Carbon nanotube dispersion and method for producing the same

Abstract

The present invention relates to a carbon nanotube dispersion liquid comprising carbon nanotubes, 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 90, the first dispersant being a dispersant containing an N atom, and the second dispersant being a compound containing a sulfone group, a hydroxyl group, and an aromatic ring in its molecular structure, and the weight ratio of the carbon nanotubes to the dispersant being 100:25 to 500, the carbon nanotube dispersion liquid having low viscosity and minimal change in viscosity over time.

Description

[Technical Field]

[0001] This application claims priority under Korean Patent Application No. 10-2023-0085868 dated 3 July 2023, and all content disclosed in the said Korean Patent Application is incorporated herein by reference.

[0002] This invention relates to a carbon nanotube dispersion and a method for producing the same, and more specifically, to a carbon nanotube dispersion having low viscosity and minimal change in viscosity over time, and a method for producing the same. [Background technology]

[0003] With the technological development and increasing demand for mobile devices, the demand for rechargeable batteries as an energy source is rapidly increasing. Among these rechargeable batteries, lithium-ion batteries, which have high energy density and voltage, long cycle life, and low self-discharge rate, have been commercialized and are widely used. Furthermore, research is actively being conducted on methods to improve electrode density and manufacture electrodes with even higher energy density per unit volume for such high-capacity lithium-ion batteries.

[0004] Generally, high-density electrodes are formed by molding electrode active material particles having a size of several micrometers to tens of micrometers using high-pressure pressing. However, during the molding process, the particles may deform, reducing the space between them, which tends to decrease electrolyte permeability.

[0005] To solve the above problems, conductive materials with excellent electrical conductivity and strength are used during the manufacture of electrodes. Even when the conductive material is positioned between the electrode active materials and undergoes a molding process, it maintains fine pores between the active material particles, allowing the electrolyte to easily penetrate, and its excellent electrical conductivity reduces resistance within the electrode. Among such conductive materials, the use of carbon nanotubes, which are fibrous carbon-based conductive materials that can further reduce electrode resistance by forming electrical conductive paths within the electrode, is increasing.

[0006] Carbon nanotubes, a type of fine carbon fiber, are tubular carbon fibers with a diameter of 1 μm or less. Due to their unique structure, they possess high conductivity, tensile strength, and heat resistance, making them promising for application and practical use in various fields. However, carbon nanotubes have a high specific surface area, which leads to strong van der Waals attractive forces between them, resulting in poor dispersibility and the problem of aggregation.

[0007] To solve these problems, methods have been proposed to disperse carbon nanotubes in a dispersion medium using mechanical dispersion treatments such as ultrasonic treatment. However, with mechanical dispersion treatments, there is a problem in that the carbon nanotubes aggregate as soon as the ultrasonic irradiation ends.

[0008] Therefore, there is a need to develop a method for producing a carbon nanotube dispersion that can improve the dispersibility of carbon nanotubes, has low viscosity, and suppresses the increase in viscosity over time. [Overview of the project] [Problems that the invention aims to solve]

[0009] The present invention aims to solve the problems of the above-mentioned prior art and to provide a carbon nanotube dispersion with excellent dispersibility, low viscosity, and minimal change in viscosity over time, by including compounds containing N atoms and compounds containing sulfone groups, hydroxyl groups, and aromatic rings in their molecular structure in predetermined weight ratios and predetermined amounts.

[0010] Furthermore, the present invention aims to provide a negative electrode slurry composition for lithium secondary batteries containing the carbon nanotube dispersion.

[0011] Furthermore, the present invention aims to provide a method for producing the carbon nanotube dispersion. [Means for solving the problem]

[0012] To solve the above problems, the present invention provides a carbon nanotube dispersion.

[0013] The present invention provides a carbon nanotube dispersion comprising carbon nanotubes, a dispersant, and a dispersion medium, wherein the specific surface area (BET) of the carbon nanotubes is less than 800 m 2 / g, the dispersion contains a first dispersant and a second dispersant in a weight ratio of 100:10 to 90, the first dispersant is a compound containing N atoms, the second dispersant is a compound containing all of a sulfone group, a hydroxyl group, and an aromatic ring, and the weight ratio of the carbon nanotubes to the dispersant is 100:25 to 500.

[0014] In the above [1], the present invention provides a carbon nanotube dispersion in which the specific surface area (BET) of the carbon nanotubes is 200 m 2 / g or more and less than 800 m 2 / g.

[0015] In the above [1] or [2], the present invention provides a carbon nanotube dispersion in which the carbon nanotubes are multi-walled carbon nanotubes.

[0016] In any one of the above [1] to [3], the present invention provides a carbon nanotube dispersion in which the carbon nanotubes are contained in an amount of 0.1 parts by weight to 7 parts by weight with respect to 100 parts by weight of the carbon nanotube dispersion

[0017] In any one of the above [1] to [4], the present invention provides a carbon nanotube dispersion in which the first dispersant is one or more selected from the group consisting of polyvinylpyrrolidone, polyacrylic acid hydrazide, poly-N-vinyl-5-methoxazolidon, N-alkyl polyimine, N-acetyl polyimine, polyacrylamide, poly-L-lysine hydrobromide, benzyl-dodecyl-dimethylammonium chloride, and polyethyleneimine.

[0018] In any one of the above [1] to [5], the present invention provides a carbon nanotube dispersion in which the second dispersant is a lignin sulfonate compound.

