes have high conductivity, but they also tend to aggregate due to the van der Waals force that occurs between them. When conductive materials aggregate, conductive paths are not smoothly formed, and a relatively large amount of conductive material is required, which reduces the amount of active material, potentially resulting in a decrease in electrode performance. This has made it difficult to commercialize carbon nanotubes as a conductive material.

[0043] The carbon nanotube dispersion of the present invention contains both a dispersant containing a cyclic amide group and a polymer compound containing both a sulfone group and styrene, which prevents the viscosity of the carbon nanotube dispersion from changing over time, thereby showing a low viscosity increase rate and providing advantageous effects in the storage and use of the carbon nanotube dispersion.In addition, the dispersibility is improved and carbon nanotube aggregates with small particle sizes are dispersed, which allows the carbon nanotube dispersion to exhibit uniform coating properties.

[0044] Furthermore, when the carbon nanotube dispersion according to the present invention is applied to the preparation of an electrode slurry, the carbon nanotubes are uniformly positioned among the active materials, and the fine spaces among the electrode active materials can be uniformly maintained even during the process of manufacturing an electrode by coating, drying, and rolling the electrode slurry. Furthermore, the carbon nanotubes are uniformly distributed without agglomeration, and even a small amount of carbon nanotubes can sufficiently form a conductive path.

[0045] The carbon nanotube dispersion according to an embodiment of the present invention may include one or more of single-walled, double-walled, and multi-walled carbon nanotube units as the carbon nanotubes, and specifically may include single-walled carbon nanotubes (SWCNTs).

[0046] The carbon nanotubes are 800 m 2 / g or more, specifically, 800 m 2 / g~2,000m2 The carbon nanotube dispersion of the present invention exhibits excellent dispersibility by containing both a dispersant containing a cyclic amide group and a polymer compound containing both a sulfone group and styrene. 2 The carbon nanotube dispersion exhibits excellent dispersibility even for carbon nanotubes having a high specific surface area (BET) of 1 / g or more, and the carbon nanotube dispersion exhibits low viscosity, resulting in little change in viscosity over time.

[0047] The carbon nanotubes may be contained in an amount of 0.1 to 5 parts by weight, specifically 0.2 to 3 parts by weight, more specifically 0.4 to 2 parts by weight, relative to 100 parts by weight of the conductive material dispersion liquid.

[0048] The carbon nanotube dispersion according to one embodiment of the present invention contains a dispersant with excellent dispersibility, thereby exhibiting excellent dispersibility even for carbon nanotubes with a high specific surface area, thereby enabling carbon nanotubes with a relatively high specific surface area to be uniformly dispersed. The carbon nanotube content may be higher than that of conventionally used carbon nanotube dispersions, as described above. When a carbon nanotube dispersion with a low carbon nanotube content is used to prepare an electrode slurry, the solids content of the prepared electrode slurry decreases, resulting in a thicker thickness (wet thickness) of the electrode slurry before coating and drying. The rolling ratio measured after subsequent drying and rolling processes increases, resulting in a larger difference in thickness ratio before and after drying and rolling. Such a high rolling ratio can damage the components in the slurry, including the positive electrode active material, during the process, potentially resulting in a decrease in battery performance.

[0049] (2) Dispersant The carbon nanotube dispersion liquid according to the present invention contains a first dispersant and a second dispersant as dispersants in a weight ratio of 100:10 to 100:90 in order to improve the dispersibility of the carbon nanotubes. The first dispersant may be a dispersant containing a cyclic amide group, and the second dispersant may be a polymer compound containing both a sulfone group and styrene.

[0050] The dispersant containing a cyclic amide group contained as the first dispersant, and the polymer compound containing both a sulfone group and styrene contained as the second dispersant, function as dispersants that increase the dispersibility of carbon nanotubes in the carbon nanotube dispersion, and can suppress the increase in viscosity of the carbon nanotube dispersion and the change in viscosity over time.

[0051] In particular, the carbon nanotube dispersion of the present invention contains, in addition to the first dispersant containing a cyclic amide group, a second dispersant containing a polymeric compound containing both a sulfone group and styrene, thereby exhibiting superior dispersibility compared to carbon nanotube dispersions containing only dispersants that have been commonly used in the past, and the slurry composition has less particle aggregation, a low settling rate, a low viscosity, and excellent adhesion to the separator substrate.

