Carbon nanotube dispersion and preparation method therefor

Abstract

The present invention relates to a carbon nanotube dispersion and a preparation method therefor, the carbon nanotube dispersion comprising: carbon nanotubes; a first dispersant containing a nitrogen atom; a second dispersant containing a substituted benzopyran-based compound; and a solvent, wherein the substituted benzopyran-based compound contained in the second dispersant contains at least three hydroxyl groups.

Description

Carbon nanotube dispersion and method for producing the same

[0001] This application claims the benefit of priority to Republic of Korea Patent Application No. 10-2023-0092200, dated July 17, 2023, and Republic of Korea Patent Application No. 10-2024-0077181, dated June 13, 2024, the entire contents of which are incorporated herein by reference.

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

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

[0004] In general, high-density electrodes are formed by molding electrode active material particles having a size of several μm to several tens of μm using a high-pressure press. During the molding process, the particles may be deformed and the space between the particles may be reduced, so that the electrolyte permeability is likely to deteriorate.

[0005] To address the above issues, conductive materials with superior electrical conductivity and strength are used during electrode manufacturing. These conductive materials are positioned between the electrode active materials, and even during the molding process, they maintain micropores between the active material particles, facilitating the penetration of the electrolyte. Their superior electrical conductivity reduces electrode resistance. Among these conductive materials, carbon nanotubes, a fibrous carbon-based conductive material that can further reduce electrode resistance by forming electrically conductive paths within the electrode, are increasingly being used.

[0006] Carbon nanotubes, a type of microscopic carbon fiber, are tubular carbon fibers with a diameter of less than 1 ㎛. Their unique structure, resulting in high conductivity, tensile strength, and heat resistance, has raised expectations for practical application in various fields. However, carbon nanotubes have low dispersibility and are prone to agglomeration due to the strong van der Waals attraction between them due to their high specific surface area.

[0007] To address these issues, mechanical dispersion techniques, such as ultrasonic treatment, have been proposed to disperse carbon nanotubes in a dispersion medium. However, mechanical dispersion techniques have problems, such as carbon nanotubes agglomerating immediately after ultrasonic treatment or reagglomerating over time after dispersion.

[0008] Accordingly, there is a need to develop a method for producing a carbon nanotube dispersion that can improve the dispersibility of carbon nanotubes, while having low viscosity and suppressing the increase in viscosity over time.

[0009] [Prior Art Literature]

[0010] [Patent Document]

[0011] (Patent Document 1) Chinese Patent Publication No. 110128784 (August 16, 2019)

[0012] The purpose of the present invention is to provide a carbon nanotube dispersion comprising carbon nanotubes, a first dispersant containing nitrogen atoms, a second dispersant containing a substituted benzopyran-based compound, and a solvent, wherein the substituted benzopyran-based compound contained in the second dispersant contains at least three hydroxyl groups, thereby providing a carbon nanotube dispersion having excellent dispersibility, low viscosity of the dispersion, low particle size of the dispersed particles, and little change in viscosity over time.

[0013] Another object of the present invention is to provide an electrode slurry composition for a lithium secondary battery comprising the carbon nanotube dispersion.

[0014] Another object of the present invention is to provide a method for producing the carbon nanotube dispersion.

[0015] One embodiment of the present invention provides a carbon nanotube dispersion comprising carbon nanotubes, a first dispersant including a nitrogen atom, a second dispersant including a substituted benzopyran-based compound, and a solvent, wherein the substituted benzopyran-based compound included in the second dispersant includes at least three hydroxyl groups.

[0016] The second dispersant may include a compound represented by the following chemical formula 1.