[0019] In any one of the above [1] to [6], the present invention provides a carbon nanotube dispersion in which the second dispersant is sodium lignin sulfonate, calcium lignin sulfonate or a mixture thereof.

[0020] In any one of the above [1] to [7], the present invention provides a carbon nanotube dispersion in which the dispersant contains the first dispersant and the second dispersant in a weight ratio of 100:15 to 75.

[0021] In any one of the above [1] to [8], the present invention provides a carbon nanotube dispersion in which the weight ratio of the carbon nanotubes to the dispersant is 100:25 to 150.

[0022] The present invention provides a carbon nanotube dispersion in any one of the above [1] to

[10] , 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-based solvents.

[0023] The present invention provides a carbon nanotube dispersion in any one of the above [1] to

[10] , wherein the viscosity of the carbon nanotube dispersion is 10 to 1,000 cps.

[0024] Furthermore, in order to solve the aforementioned other problems, the present invention provides an electrode slurry composition for lithium secondary batteries containing the carbon nanotube dispersion.

[0025] The present invention provides an electrode slurry composition for lithium secondary batteries comprising a carbon nanotube dispersion and an electrode active material according to any one of the above [1] to

[11] .

[0026] Furthermore, in order to solve the aforementioned other problems, the present invention provides a method for producing a carbon nanotube dispersion.

[0027] The present invention provides a method for producing a carbon nanotube dispersion, comprising 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 comprises a first dispersant and a second dispersant in a weight ratio of 100:10 to 90, the first dispersant is a dispersant containing an N atom, the second dispersant is a compound containing a sulfone group, a hydroxyl group, and an aromatic ring in its molecular structure, and the weight ratio of the carbon nanotubes to the dispersant is 100:50 to 500, and provides a method for producing any one of the carbon nanotube dispersions described in [1] to

[11] above. [Effects of the Invention]

[0028] The carbon nanotube dispersion of the present invention contains both a dispersant containing N atoms and a compound containing sulfone groups, hydroxyl groups, and aromatic rings in its molecular structure. It exhibits excellent dispersibility of carbon nanotubes, low viscosity, and minimal change in viscosity over time, making it advantageous for storage and use. [Modes for carrying out the invention]

[0029] The terms and words used herein and in the claims should not be interpreted in a manner limited to their ordinary or dictionary meanings, but rather in a manner consistent with the technical idea of ​​the present invention, in accordance with the principle that inventors may define the concepts of terms as appropriate to best describe their invention.

[0030] The terms used herein are used solely to describe exemplary embodiments and are not intended to limit the invention. Singular expressions include plural expressions unless the context clearly indicates otherwise.

[0031] In this specification, terms such as “includes,” “equip,” or “have” specify the presence of an implemented feature, figure, step, component, or combination thereof, and should be understood not to preclude the existence or possibility of adding one or more other features, figures, steps, components, or combinations thereof.

[0032] In this specification, "%" means weight percent unless otherwise explicitly indicated.

[0033] In this specification, the average particle size "D 50 " refers to a particle size where the cumulative volume is 50%, and "D 90 " refers to a particle size that corresponds to 90% of the cumulative volume. 50 and D 90It can be measured, for example, using the laser diffraction method. The laser diffraction method can generally measure particle sizes ranging from the submicron region to about several millimeters, and can obtain highly reproducible and highly resolved results.

[0034] In this specification, the "specific surface area" is measured by the BET method. Specifically, it can be calculated from the nitrogen gas adsorption amount at liquid nitrogen temperature (77K) using BELSORP-mini II manufactured by BEL Japan.

[0035] Hereinafter, the present invention will be specifically described.

[0036] The carbon nanotube dispersion according to the present invention is a carbon nanotube dispersion containing carbon nanotubes, a dispersant, and a dispersion medium. The specific surface area (BET) of the carbon nanotubes is less than 800 m 2 / g. The dispersion contains the first dispersant and the second dispersant in a weight ratio of 100:10 to 90. The first dispersant is a compound containing an N atom, and the second dispersant is a compound containing all of a sulfone group, a hydroxyl group, and an aromatic ring. The weight ratio of the carbon nanotubes to the dispersant is 100:25 to 500.

[0037] Carbon nanotube dispersion The carbon nanotube dispersion according to the present invention is a carbon nanotube dispersion containing carbon nanotubes, a dispersant, and a dispersion medium. The specific surface area (BET) of the carbon nanotubes is less than 800 m 2 / g. The dispersion contains the first dispersant and the second dispersant in a weight ratio of 100:10 to 90. The first dispersant is a compound containing an N atom, and the second dispersant is a compound containing all of a sulfone group, a hydroxyl group, and an aromatic ring. The weight ratio of the carbon nanotubes to the dispersant is 100:25 to 500.

[0038] The following describes in detail each component of the carbon nanotube dispersion of the present invention.

[0039] (1) Carbon nanotubes The term "carbon nanotube" as used in this invention refers to a secondary structure formed by the aggregation of carbon nanotube units, either entirely or partially, into a bundle type, wherein the carbon nanotube units have the form of a cylinder with a nanoscale diameter, and sp 2 It has a bonded structure. Here, depending on the angle and structure in which the graphite sheet is wound, it can exhibit conductive or semiconductor properties. Carbon nanotube units are classified into single-walled carbon nanotubes (SWCNTs), double-walled carbon nanotubes (DWCNTs), and multi-walled carbon nanotubes (MWCNTs) depending on the number of bonds forming the wall.

