Carbon nanotube dispersion and its manufacturing method

Abstract

The present invention relates to a carbon nanotube dispersion liquid and a method for producing the same, which comprises carbon nanotubes, a mixture of a first dispersant containing nitrogen atoms, a second dispersant and cations, and a solvent, wherein the second dispersant contains at least one hydroxy group and at least one carboxy group in an aromatic ring, and the cations include one or more selected from the group consisting of alkali metal ions, alkaline earth metal ions, aluminum ions, transition metal ions, ammonium ions, and sulfonium ions.

Description

[Technical Field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2023-0080140, filed June 22, 2023, and Korean Patent Application No. 10-2024-0077176, filed June 13, 2024, and all contents disclosed in the documents of the relevant Korean patent applications are incorporated herein by reference.

[0002] The present invention relates to a carbon nanotube dispersion and a method for producing the same. [Background technology]

[0003] As technological development and demand for mobile devices increase, 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, active research is being conducted on methods for manufacturing electrodes for such high-capacity lithium secondary batteries that have higher energy density per unit volume by improving electrode density.

[0004] Generally, 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. During the molding process, the particles may deform and the spaces between the particles may decrease, which may reduce the permeability of the electrolyte.

[0005] To address these issues, conductive materials with excellent electrical conductivity and strength are used in the manufacture of electrodes. These conductive materials are located between the electrode active materials, maintaining micropores between the active material particles even during the molding process, allowing the electrolyte to easily penetrate. They also have excellent electrical conductivity and can reduce the resistance within the electrode. Among these conductive materials, carbon nanotubes, a fibrous carbon-based conductive material, are increasingly being used, as they can further reduce electrode resistance by forming electrical conductive paths 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, due to their high specific surface area, carbon nanotubes have the problem of poor dispersibility and aggregation due to the strong van der Waals forces between them.

[0007] To solve this problem, a method of dispersing carbon nanotubes in a dispersion medium through a mechanical dispersion process such as ultrasonic treatment has been proposed. However, the mechanical dispersion process has problems such as the carbon nanotubes agglomerating immediately after the ultrasonic treatment is stopped or re-agglomerating over time after dispersion.

[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, has low viscosity, and is inhibited from increasing in viscosity over time. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] China Patent Publication No. 110128784 (August 16, 2019) Summary of the Invention [Problem to be solved by the invention]

[0010] The object of the present invention is to provide a carbon nanotube dispersion comprising carbon nanotubes, a first dispersant containing nitrogen atoms, a mixture of a second dispersant and cations, and a solvent, wherein the second dispersant contains at least one hydroxy group and at least one carboxy group in an aromatic ring, and the cations include one or more selected from the group consisting of alkali metal ions, alkaline earth metal ions, aluminum ions, transition metal ions, ammonium ions, and sulfonium ions, and which has excellent dispersibility, low viscosity of the dispersion, low particle size of the dispersed particles, and little change in viscosity over time.

[0011] Another object of the present invention is to provide an electrode slurry composition for a lithium secondary battery, which contains the carbon nanotube dispersion.

[0012] It is still another object of the present invention to provide a method for producing the carbon nanotube dispersion liquid. [Means for solving the problem]

[0013] One embodiment of the present invention provides a carbon nanotube dispersion liquid comprising carbon nanotubes, a first dispersant containing nitrogen atoms, a mixture of a second dispersant and cations, and a solvent, wherein the second dispersant contains at least one hydroxy group and at least one carboxy group in an aromatic ring, and the cations include one or more selected from the group consisting of alkali metal ions, alkaline earth metal ions, aluminum ions, transition metal ions, ammonium ions, and sulfonium ions.

[0014] The second dispersant may have a molecular structure that does not contain two or more aromatic rings.

[0015] The second dispersant may include a compound represented by the following Formula 1:

[0016] [ka]

[0017] In the above Chemical Formula 1, R1 to R5 are the same or different and each independently represent hydrogen, deuterium, a halogen, a cyano group, a hydroxy group, a carboxy group, a substituted or unsubstituted C1 to C10 alkyl group, a substituted or unsubstituted C2 to C10 alkenyl group, a substituted or unsubstituted C2 to C10 alkynyl group, a substituted or unsubstituted C1 to C10 alkoxy group, a substituted or unsubstituted C3 to C10 cycloalkyl group, or a substituted or unsubstituted C2 to C10 heterocycloalkyl group, and at least one of R1 to R5 is a hydroxy group, R6 is a carboxy group; L is a single bond; a substituted or unsubstituted C1 to C10 alkylene group; a substituted or unsubstituted C2 to C10 alkenylene group; or a substituted or unsubstituted C2 to C10 alkynylene group.

[0018] The second dispersing agent may be at least one selected from the group consisting of gallic acid, protocatechuic acid, syringic acid, ferulic acid, vanillic acid, caffeic acid, p-coumaric acid, salicylic acid, 2,4-dihydroxybenzoic acid, homogentisic acid, and sinapinic acid.

[0019] The BET specific surface area of ​​the carbon nanotubes is 800 to 2,000 m 2 / g.

[0020] The carbon nanotube dispersion may include 25 to 450 parts by weight of the first dispersant based on 100 parts by weight of the carbon nanotubes.

[0021] The carbon nanotube dispersion may include 5 to 250 parts by weight of the mixture of the second dispersant and the cations based on 100 parts by weight of the carbon nanotubes.

[0022] The cation may be included in an amount of 2 to 20 parts by weight based on 100 parts by weight of the second dispersant.

[0023] The first dispersant may be at least one selected from the group consisting of polyvinylpyrrolidone, polyacrylic acid hydrazide, poly-N-vinyl-5-methoxazolidone, N-alkyl polyimine, N-acetyl polyimine, polyacrylamide, poly-L-lysine hydrobromide, benzyl-dodecyl-dimethylammonium chloride, and polyethyleneimine.

[0024] The first dispersant and the mixture of the second dispersant and cation may be contained in a weight ratio of 100:10 to 100:90.

[0025] The carbon nanotube dispersion may have an initial viscosity of 1 to 10 Pa·s measured at 25° C. and 1 rpm.

[0026] The carbon nanotube dispersion may have a viscosity increase rate represented by the following formula (1) of 15% or less.

[0027] [Formula 1] Viscosity increase rate (%) = {(viscosity measured after leaving at 25°C for 1 week - initial viscosity) / initial viscosity} x 100

[0028] Another embodiment of the present invention provides a method for producing a carbon nanotube dispersion, comprising: (1) mixing carbon nanotubes, a first dispersant containing nitrogen atoms, a second dispersant containing at least one hydroxy group and at least one carboxy group in an aromatic ring, a cation precursor, and a solvent to produce a primary dispersion of carbon nanotubes; and (2) dispersing the primary dispersion of carbon nanotubes to produce a secondary dispersion of carbon nanotubes.

[0029] The cation precursor may comprise a hydroxide of one or more cations selected from the group consisting of alkali metal ions, alkaline earth metal ions, aluminum ions, transition metal ions, ammonium ions, and sulfonium ions.

[0030] Another embodiment of the present invention provides an electrode slurry composition for a lithium secondary battery, comprising the carbon nanotube dispersion and an electrode active material. [Effects of the Invention]

[0031] The carbon nanotube dispersion according to the present invention uses a first dispersant containing a nitrogen atom, a second dispersant containing at least one hydroxyl group and at least one carboxyl group in an aromatic ring, and a mixture of one or more cations selected from the group consisting of alkali metal ions, alkaline earth metal ions, aluminum ions, transition metal ions, ammonium ions, and sulfonium ions. This allows the dispersion to exhibit a relatively low viscosity with little change over time despite the use of carbon nanotubes with a large specific surface area, and the carbon nanotubes are uniformly and effectively dispersed, resulting in a small particle size of the dispersed particles.

[0032] Furthermore, when the carbon nanotube dispersion of the present invention is used in an electrode slurry composition, an electrode and a secondary battery having excellent capacity characteristics and cycle characteristics can be manufactured. BEST MODE FOR CARRYING OUT THE INVENTION

[0033] Hereinafter, embodiments of the present invention will be described in detail. Prior to this, the terms and words used in the present specification and claims should not be interpreted in a limited manner based on their ordinary or dictionary meanings, but should be interpreted in a meaning and concept that corresponds to the technical idea of ​​the present invention, based on the principle that the inventor can appropriately define the concept of terms in order to best describe his or her invention. Therefore, it should be understood that the configurations described in the embodiments described in this specification are merely the most preferred embodiments of the present invention and do not represent the entire technical idea of ​​the present invention, and therefore various equivalents and modifications that can replace them may exist at the time of filing this application.