[0017] [Chemical Formula 1]

[0018]

[0019] In the above chemical formula 1,

[0020] is a single or double bond;

[0021] A1 to A6 are the same as or different from each other, and each independently represent hydrogen; deuterium; halogen; cyano group; hydroxy group; carboxyl group; substituted or unsubstituted C1 to C10 alkyl group; substituted or unsubstituted C2 to C10 alkenyl group; substituted or unsubstituted C2 to C10 alkynyl group; substituted or unsubstituted C1 to C10 alkoxy group; substituted or unsubstituted C3 to C10 cycloalkyl group; substituted or unsubstituted C2 to C10 heterocycloalkyl group; or a substituent represented by the following chemical formula 2, wherein at least one of A1 to A6 is represented by the following chemical formula 2,

[0022] [Chemical Formula 2]

[0023]

[0024] In the above chemical formula 2,

[0025] B1 to B5 are the same or different and are each independently hydrogen; deuterium; halogen; cyano group; hydroxy group; carboxyl group; substituted or unsubstituted C1 to C10 alkyl group; substituted or unsubstituted C2 to C10 alkenyl group; substituted or unsubstituted C2 to C10 alkynyl group; substituted or unsubstituted C1 to C10 alkoxy group; substituted or unsubstituted C3 to C10 cycloalkyl group; or substituted or unsubstituted C2 to C10 heterocycloalkyl group,

[0026] Among A1 to A6 of the above chemical formula 1, at least three or more substituents not represented by the above chemical formula 2 and among B1 to B5 of the above chemical formula 2 are hydroxy groups.

[0027] The second dispersant may include a compound represented by any one of the following chemical formulas 3 to 5.

[0028] [Chemical Formula 3]

[0029]

[0030] [Chemical Formula 4]

[0031]

[0032] [Chemical Formula 5]

[0033]

[0034] In the above chemical formulas 3 to 5,

[0035] A1 to A5 and B1 to B5 are the same as or different from each other, and each independently represent hydrogen; deuterium; halogen; cyano group; hydroxy group; carboxyl group; substituted or unsubstituted C1 to C10 alkyl group; substituted or unsubstituted C2 to C10 alkenyl group; substituted or unsubstituted C2 to C10 alkynyl group; substituted or unsubstituted C1 to C10 alkoxy group; substituted or unsubstituted C3 to C10 cycloalkyl group; or substituted or unsubstituted C2 to C10 heterocycloalkyl group,

[0036] At least three of A1 to A5 and B1 to B5 in the above chemical formula 1 are hydroxy groups.

[0037] The second dispersant may be at least one selected from the group consisting of luteolin, quercetin, kaempferol, myricetin, fisetin, morin, hesperetin, naringenin, and eriodictyol.

[0038] The BET surface area of ​​the above carbon nanotubes is 800 to 2,000 m 2 / g may be.

[0039] The above carbon nanotube dispersion may contain 25 to 450 parts by weight of the first dispersant based on 100 parts by weight of the carbon nanotubes.

[0040] The above carbon nanotube dispersion may contain 5 to 250 parts by weight of the second dispersant based on 100 parts by weight of the carbon nanotubes.

[0041] The first dispersant may be at least one 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 polyethylenimine.

[0042] The first dispersant and the second dispersant may be included in a weight ratio of 100:10 to 100:90.

[0043] The above carbon nanotube dispersion may have an initial viscosity of 1 to 10 Pa·s measured at 25°C and 1 rpm.

[0044] The above carbon nanotube dispersion may have a viscosity increase rate of 15% or less, as expressed by the following equation (1).

[0045] [Formula 1]

[0046] Viscosity increase rate (%) = {(Viscosity measured after leaving at 25℃ for 1 week - Initial viscosity) / Initial viscosity} × 100

[0047] Another embodiment of the present invention provides a method for producing a carbon nanotube dispersion, comprising the steps of (1) preparing a carbon nanotube primary dispersion by mixing carbon nanotubes, a first dispersant including a nitrogen atom, a second dispersant including a substituted benzopyran compound including at least three hydroxyl groups, and a solvent, and (2) dispersing the carbon nanotube primary dispersion to prepare a carbon nanotube secondary dispersion.

[0048] 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.

[0049] The carbon nanotube dispersion according to the present invention uses a first dispersant containing a nitrogen atom and a second dispersant containing a substituted benzopyran-based compound containing at least three hydroxyl groups, thereby exhibiting a small change in viscosity over time and a relatively low viscosity despite the use of carbon nanotubes having a large specific surface area, and has the characteristics of uniformly and effectively dispersing the carbon nanotubes, thereby having a small particle size of the dispersed particles.