[0040] As used in this invention, the term "bundle type" refers to a secondary shape in which multiple carbon nanotube units are arranged in parallel with substantially the same orientation along their longitudinal axes, or are twisted or entangled after being arranged, unless otherwise specified. The term "non-bundle type" or "entangled type" refers to a form in which carbon nanotube units are entangled without a predetermined shape such as a bundle or rope.

[0041] Carbon nanotubes have high conductivity, but they also have high cohesiveness due to van der Waals forces that occur between them. When conductive materials aggregate, they cannot properly form conductive pathways, requiring relatively more conductive material and reducing the amount of active material, which can actually degrade electrode performance. Therefore, it has been difficult to commercialize carbon nanotubes as a conductive material.

[0042] The carbon nanotube dispersion according to the present invention contains, as a dispersant, a compound containing an N atom and a compound containing a sulfone group, a hydroxyl group, and an aromatic ring in its molecular structure. This provides excellent dispersibility with carbon nanotubes, suppresses changes in viscosity over time, exhibits a low viscosity increase rate, and offers advantageous effects in the storage and use of the carbon nanotube dispersion.

[0043] Furthermore, when the carbon nanotube dispersion according to the present invention is applied to the production of an electrode slurry, the carbon nanotubes are uniformly positioned between the active materials, and even during the process of manufacturing electrodes by rolling after coating and drying the electrode slurry, the fine spaces between the electrode active materials can be maintained at a constant level. In addition, the carbon nanotubes do not aggregate and are uniformly distributed, and conductive pathways can be sufficiently formed even with a small amount of carbon nanotubes.

[0044] A carbon nanotube dispersion according to an example of the present invention may contain one or more carbon nanotube units from among single-wall, double-wall, and multi-wall carbon nanotube units, and specifically may contain single-wall carbon nanotubes (SWCNTs).

[0045] The carbon nanotubes mentioned above are 800m 2 It can have a specific surface area (BET) of less than 200 m². 2 / g or more, 220m 2 / g or more, 240m 2 / g or more, 260m 2 / g or more, 280m 2 / g or more, 290m 2 / g or more, 300m 2 / g or more, 800m 2 Less than / g, 780m 2 Less than / g, 760m 2 Less than / g, 740m 2 Less than / g, 720m 2 Less than / g, 700m 2 Less than / g, 650m 2 It can have a specific surface area (BET) of less than 1 / g. The carbon nanotube dispersion of the present invention exhibits excellent dispersibility by containing both a compound containing an N atom and a compound containing a sulfone group, a hydroxyl group, and an aromatic ring in its molecular structure as a dispersant, and is suitable for 800m 2 It exhibits excellent dispersibility for carbon nanotubes with a low specific surface area (BET) of less than 1 / g, resulting in a carbon nanotube dispersion with low viscosity and minimal change in viscosity over time.

[0046] The carbon nanotubes can be included in an amount of 0.1 to 7 parts by weight per 100 parts by weight of the conductive material dispersion, more specifically in an amount of 0.5 to 5 parts by weight, and more specifically in an amount of 1 to 4 parts by weight.

[0047] A carbon nanotube dispersion according to an example of the present invention contains a dispersant with excellent dispersibility, and therefore can exhibit excellent dispersibility even for carbon nanotubes with a high specific surface area, allowing for uniform dispersion of carbon nanotubes with a high specific surface area. It can have a higher carbon nanotube content compared to conventional carbon nanotube dispersions commonly used in the range described above. When a carbon nanotube dispersion with a low carbon nanotube content is used in the manufacture of an electrode slurry, the solid content of the manufactured electrode slurry decreases, the thickness before coating and drying (wetting thickness) of the electrode slurry becomes thicker, and the rolling ratio measured after drying and rolling becomes higher, resulting in a large difference in the ratio of thickness before and after drying and rolling. When the rolling ratio is high in this way, the composition inside the slurry, including the positive electrode active material, may be damaged during the process, which can lead to problems such as a decrease in battery performance.

[0048] (2) Dispersant The carbon nanotube dispersion according to the present invention contains a first dispersant and a second dispersant in a weight ratio of 100:10 to 90 in order to improve the dispersibility of the carbon nanotubes. The first dispersant is a compound containing an N atom, and the second dispersant is a compound containing a sulfone group, a hydroxyl group, and an aromatic ring in its molecular structure.

[0049] The N atom-containing compound included in the first dispersant and the compound containing a sulfone group, a hydroxyl group, and an aromatic ring in its molecular structure included in the second dispersant play a role in increasing the dispersibility of carbon nanotubes as dispersants in the carbon nanotube dispersion, and can exert the effect of suppressing the increase in viscosity of the carbon nanotube dispersion and the change in viscosity over time.

[0050] In particular, the carbon nanotube dispersion according to the present invention contains, in addition to the N atom-containing compound as the first dispersant, a compound containing a sulfone group, a hydroxyl group, and an aromatic ring in its molecular structure as a second dispersant. Therefore, compared to conventional carbon nanotube dispersions containing only one type of dispersant, it exhibits superior dispersibility, resulting in less aggregation of particles in the slurry composition, a lower sedimentation rate, lower viscosity, and excellent adhesion to the separator substrate.