[0034] Throughout this specification, when a part "comprises" a certain element, this does not mean that it excludes other elements, but that it may further include other elements, unless otherwise specified.

[0035] Throughout this specification, "%" means % by weight unless expressly indicated otherwise.

[0036] As used herein, the average particle size "D 50 " means the particle size corresponding to 50% of the cumulative volume. 50 can be measured, for example, by using a laser diffraction method. The laser diffraction method generally enables measurement of particle sizes from the submicron range to several mm, and provides results with high reproducibility and high resolution.

[0037] In this specification, the "specific surface area" is measured by the BET method (Brunauer-Emmett-Teller analysis), and specifically, is calculated from the amount of nitrogen gas adsorbed at liquid nitrogen temperature (77K) using a BELSORP-mino II manufactured by BEL Japan.

[0038] As used herein, the term "precursor" may refer to a substance in a precursor stage to become a specific substance through a reaction. For example, a "cation precursor" refers to a substance that can be ionized in an aqueous solvent or the like to provide a "cation."

[0039] Carbon nanotube dispersion The carbon nanotube dispersion according to the present invention comprises carbon nanotubes, a first dispersant containing nitrogen atoms, a second dispersant containing at least one hydroxy group and at least one carboxy group in an aromatic ring, and a mixture of one or more cations selected from the group consisting of alkali metal ions, alkaline earth metal ions, aluminum ions, transition metal ions, ammonium ions, and sulfonium ions, and a solvent. Each component of the carbon nanotube dispersion according to 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 aggregation of carbon nanotube units in a bundle type, either entirely or partially. The carbon nanotube units have a cylindrical shape with a graphite sheet of nano-sized diameter, and are separated by a sp 2 Carbon nanotubes have a bond structure. Depending on the angle and structure of the graphite plane, they can exhibit conductive or semiconductive properties. Carbon nanotubes are classified into single-walled carbon nanotubes (SWCNT), double-walled carbon nanotubes (DWCNT), and multi-walled carbon nanotubes (MWCNT) depending on the number of bonds forming the wall.

[0041] The term "bundle type" as used herein, unless otherwise specified, refers to a secondary shape in the form of a bundle or rope in which multiple carbon nanotube units are aligned with their longitudinal axes in substantially the same direction, or are twisted or tangled after being aligned. The term "non-bundle type or entangled type" refers to a shape in which the carbon nanotube units are tangled rather than in 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, they are unable to form proper conductive paths, which means that more conductive material is needed, reducing the amount of active material, which can lead to a decline in electrode performance. This has made it difficult to commercialize carbon nanotubes as conductive materials.

[0043] The carbon nanotube dispersion according to the present invention comprises a mixture of a first dispersant containing a nitrogen atom, a second dispersant containing at least one hydroxy group and at least one carboxy group in an aromatic ring, and one or more cations selected from the group consisting of alkali metal ions, alkaline earth metal ions, aluminum ions, transition metal ions, ammonium ions, and sulfonium ions, thereby significantly reducing the initial viscosity of the carbon nanotube dispersion and suppressing viscosity changes over time. When applied to electrode slurries for lithium secondary batteries, the carbon nanotube dispersion can exhibit high conductivity due to the high conductivity of the carbon nanotubes.

[0044] Therefore, when the carbon nanotube dispersion according to the present invention is applied to the preparation of electrode slurry, the carbon nanotubes are uniformly positioned among the active materials, and the microspaces 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, so that 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, but is not limited to, one or more of single-walled, double-walled, and multi-walled carbon nanotubes as the carbon nanotubes. The single-walled or double-walled carbon nanotubes have a higher specific surface area than multi-walled carbon nanotubes, and therefore are more effective in improving cycle characteristics when used in secondary batteries.

[0046] On the other hand, the carbon nanotubes may have an average diameter of, for example, 0.6 to 10 nm, preferably 0.8 to 5 nm, and more preferably 0.8 to 3 nm, or may be 0.8 nm or more, 0.9 nm or more, 1.0 nm or more, 1.1 nm or more, 1.2 nm or more, 1.3 nm or more, 1.4 nm or more, 1.5 nm or more, 1.6 nm or more, 1.7 nm or more, 1.8 nm or more, or 1.9 nm or more, or may be 3.0 nm or less, 2.9 nm or less, 2.8 nm or less, 2.7 nm or less, 2.6 nm or less, 2.5 nm or less, 2.4 nm or less, 2.3 nm or less, 2.2 nm or less, 2.1 nm or less, or 2.0 nm or less.

[0047] The carbon nanotubes may have an average length of 0.5 to 20 μm, preferably 1 to 20 μm, and more preferably 5 to 20 μm, and may be 5 μm or more, 7 μm or more, 9 μm or more, 11 μm or more, or 13 μm or more, or 20 μm or less, 18 μm or less, 16 μm or less, or 14 μm or less. When the average diameter and average length of the carbon nanotubes satisfy the above ranges, it is effective in reducing the viscosity of the dispersion and improving storage stability, and excellent cycle characteristics can be achieved when used as an electrode active material. The average diameter of the carbon nanotubes can be measured by photographing carbon nanotube powder with a scanning electron microscope, and the average length of the carbon nanotubes can be measured by photographing the carbon nanotube dispersion with a scanning electron microscope.

[0048] The carbon nanotubes may be included in an amount of 0.1 to 5 wt %, preferably 0.1 to 3 wt %, and more preferably 0.5 to 2 wt %, based on the total weight of the carbon nanotube dispersion, and may be included in an amount of 0.1 wt % or more, 0.3 wt % or more, 0.5 wt % or more, 0.7 wt % or more, 0.9 wt % or more, 1.0 wt %, 1.1 wt % or more, or 1.3 wt % or less, 2 wt % or less, 1.8 wt % or less, 1.6 wt % or less, or 1.4 wt % or less. When the carbon nanotube content satisfies this range, the viscosity of the dispersion and the cycle characteristics of the secondary battery are improved effectively.

[0049] The BET specific surface area of ​​the carbon nanotubes is 800 m 2 / g or more, preferably 800m 2 / g~5,000m 2 / g, more preferably 800m 2 / g~2,000m 2 / g, and 800m 2 / g or more, 900m 2 / g or more, 1,000m 2 / g or more, 1,100m 2 / g or more, 1,160m 2 / g or more, 1,200m 2 / g or more, 1,300m 2 / g or more or 1,400m 2 / g or more, and 2 / g or less, 1,900m 2 / g or less, 1,800m 2 / g or less, 1,700m 2 / g or less, 1,600m 2 / g or less or 1,500m 2 / g or less. When carbon nanotubes having a high BET specific surface area are used, a conductive network can be formed between the electrode active materials, and the cycle characteristics of the secondary battery can be improved.

[0050] A carbon nanotube dispersion according to an embodiment of the present invention can have a relatively high carbon nanotube content because carbon nanotubes can be uniformly dispersed. When a carbon nanotube dispersion with a low carbon nanotube content is used to prepare an electrode slurry, the solid content of the prepared electrode slurry decreases, resulting in a thick thickness (wet thickness) before coating and drying the electrode slurry. The rolling ratio measured after subsequent drying and rolling processes increases, resulting in a large difference in the thickness ratio before and after drying and rolling. If the rolling ratio increases, the cathode active material and other components within the slurry may be damaged during the process, resulting in a problem of reduced battery performance.

[0051] (2) A mixture of a first dispersant, a second dispersant, and a cation The carbon nanotube dispersion according to the present invention comprises a first dispersant containing a nitrogen atom to improve the dispersibility of the carbon nanotubes, a second dispersant containing at least one hydroxyl group and at least one carboxyl group in an aromatic ring, and a mixture of cations.