[0052] The second dispersant contains both a sulfone group and an aromatic ring in its molecular structure, and the bulky structure of the compound and the effect of the sulfone group enable it to reduce the viscosity of carbon nanotube dispersions, particularly aqueous carbon nanotube dispersions, compared to conventional methods, and significantly improve viscosity increase over time.

[0053] A dispersant containing a cyclic amide group can be used as the first dispersant, which can exert an even more improved viscosity improving effect and an effect of suppressing the change in viscosity over time. The dispersant containing a cyclic amide group may be one that is soluble in water, and may be, for example, one or more selected from the group consisting of polyvinylpyrrolidone, poly-N-vinyl-5-methoxazolidone, polyvinylaziridinone, polyvinylazetidinone, polyvinylpiperidone, polyvinylcaprolactam, polymethylenepyrrolidone (poly(3-methylene-2-pyrrolidone)), polymethylmethylenepyrrolidone (poly(N-methyl-3-methylene-2-pyrrolidone)), and polyvinylphthalimide.

[0054] Furthermore, a polymeric compound containing both a sulfonic acid group and styrene can be used as the second dispersant, and the polymeric compound containing both a sulfonic acid group and styrene may be one or more selected from the group consisting of polystyrene sulfonic acid, a salt of polystyrene sulfonic acid, and a sulfonate styrene-maleic acid copolymer.

[0055] The second dispersant may be, for example, one or more selected from the group consisting of sulfonated polystyrene, sulfonated styrene-maleic acid copolymer, sodium polystyrene sulfonate, polystyrene sulfonic acid, and ammonium polystyrene sulfonate.

[0056] When the dispersant includes a dispersant containing a cyclic amide group as the first dispersant and a polymer compound containing both a sulfone group and styrene as the second dispersant, the dispersibility of the carbon nanotubes in the carbon nanotube dispersion is improved due to the interaction between the aromatic ring and the carbon nanotubes and the electrostatic shielding effect of the negatively charged sulfone group, thereby reducing the viscosity of the dispersion and the aggregation of the carbon nanotubes, thereby reducing the particle size of the particles contained in the dispersion.

[0057] The dispersant may contain a first dispersant and a second dispersant together in a weight ratio of 100:10 to 100:90, specifically a weight ratio of 100:10 to 100:80 or 100:20 to 100:80, more specifically a weight ratio of 100:20 to 100:50. When the carbon nanotube dispersion contains the first dispersant and the second dispersant as the dispersants in the above weight ratio, the carbon nanotubes are uniformly dispersed in the carbon nanotube dispersion, the carbon nanotube dispersion exhibits low viscosity, and the particle size of the particles contained in the carbon nanotube dispersion can be kept at a small level.

[0058] The weight ratio of the carbon nanotubes to the dispersant may be 100:80 to 100:500, specifically 100:100 to 100:400, 100:100 to 100:300, 100:100 to 100:250, 100:120 to 100:300, or 100:120 to 100:250, more specifically 100:120 to 100:200.

[0059] If the dispersant is contained in an amount exceeding the above range, the conductivity of the electrode may be impaired when the carbon nanotube dispersion is applied to the electrode, and the dispersant may act as an impurity in the electrode. On the other hand, if the dispersant is contained in an amount less than the above range, the effects of improving dispersibility, reducing viscosity, and inhibiting carbon nanotube aggregation may be insufficient.

[0060] (3) Dispersion medium The dispersion medium is a dispersion medium for dispersing the carbon nanotubes and the dispersant, and can be used to preferentially disperse the carbon nanotubes and supply them as a carbon nanotube dispersion in order to prevent aggregation when powdered carbon nanotubes are directly applied to the preparation of an electrode slurry composition.

[0061] The dispersion medium may be one that can dissolve or disperse the carbon nanotubes and dispersant to a certain level or more, and may be included in an amount that allows the electrode slurry composition to have an appropriate viscosity, taking into consideration the coatability of the electrode slurry composition that will be prepared later using the carbon nanotube dispersion.

[0062] The dispersion medium is not particularly limited as long as it is one that is commonly used in the art for dispersing the carbon nanotubes and dispersants, and may be, for example, one or more selected from the group consisting of amide-based polar organic solvents, alcohol-based solvents, glycol-based solvents, glycol ether-based solvents, ketone-based solvents, ester-based solvents, and aqueous solvents.