[0051] Because the second dispersant contains a sulfone group, a hydroxyl group, and an aromatic ring in its molecular structure, the bulky structure of the compound and the influence of the sulfone and hydroxyl groups reduce the viscosity of carbon nanotube dispersions, especially aqueous carbon nanotube dispersions, compared to conventional methods, and significantly improve the increase in viscosity over time.

[0052] As the first dispersant, a compound containing an N atom can be used, and when a specific dispersant containing an N atom in its structure, such as an amine structure, amide structure, imine structure, or ammonium structure, is applied as the first dispersant, it can exhibit a more improved viscosity improvement effect and an effect of suppressing viscosity changes over time. The dispersant containing the N atom is soluble in water and can be one or more selected from the group consisting of, for example, polyvinylpyrrolidone, polyacrylic acid hydrazide, poly-N-vinyl-5-methoxazolidon, N-alkyl polyimine, N-acetyl polyimine, polyacrylamide, poly-L-lysine hydrobromide, benzyl-dodecyl-dimethylammonium chloride, and polyethyleneimine.

[0053] Furthermore, as a second dispersant, a compound containing a sulfone group, a hydroxyl group, and an aromatic ring in its molecular structure can be used. For example, a compound containing a sulfone group, a hydroxyl group, and an aromatic ring in its molecular structure can be a lignin sulfonate compound. Specifically, the second dispersant can be sodium lignin sulfonate, calcium lignin sulfonate, or a mixture thereof.

[0054] If the dispersant includes a dispersant containing an N atom as the first dispersant and a compound containing a sulfone group, a hydroxyl group, and an aromatic ring in its molecular structure as the second dispersant, then in the carbon nanotube dispersion, the interaction between the aromatic ring and the carbon nanotubes and the interaction between the hydroxyl group and the polymer dispersant via hydrogen bonding are appropriately balanced, thereby suppressing the decrease in viscosity of the carbon nanotube dispersion and the increase in viscosity over time. Furthermore, the negatively charged sulfone group can induce an electrostatic shielding effect, which can suppress aggregation between carbon nanotubes.

[0055] The dispersant contains both the first dispersant and the second dispersant in a weight ratio of 100:10 to 90, specifically in a weight ratio of 100:10 to 80, or 100:15 to 75, and more specifically in a weight ratio of 100:15 to 50. When the carbon nanotube dispersion contains the first dispersant and the second dispersant in the aforementioned weight ratios as the dispersant, the carbon nanotubes are uniformly dispersed in the carbon nanotube dispersion, and the viscosity can be maintained at a predetermined level over time, along with a low viscosity.

[0056] The weight ratio of the carbon nanotubes and dispersant can be 100:25 to 500, specifically 100:25 to 300, 100:25 to 250, 100:25 to 200, 100:25 to 180, 100:25 to 160, 100:25 to 150, 100:25 to 140, 100:25 to 120, 100:25 to 1 It can be 00, 100:25~90, 100:30~500, 100:30~300, 100:30~250, 100:30~200, 100:30~180, 100:30~160, 100:30~150, 100:30~140, 100:30~120, 100:30~100, or 100:30~90.

[0057] Furthermore, in one embodiment of the present invention, the weight ratio of the carbon nanotube and the dispersant can be more specifically 100:30 to 90, 100:30 to 75, 100:30 to 60, or 100:30 to 45.

[0058] If the dispersant is present in an excessive amount exceeding the range, the excess dispersant may inhibit the conductivity of the electrode when the carbon nanotube dispersion is applied to the electrode, and the dispersant may act as an impurity within the electrode. On the other hand, if it is present in a small amount below the range, the effect of improving dispersibility, reducing viscosity, and suppressing changes in viscosity over time may be insufficient.

[0059] (3) Dispersion medium The dispersion medium is a dispersion medium for dispersing the carbon nanotubes and the dispersant, and can be used to preferentially pre-disperse the carbon nanotubes and supply them as a carbon nanotube dispersion liquid in order to prevent aggregation when carbon nanotubes in powder form are applied directly to the manufacture of an electrode slurry composition.

[0060] The dispersion medium can be one that can dissolve or disperse the carbon nanotubes and dispersant at a predetermined level or higher. The dispersion medium can be included in a content that allows the electrode slurry composition to have an appropriate viscosity, taking into consideration the coating properties of the electrode slurry composition subsequently produced using the carbon nanotube dispersion.

[0061] The dispersion medium is not particularly limited, as long as it is commonly used in the art for dispersing the carbon nanotubes and the dispersant, and can 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-based solvents.

[0062] The aforementioned amide-based polar organic solvent can be one or more selected from the group consisting of dimethylformamide (DMF), diethylformamide, dimethylacetamide (DMAc), N-methylpyrrolidone (NMP), 3-methoxy-N,N-dimethylpropanamide (Equamid M100, manufactured by Idemitsu Kosan Co., Ltd.), and 3-butoxy-N,N-dimethylpropanamide (Equamid B100, manufactured by Idemitsu Kosan Co., Ltd.).

[0063] The alcohol-based 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.

[0064] 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.

[0065] The glycol ether solvent can 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, atelen glycol monobutyl ether, diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, and tetraethylene glycol monobutyl ether.

[0066] The ketone solvent can be one or more selected from the group consisting of acetone, methyl ethyl ketone, methyl propyl ketone, and cyclopentanone.