[0052] In the carbon nanotube dispersion, the mixture of the first dispersant containing the nitrogen atom, the second dispersant containing at least one hydroxyl group and at least one carboxyl group in the aromatic ring, and a cation acts as a dispersant to increase the dispersibility of the carbon nanotubes so that the carbon nanotubes are uniformly dispersed without agglomeration in the dispersion, and in particular exhibits the effect of suppressing changes in the viscosity of the carbon nanotube dispersion over time.

[0053] In the carbon nanotube dispersion according to an embodiment of the present invention, the first dispersant containing a nitrogen atom may be dissolved in an aqueous solvent, as described below, and may be, for example, one or more selected from the group consisting of polyvinylpyrrolidone, polyacrylic acid hydrazide, poly-N-vinyl-5-methoxazolidone, N-alkyl polyimine, N-acetyl polyimine, polyacrylamide, poly-L-lysine hydrobromide, benzyl-dodecyl-dimethylammonium chloride, and polyethyleneimine, and preferably, polyvinylpyrrolidone. The carbon nanotube dispersion according to an embodiment of the present invention includes the first dispersant containing a nitrogen atom, thereby improving the viscosity of the dispersion and suppressing the change in viscosity over time.

[0054] In one embodiment of the present invention, the carbon nanotube dispersion liquid may contain 25 to 450 parts by weight of the first dispersant based on 100 parts by weight of the carbon nanotubes, for example, 25 parts by weight or more, 30 parts by weight or more, 35 parts by weight or more, 40 parts by weight or more, 45 parts by weight or more, 50 parts by weight or more, 55 parts by weight or more, 60 parts by weight or more, 65 parts by weight or more, 70 parts by weight or more, 75 parts by weight or more, 80 parts by weight or more, 85 parts by weight or more, 90 parts by weight or more, 95 parts by weight or more, 100 parts by weight or more, 105 parts by weight or more 110 parts by weight or more, 112.5 parts by weight or more, 115 parts by weight or more, 120 parts by weight or more, 125 parts by weight or more, 127.5 parts by weight or more, or 130 parts by weight or more, and 450 parts by weight or less, 445 parts by weight or less, 440 parts by weight or less, 435 parts by weight Parts by weight or less, 430 parts by weight or less, 425 parts by weight or less, 420 parts by weight or less, 415 parts by weight or less, 410 parts by weight or less, 405 parts by weight or less, 400 parts by weight or less, 395 parts by weight or less, 390 parts by weight or less, 385 parts by weight or less, 380 parts by weight or less, 375 parts by weight or less Bottom, 370 parts by weight or less, 365 parts by weight or less, 360 parts by weight or less, 355 parts by weight or less, 350 parts by weight or less, 345 parts by weight or less, 340 parts by weight or less, 335 parts by weight or less, 330 parts by weight or less, 325 parts by weight or less, 320 parts by weight or less, 315 parts by weight or less, 310 parts by weight or less, 305 parts by weight or less, 300 parts by weight or less, 295 parts by weight or less, 290 parts by weight or less, 285 parts by weight or less, 280 parts by weight or less, 275 parts by weight or less, 270 parts by weight or less, 265 parts by weight or less, 260 parts by weight or less, 255 parts by weight or less, 250 parts by weight or less, 245 parts by weight or less, 240 parts by weight or less, 235 parts by weight or less, 230 parts by weight or less, 225 parts by weight or less, 220 parts by weight or less, 215 parts by weight or less, 210 parts by weight or less, 205 parts by weight or less, 200 parts by weight or less, 195 parts by weight or less, 190 parts by weight or less, 185 parts by weight or less, 180 parts by weight or less, 175 parts by weight or less, 170 parts by weight or less, 165 parts by weight or less, 160 parts by weight or less, 155 parts by weight or less, 150 parts by weight or less, 145 parts by weight or less, 140 parts by weight or less, or 135 parts by weight or less.

[0055] If the content of the first dispersant is less than 25 parts by weight based on 100 parts by weight of carbon nanotubes, the insufficient content of the dispersant results in an insufficient dispersion effect, resulting in a problem that the viscosity of the dispersion is not formed low and the viscosity increases over time. If the content of the first dispersant exceeds 450 parts by weight, the content of the first dispersant is too high, resulting in a problem that the aggregation of solids in the dispersion is promoted, resulting in a problem that the viscosity of the dispersion is formed high.

[0056] In addition, in order to solve the problem that the viscosity of the dispersion increases as the carbon nanotube content increases in a carbon nanotube dispersion containing only the first dispersant, the carbon nanotube dispersion according to one embodiment of the present invention contains a mixture of the first dispersant, a second dispersant containing at least one hydroxy group and at least one carboxy group in an aromatic ring, and one or more cations selected from the group consisting of alkali metal ions, alkaline earth metal ions, aluminum ions, transition metal ions, ammonium ions, and sulfonium ions. As a result, the carbon nanotube dispersion has better dispersibility than carbon nanotube dispersions that use only conventional dispersants, and the particles of the slurry composition are less likely to agglomerate, resulting in a lower settling rate.

[0057] In one embodiment of the present invention, the second dispersant may not contain two or more aromatic rings in its molecular structure.

[0058] Since the second dispersant, which contains at least one hydroxy group and at least one carboxy group in the aromatic ring, does not contain two or more aromatic rings in its molecular structure, the molecular weight of the second dispersant is relatively low, and the molecular size is small, so that the second dispersant can adsorb to the surface of the carbon nanotubes that the first dispersant containing the nitrogen atom could not wrap, thereby exhibiting a more effective dispersion effect.If the carbon nanotube dispersion does not contain the second dispersant of the present invention, the area on the surface of the carbon nanotubes that is not sufficiently wrapped by the dispersant may become large, and as a result, the carbon nanotubes may exhibit a stronger than appropriate level of bonding force between them, causing them to aggregate, resulting in a high viscosity of the dispersion.

[0059] Furthermore, if the second dispersant contains, for example, a phenolic compound structure containing two or more aromatic rings within its molecular structure, the molecules may form a linear, angular, or densely packed structure, which may be unfavorable for surface adsorption of carbon nanotubes, particularly single-walled carbon nanotubes, which have low direct impact. Furthermore, the π-π interactions formed by the intramolecular ring structure may be strong, which may deepen the aggregation of the dispersant. This may result in insufficient charge control by cations that form a mixture with the second dispersant, resulting in a high viscosity dispersion, which may increase significantly over time.

[0060] In order to effectively exhibit the above properties, the secondary dispersant may not have a molecular structure in which two or more independent aromatic rings are linked to each other by a linking group or a structure in which two or more aromatic rings are fused together.

[0061] In one embodiment of the present invention, the second dispersant may include a compound represented by the following Formula 1:

[0062] [ka]

[0063] In the above Chemical Formula 1, R1 to R5 are the same or different and each independently represent hydrogen, deuterium, a halogen, a cyano group, a hydroxy group, a carboxy group, a substituted or unsubstituted C1 to C10 alkyl group, a substituted or unsubstituted C2 to C10 alkenyl group, a substituted or unsubstituted C2 to C10 alkynyl group, a substituted or unsubstituted C1 to C10 alkoxy group, a substituted or unsubstituted C3 to C10 cycloalkyl group, or a substituted or unsubstituted C2 to C10 heterocycloalkyl group, and at least one of R1 to R5 is a hydroxy group, R6 is a carboxy group; L is a single bond; a substituted or unsubstituted C1 to C10 alkylene group; a substituted or unsubstituted C2 to C10 alkenylene group; or a substituted or unsubstituted C2 to C10 alkynylene group.

[0064] As represented by Chemical Formula 1, the second dispersant simultaneously contains at least one hydroxy group and one carboxy group in the aromatic ring, thereby appropriately balancing the π-π (π-π) interaction between the carbon nanotubes in the dispersion and the aromatic ring of the second dispersant, and the hydrogen bonding interaction between the nitrogen atom contained in the first dispersant and the hydroxy group and carboxy group of the second dispersant, thereby further improving the effect of reducing the viscosity of the carbon nanotube dispersion and suppressing the viscosity increase due to changes over time.

[0065] In Chemical Formula 1, R1 to R5 are the same or different and each independently represent hydrogen; deuterium; a hydroxy group; a carboxy group; a substituted or unsubstituted C1 to C5 alkyl group; a substituted or unsubstituted C2 to C5 alkenyl group; a substituted or unsubstituted C2 to C5 alkynyl group; a substituted or unsubstituted C1 to C5 alkoxy group; a substituted or unsubstituted C3 to C5 cycloalkyl group; or a substituted or unsubstituted C2 to C5 heterocycloalkyl group, and at least one of R1 to R5 may be a hydroxy group.