[0050] Furthermore, by using the carbon nanotube dispersion of the present invention in an electrode slurry composition, an electrode and secondary battery having excellent capacity characteristics and cycle characteristics can be manufactured.

[0051] Hereinafter, embodiments of the present invention will be described in detail. Prior to this, terms and words used in this specification and claims should not be interpreted as limited to their conventional or dictionary meanings. Rather, they should be interpreted with meanings and concepts that conform to the technical spirit of the present invention, based on the principle that the inventor can appropriately define the concept of a term to best explain his or her invention. Accordingly, the configurations described in the embodiments described in this specification are merely the most preferred embodiments of the present invention and do not represent all of the technical spirit of the present invention. Therefore, it should be understood that various equivalents and modified examples may exist as of the time of this application.

[0052] In this specification, the term "substitution" means that a hydrogen atom bonded to a carbon atom of a compound is replaced with another substituent, and the position of substitution is not limited as long as it is a position where a hydrogen atom is replaced, i.e., a position where a substituent can be replaced, and when two or more are replaced, the two or more substituents may be the same or different from each other.

[0053] In this specification, "substituted or unsubstituted" means: deuterium; cyano group; straight or branched chain alkyl group having 1 to 60 carbon atoms; straight or branched chain alkenyl group having 2 to 60 carbon atoms; straight or branched chain alkynyl group having 2 to 60 carbon atoms; monocyclic or polycyclic cycloalkyl group having 3 to 60 carbon atoms; monocyclic or polycyclic heterocycloalkyl group having 2 to 60 carbon atoms; monocyclic or polycyclic aryl group having 6 to 60 carbon atoms; monocyclic or polycyclic heteroaryl group having 2 to 60 carbon atoms; -SiRR'R"; -P(=O)RR'; C1 to C20 alkylamine group; C6 to C60 monocyclic or polycyclic arylamine group; and C2 to C60 monocyclic or polycyclic heteroarylamine group, which is substituted or unsubstituted with one or more substituents selected from the group consisting of a C1 to C20 alkylamine group; a C6 to C60 monocyclic or polycyclic arylamine group; and a C2 to C60 monocyclic or polycyclic heteroarylamine group, or substituted or unsubstituted with a substituent in which two or more substituents selected from the above-mentioned substituents are connected.

[0054] Throughout this specification, whenever a part is said to 'include' a component, this does not mean that it excludes other components, but rather that it may include other components, unless otherwise specifically stated.

[0055] Throughout this specification, “%” means weight percent unless explicitly stated otherwise.

[0056] In this specification, the average particle size "D 50 " means the particle size corresponding to 50% of the volume accumulation. The above D 50 For example, it can be measured using the laser diffraction method. The laser diffraction method can generally measure particle sizes from the submicron range to several mm, and can obtain results with high reproducibility and high resolution.

[0057] In this specification, the “specific surface area” is measured by the BET method (Brunauer-Emmett-Teller Analysis), and specifically, can be calculated from the nitrogen gas adsorption amount at liquid nitrogen temperature (77 K) using BELSORP-mino II of BEL Japan.

[0058]

[0059] carbon nanotube dispersion

[0060] A carbon nanotube dispersion according to the present invention comprises carbon nanotubes, a first dispersant comprising nitrogen atoms, a second dispersant comprising a substituted benzopyran-based compound comprising at least three hydroxyl groups, and a solvent. Hereinafter, each component of the carbon nanotube dispersion of the present invention will be described in detail.