[0067] The ester solvent can be one or more selected from the group consisting of ethyl acetate, gamma-butyrolactone, and epsilon-propiolactone.

[0068] Furthermore, the aqueous solvent may be water.

[0069] The carbon nanotube dispersion of the present invention, containing the components described above, exhibits excellent dispersibility, low viscosity, and minimal viscosity increase over time.

[0070] The carbon nanotube dispersion can have a viscosity of 10 to 1,000 cps when its viscosity is measured using a viscometer (Toki Sangyo Co., Ltd., viscometer TV-25) at 25°C and 1 rpm using Rotor 1. Specifically, it can have viscosities of 20 cps or more, 30 cps or more, 40 cps or more, 50 cps or more, 60 cps or more, 70 cps or more, 1,000 cps or less, 800 cps or less, 600 cps or less, 500 cps or less, 400 cps or less, and 300 cps or less. When the carbon nanotube dispersion has a viscosity within the above range, it can be used to manufacture an electrode slurry more smoothly, and the electrode slurry containing the carbon nanotube dispersion can have an appropriate viscosity for electrode formation.

[0071] Furthermore, when the viscosity of the carbon nanotube dispersion is measured using a viscometer (Toki Sangyo Co., Ltd., viscometer TV-25) at 25°C and Rotor 1 at 1 rpm, two weeks after manufacturing, it can have viscosities of 20 cps or more, 30 cps or more, 40 cps or more, 50 cps or more, 60 cps or more, 70 cps or more, 1,500 cps or less, 1,300 cps or less, 1,000 cps or less, 800 cps or less, 600 cps or less, 500 cps or less, and 400 cps or less.

[0072] Furthermore, when the carbon nanotube dispersion is left at 25°C for one week, the viscosity increase rate can be 50% or less, specifically 40% or less, 35% or less, 30% or less, or 25% or less.

[0073] Method for producing a carbon nanotube dispersion The method for producing a carbon nanotube dispersion will be described below. The method for producing a conductive material dispersion according to the present invention includes (1) the step of mixing carbon nanotubes, a dispersant, and a dispersion medium to produce a mixture, and (2) the step of dispersing the mixture. Here, the dispersant contains a first dispersant and a second dispersant in a weight ratio of 100:10 to 90, the first dispersant is a compound containing an N atom, and the second dispersant is a compound containing a sulfone group, a hydroxyl group, and an aromatic ring in its molecular structure, and the weight ratio of the carbon nanotubes to the dispersant is 100:25 to 500.

[0074] In step (1), carbon nanotubes, a dispersant, and a dispersion medium are mixed to produce a mixture.

[0075] The manufacturing step of the mixture can be carried out under temperature conditions in which the physical properties of the mixture, including its viscosity, do not change due to the evaporation of the dispersion medium. For example, it can be carried out at a temperature of 50°C or lower, more specifically, between 5°C and 50°C.

[0076] In step (2), the mixture is dispersed to produce a carbon nanotube dispersion.

[0077] The dispersion can be carried out by milling methods such as a ball mill, bead mill, disc mill, or basket mill, or a high-pressure homogenizer, and more specifically, by milling methods using a disc mill or a high-pressure homogenizer.

[0078] During milling with the bead mill described above, the bead size can be appropriately determined according to the type and amount of carbon nanotubes and the type of dispersant. Specifically, the diameter of the bead can be 0.1 mm to 5 mm, more specifically 0.5 mm to 4 mm. The bead milling process can be carried out at a speed of 1,000 rpm to 15,000 rpm, more specifically 2,000 rpm to 12,000 rpm. The dispersion process can be carried out according to the degree of dispersion of the carbon nanotube dispersion, specifically 30 minutes to 120 minutes, more specifically 60 minutes to 90 minutes.

[0079] Milling by the high-pressure homogenizer is performed, for example, by pressurizing the mixture with the plunger pump of the high-pressure homogenizer and pushing it out through the gap of the homogenization valve, using forces such as cavitation, shear, impact, and explosion as it passes through the gap. The pressure of the high-pressure homogenizer can be 5,000 psi to 40,000 psi, more specifically 10,000 psi to 30,000 psi, and more specifically 14,000 psi to 25,000 psi. The dispersion process by the high-pressure homogenizer can be performed 1 to 15 times, more specifically 2 to 10 times, and more specifically 3 to 7 times.

[0080] Electrode slurry composition The present invention also provides an electrode slurry composition for a lithium secondary battery containing the carbon nanotube dispersion liquid and an electrode active material.

[0081] The electrode slurry composition for a lithium secondary battery can be a positive electrode slurry composition or a negative electrode slurry composition, and specifically can be a negative electrode slurry composition.

[0082] The electrode slurry composition for a lithium secondary battery can 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, if necessary, a solvent and / or other additives.

[0083] As the positive electrode active material, well-known positive electrode active materials in the art can be used without limitation. For example, lithium cobalt-based oxides, lithium nickel-based oxides, lithium manganese-based oxides, lithium iron phosphate, 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 LiNi a Mn b Co c O2 (where 0 < a, b, c < 1) and the like can be used, but are not limited thereto.

[0084] As the negative electrode active material, natural graphite, artificial graphite, carbonaceous materials; lithium-containing titanium composite oxides (LTO), Si, Sn, Li, Zn, Mg, Cd, Ce, Ni, or metals (Me) such as Fe; alloys composed of the metals (Me); oxides (MeO x ); and one or more negative electrode active materials selected from the group consisting of composites of the metals (Me) and carbon. The negative electrode active material can be contained in an amount of 60 to 98% by weight, more preferably 70 to 98% by weight, based on the total weight of the solids other than the solvent in the negative electrode slurry.