[0063] The amide-based polar organic solvent may be one or more selected from the group consisting of dimethylformamide (DMF), diethylformamide, dimethylacetamide (DMAc), N-methylpyrrolidone (NMP), 3-methoxy-N,N-dimethylpropanamide (Equamide M100, manufactured by Idemitsu Kosan Co., Ltd.), and 3-butoxy-N,N-dimethylpropanamide (Equamide B100, manufactured by Idemitsu Kosan Co., Ltd.).

[0064] The alcohol solvent may be one or more selected from the group consisting of methanol, ethanol, 1-propanol, 2-propanol (or isopropyl alcohol), 1-butanol, 2-methyl-1-propanol, 2-butanol, 1-methyl-2-propanol, pentanol, hexanol, heptanol, octanol, glycerin, trimethylolpropane, pentaerythritol, and sorbitol.

[0065] The glycol-based solvent may be one or more selected from the group consisting of ethylene glycol, diethyl glycol, triethylene glycol, propylene glycol, 1,3-propanediol, 1,3-butanediol, 1,5-pentanediol, and hexylene glycol.

[0066] The glycol ether solvent may be one or more selected from the group consisting of ethylene glycol monomethyl ether, diethylene glycol monomethyl ether, triethylene glycol monomethyl ether, tetraethylene glycol monomethyl ether, ethylene glycol monoethyl ether, diethylene glycol monoethyl ether, triethylene glycol monoethyl ether, tetraethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, and tetraethylene glycol monobutyl ether.

[0067] The ketone solvent may be one or more selected from the group consisting of acetone, methyl ethyl ketone, methyl propyl ketone, and cyclopentanone.

[0068] The ester solvent may be one or more selected from the group consisting of ethyl acetate, gamma-butyrolactone, and upsilon-propiolactone.

[0069] The aqueous solvent may be water.

[0070] The carbon nanotube dispersion of the present invention containing the above components has excellent dispersibility, low viscosity of the dispersion, and small particle size of the particles contained therein.

[0071] The carbon nanotube dispersion may have a viscosity of 1,000 to 11,000 cps, specifically 3,000 to 10,500 cps, and more specifically 5,000 to 10,000 cps, when measured at 25°C and 1 rpm using a rotor 1 with a viscometer (Tohki Sangyo Co., Ltd., Viscometer TV-25). When the carbon nanotube dispersion has a viscosity within the above range, it can be used to more smoothly produce an electrode slurry, and the electrode slurry containing the carbon nanotube dispersion can have a viscosity appropriate for forming an electrode.

[0072] Furthermore, the carbon nanotube dispersion may have a viscosity of 1,000 to 12,000 cps, specifically 3,000 to 11,500 cps, more specifically 5,000 to 11,000 cps, when the viscosity is measured one week after production using a viscometer (viscometer TV-25, manufactured by Toki Sangyo Co., Ltd.) at 25°C and 1 rpm using Rotor 1.

[0073] Furthermore, when the carbon nanotube dispersion is left at 25°C for one week, the viscosity increase rate may be 20% or less, specifically 0.1% to 20%, 0.1% to 18%, 0.5% to 18%, and more specifically 1.0% to 16%.

[0074] The carbon nanotube dispersion may contain particulate carbon nanotubes, and the particulate carbon nanotubes may be formed by agglomeration of a plurality of carbon nanotubes.

[0075] The carbon nanotube dispersion of the present invention contains the first dispersant and the second dispersant in the aforementioned specific weight ratio, and the carbon nanotube content and the total amount of the first dispersant and the second dispersant satisfy the aforementioned specific weight ratio, so that the carbon nanotubes are uniformly dispersed in the dispersion and the aggregation of the carbon nanotubes can be reduced. Therefore, the carbon nanotube dispersion of the present invention can contain particles having a small particle size, specifically, agglomerated particles of carbon nanotubes having a small particle size.

[0076] The average particle size (D50) of the carbon nanotube aggregate particles dispersed in the carbon nanotube dispersion liquid may be, for example, 0.5 μm to 5.5 μm, specifically 1 μm to 5 μm, and more specifically 1.5 μm to 5 μm.

[0077] The average particle size (D90) of the carbon nanotube aggregate particles may be, for example, 2 μm to 15 μm, specifically 3 μm to 14 μm, and more specifically 5 μm to 13 μm.

[0078] In order to measure the average particle size of the carbon nanotubes, the particle size of the carbon nanotube aggregate particles can be measured by laser diffraction.