[0061]

[0062] (1) Carbon nanotubes

[0063] The term 'carbon nanotube' used in the present invention refers to a secondary structure formed by assembling carbon nanotube units in a bundle shape, in whole or in part, wherein the carbon nanotube units have a graphite sheet in the shape of a cylinder with a nano-sized diameter, and sp 2 It has a bonding structure. At this time, depending on the angle and structure at which the graphite plane is rolled, it can exhibit the characteristics of a conductor or a semiconductor. The carbon nanotube unit can be classified into single-walled carbon nanotube (SWCNT, single-walled carbon nanotube), double-walled carbon nanotube (DWCNT, double-walled carbon nanotube), and multi-walled carbon nanotube (MWCNT, multi-walled carbon nanotube) depending on the number of bonds forming the wall.

[0064] The term 'bundle type' used in the present invention, unless otherwise stated, refers to a secondary shape in the form of a bundle or rope in which a plurality of carbon nanotube units are arranged in a parallel manner with their longitudinal axes substantially in the same orientation, or are arranged and then twisted or entangled. The term 'non-bundle type or entangled type' refers to a shape in which carbon nanotube units are entangled without a definite shape such as a bundle or rope.

[0065] Carbon nanotubes are highly conductive, but they tend to aggregate due to the van der Waals forces that exist between them. When a conductive material aggregates, it fails to properly form a conductive path. This leads to the use of a relatively larger amount of conductive material, which reduces the amount of active material and can actually degrade electrode performance. Consequently, commercializing carbon nanotubes as a conductive material has been challenging.

[0066] The carbon nanotube dispersion according to the present invention comprises a first dispersant containing nitrogen atoms and a second dispersant containing a substituted benzopyran-based compound containing at least three hydroxyl groups, thereby significantly reducing the initial viscosity of the carbon nanotube dispersion and suppressing changes in viscosity over time. Therefore, when applied to an electrode slurry of a lithium secondary battery, the carbon nanotube dispersion can exhibit high conductivity due to the high conductivity of the carbon nanotubes.

[0067] Therefore, 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, so that even during the process of manufacturing an electrode by coating and drying the electrode slurry and then rolling, the microscopic spaces between the electrode active materials can be maintained at a constant level. In addition, since the carbon nanotubes are uniformly distributed without agglomeration, a sufficient conductive path can be formed even with a small amount of carbon nanotubes.

[0068] A carbon nanotube dispersion according to one embodiment of the present invention may include, but is not limited to, any one or more of single-walled, double-walled, and multi-walled carbon nanotubes as the carbon nanotubes, and specifically may include single-walled carbon nanotubes. Since the single-walled carbon nanotubes or double-walled carbon nanotubes have a higher specific surface area than multi-walled carbon nanotubes, they are more effective in improving cycle characteristics when applied to secondary batteries.

[0069] Meanwhile, the average diameter of the carbon nanotube may be, for example, 0.6 to 10 nm, preferably 0.8 to 5 nm, more preferably 0.8 to 3 nm, and 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, and 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.

[0070] In addition, the carbon nanotubes may have an average length of 0.5 to 20 μm, preferably 1 to 20 μm, more preferably 5 to 20 μm, and may be 5 μm or more, 5 μm or more, 7 μm or more, 9 μm or more, 11 μm or more, or 13 μm or more, and may be 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 the storage stability, and excellent cycle characteristics can be implemented even when applying an electrode active material. At this time, the average diameter of the carbon nanotubes can be measured by photographing a carbon nanotube powder with a scanning electron microscope, and the average length of the carbon nanotubes can be measured by photographing a carbon nanotube dispersion with a scanning electron microscope.

[0071] 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 0.1 wt% or more, 0.3 wt% or more, 0.5 wt% or more, 0.6 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, 1.8 wt% or less, 1.6 wt% or less, or 1.4 wt% or less. When the content of the carbon nanotubes satisfies the above range, the effect of improving the viscosity of the dispersion and the effect of improving the cycle characteristics of a secondary battery are excellent.