[0066] In the above Chemical Formula 1, R1 to R5 are the same or different and each independently represent hydrogen, deuterium, a hydroxy group, or a carboxy group, and at least one of R1 to R5 may be a hydroxy group.

[0067] In the above Chemical Formula 1, at least two of R1 to R5 may be hydroxy groups.

[0068] In the above Chemical Formula 1, at least three of R1 to R5 may be hydroxy groups.

[0069] In the above Chemical Formula 1, L may be a single bond; a substituted or unsubstituted C1 to C5 alkylene group; a substituted or unsubstituted C2 to C5 alkenylene group; or a substituted or unsubstituted C2 to C5 alkynylene group.

[0070] In the above Chemical Formula 1, L may be a single bond; a substituted or unsubstituted C1 to C5 alkylene group; or a substituted or unsubstituted C2 to C5 alkenylene group.

[0071] In one embodiment of the present invention, specific examples of the second dispersant may be one or more selected from the group consisting of gallic acid, protocatechuic acid, syringic acid, ferulic acid, vanillic acid, caffeic acid, p-coumaric acid, salicylic acid, 2,4-dihydroxybenzoic acid, homogentisic acid, and sinapinic acid, as shown in Table 1 below, but are not limited to the above types as long as the second dispersant contains at least one hydroxy group and at least one carboxy group in an aromatic ring and can enhance the dispersibility of carbon nanotubes.

[0072] [Table 1A]

[0073] [Table 1B]

[0074] In one embodiment of the present invention, the carbon nanotube dispersion may contain 5 to 250 parts by weight of the mixture of the second dispersant and cations, based on 100 parts by weight of the carbon nanotubes. For example, the amount may be 5 parts by weight or more, 10 parts by weight or more, 15 parts by weight or more, 20 parts by weight or more, 22.5 parts by weight or more, 25 parts by weight or more, 30 parts by weight or more, 35 parts by weight or more, 37.5 parts by weight or more, 40 parts by weight or more, 45 parts by weight or more, 50 parts by weight or more, 55 parts by weight or more, or 60 parts by weight or more, and may be 250 parts by weight or less, 245 parts by weight or less, 240 parts by weight or less, 235 parts by weight or less, 230 parts by weight or less, 225 parts by weight or less, or 220 parts by weight or less. , 215 parts by weight or less, 210 parts by weight or less, 205 parts by weight or less, 200 parts by weight or less, 195 parts by weight or less, 190 parts by weight or less, 185 parts by weight or less, 180 parts by weight or less, 175 parts by weight or less, 170 parts by weight or less, 165 parts by weight or less, 160 parts by weight or less, 155 parts by weight or less, 150 parts by weight or less, 145 parts by weight or less, 140 parts by weight or less, 135 parts by weight or less, 130 parts by weight or less, 125 parts by weight or less, 120 parts by weight or less, 115 parts by weight or less, 110 parts by weight or less, 105 parts by weight or less, 100 parts by weight or less, 95 parts by weight or less, 90 parts by weight or less, 85 parts by weight or less, 80 parts by weight or less, 75 parts by weight or less, 70 parts by weight or less, or 65 parts by weight or less.

[0075] If the content of the mixture of the second dispersant and cations is less than 5 parts by weight based on 100 parts by weight of carbon nanotubes, the mixture of the first dispersant and the second dispersant and cations cannot form sufficient hydrogen bonds, resulting in an ineffective dispersion effect. As a result, the viscosity of the dispersion may not be low and may increase over time. If the content of the mixture of the second dispersant and cations is more than 250 parts by weight, the content of the mixture of the second dispersant and cations is too high, which may cause aggregation between the solids in the dispersion and result in a high viscosity of the dispersion.

[0076] In one embodiment of the present invention, the mixture of the first dispersant, the second dispersant, and the cation in the carbon nanotube dispersion may be included in a weight ratio of 100:10 to 100:90. For example, the mixture of the first dispersant to the second dispersant and the cation may be 100:10 or more, 100:15 or more, 100:17.65 or more, 100:20 or more, 100:25 or more, 100:30 or more, 100:33.33 or more, or 100:35 or more. The mixture of the first dispersant to the second dispersant and the cation may be 100:90 or less, 100:85 or less, 100:80 or less, 100:75 or less, 100:70 or less, 100:65 or less, 100:60 or less, 100:55 or less, 100:50 or less, 100:45 or less, or 100:40 or less. When the content of the mixture of the first dispersant, the second dispersant, and the cation is contained in the carbon nanotube dispersion in the above weight ratio, the carbon nanotubes are uniformly dispersed in the carbon nanotube dispersion, and the viscosity can be maintained at a constant level over time along with low viscosity.

[0077] In one embodiment of the present invention, the cations contained in the second dispersant to form a mixture include at least one selected from the group consisting of alkali metal ions, alkaline earth metal ions, aluminum ions, transition metal ions, ammonium ions, and sulfonium ions. The cations are contained in the second dispersant and the carbon nanotube dispersion as a mixture, thereby carrying an anionic charge at the end of the dispersant, thereby increasing the surface charge, and the cations remain in the dispersion medium, thereby increasing the electrostatic repulsion between the carbon nanotubes, thereby inhibiting aggregation.

[0078] The ammonium ion may be an ammonium ion in which one, two, three or all four of the hydrogen atoms have been replaced by hydrogen or a C1-C5-alkyl group, either by the same or different radicals, or a tertiary aliphatic or heteroaliphatic ammonium ion, or a heterocyclic ammonium cation, such as, in each case, protonated pyridine, quinoline, cinoxaline, 1,2-dimethylimidazole, 1,3-dimethylimidazolium methylsulfate.

[0079] In one embodiment of the present invention, the cation may be included in an amount of 2 to 20 parts by weight relative to a total of 100 parts by weight of the second dispersant, for example, 2 parts by weight or more, 3 parts by weight or more, 3.5 parts by weight or more, 4 parts by weight or more, 5 parts by weight or more, 6 parts by weight or more, 7 parts by weight or more, 8 parts by weight or more, 9 parts by weight or more, or 10 parts by weight or more, or 20 parts by weight or less, 19 parts by weight or less, 18 parts by weight or less, 17 parts by weight or less, 16 parts by weight or less, 15 parts by weight or less, 14 parts by weight or less, 13 parts by weight or less, 12 parts by weight or less, or 11 parts by weight or less.

[0080] If the content of the cation is less than 2 parts by weight based on a total of 100 parts by weight of the second dispersant, the repulsive force between the carbon nanotubes is insufficient, causing aggregation and making it difficult to ensure low viscosity of the dispersion. Conversely, if the content exceeds 20 parts by weight, the surface charge of the carbon nanotubes becomes too high, leading to a level that destroys electrostatic stability, making the dispersion highly viscous, or the stability of the dispersion decreases and the viscosity increases over time.

[0081] (3) Solvent The solvent of the carbon nanotube dispersion liquid according to one embodiment of the present invention is a dispersant for dispersing the carbon nanotubes, the first dispersant, the second dispersant, and one or more cations selected from the group consisting of alkali metal ions, alkaline earth metal ions, aluminum ions, transition metal ions, ammonium ions, and sulfonium ions, and is used to disperse the powdered carbon nanotubes first and then supply them to the carbon nanotube dispersion liquid to prevent them from agglomerating when they are used immediately in preparing an electrode slurry composition.

[0082] The solvent can dissolve or disperse the carbon nanotubes, the first dispersant, the second dispersant, and one or more cations selected from the group consisting of alkali metal ions, alkaline earth metal ions, aluminum ions, transition metal ions, ammonium ions, and sulfonium ions to a certain level or more. The aqueous solvent may be, for example, water, and may be included in an amount that allows the electrode slurry composition to have an appropriate viscosity in consideration of the coatability of the electrode slurry composition to be prepared using the carbon nanotube dispersion.

[0083] In one embodiment of the carbon nanotube dispersion according to the present invention, the first dispersant, the second dispersant, and the cations uniformly disperse the carbon nanotubes in the solvent, thereby reducing the average particle size distribution of the dispersed particles contained in the dispersion, for example, the composite of the carbon nanotubes and each dispersant.