[0079] Method for producing carbon nanotube dispersion A method for producing a carbon nanotube dispersion liquid will be described below. The method for producing a conductive material dispersion liquid according to the present invention includes the steps of (1) mixing carbon nanotubes, a dispersant, and a dispersion medium to produce a mixture, and (2) dispersing the mixture. Here, the dispersant contains a first dispersant and a second dispersant in a weight ratio of 100:10 to 100:90, the first dispersant is a dispersant containing a cyclic amide group, and the second dispersant is a polymer compound containing both a sulfone group and styrene, and the weight ratio of the carbon nanotubes to the dispersant is 100:50 to 100:500.

[0080] In step (1), carbon nanotubes, a dispersant, and a dispersion medium are mixed to produce a mixture.

[0081] The step of preparing the mixture may be carried out under temperature conditions that do not cause changes in the physical properties of the mixture, such as viscosity, due to evaporation of the dispersion medium, for example, at a temperature of 50°C or lower, more specifically, 5°C to 50°C.

[0082] In step (2), the mixture is subjected to a dispersion treatment to produce a carbon nanotube dispersion liquid.

[0083] The dispersion may be carried out by a milling method using a ball mill, a bead mill, a disc mill, a basket mill, a high-pressure homogenizer, or the like, and more specifically, by a milling method using a disc mill or a high-pressure homogenizer.

[0084] When milling using the bead mill, the bead size is determined appropriately depending on the type and amount of carbon nanotubes and the type of dispersant. Specifically, the diameter of the beads may be 0.1 mm to 5 mm, more specifically 0.5 mm to 4 mm. The bead milling process may be performed at a speed of 1,000 rpm to 15,000 rpm, more specifically 2,000 rpm to 12,000 rpm. The dispersion process is performed depending on the degree of dispersion of the carbon nanotube dispersion, specifically 30 minutes to 120 minutes, more specifically 60 minutes to 90 minutes.

[0085] The milling by the high-pressure homogenizer (high-pressure disperser) is performed, for example, by pressurizing the mixture with a plunger pump of the high-pressure homogenizer and extruding it into the gap of the homogenizing valve, so that the mixture is subjected to forces such as cavitation, shear, impact, and explosion when passing through the gap. The pressure of the high-pressure homogenizer may be 5,000 psi to 40,000 psi, specifically 10,000 psi to 30,000 psi, and more specifically may be 14,000 psi to 25,000 psi. The dispersion treatment by the high-pressure homogenizer may be performed 1 to 15 times, specifically 2 to 10 times, and more specifically 3 to 7 times.

[0086] Electrode Slurry Composition In addition, the present invention provides an electrode slurry composition for a lithium secondary battery containing the carbon nanotube dispersion liquid and an electrode active material.

[0087] The electrode slurry composition for the lithium secondary battery may be a positive electrode slurry composition or a negative electrode slurry composition, specifically, it may be a negative electrode slurry composition.

[0088] The electrode slurry composition for the lithium secondary battery may contain the carbon nanotube dispersion liquid, a positive electrode active material or a negative electrode active material as an electrode active material, a binder, and optionally a solvent and / or other additives.

[0089] As the positive electrode active material, well-known positive electrode active materials in the technical field can be used without limitation. For example, lithium cobalt-based oxides, lithium nickel-based oxides, lithium manganese-based oxides, lithium iron phosphate oxides, lithium nickel manganese cobalt-based oxides, or combinations thereof can be used. Specifically, as the positive electrode active material, LiCoO2, LiNiO2, LiMn2O4, LiCoPO4, LiFePO4, and LiNiaMnbCocO2 (where 0 < a, b, c < 1) can be used, but are not limited thereto.

[0090] The negative electrode active material may be one or more negative electrode active materials selected from the group consisting of natural graphite, artificial graphite, carbonaceous materials, lithium-containing titanium composite oxide (LTO), metals (Me) such as Si, Sn, Li, Zn, Mg, Cd, Ce, Ni, or Fe, alloys composed of the metals (Me), oxides (MeOx) of the metals (Me), and composites of the metals (Me) and carbon. The negative electrode active material may be contained in an amount of 60 to 98 wt %, more preferably 70 to 98 wt %, based on the total weight of solids in the negative electrode slurry excluding the solvent.