[0072] The BET surface area of ​​the above carbon nanotubes is 800 m 2 / g or more, preferably 800 m 2 / g to 5,000 m 2 / g, more preferably 800 m 2 / g to 2,000 m 2 / g may be 800 m 2 / g or more, 900 m 2 / g or more, 1,000 m 2 / g or more, 1,100 m 2 / g or more, 1,160 m 2 / g or more, 1,200 m 2 / g or more, 1,300 m 2 / g or more or 1,400 m 2 / g can be more than 2,000 m 2 / g or less, 1,900 m 2 / g or less, 1,800 m 2 / g or less, 1,700 m 2 / g or less, 1,600 m 2 / g or less or 1,500 m 2 / g or less. By using carbon nanotubes having a high BET surface area as described above, the formation of a conductive network between electrode active materials is excellent, thereby improving the cycle characteristics of secondary batteries.

[0073] The carbon nanotube dispersion according to one embodiment of the present invention can have a relatively high carbon nanotube content because the carbon nanotubes can be uniformly dispersed. When a carbon nanotube dispersion having a low carbon nanotube content is used in the production of an electrode slurry, the solid content of the produced electrode slurry decreases, so that the thickness (wet thickness) before applying and drying the electrode slurry becomes thick, and the rolling ratio measured after subsequent drying and rolling treatment increases, so that the difference in the thickness ratio before and after drying and rolling becomes large. In this way, if the rolling ratio increases, the compositions inside the slurry, including the positive electrode active material, may be damaged during the process, which may cause a problem of deterioration in the performance of the battery.

[0074]

[0075] (2) First dispersant and second dispersant

[0076] The carbon nanotube dispersion according to the present invention comprises a first dispersant containing a nitrogen atom and a second dispersant containing a substituted benzopyran compound containing at least three hydroxyl groups to improve the dispersibility of the carbon nanotubes.

[0077] In the carbon nanotube dispersion, the first dispersant including the nitrogen atom and the second dispersant including a substituted benzopyran-based compound including at least three hydroxyl groups serve to increase the dispersibility of the carbon nanotubes so that the carbon nanotubes can be evenly dispersed without agglomeration in the dispersion, and in particular, exhibit the effect of suppressing changes in the viscosity of the carbon nanotube dispersion over time.

[0078] In a carbon nanotube dispersion according to one specific example of the present invention, the first dispersant containing the nitrogen atom may be one that can be dissolved in an aqueous solvent to be described later, and may be, for example, at least one 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 polyethylenimine, and preferably Polyvinylpyrrolidone can be used. According to one specific example of the present invention, the carbon nanotube dispersion can exhibit an effect of improving the viscosity of the dispersion and an effect of suppressing changes in viscosity over time by including the first dispersing agent containing the nitrogen atom.

[0079] In one specific embodiment of the present invention, the carbon nanotube dispersion 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.It may be 5 parts by weight or more or 130 parts by weight or more, 450 parts by weight or less, 445 parts by weight or less, 440 parts by weight or less, 435 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, 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 Below, it may be 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.

[0080] If the content of the first dispersant is less than 25 parts by weight based on 100 parts by weight of carbon nanotubes, the content of the dispersant is insufficient, so that a sufficient dispersing effect is not achieved, and there may be a problem in that the viscosity of the dispersion is not formed low and the viscosity increases over time. If it exceeds 450 parts by weight, the content of the first dispersant is excessive, so that coagulation between solids in the dispersion progresses, and there may be a problem in that the viscosity of the dispersion is formed high.

[0081] In addition, a carbon nanotube dispersion according to one embodiment of the present invention includes, in addition to the first dispersant, a second dispersant including a substituted benzopyran-based compound having at least three hydroxyl groups, in order to solve the problem of the viscosity of the dispersion increasing as the content of carbon nanotubes increases in a carbon nanotube dispersion including only the first dispersant, and thus, compared to a carbon nanotube dispersion using only a conventional dispersant, the dispersion has excellent dispersibility, and can exhibit the effects of less particle agglomeration of the slurry composition and a low sedimentation rate.