[0084] The average particle size distribution (D 50 ) may be, for example, 0.5 to 10 μm, 1 to 10 μm, 1 to 8 μm, or preferably 1 to 5 μm.

[0085] The carbon nanotube dispersion of the present invention containing the above-mentioned components has excellent dispersibility, a low viscosity of the dispersion, and a small degree of increase in viscosity over time.

[0086] The carbon nanotube dispersion may have an initial viscosity of 1 to 10 Pa s measured at 25° C. and 1 rpm using a viscometer (TOKISANGYO Co., Ltd., viscometer TV-25, Rotor Code 01), for example, 1 Pa s or more, 2 Pa s or more, 3 Pa s or more, 4 Pa ​​s or more, or 5 Pa s or more, or 10 Pa s or less, 9.6 Pa s or less, 9.3 Pa s or less, 9 Pa s or less, 8.8 Pa s or less, 8 Pa s or less, 7.7 Pa s or less, 7 Pa s or less, or 6 Pa s or less. When the carbon nanotube dispersion has an initial viscosity within this range, it can be used to more smoothly prepare an electrode slurry, and the electrode slurry containing the carbon nanotube dispersion can have an appropriate viscosity for forming an electrode.

[0087] Furthermore, when the carbon nanotube dispersion is left at 25°C for one week, the viscosity increase rate calculated by the following formula (1) may be 15% or less, specifically 15% or less, 14% or less, 13% or less, 12% or less, 11% or less, 10% or less, 9% or less, 8.9% or less, 8.3% or less, 8% or less, 7% or less, 6.8% or less, 6% or less, 5.4% or less, 5% or less, 4% or less, 3% or less, 2.6% or less, 2% or less, or 1% or less.

[0088] [Formula 1] Viscosity increase rate (%) = {(viscosity measured after leaving at 25°C for 1 week - initial viscosity) / initial viscosity} x 100 At this time, the viscosity after standing for one week and the initial viscosity were measured at 25°C and 1 rpm.

[0089] Method for producing carbon nanotube dispersion The method for producing a carbon nanotube dispersion will now be described. The method for producing a conductive material dispersion according to the present invention includes the steps of (1) preparing a primary dispersion of carbon nanotubes by mixing carbon nanotubes, a first dispersant containing nitrogen atoms, a second dispersant containing at least one hydroxyl group and at least one carboxyl group in an aromatic ring, a cation precursor, and a solvent; and (2) dispersing the primary dispersion of carbon nanotubes to prepare a secondary dispersion of carbon nanotubes.

[0090] In step (1), a primary dispersion of carbon nanotubes is prepared by mixing carbon nanotubes, a first dispersant containing nitrogen atoms, a second dispersant containing at least one hydroxyl group and at least one carboxyl group in an aromatic ring, a cation precursor, and a solvent. The step of preparing the primary dispersion of carbon nanotubes is carried out by a wetting process in which each component is uniformly mixed.

[0091] The mixing for preparing the primary dispersion of carbon nanotubes may be carried out using a conventional mixing method, specifically, a mixing device such as a pony mixer, a change-can mixer, a Hobert mixer, a pulley mixer, a butterfly mixer, a stone mill, a homogenizer, a bead mill, a ball mill, a basket mill, an attrition mill, a universal mixer, a clear mixer, or a TK mixer, and may include a mixing step at a rotation speed of 300 to 5,000 rpm for 30 minutes to 7 hours.

[0092] In addition, during mixing to prepare the primary dispersion of carbon nanotubes, a cavitation dispersion process may be performed to improve the mixability of the carbon nanotubes with the solvent or the dispersibility of the carbon nanotubes in the solvent. The cavitation dispersion process is a dispersion process that uses shock waves generated by the bursting of vacuum bubbles generated in water when high energy is applied to the liquid, and this process allows for dispersion of carbon nanotubes without damaging their properties. Specifically, the cavitation dispersion process may be performed using ultrasound, a jet mill, or shear dispersion.

[0093] In the method for producing a carbon nanotube dispersion according to one embodiment of the present invention, the cation precursor may include a hydroxide of one or more cations selected from the group consisting of alkali metal ions, alkaline earth metal ions, aluminum ions, transition metal ions, ammonium ions, and sulfonium ions.

[0094] The step of preparing the primary dispersion of carbon nanotubes 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 aqueous solvent, for example, at a temperature of 50°C or less, more specifically, 5°C to 50°C.

[0095] The carbon nanotubes, the first dispersant containing nitrogen atoms, the second dispersant containing at least one hydroxy group and at least one carboxy group in an aromatic ring, the cation precursor, and the solvent used in the method for producing the carbon nanotube dispersion are described above in detail, and therefore will not be described in detail below.

[0096] In step (2), the primary dispersion of carbon nanotubes is dispersed to prepare a secondary dispersion of carbon nanotubes.

[0097] The stirring step may be performed by a method such as a ball mill, a bead mill, a disc mill, a basket mill, or a high pressure homogenizer, and more specifically, may be performed by a milling method using a disc mill or a high pressure homogenizer.

[0098] The size of the beads used in the disc milling may be determined appropriately depending on the type and amount of carbon nanotubes and the type of dispersant, and 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 2,000 rpm to 10,000 rpm, more specifically, 5,000 rpm to 9,000 rpm.

[0099] Milling using the high-pressure homogenizer is performed by, for example, pressing the mixture with a plunger pump of the high-pressure homogenizer and forcing it through a gap in a homogenizing valve, and by forces such as cavitation, shear, impact, and explosion when passing through the gap.

[0100] The dispersion process may be performed depending on the degree of dispersion of the carbon nanotube dispersion liquid, specifically, under a pressure of 5,000 to 30,000 psi for 30 to 120 minutes, more specifically, for 60 to 90 minutes, and the process may be repeated 1 to 10 times.

[0101] The carbon nanotube dispersion according to the present invention may refer to a secondary dispersion of the carbon nanotubes.

[0102] Electrode slurry composition for lithium secondary battery The present invention also provides an electrode slurry composition for a lithium secondary battery containing the carbon nanotube dispersion and an electrode active material.

[0103] 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.

[0104] The electrode slurry composition for the lithium secondary battery may contain the carbon nanotube dispersion, a positive electrode active material or a negative electrode active material as the electrode active material, a binder, and optionally a solvent and / or other additives.

[0105] As the positive electrode active material, well-known positive electrode active materials in the technical field may 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 may be used. Specifically, as the positive electrode active material, LiCoO2, LiNiO2, LiMn2O4, LiCoPO4, LiFePO4 and LiNiaMnbCocO2 (where 0 < a, b, c < 1) etc. may be used, but it is not limited thereto.

[0106] 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 Fe metals (Me); alloys composed of the metals (Me); oxides of the metals (Me) (MeO x ); and one or more negative electrode active materials selected from the group consisting of composites of the metals (Me) and carbon can be mentioned. The negative electrode active material may be contained at 60 to 98% by weight, more preferably 70 to 98% by weight, based on the total weight of the solids excluding the solvent in the negative electrode slurry.

[0107] The binder is a component that aids in binding the active material and conductive material, etc., and binding them to the current collector, and is typically 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.

[0108] The solvent may be an organic solvent such as N-methylpyrrolidone (NMP), dimethylformamide (DMF), acetone, or dimethylacetamide, or water. These solvents may be used alone or in combination. The amount of solvent used should be sufficient to dissolve and disperse the electrode active material, binder, and conductive material, taking into consideration the thickness of the applied slurry and the production yield.

[0109] The viscosity adjuster may be carboxymethyl cellulose, polyacrylic acid, or the like, and the viscosity of the electrode slurry may be adjusted by adding the viscosity adjuster to facilitate the electrode slurry preparation and coating process on the electrode current collector.

[0110] The filler is selectively used as a component to suppress the expansion of the electrode, and is not particularly limited as long as it is a fibrous material that does not cause chemical changes in the battery. For example, olivine polymers such as polyethylene and polypropylene; glass fiber, carbon fiber, and other fibrous materials are used.

[0111] When the electrode slurry composition is a positive electrode slurry composition for forming a positive electrode, the positive electrode can be manufactured by coating the positive electrode slurry composition on a positive electrode current collector, drying, and rolling the composition, or by casting the positive electrode slurry on a separate support, peeling it off from the support, and laminating the resulting film on the positive electrode current collector.