[0091] The binder is a component that assists in bonding the active material with the conductive material and the current collector, and is usually added in an amount of 1 to 30 wt% based on the total weight of the mixture including the electrode active material. Examples of such binders include 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, fluororubber, and various copolymers.

[0092] Examples of the solvent include organic solvents such as N-methylpyrrolidone (NMP), dimethylformamide (DMF), acetone, and dimethylacetamide, or water. These solvents may be used alone or in combination. The amount of solvent used may be an amount that can dissolve and disperse the electrode active material, binder, and conductive material, taking into consideration the coating thickness of the slurry and the production yield.

[0093] The viscosity adjuster may be carboxymethyl cellulose, polyacrylic acid, or the like, and the addition thereof can adjust the viscosity of the electrode slurry so as to facilitate the preparation of the electrode slurry and the coating process onto the electrode current collector.

[0094] The filler is selectively used as a component that suppresses expansion of the electrode, and is not particularly limited as long as it does not cause chemical changes in the battery and is a fibrous material. For example, olefin polymers such as polyethylene and polypropylene; glass fiber, carbon fiber, and other fibrous materials are used.

[0095] When the electrode slurry composition is a positive electrode slurry composition for forming a positive electrode, the positive electrode can be manufactured by applying the positive electrode slurry composition onto a positive electrode current collector, followed by drying and rolling. Alternatively, the positive electrode slurry can be cast onto a separate support, and then peeled off from the support to obtain a film, which can be laminated onto the positive electrode current collector.

[0096] The thickness of the positive electrode active material layer formed from the positive electrode slurry may vary depending on the loading amount and loading speed for applying the positive electrode slurry.

[0097] The positive electrode current collector generally has a thickness of 3 μm to 500 μm. There are no particular limitations on the positive electrode current collector, as long as it does not cause chemical changes in the battery and has high conductivity. For example, stainless steel, aluminum, nickel, titanium, baked carbon, or aluminum or stainless steel whose surface has been surface-treated with carbon, nickel, titanium, silver, or the like may be used. Furthermore, the bonding strength of the positive electrode active material may be strengthened by forming fine irregularities on the surface of the positive electrode current collector, and it may be used in a variety of forms, such as a film, sheet, foil, mesh, porous material, foam, or nonwoven fabric.

[0098] When the electrode slurry composition is a negative electrode slurry composition for forming a negative electrode, the negative electrode can be manufactured by applying the negative electrode slurry composition onto a negative electrode current collector, followed by drying and rolling. Alternatively, the negative electrode slurry can be cast onto a separate support, and then peeled off from the support to obtain a film, which can be laminated onto the negative electrode current collector.

[0099] The thickness of the negative electrode active material layer formed from the negative electrode slurry may vary depending on the loading amount and loading speed for applying the negative electrode slurry.

[0100] The negative electrode current collector generally has a thickness of 3 μm to 500 μm. There are no particular limitations on the negative electrode current collector, so long as it does not cause chemical changes in the battery and has high conductivity. Examples of the negative electrode current collector that can be used include copper, stainless steel, aluminum, nickel, titanium, baked carbon, copper or stainless steel surfaces that have been surface-treated with carbon, nickel, titanium, silver, or the like, and aluminum-cadmium alloys. Similarly to the negative electrode current collector, the surface may be provided with fine irregularities to strengthen the binding strength of the negative electrode active material, and the negative electrode current collector can be used in a variety of forms, such as a film, sheet, foil, mesh, porous material, foam, or nonwoven fabric.

[0101] Lithium secondary battery The lithium secondary battery includes a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and an electrolyte. The positive electrode and the negative electrode are the same as those described above, and therefore, detailed description thereof will be omitted.

[0102] The separator separates the negative electrode and the positive electrode and provides a path for lithium ions to move. Any separator commonly used in lithium secondary batteries can be used without particular limitations. In particular, a separator that exhibits low resistance to electrolyte ion movement and excellent humidification ability for the electrolyte solution is preferred. Specifically, porous polymer films, such as those made of polyolefin-based polymers such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers, or laminate structures of two or more layers thereof can be used. Conventional porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fibers or polyethylene terephthalate fibers, can also be used. To ensure heat resistance or mechanical strength, a coated separator containing a ceramic component or a polymeric material can also be used, and it can be selectively used in a single-layer or multi-layer structure.