[0082] Since the substituted benzopyran-based compound included in the second dispersant contains at least three hydroxyl groups, the molecular weight of the second dispersant is relatively low and the molecular size is small, so that the second dispersant can adsorb onto the surface of carbon nanotubes that the first dispersant containing the nitrogen atom could not wrap, thereby exhibiting an additional dispersing effect. In addition, the benzopyran structure included in the second dispersant stably generates pi-pi (π-π) interactions with carbon nanotubes in a local region, thereby sufficiently enhancing the bonding strength between the dispersant and the carbon nanotubes and reducing the content of the excess dispersant that is not effectively adsorbed onto the surface of the carbon nanotubes, thereby preventing aggregation of the remaining dispersants. In addition, the substituted benzopyran-based compound included in the second dispersant, having at least three hydroxyl groups, forms hydrogen bonds with the solvent in the dispersion, thereby allowing the 'carbon nanotube-dispersant' complex to stably maintain a dispersed state in the solvent.

[0083] If the carbon nanotube dispersion does not include the second dispersant according to the present invention, the area where the surface of the carbon nanotube is not sufficiently covered by the dispersant may increase, and as a result, a strong bonding force greater than an appropriate level may be generated between the carbon nanotubes, resulting in agglomeration of the carbon nanotubes, and thus a high viscosity of the dispersion may be formed.

[0084] In addition, when the second dispersant contains, for example, three or more aromatic rings in its molecular structure, the molecules form a linear, angular, or densely packed structure, which is disadvantageous for surface adsorption of small-diameter carbon nanotubes, particularly single-walled carbon nanotubes. In addition, strong π-π interactions occur between non-adsorbed dispersants, which intensifies the aggregation of the dispersants, thereby forming a high viscosity of the dispersion, and the viscosity of the dispersion may increase significantly over time.

[0085] In addition, when the substituted benzopyran-based compound included in the second dispersant contains more than six hydroxyl groups, such as tannic acid or epigallocatechin gallate (EGCG), when applied to a carbon nanotube dispersion together with the first dispersant containing the nitrogen atom, a hydrogel or insoluble binder may be formed due to the formation of very strong hydrogen bonds between the dispersants, which may cause the viscosity of the dispersion to become excessively high.

[0086] In order to effectively exhibit the above characteristics, the substituted benzopyran compound included in the second dispersant may be excluded if it includes three or more aromatic rings in its molecular structure or includes a structure having more than six hydroxyl groups.

[0087]

[0088] In one specific example of the present invention, the second dispersant may include a compound represented by the following chemical formula 1.

[0089] [Chemical Formula 1]

[0090]

[0091] In the above chemical formula 1,

[0092] is a single or double bond;

[0093] A1 to A6 are the same as or different from each other, and each independently represent hydrogen; deuterium; halogen; cyano group; hydroxy group; carboxyl group; substituted or unsubstituted C1 to C10 alkyl group; substituted or unsubstituted C2 to C10 alkenyl group; substituted or unsubstituted C2 to C10 alkynyl group; substituted or unsubstituted C1 to C10 alkoxy group; substituted or unsubstituted C3 to C10 cycloalkyl group; substituted or unsubstituted C2 to C10 heterocycloalkyl group; or a substituent represented by the following chemical formula 2, wherein at least one of A1 to A6 is represented by the following chemical formula 2,

[0094] [Chemical Formula 2]

[0095]

[0096] In the above chemical formula 2,

[0097] B1 to B5 are the same or different and are each independently hydrogen; deuterium; halogen; cyano group; hydroxy group; carboxyl group; substituted or unsubstituted C1 to C10 alkyl group; substituted or unsubstituted C2 to C10 alkenyl group; substituted or unsubstituted C2 to C10 alkynyl group; substituted or unsubstituted C1 to C10 alkoxy group; substituted or unsubstituted C3 to C10 cycloalkyl group; or substituted or unsubstituted C2 to C10 heterocycloalkyl group,

[0098] Among A1 to A6 of the above chemical formula 1, at least three or more substituents not represented by the above chemical formula 2 and among B1 to B5 of the above chemical formula 2 are hydroxy groups.