[0085] The aforementioned binder is a component that helps in the bonding of the active material to conductive materials and to the current collector, and is usually added in an amount of 1 to 30% by weight relative to the total weight of the mixture containing the electrode active material. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-dientelpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluororubber, and various copolymerizers.

[0086] The solvent may be an organic solvent such as N-methylpyrrolidone (NMP), dimethylformamide (DMF), acetone, or dimethylacetamide, or water. These solvents can be used individually or in combination of two or more. The amount of solvent used should be sufficient to dissolve and disperse the electrode active material, binder, and conductive material, taking into consideration the slurry coating thickness and production yield.

[0087] The viscosity modifier can be carboxymethylcellulose or polyacrylic acid, and by adding it, the viscosity of the electrode slurry can be adjusted to facilitate the manufacturing of the electrode slurry and the coating process on the electrode current collector.

[0088] The aforementioned filler is used selectively as a component to suppress electrode expansion, does not cause chemical changes in the battery, and is not particularly limited as long as it is a fibrous material; for example, olefin polymers such as polyethylene and polypropylene; and fibrous materials such as glass fibers and carbon fibers can be used.

[0089] If the electrode slurry composition is a composition for a positive electrode slurry to form 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 another support, and the resulting film obtained by peeling it off the support can be laminated onto the positive electrode current collector.

[0090] The thickness of the positive electrode active material layer formed by the positive electrode slurry may vary depending on the loading amount and loading speed for applying the positive electrode slurry.

[0091] The positive electrode current collector generally has a thickness of 3 μm to 500 μm. Such a positive electrode current collector is not particularly limited as long as it does not cause chemical changes in the battery and has high conductivity. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel with surface treatment using carbon, nickel, titanium, silver, etc. can be used. Furthermore, fine irregularities can be formed on the surface of the positive electrode current collector to strengthen the bonding force of the positive electrode active material, and it can be used in various forms such as film, sheet, foil, mesh, porous material, foam, and nonwoven fabric.

[0092] If 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 another support, and the resulting film, obtained by peeling it off the support, can be laminated onto the negative electrode current collector.

[0093] The thickness of the negative electrode active material layer formed by the negative electrode slurry may vary depending on the loading amount and loading speed for applying the negative electrode slurry.

[0094] The negative electrode current collector generally has a thickness of 3 μm to 500 μm. Such a negative electrode current collector is not particularly limited as long as it does not cause chemical changes in the battery and has high conductivity. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel with surface treatment using carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloys can be used. In addition, similar to the negative electrode current collector, fine irregularities can be formed on the surface to strengthen the bonding force of the negative electrode active material, and it can be used in various forms such as film, sheet, foil, mesh, porous material, foam, and nonwoven fabric.

[0095] Lithium-ion rechargeable battery A lithium secondary battery includes a positive electrode, a negative electrode, a separator placed between the positive and negative electrodes, and an electrolyte. Since the positive and negative electrodes are the same as described above, a detailed explanation is omitted.

[0096] The separator separates the negative and positive electrodes and provides a passage for lithium ions to move. It can be used without particular limitations as long as it is a separator typically used in lithium secondary batteries. Particularly preferred is one that exhibits low resistance to ion movement in the electrolyte and has excellent electrolyte moisture retention capacity. Specifically, porous polymer films, such as polyolefin polymers like ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or laminated structures of two or more layers thereof, can be used. Alternatively, ordinary porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fibers or polyethylene terephthalate fibers, can also be used. Furthermore, coated separators containing ceramic components or polymeric substances can be used to ensure heat resistance or mechanical strength, and can be selectively used in single-layer or multi-layer structures.

[0097] The electrolyte mentioned above includes, but is not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the manufacture of lithium secondary batteries. Specifically, the electrolyte may contain an organic solvent and a lithium salt.

[0098] The organic solvent can be used without particular limitations as long as it serves as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the organic solvents include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (propylene Carbonate solvents such as carbonate (PC); alcoholic 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, and may include a double-bonded aromatic ring or ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes can be used. Among these, carbonate solvents are preferred, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate) having high ionic conductivity and high dielectric constant that can improve the charge and discharge performance of the battery, and a low-viscosity linear carbonate compound (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) is more preferred. In this case, mixing the cyclic carbonate and linear carbonate in a volume ratio of about 1:1 to about 1:9 can result in excellent performance of the electrolyte.

[0099] The lithium salt can be used without particular limitations as long as it is a compound that can provide lithium ions for use in lithium secondary batteries. Specifically, the lithium salt can be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2. The lithium salt is preferably used within a concentration range of 0.1M to 2.0M. When the concentration of the lithium salt falls within this range, the electrolyte has appropriate conductivity and viscosity, exhibiting excellent electrolyte performance and allowing lithium ions to move effectively.

[0100] In addition to the components of the electrolyte, the electrolyte may also contain one or more additives, such as haloalkylene carbonate compounds like difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexaphosphate triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, for purposes such as improving battery life characteristics, suppressing battery capacity reduction, and improving battery discharge capacity. In this case, the additive may be present in an amount of 0.1% to 5% by weight relative to the total weight of the electrolyte.