[0103] Examples of the electrolyte include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, molten inorganic electrolytes, etc. that can be used in manufacturing lithium secondary batteries. Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0104] The organic solvent may be any solvent capable of acting as a medium for the movement of ions involved in the electrochemical reaction of the battery. Specific examples of the organic solvent include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether and tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), and propylene carbonate. Examples of suitable solvents include carbonate-based solvents such as ethylene carbonate (PC), alcohol-based solvents such as ethyl alcohol and isopropyl alcohol, nitriles such as R-CN (where R is a C2-C20 linear, branched, or cyclic hydrocarbon group that may contain a double-bonded aromatic ring or an ether bond), amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane, and sulfolanes. Among these, carbonate-based solvents are preferred, and mixtures of cyclic carbonates (e.g., ethylene carbonate or propylene carbonate) with low viscosity linear carbonate compounds (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) that have high ionic conductivity and a high dielectric constant, which can improve the charge / discharge performance of batteries, are more preferred. In this case, excellent electrolyte performance can be achieved when the cyclic carbonate and the linear carbonate are mixed in a volume ratio of about 1:1 to about 1:9.

[0105] The lithium salt can be any compound capable of providing lithium ions used in lithium secondary batteries. Specifically, examples of the lithium salt include LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, and LiB(C2O4)2. The concentration of the lithium salt is preferably within the range of 0.1M to 2.0M. When the lithium salt concentration is within the above range, the electrolyte has appropriate conductivity and viscosity, resulting in excellent electrolyte performance and efficient lithium ion migration.

[0106] In addition to the electrolyte components, the electrolyte may further include one or more additives, such as haloalkylene carbonate compounds (e.g., difluoroethylene carbonate), pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, for the purpose of improving battery life characteristics, suppressing battery capacity reduction, improving battery discharge capacity, etc. In this case, the additives may be included in an amount of about 0.1 wt % to 5 wt % based on the total weight of the electrolyte.

[0107] A lithium secondary battery including an electrode prepared using the carbon nanotube dispersion according to the present invention, specifically, a lithium secondary battery including an anode prepared using the carbon nanotube dispersion, has carbon nanotubes uniformly dispersed in the anode, and can reduce the amount of a conductive material, such as carbon black, compared to conventional batteries that include such a conductive material, thereby exhibiting excellent discharge capacity and stable output characteristics. As a result, the battery can be useful in portable devices such as mobile phones, laptops, and digital cameras, as well as electric vehicles such as hybrid electric vehicles (HEVs).

[0108] Therefore, according to another embodiment of the present invention, there are provided the lithium secondary battery, a battery module including the lithium secondary battery as a unit cell, and a battery pack including the same.

[0109] The battery module or battery pack can be used as a power source for one or more medium- to large-sized devices, such as power tools; electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); or power storage systems.

[0110] The present invention will be described in more detail below with reference to examples. However, the following examples are for illustrative purposes only and are not intended to limit the scope of the present invention.

[0111] Example Example 1 A 497g mixture was prepared by mixing 0.675wt% polyvinylpyrrolidone (PVP K15, Zhangzhou Huafu Chemical Co., Ltd.), 0.225wt% sulfonated polystyrene (Nouryon Co., Ltd.), and water as a dispersant. The impeller and container were attached to a dissolver (VMA-Getzmann Dispermat-CA) and rotated at 400 rpm for 10 minutes to mix the dispersant and dispersant.

[0112] 0.6 wt% of single-walled carbon nanotubes (SWCNT, TUBALL, manufactured by OCSiAl) with a specific surface area of ​​1,160 m2 / g and a length of 5 μm or more were added and dispersed at 8,000 rpm for 60 minutes.

[0113] The resultant was treated five times at a pressure of 20,000 psi using a high-pressure disperser (PICOMAX, manufactured by Micronox) to prepare a carbon nanotube dispersion.

[0114] Example 2 A carbon nanotube dispersion was prepared in the same manner as in Example 1, except that a sulfonated styrene-maleic acid copolymer was used instead of the sulfonated polystyrene.

[0115] Example 3 A carbon nanotube dispersion was prepared in the same manner as in Example 1, except that the content of polyvinylpyrrolidone was changed to 0.750 wt % and the content of sulfonated polystyrene was changed to 0.150 wt %.

[0116] Example 4 A carbon nanotube dispersion was prepared in the same manner as in Example 1, except that the content of polyvinylpyrrolidone was changed to 0.500 wt % and the content of sulfonated polystyrene was changed to 0.400 wt %.