[0099] The second dispersant includes a substituted benzopyran-based compound having a benzene ring represented by chemical formula 2 on a benzopyran nucleus represented by chemical formula 1, and at least three or more of the substituents of the substituted benzopyran-based compound are substituted with hydroxy groups, so that the pi-pi (π-π) interaction between the carbon nanotubes in the dispersion and the aromatic ring of the second dispersant and the interaction by hydrogen bonding between the nitrogen atom contained in the first dispersant and the hydroxy group of the second dispersant are appropriately balanced, thereby further improving the effect of reducing the viscosity of the carbon nanotube dispersion and suppressing the increase in viscosity over time.

[0100] In the above chemical formula 1, A1 to A6 are the same as or different from each other, and are each independently hydrogen; deuterium; halogen; cyano group; hydroxy group; carboxyl group; substituted or unsubstituted C1 to C5 alkyl group; substituted or unsubstituted C2 to C5 alkenyl group; substituted or unsubstituted C2 to C5 alkynyl group; substituted or unsubstituted C1 to C5 alkoxy group; substituted or unsubstituted C3 to C5 cycloalkyl group; substituted or unsubstituted C2 to C5 heterocycloalkyl group; or a substituent represented by the above chemical formula 2, wherein at least one of A1 to A6 is represented by the above chemical formula 2,

[0101] In the above chemical formula 2, B1 to B5 are the same as or different from each other, and are each independently hydrogen; deuterium; halogen; cyano group; hydroxy group; carboxyl group; substituted or unsubstituted C1 to C5 alkyl group; substituted or unsubstituted C2 to C5 alkenyl group; substituted or unsubstituted C2 to C5 alkynyl group; substituted or unsubstituted C1 to C5 alkoxy group; substituted or unsubstituted C3 to C5 cycloalkyl group; or substituted or unsubstituted C2 to C5 heterocycloalkyl group, wherein among A1 to A6 of the above chemical formula 1, at least three or more substituents not represented by the above chemical formula 2 and B1 to B5 of the above chemical formula 2 may be hydroxy groups.

[0102] In the above chemical formula 1, A1 to A6 are the same as or different from each other, and each independently represents hydrogen; deuterium; a hydroxyl group; a substituted or unsubstituted C1 to C5 alkoxy group; or a substituent represented by the above chemical formula 2, wherein at least one of A1 to A6 is represented by the above chemical formula 2,

[0103] In the above chemical formula 2, B1 to B5 are the same as or different from each other, and each independently represent hydrogen; deuterium; a hydroxyl group; or a substituted or unsubstituted C1 to C5 alkoxy group, but among A1 to A6 of the above chemical formula 1, a substituent not represented by the above chemical formula 2 and at least three or more of B1 to B5 of the above chemical formula 2 may be hydroxyl groups.

[0104] In the above chemical formula 1, at least two of A1 to A6 may be hydroxy groups.

[0105] In the above chemical formula 2, at least one of B1 to B5 may be a hydroxy group.

[0106] In one specific embodiment of the present invention, the second dispersant may include a compound represented by any one of the following chemical formulas 3 to 5.

[0107] [Chemical Formula 3]

[0108]

[0109] [Chemical Formula 4]

[0110]

[0111] [Chemical Formula 5]

[0112]

[0113] In the above chemical formulas 3 to 5,

[0114] A1 to A5 and B1 to B5 are the same as or different from each other, and each independently represent hydrogen; deuterium; halogen; cyano group; hydroxy group; carboxyl group; substituted or unsubstituted C1 to C10 alkyl group; substituted or unsubstituted C2 to C10 alkenyl group; substituted or unsubstituted C2 to C10 alkynyl group; substituted or unsubstituted C1 to C10 alkoxy group; substituted or unsubstituted C3 to C10 cycloalkyl group; or substituted or unsubstituted C2 to C10 heterocycloalkyl group,

[0115] At least three of A1 to A5 and B1 to B5 in the above chemical formula 1 are hydroxy groups.