[0101] A lithium secondary battery containing an electrode manufactured using the carbon nanotube dispersion according to the present invention, specifically a lithium secondary battery containing a negative electrode manufactured using the carbon nanotube dispersion, has uniformly dispersed carbon nanotubes within the negative electrode. Compared to conventional batteries containing conductive materials such as carbon black, the amount of such material can be reduced, and excellent discharge capacity and output characteristics can be stably demonstrated. As a result, it can be usefully used in portable devices such as mobile phones, notebook computers, and digital cameras, as well as in the field of electric vehicles such as hybrid electric vehicles (HEVs).

[0102] Accordingly, according to another embodiment of the present invention, a lithium secondary battery, a battery module including the lithium secondary battery as a unit cell, and a battery pack including the same can be provided.

[0103] The aforementioned battery module or battery pack can be used as a power source for one or more medium-to-large devices, including power tools; electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); or power storage systems.

[0104] The present invention will be described in more detail below with reference to examples. However, the following examples are for illustrative purposes only and do not limit the scope of the present invention to these examples alone.

[0105] Examples Example 1 A 300g mixture was prepared by mixing 0.72 wt% polyvinylpyrrolidone (PVP K15, manufactured by Zhangzhou Huafu Chemical) and 0.18 wt% sodium lignin sulfonate (manufactured by Borregaard) with water as the dispersion medium. After installing the impeller and container in a dissolver (VMA-Getzmann, Dispermat-CA), the mixture was rotated at 400 rpm for 10 minutes to mix the dispersant and dispersion medium.

[0106] Specific surface area 380m 2 3% by weight of multi-walled carbon nanotubes (MWCNT, BT2001M, manufactured by LG Chem) were added and dispersed at 10,000 rpm for 60 minutes.

[0107] The resulting material was processed three times at a pressure of 20,000 psi using a high-pressure disperser (PICOMAX, Micronox) to produce a carbon nanotube dispersion.

[0108] Examples 2-8 A carbon nanotube dispersion was prepared in the same manner as in Example 1, except that the content of polyvinylpyrrolidone and sodium lignin sulfonate was varied as shown in Table 1 below.

[0109] Example 9 A carbon nanotube dispersion was prepared in the same manner as in Example 1, except that polyethyleneimine (Sigma-Aldrich) was used in the quantities listed in Table 1 below, instead of polyvinylpyrrolidone.

[0110] Examples 10 and 11 A carbon nanotube dispersion was prepared in the same manner as in Example 1, except that calcium lignin sulfonate (Borregaard) was used in the quantities listed in Table 1 below, instead of sodium lignin sulfonate.

[0111] Comparative Example 1 A carbon nanotube dispersion was prepared in the same manner as in Example 1, except that sodium lignin sulfonate was not used and the polyvinylpyrrolidone content was changed to 1.35%.

[0112] Comparative Example 2 A carbon nanotube dispersion was prepared using the same method as in Example 1, except that polyvinylpyrrolidone was not used and the sodium lignin sulfonate content was changed to 1.35%.

[0113] Comparative Examples 3-7 A carbon nanotube dispersion was prepared using the same method as in Example 1, except that polyphenols (Tannic acid, Sigma-Aldrich) were used instead of sodium lignin sulfonate, and their content was varied as shown in Table 1 below.

[0114] Comparative Examples 8 and 9 A carbon nanotube dispersion was prepared in the same manner as in Example 1, except that the content of polyvinylpyrrolidone and sodium lignin sulfonate was varied as shown in Table 1 below.

[0115] Comparative Examples 10 and 11 A carbon nanotube dispersion was prepared using the same method as in Example 1, except that polyethyleneimine was used as the first dispersant and polyphenol as the second dispersant, with the content of each varying as shown in Table 1 below.

[0116] Comparative Examples 12 and 13 A carbon nanotube dispersion was prepared using the same method as in Example 1, except that polyvinylpyrrolidone was used as the first dispersant and sodium dodecylbenzenesulfonate (Sigma-Aldrich) was used as the second dispersant, with the content of each varying as shown in Table 1 below.

[0117] Comparative Example 14 A carbon nanotube dispersion was prepared in the same manner as in Example 1, except that the content of polyvinylpyrrolidone and sodium lignin sulfonate was varied as shown in Table 1 below.

[0118] [Table 1A]

[0119] [Table 1B]

[0120] [Table 1C]

[0121] [Table 1D]

[0122] Experimental example The initial viscosity of the carbon nanotube dispersions produced in the above examples and comparative examples was measured after dispersion, and the viscosity was measured again after leaving them at 25°C for one week. The results are shown in Table 2 below.

[0123] Viscosity was measured using a viscometer (viscometer TV-25, manufactured by TOKI Corporation) at 25°C and Rotor 1 at 1 rpm.

[0124] [Table 2A]

[0125] [Table 2B]

[0126] As can be seen from Table 2 above, in Examples 1 to 11, the viscosity of the carbon nanotube dispersions was maintained even after being left at 25°C for one week, and even when viscosity increased, it showed only a very low rate of increase. Comparative Examples 1 and 2 were carbon nanotube dispersions using only PVP and sodium lignin sulfonate, respectively. Due to their low dispersibility, their initial viscosity after dispersion was high, and even after two weeks, they showed a significantly higher viscosity increase rate compared to Examples 1 to 8.