[0112] The thickness of the positive electrode active material layer formed by the positive electrode slurry varies depending on the loading amount and loading speed for applying the positive electrode slurry.

[0113] 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 has high conductivity and does not cause chemical changes in the battery. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel whose surface has been treated with carbon, nickel, titanium, silver, or the like may be used. Furthermore, the surface of the positive electrode current collector may be provided with fine irregularities to strengthen the bonding strength of the positive electrode active material, and the positive electrode current collector may be used in various forms, such as a film, sheet, foil, net, porous material, foam, or nonwoven fabric.

[0114] When the electrode slurry composition is a negative electrode slurry composition for forming a negative electrode, the negative electrode can be manufactured by coating the negative electrode slurry composition on a negative electrode current collector, drying and rolling the composition, or by casting the negative electrode slurry on a separate support, peeling it off from the support, and laminating the resulting film on the negative electrode current collector.

[0115] The thickness of the negative electrode active material layer formed by the negative electrode slurry varies depending on the loading amount and loading speed for applying the negative electrode slurry.

[0116] 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 has high conductivity without causing chemical changes in the battery, and examples of such a negative electrode current collector include copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surfaces treated with carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloys. Similarly to the negative electrode current collector, the surface may be formed with fine irregularities to strengthen the binding strength of the negative electrode active material, and the negative electrode current collector may be used in various forms such as a film, sheet, foil, net, porous material, foam, or nonwoven fabric.

[0117] 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.

[0118] The separator separates the anode and cathode and provides a path for lithium ions to move. Any separator commonly used in lithium secondary batteries can be used without limitation. In particular, a separator with low resistance to electrolyte ion movement and excellent humidifying ability for the electrolyte is preferred. Specifically, a porous polymer film, such as a porous polymer film made of a polyolefin-based polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, or an ethylene / methacrylate copolymer, or a laminate structure 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 separator coated with a ceramic component or a polymer material can also be used, and can be used in a single-layer or multi-layer structure.

[0119] The electrolyte may be, but is not limited to, an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel polymer electrolyte, a solid inorganic electrolyte, a molten inorganic electrolyte, etc. that can be used in manufacturing a lithium secondary battery. Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0120] The organic solvent may be any solvent that can act as a medium through which ions involved in the electrochemical reaction of the battery can move. 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 ethanol 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) are more preferred, as they have high ionic conductivity and a high dielectric constant, which can improve the charge / discharge performance of batteries. In this case, the cyclic carbonate and chain carbonate should be mixed in a volume ratio of about 1:1 to about 1:9 to achieve excellent electrolyte performance.

[0121] The lithium salt may 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 lithium salt concentration is preferably in the range of 0.1M to 2.0M. When the lithium salt concentration is within this range, the electrolyte has appropriate conductivity and viscosity, resulting in excellent electrolyte performance and efficient lithium ion migration.

[0122] In addition to the electrolyte components, the electrolyte may further contain 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, and improving battery discharge capacity. In this case, the additives may be contained in an amount of 0.1 wt % to 5 wt % based on the total weight of the electrolyte.

[0123] 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. This allows the battery to stably exhibit excellent discharge capacity and output characteristics. As a result, the battery is useful in portable devices such as mobile phones, laptops, and digital cameras, and electric vehicles such as hybrid electric vehicles (HEVs).

[0124] Accordingly, 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.

[0125] The battery module or battery pack may be used as a power source for one or more medium- to large-sized devices in a power tool; an electric vehicle (EV), a hybrid electric vehicle, and an electric vehicle (PHEV), including a plug-in hybrid electric vehicle; or a power storage system. DETAILED DESCRIPTION OF THE INVENTION

[0126] Specific examples of the present invention will be presented below. However, the following examples are merely intended to specifically illustrate and explain the present invention, and are not intended to limit the present invention. Furthermore, details not described herein can be easily inferred by those skilled in the art, and therefore, a detailed description thereof will be omitted.

[0127] Example Example 1 (1) 5.625 g (1.125 wt % relative to 100 parts by weight of the total carbon nanotube dispersion) of polyvinylpyrrolidone (PVP, manufactured by Zhangzhou Huafu Chemical Co., Ltd.) as a first dispersant containing nitrogen atoms, a mixture of gallic acid and NaOH as a second dispersant containing at least one hydroxyl group and at least one carboxyl group in an aromatic ring, and Na + 1.69 g of gallic acid (manufactured by Sigma-Aldrich) and 8.28 g of a 1N (3.8 wt%) NaOH aqueous solution (manufactured by Daejeon Chemical Industries) were mixed together with 479.4 g of water as a solvent to prepare 495 g of a mixed solution, so that the ions were 11 parts by weight relative to 100 parts by weight of gallic acid, and 0.375 wt% relative to the total 100 parts by weight of the carbon nanotube dispersion. This mixed solution was then placed in a dissolver (Dispermat-CA, manufactured by VMA-GETZMANN) equipped with an impeller and a container, and stirred at 400 rpm for 10 minutes.

[0128] (2) The mixture has a specific surface area of ​​1,160 m 2 / g, average particle size (D 50 ) 5.0 g (1.0 wt % based on 100 parts by weight of the total carbon nanotube dispersion) of 5 μm single-walled carbon nanotubes (SWCNT, TUBALL, manufactured by OCSiAl) was further added and stirred at 8,000 rpm for 60 minutes to produce a total of 500 g of a primary dispersion of carbon nanotubes.

[0129] (3) The primary dispersion of carbon nanotubes was homogenously dispersed seven times using a high-pressure disperser (PICOMAX, manufactured by Micronox) at a pressure of 20,000 psi to prepare a secondary dispersion of carbon nanotubes.

[0130] Example 2 In Example 1, the content of the first dispersant was 1.275 wt % based on the total 100 parts by weight of the carbon nanotube dispersion. +A carbon nanotube dispersion was prepared in the same manner as in Example 1, except that the ions were mixed at 13 parts by weight with 100 parts by weight of gallic acid to make the total amount of the carbon nanotube dispersion 0.225% by weight with respect to the total amount of the carbon nanotube dispersion 100 parts by weight.

[0131] Example 3 In Example 1, Li + A carbon nanotube dispersion was prepared in the same manner as in Example 1, except that LiOH (Sigma-Aldrich) was added instead of NaOH so that the ions were 3.5 parts by weight relative to 100 parts by weight of gallic acid.

[0132] Example 4 In Example 1, K + A carbon nanotube dispersion was prepared in the same manner as in Example 1, except that KOH (Sigma-Aldrich) was added instead of NaOH so that the ions were 17 parts by weight relative to 100 parts by weight of gallic acid.

[0133] Example 5 A carbon nanotube dispersion was prepared in the same manner as in Example 1, except that tetramethylammonium hydroxide (Sigma-Aldrich) was added so that the amount of tetramethylammonium ions was 19 parts by weight relative to 100 parts by weight of gallic acid.

[0134] Example 6 A carbon nanotube dispersion was prepared in the same manner as in Example 1, except that 5.625 g (1.125 wt % based on 100 parts by weight of the total carbon nanotube dispersion) of polyethyleneimine (PEI, manufactured by Zhangzhou Huafu Chemical Co., Ltd.) was added instead of polyvinylpyrrolidone as the first dispersant.

[0135] Example 7 In Example 1, instead of a mixture of gallic acid and NaOH, Na was used as the second dispersant containing at least one hydroxyl group and at least one carboxyl group in the aromatic ring. + A carbon nanotube dispersion was prepared in the same manner as in Example 1, except that 1.69 g of protocatechuic acid (Sigma-Aldrich) and 8.28 g of 1N (3.8 wt%) NaOH aqueous solution (Daijong Chemical Industry Co., Ltd.) were added so that the ions were a mixture of 11 parts by weight relative to 100 parts by weight of protocatechuic acid, making the total weight of the carbon nanotube dispersion 0.375 wt% relative to 100 parts by weight of the total carbon nanotube dispersion.