[0117] Comparative Example 1 A carbon nanotube dispersion was prepared in the same manner as in Example 1, except that sulfonated polystyrene was not used and the content of polyvinylpyrrolidone was changed to 0.9 wt %.

[0118] Comparative Example 2 A carbon nanotube dispersion was prepared in the same manner as in Example 1, except that the sulfonated polystyrene was replaced with polyvinyl alcohol in the same amount.

[0119] Comparative Example 3 A carbon nanotube dispersion was prepared in the same manner as in Example 2, except that a styrene-maleic acid copolymer was used instead of the sulfonated styrene-maleic acid copolymer.

[0120] Comparative Example 4 A carbon nanotube dispersion was prepared in the same manner as in Example 2, except that polyvinylpyrrolidone was not used and the content of sulfonated styrene-maleic acid copolymer was changed to 0.9 wt %.

[0121] Comparative Example 5 A carbon nanotube dispersion was prepared in the same manner as in Example 1, except that the content of polyvinylpyrrolidone was changed to 0.450 wt % and the content of sulfonated polystyrene was changed to 0.450 wt %, respectively.

[0122] Comparative Example 6 A carbon nanotube dispersion was prepared in the same manner as in Example 1, except that the content of polyvinylpyrrolidone was changed to 0.825 wt % and the content of sulfonated polystyrene was changed to 0.075 wt %, respectively.

[0123] Comparative Example 7 A carbon nanotube dispersion was prepared in the same manner as in Example 1, except that the same amount of polyacrylamide was used instead of polyvinylpyrrolidone.

[0124] Comparative Example 8 A carbon nanotube dispersion was prepared in the same manner as in Example 1, except that the same amount of polyglyceryl-3-diisostearate was used instead of polyvinylpyrrolidone.

[0125] [Table 1]

[0126] Experimental Example The viscosity of the carbon nanotube dispersions of Examples 1 to 4 and Comparative Examples 1 to 8 was measured, and the viscosity was further measured after leaving them to stand at 25° C. for one week. The results are shown in Table 2 below.

[0127] The viscosity was measured using a viscometer (Viscometer TV-25, manufactured by Toki Sangyo Co., Ltd.) at 25°C and Rotor 1 at 1 rpm.

[0128] Furthermore, the particle sizes of the particles contained in the carbon nanotube dispersions of Examples 1 to 4 and Comparative Examples 1 to 8 were measured using a particle size analyzer (Mastersizer 3000, manufactured by Malvern), and the results are shown in Table 2 below.

[0129] [Table 2]

[0130] Referring to Table 2, Examples 1 to 5 showed low viscosity levels and low viscosity increase rates even after being left at 25°C for one week, and the particle sizes of the particles contained in the carbon nanotube dispersions were all small. In contrast, Comparative Examples 1 to 8 showed either a high viscosity increase rate or a high particle size of the particles contained in the carbon nanotube dispersion, or viscosity measurement was impossible. Specifically, Comparative Example 1, which contained only PVP, showed a viscosity increase rate and particle size of the carbon nanotube dispersion that were inferior to Examples 1 to 5. Comparative Examples 2 and 3 used a second dispersant, but because they used polyvinyl alcohol and styrene-maleic acid copolymer rather than a polymer compound containing both sulfonic acid and styrene, they showed poor particle size of the particles contained in the carbon nanotube dispersion, an increase in the viscosity increase rate of the carbon nanotube dispersion, and particle size. In addition, in Comparative Example 4, only the second dispersant was used, and in this case too, the carbon nanotube dispersion showed poor results in terms of the increase in viscosity increase rate and particle size.

[0131] On the other hand, Comparative Examples 5 and 6 contained both PVP and sulfonated polystyrene as in Example 1, but showed poor results in both the increase in viscosity increase rate of the carbon nanotube dispersion and the particle size. Comparative Example 5 used a relatively large amount of sulfonated polystyrene, while Comparative Example 6 used a small amount of sulfonated polystyrene. This confirmed that even when appropriate types of dispersants are used together, the dispersion effect can be improved only when the appropriate mixing ratio is met.

[0132] Finally, Comparative Examples 7 and 8 used a component not having a cyclic amide group as the first dispersant, but Comparative Example 7 also showed high viscosity and viscosity change rate, and the particle size of the particles in the dispersion was confirmed to be large, while Comparative Example 8 did not disperse smoothly enough to even measure the viscosity. From these results, it was confirmed that the superior dispersibility and stability of the dispersion of the present invention is the result of using a combination of specific types of first dispersant and second dispersant in a specific ratio.