[0127] Furthermore, in Comparative Examples 3 to 7, a first dispersant and a second dispersant were used, similar to the examples. However, instead of using a compound containing sulfone groups, hydroxyl groups, and aromatic rings as the second dispersant, a polyphenol containing only hydroxyl groups and aromatic rings was used. When the amount of dispersant used relative to carbon nanotubes was increased, the initial viscosity after dispersion could be reduced, but the viscosity increase rate after two weeks actually increased. When the amount of dispersant used relative to carbon nanotubes exceeded 1:0.6 and increased to 1:0.7 and 1:0.9, the viscosity increase rate after two weeks decreased, but it was still significantly higher than in Examples 1 to 8.

[0128] Comparative Example 8 is an example where a small amount of dispersant was used relative to the carbon nanotubes. Although the initial viscosity after dispersion was low, the viscosity increase rate after two weeks was also low. This confirmed that an appropriate amount of dispersant must be used relative to the carbon nanotubes in order to suppress the viscosity increase rate.

[0129] Comparative Example 9 was an example where the first and second dispersants were used in a 1:1 weight ratio. The relative amount of the second dispersant used was large, resulting in a significant increase in both the initial viscosity after dispersion and the viscosity increase rate after two weeks. Comparative Example 14, conversely to Comparative Example 9, was an example where the first and second dispersants were used in a 1:0.05 weight ratio. The relative amount of the second dispersant used was too small, resulting in a very high initial viscosity and a high viscosity increase rate. This confirmed that it is necessary to maintain an appropriate content ratio when using the first and second dispersants.

[0130] Comparative Examples 10 and 11 used polyethyleneimine, which is used in the examples of the present invention, as the first dispersant, but used a polyphenol without a sulfone group as the second dispersant. Not only was the initial viscosity higher than in the examples, but the viscosity increase rate after two weeks was also significantly higher. Comparative Examples 12 and 13 also used polyvinylpyrrolidone, which is used in the examples of the present invention, as the first dispersant, but used sodium dodecylbenzenesulfonate, which does not have a hydroxyl group, as the second dispersant. These also showed a higher initial viscosity than in the examples, a very high viscosity increase rate after two weeks, or the phenomenon of phase separation. From this, it was confirmed that when the second dispersant used in combination with the first dispersant of the present invention contains a sulfone group, a hydroxyl group, and an aromatic ring, it can have the effect of lowering the initial viscosity and improving viscosity stability.

Claims

1. A carbon nanotube dispersion comprising carbon nanotubes, a dispersant, and a dispersion medium, The specific surface area (BET) of the carbon nanotube is 800 m². ２ Less than / g, The dispersion contains a first dispersant and a second dispersant in a weight ratio of 100:10 to 90. The first dispersant is a compound containing an N atom, and the second dispersant is a compound containing a sulfone group, a hydroxyl group, and an aromatic ring. A carbon nanotube dispersion in which the weight ratio of carbon nanotubes to dispersant is 100:25 to 500.

2. The specific surface area (BET) of the carbon nanotube is 200 m². ２ / g or more 800m ２ A carbon nanotube dispersion according to claim 1, wherein the amount is less than / g.

3. The carbon nanotube dispersion according to claim 1, wherein the carbon nanotube is a multi-walled carbon nanotube.

4. The carbon nanotube dispersion according to claim 1, wherein the carbon nanotube is contained in an amount of 0.1 to 7 parts by weight per 100 parts by weight of the carbon nanotube dispersion.

5. The first dispersant is polyvinylpyrrolidone, polyacrylate hydrazide, poly-N-vinyl-5-methoxazolidon, N-alkyl polyimine, N-acetyl polyimine, polyacrylamide, poly-L-lysine hydrobromide, benzyl-dodecyl-dimethylammonium chloride The carbon nanotube dispersion according to claim 1, comprising one or more selected from the group consisting of chloride and polyethyleneimine.

6. The carbon nanotube dispersion according to claim 1, wherein the second dispersant is a lignin sulfonate compound.

7. The carbon nanotube dispersion according to claim 1, wherein the second dispersant is sodium lignin sulfonate, calcium lignin sulfonate, or a mixture thereof.

8. The carbon nanotube dispersion according to claim 1, wherein the dispersant comprises a first dispersant and a second dispersant in a weight ratio of 100:15 to 75.

9. The carbon nanotube dispersion according to claim 1, wherein the weight ratio of the carbon nanotubes and the dispersant is 100:25 to 150.

10. The carbon nanotube dispersion according to claim 1, 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-based solvents.

11. The carbon nanotube dispersion according to claim 1, wherein the viscosity of the carbon nanotube dispersion is 10 cps or more and 1,000 cps or less.

12. An electrode slurry composition for lithium secondary batteries comprising a carbon nanotube dispersion and an electrode active material as described in claim 1.

13. (1) A step of mixing carbon nanotubes, a dispersant and a dispersion medium to produce a mixture, (2) A method for producing a carbon nanotube dispersion, comprising the step of dispersing the mixture, The aforementioned dispersant contains a first dispersant and a second dispersant in a weight ratio of 100:10 to 90. The first dispersant is a compound containing an N atom, and the second dispersant is a compound containing a sulfone group, a hydroxyl group, and an aromatic ring in its molecular structure. A method for producing a carbon nanotube dispersion according to any one of claims 1 to 12, wherein the weight ratio of the carbon nanotube and the dispersant is 100:50 to 500.

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