[0136] Example 8 In Example 1, instead of a mixture of gallic acid and NaOH, K was used as the second dispersant containing at least one hydroxyl group and at least one carboxyl group in the aromatic ring. + A carbon nanotube dispersion was prepared in the same manner as in Example 1, except that 1.69 g of protocatechuic acid (Sigma-Aldrich) and 8.28 g of 1N (3.8 wt%) KOH aqueous solution (Daijong Chemical Industry Co., Ltd.) were added so that the ions were a mixture of 11 parts by weight relative to 100 parts by weight of protocatechuic acid, making the total weight of the carbon nanotube dispersion 0.375 wt% relative to 100 parts by weight of the total carbon nanotube dispersion.

[0137] Example 9 In Example 1, instead of a mixture of gallic acid and NaOH, Na was used as the second dispersant containing at least one hydroxyl group and at least one carboxyl group in the aromatic ring. + A carbon nanotube dispersion was prepared in the same manner as in Example 1, except that 1.69 g of syringic acid (Sigma-Aldrich) and 8.28 g of 1N (3.8 wt%) NaOH aqueous solution (Daijong Chemical Industry Co., Ltd.) were added so that the ions were a mixture of 11 parts by weight relative to 100 parts by weight of syringic acid, making the total weight of the carbon nanotube dispersion 0.375 wt% relative to 100 parts by weight of the total carbon nanotube dispersion.

[0138] Example 10 In Example 1, instead of a mixture of gallic acid and NaOH, Na was used as the second dispersant containing at least one hydroxyl group and at least one carboxyl group in the aromatic ring. + A carbon nanotube dispersion was prepared in the same manner as in Example 1, except that 1.69 g of 2,4-dihydroxybenzoic acid (Sigma-Aldrich) and 8.28 g of 1N (3.8 wt%) NaOH aqueous solution (Daejon Chemical Industries) were added so that the ions were 0.375 wt% relative to 100 parts by weight of the total carbon nanotube dispersion, which was a mixture of 11 parts by weight of 2,4-dihydroxybenzoic acid relative to 100 parts by weight of the 2,4-dihydroxybenzoic acid.

[0139] Comparative Example 1 A carbon nanotube dispersion was prepared in the same manner as in Example 1, except that the mixture of the second dispersant and NaOH was not added.

[0140] Comparative Example 2 The carbon nanotube dispersion was prepared in the same manner as in Example 1, except that the carbon nanotubes were used in an amount of 0.6 wt % based on 100 parts by weight of the total carbon nanotube dispersion, polyvinylpyrrolidone was used as the first dispersant in an amount of 0.9 wt % based on 100 parts by weight of the total carbon nanotube dispersion, and the second dispersant and NaOH mixture were not added.

[0141] Comparative Example 3 A carbon nanotube dispersion was prepared in the same manner as in Example 1, except that NaOH was not added and the second dispersant, gallic acid, was added in an amount of 0.375 wt % based on 100 parts by weight of the total carbon nanotube dispersion.

[0142] Comparative Example 4 In Example 1, polyvinylpyrrolidone was not used as the first dispersant, and NaOH was used as the second dispersant in the form of a mixture of gallic acid and NaOH. +A carbon nanotube dispersion was prepared in the same manner as in Example 1, except that the ions were added in a mixture of 11 parts by weight relative to 100 parts by weight of gallic acid, so that the amount was 1.0 wt% relative to the total 100 parts by weight of the carbon nanotube dispersion.

[0143] Comparative Example 5 In Example 1, the first dispersant was polyvinylpyrrolidone in an amount of 0.045 wt % based on 100 parts by weight of the total carbon nanotube dispersion, and the second dispersant was a mixture of gallic acid and NaOH. + A carbon nanotube dispersion was prepared in the same manner as in Example 1, except that the ions were added in a mixture of 11 parts by weight relative to 100 parts by weight of gallic acid, so that the amount was 1.455% by weight relative to the total 100 parts by weight of the carbon nanotube dispersion.

[0144] Comparative Example 6 In Example 1, Na + A carbon nanotube dispersion was prepared in the same manner as in Example 1, except that the ions were mixed with 30 parts by weight of gallic acid (100 parts by weight) to make the total amount of the carbon nanotube dispersion 0.375% by weight based on the total amount of the carbon nanotube dispersion 100 parts by weight.

[0145] Comparative Example 7 In Example 1, the content of the first dispersant was 1.455 wt % based on 100 parts by weight of the total carbon nanotube dispersion. + A carbon nanotube dispersion was prepared in the same manner as in Example 1, except that the ions were mixed at 11 parts by weight relative to 100 parts by weight of gallic acid, resulting in a concentration of 0.045% by weight relative to the total 100 parts by weight of the carbon nanotube dispersion.

[0146] Comparative Example 8 A carbon nanotube dispersion was prepared in the same manner as in Example 1, except that the carbon nanotubes were used in an amount of 0.6 wt% based on 100 parts by weight of the carbon nanotube dispersion, the content of the first dispersant was 0.675 wt% based on 100 parts by weight of the carbon nanotube dispersion, and the content of the second dispersant was 0.225 wt% based on 100 parts by weight of the carbon nanotube dispersion instead of gallic acid and NaOH.

[0147] Comparative Example 9 A carbon nanotube dispersion was prepared in the same manner as in Example 1, except that the carbon nanotubes were used in an amount of 0.6 wt % based on 100 parts by weight of the carbon nanotube dispersion, the content of the first dispersant was 0.675 wt % based on 100 parts by weight of the carbon nanotube dispersion, and the content of the second dispersant was 0.225 wt % based on 100 parts by weight of the carbon nanotube dispersion instead of gallic acid and NaOH.

[0148] Comparative Example 10 In Example 1, instead of a mixture of gallic acid and NaOH, Na was used as the second dispersant containing at least one hydroxyl group and at least one carboxyl group in the aromatic ring. + A carbon nanotube dispersion was prepared in the same manner as in Example 1, except that 1.69 g of protocatechuic acid (Sigma-Aldrich) and 22.58 g of 1N (3.8 wt%) NaOH aqueous solution (Daijong Chemical Industry Co., Ltd.) were added so that the ions were a mixture of 30 parts by weight relative to 100 parts by weight of protocatechuic acid, resulting in a concentration of 0.375 wt% relative to 100 parts by weight of the total carbon nanotube dispersion.

[0149] Comparative Example 11 In Example 1, instead of a mixture of gallic acid and NaOH, Na was used as the second dispersant containing at least one hydroxyl group and at least one carboxyl group in the aromatic ring. +A carbon nanotube dispersion was prepared in the same manner as in Example 1, except that 1.69 g of epigallocatechin gallate (Sigma-Aldrich) and 8.28 g of 1N (3.8 wt%) NaOH aqueous solution (Daejeong Chemical Industry Co., Ltd.) were added so that the ions were 11 parts by weight relative to 100 parts by weight of epigallocatechin gallate, making the total weight of the carbon nanotube dispersion 0.375% by weight relative to 100 parts by weight of the total carbon nanotube dispersion.

[0150] Experimental example The viscosity of the carbon nanotube dispersions of Examples 1 to 10 and Comparative Examples 1 to 11 was measured, and the viscosity was measured again after leaving them to stand at 25° C. for one week. The results are shown in Table 2 below.

[0151] The viscosity was measured at 25°C and 1 rpm using a viscometer (TOKI SANGYO, viscometer TV-25, Rotor Code 01).

[0152] [Table 2A]

[0153] [Table 2B]

[0154] [Table 2C]

[0155] *TMAH: Tetramethylammonium hydroxide *TMA: Tetramethylammonium *PEI: Polyethylenimine

[0156] Referring to Table 2, compared to the carbon nanotube dispersion of Comparative Example 1, which contains only polyvinylpyrrolidone as the first dispersant, the carbon nanotube dispersions of Examples 1 to 10, which contain a mixture of the first dispersant, the second dispersant, and a cation, have a lower initial viscosity immediately after dispersing carbon nanotubes in an aqueous solvent, and it can be seen that the increase in viscosity of the carbon nanotube dispersion over time is particularly effectively suppressed.

[0157] In the case of the carbon nanotube dispersion of Comparative Example 2, the carbon nanotube content was reduced compared to the carbon nanotube dispersion of Comparative Example 1, and the initial viscosity immediately after dispersing the carbon nanotubes in the aqueous solvent was reduced compared to the carbon nanotube dispersion of Comparative Example 1. However, as with the carbon nanotube dispersion of Comparative Example 1, it was found that, compared to Examples 1 to 10, the dispersion did not contain a mixture of a second dispersant and a cation, and therefore did not exhibit the effect of suppressing the increase in viscosity of the dispersion over time.