Claims

1. A carbon nanotube dispersion liquid containing carbon nanotubes, a dispersant, and a dispersion medium, the dispersant comprises a first dispersant and a second dispersant in a weight ratio of 100:10 to 100:90; the first dispersant is a dispersant containing a cyclic amide group, and the second dispersant is a polymer compound containing both a sulfone group and styrene, The carbon nanotube dispersion liquid has a weight ratio of the carbon nanotubes to the dispersant of 100:50 to 100:

500.

2. The specific surface area (BET) of the carbon nanotubes is 800 m ２ The carbon nanotube dispersion liquid according to claim 1 , wherein the average molecular weight of the carbon nanotube dispersion liquid is 1 / g or more.

3. The carbon nanotube dispersion according to claim 1 , wherein the carbon nanotubes are single-walled carbon nanotubes.

4. 2. The carbon nanotube dispersion according to claim 1, wherein the carbon nanotubes are contained in an amount of 0.1 parts by weight or more and 5 parts by weight or less per 100 parts by weight of the carbon nanotube dispersion.

5. The first dispersant may be polyvinylpyrrolidone, poly-N-vinyl-5-methoxazolidone, polyvinylaziridinone, polyvinylazetidinone, polyvinylpiperidone, or polyvinylcaprolactone.

2. The carbon nanotube dispersion according to claim 1, wherein the polyvinylcaprolactam is at least one selected from the group consisting of poly(3-methylene-2-pyrrolidone), poly(N-methyl-3-methylene-2-pyrrolidone), and polyvinylphthalimide.

6. 2. The carbon nanotube dispersion liquid according to claim 1, wherein the second dispersant is at least one selected from the group consisting of polystyrene sulfonic acid, a salt of polystyrene sulfonic acid, and a sulfonate styrene-maleic acid copolymer.

7. 2. The carbon nanotube dispersion liquid according to claim 1, wherein the second dispersant is at least one selected from the group consisting of sulfonated polystyrene, sulfonated styrene-maleic acid copolymer, sodium polystyrene sulfonate, polystyrene sulfonic acid, and ammonium polystyrene sulfonate.

8. 2. The carbon nanotube dispersion liquid according to claim 1, wherein the dispersant comprises a first dispersant and a second dispersant in a weight ratio of 100:20 to 100:

80.

9. 2. The carbon nanotube dispersion according to claim 1, wherein the weight ratio of the carbon nanotubes to the dispersant is 100:100 to 100:

250.

10. 2. The carbon nanotube dispersion liquid according to claim 1, wherein the dispersion medium is at least one selected from the group consisting of an amide-based polar organic solvent, an alcohol-based solvent, a glycol-based solvent, a glycol ether-based solvent, a ketone-based solvent, an ester-based solvent, and an aqueous solvent.

11. 2. The carbon nanotube dispersion according to claim 1, wherein the carbon nanotube dispersion exhibits a viscosity increase rate of 20% or less when left standing at 25°C for one week.

12. The carbon nanotube dispersion according to claim 1 , wherein the carbon nanotube dispersion contains agglomerated particles of carbon nanotubes having an average particle size (D50) of 0.5 μm or more and 5.4 μm or less.

13. The carbon nanotube dispersion according to claim 1 , wherein the carbon nanotube dispersion contains agglomerated particles of carbon nanotubes having an average particle size (D90) of 1.5 μm or more and 15.0 μm or less.

14. An electrode slurry composition for a lithium secondary battery, comprising the carbon nanotube dispersion liquid according to any one of claims 1 to 13 and an electrode active material.

15. A method for producing a carbon nanotube dispersion liquid according to any one of claims 1 to 13, (1) mixing carbon nanotubes, a dispersant, and a dispersion medium to produce a mixture; (2) dispersing the mixture; the dispersant comprises a first dispersant and a second dispersant in a weight ratio of 100:10 to 100:90; the first dispersant is a dispersant containing a cyclic amide group, and the second dispersant is a polymer compound containing both a sulfone group and styrene, The carbon nanotube dispersion liquid manufacturing method, wherein the weight ratio of the carbon nanotubes to the dispersant is 100:50 to 100:500.

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