[0158] In the case of the carbon nanotube dispersion of Comparative Example 3, compared to the carbon nanotube dispersions of Examples 1 to 10, instead of a mixture of the second dispersant and cations, the dispersion contains only the second dispersant, so the initial viscosity immediately after dispersing the carbon nanotubes is relatively high, and it can be seen that the effect of suppressing the increase in viscosity of the dispersion over time is not exhibited.

[0159] In the case of the carbon nanotube dispersions of Comparative Examples 4 and 5, compared to the carbon nanotube dispersions of Examples 1 to 10, the first dispersant was not contained (Comparative Example 4) or was contained in a small amount that exceeded a certain content ratio (Comparative Example 5), and it was found that the carbon nanotubes could not be completely dispersed in the aqueous solvent.

[0160] In the case of the carbon nanotube dispersions of Comparative Examples 6 and 10, compared to the carbon nanotube dispersions of Examples 1 to 10, the cations contained together with the second dispersant are contained in an excess amount that exceeds a certain content ratio, resulting in a high initial viscosity immediately after dispersing the carbon nanotubes in the aqueous solvent, and no effect of suppressing the increase in viscosity of the carbon nanotube dispersion over time is observed.

[0161] Furthermore, in the case of the carbon nanotube dispersion of Comparative Example 7, the mixture of the second dispersant and cation is contained in a small amount that deviates from a certain content ratio compared to the carbon nanotube dispersions of Examples 1 to 10, and therefore the initial viscosity immediately after dispersing the carbon nanotubes in the aqueous solvent is high, and the effect of suppressing the increase in viscosity of the carbon nanotube dispersion over time is not exhibited.

[0162] In the case of the carbon nanotube dispersions of Comparative Examples 8 and 9, compared to the carbon nanotube dispersions of Examples 1 to 10, a substance that does not contain at least one hydroxy group and at least one carboxy group in the aromatic ring is used as the second dispersant, and no cations such as alkali metal cations are contained. As a result, the initial viscosity immediately after dispersing the carbon nanotubes in the aqueous solvent is high (Comparative Example 8), and the effect of suppressing the increase in viscosity of the carbon nanotube dispersion over time is not exhibited (Comparative Examples 8 and 9).

[0163] In the case of the carbon nanotube dispersion of Comparative Example 11, compared to the carbon nanotube dispersions of Examples 1 to 10, the second dispersant, epigallocatechin gallate, contains two or more aromatic rings in its molecular structure, causing the molecules to form linear, angular or densely packed structures.In addition, the π-π interactions formed by the ring structure within the molecule occur strongly, deepening the aggregation of the dispersant.As a result, the charge regulation by the cations that form the mixture with the second dispersant is insufficient, resulting in a high viscosity of the dispersion.As a result, the initial viscosity immediately after dispersing carbon nanotubes in an aqueous solvent is high, and the effect of suppressing the viscosity increase of the carbon nanotube dispersion over time is not exhibited. Therefore, it was confirmed that the carbon nanotube dispersion liquid in which carbon nanotubes are dispersed in an aqueous solvent contains a mixture of a first dispersant containing a nitrogen atom, a second dispersant, and a cation, the second dispersant containing at least one hydroxy group and at least one carboxy group in an aromatic ring, and the cation contains at least one selected from the group consisting of alkali metal ions, alkaline earth metal ions, aluminum ions, transition metal ions, ammonium ions, and sulfonium ions in a certain weight ratio, and the carbon nanotube dispersion liquid exhibits low viscosity and suppresses viscosity increase over time.

[0164] Although the preferred embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements made by those skilled in the art using the basic concept of the present invention defined in the following claims also fall within the scope of the present invention.

Claims

1. carbon nanotubes; a first dispersant containing a nitrogen atom; a mixture of a second dispersant and a cation; and Contains a solvent, the second dispersant comprises at least one hydroxy group and at least one carboxy group in an aromatic ring; The cation includes at least one selected from the group consisting of alkali metal ions, alkaline earth metal ions, aluminum ions, transition metal ions, ammonium ions, and sulfonium ions. Carbon nanotube dispersion.

2. the second dispersant has a molecular structure that does not contain two or more aromatic rings; The carbon nanotube dispersion liquid according to claim 1 .

3. 2. The carbon nanotube dispersion of claim 1, wherein the second dispersant comprises a compound represented by the following Chemical Formula 1: 【Chemistry 1】 In the above Chemical Formula 1, R1 to R5 are the same or different and each independently represent hydrogen, deuterium, a halogen, a cyano group, a hydroxy group, a carboxy group, a substituted or unsubstituted C1 to C10 alkyl group, a substituted or unsubstituted C2 to C10 alkenyl group, a substituted or unsubstituted C2 to C10 alkynyl group, a substituted or unsubstituted C1 to C10 alkoxy group, a substituted or unsubstituted C3 to C10 cycloalkyl group, or a substituted or unsubstituted C2 to C10 heterocycloalkyl group, and at least one of R1 to R5 is a hydroxy group, R6 is a carboxy group; L is a single bond; a substituted or unsubstituted C1 to C10 alkylene group; a substituted or unsubstituted C2 to C10 alkenylene group; or a substituted or unsubstituted C2 to C10 alkynylene group.

4. The second dispersing agent is at least one selected from the group consisting of gallic acid, protocatechuic acid, syringic acid, ferulic acid, vanillic acid, caffeic acid, coumaric acid (p-coumaric acid), salicylic acid, 2,4-dihydroxybenzoic acid, homogentisic acid, and sinapinic acid; The carbon nanotube dispersion liquid according to claim 1 .

5. The BET specific surface area of ​​the carbon nanotubes is 800 to 2,000 m ２ / g, The carbon nanotube dispersion liquid according to claim 1 .

6. The carbon nanotube dispersion liquid contains 25 to 450 parts by weight of the first dispersant based on 100 parts by weight of the carbon nanotubes. The carbon nanotube dispersion liquid according to claim 1 .

7. The carbon nanotube dispersion liquid contains 5 to 250 parts by weight of the mixture of the second dispersant and cations based on 100 parts by weight of the carbon nanotubes. The carbon nanotube dispersion liquid according to claim 1 .

8. The cation is included in an amount of 2 to 20 parts by weight based on 100 parts by weight of the second dispersant. The carbon nanotube dispersion liquid according to claim 1 .

9. The first dispersant may be 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, and benzyl-dodecyl-dimethylammonium chloride. chloride), and polyethyleneimine, The carbon nanotube dispersion liquid according to claim 1 .

10. The first dispersant, the mixture of the second dispersant and the cation are contained in a weight ratio of 100:10 to 100:

90. The carbon nanotube dispersion liquid according to claim 1 .

11. The carbon nanotube dispersion has an initial viscosity of 1 to 10 Pa s measured at 25°C and 1 rpm. The carbon nanotube dispersion liquid according to claim 1 .

12. The carbon nanotube dispersion has a viscosity increase rate represented by the following formula (1) of 15% or less: The carbon nanotube dispersion according to claim 1: [Formula 1] Viscosity increase rate (%)={(viscosity measured after standing at 25° C. for 1 week−initial viscosity) / initial viscosity}×100.

13. (1) preparing a primary dispersion of carbon nanotubes by mixing carbon nanotubes, a first dispersant containing nitrogen atoms, a second dispersant containing at least one hydroxyl group and at least one carboxyl group in an aromatic ring, a cation precursor, and a solvent; and (2) dispersing the primary dispersion of carbon nanotubes to prepare a secondary dispersion of carbon nanotubes; The method for producing the carbon nanotube dispersion liquid according to claim 1 , comprising:

14. The cation precursor is The hydroxide of one or more cations selected from the group consisting of alkali metal ions, alkaline earth metal ions, aluminum ions, transition metal ions, ammonium ions, and sulfonium ions. The method for producing a carbon nanotube dispersion liquid according to claim 13 .

15. An electrode slurry composition for a lithium secondary battery, comprising the carbon nanotube dispersion liquid according to claim 1 and an electrode active material.

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