[0116] In the above chemical formulas 3 to 5, A1 to A5 and B1 to B5 are the same as or different from each other, and each independently represent hydrogen; deuterium; halogen; cyano group; hydroxyl group; carboxyl group; substituted or unsubstituted C1 to C5 alkyl group; substituted or unsubstituted C2 to C5 alkenyl group; substituted or unsubstituted C2 to C5 alkynyl group; substituted or unsubstituted C1 to C5 alkoxy group; substituted or unsubstituted C3 to C5 cycloalkyl group; or substituted or unsubstituted C2 to C5 heterocycloalkyl group, wherein at least three or more of A1 to A5 and B1 to B5 of the above chemical formula 1 may be hydroxyl groups.

[0117] In the above chemical formulas 3 to 5, A1 to A5 and B1 to B5 are the same as or different from each other, and each independently represents hydrogen; deuterium; a hydroxyl group; or a substituted or unsubstituted C1 to C5 alkoxy group, but at least three or more of A1 to A5 and B1 to B5 of the above chemical formula 1 may be hydroxyl groups.

[0118] In the above chemical formulas 3 to 5, at least two of A1 to A5 may be hydroxy groups, and at least one of B1 to B5 may be a hydroxy group.

[0119] In one specific embodiment of the present invention, a specific example of the second dispersant may be at least one selected from the group consisting of luteolin, quercetin, kaempferol, myricetin, fisetin, morin, hesperetin, naringenin, and eriodictyol, as shown in Table 1. The substituted benzopyran compound may not be limited to the above type as long as it contains at least three hydroxyl groups in the molecule and can increase the dispersibility of carbon nanotubes.

[0120]

[0121]

[0122]

[0123] In one specific embodiment of the present invention, the carbon nanotube dispersion may contain the second dispersant in an amount of 5 to 250 parts by weight based on 100 parts by weight of the carbon nanotubes, for example, 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 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. Below, 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.

[0124] If the content of the second dispersant is less than 5 parts by weight based on 100 parts by weight of carbon nanotubes, the first dispersant and the second dispersant may not form sufficient hydrogen bonds, and thus an effective dispersing effect may not be achieved, resulting in a problem in which the viscosity of the dispersion may not be formed low and the viscosity may increase over time. If it exceeds 250 parts by weight, the content of the second dispersant is excessive, and thus coagulation between solids in the dispersion may occur, resulting in a problem in which the viscosity of the dispersion is formed high.

[0125] In one specific example of the present invention, the first dispersant and the second dispersant of the carbon nanotube dispersion may be included in a weight ratio of 100:10 to 100:90, for example, the second dispersant may be included in a weight ratio of 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, 100:35 or more, 100:40 or more, 100:45 or more, 100:50 or more, or 100:55 or more, relative to the first dispersant, the second dispersant may be included in a weight ratio of 100:90 or less, 100:85 or less, 100:80 or less, 100:75 or less, 100:70 or less, 100:65 or less, or It can be included in 100:60 or less.

[0126] When the contents of the first dispersant and the second dispersant are included 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 with low viscosity.

[0127]

[0128] (3) Solvent

[0129] The solvent of the carbon nanotube dispersion according to one embodiment of the present invention is a dispersion medium for dispersing the carbon nanotubes, the first dispersant, and the second dispersant, and is used to supply the carbon nanotube dispersion by pre-dispersing it to prevent agglomeration when using the carbon nanotubes in a powdered state directly in the manufacture of an electrode slurry composition.

[0130] The solvent is capable of dissolving or dispersing the carbon nanotubes, the first dispersant, and the second dispersant to a certain level or higher. The aqueous solvent may be, for example, water, and the aqueous solvent may be included in an amount such that the electrode slurry composition can have an appropriate viscosity, taking into account the coating properties of the electrode slurry composition manufactured thereafter using the carbon nanotube dispersion.

[0131] A carbon nanotube dispersion according to one embodiment of the present invention can reduce the average particle size distribution of dispersed particles included in the dispersion, such as a composite of carbon nanotubes and each dispersant, by enabling the first dispersant and the second dispersant to uniformly disperse carbon nanotubes in a solvent as described above.

[0132] Average particle size distribution (D) of the dispersed particles contained in the above dispersion 50 ) may be, for example, 0.5 to 10 μm, 1 to 10 μm, 1 to 8 μm, and preferably 1 to 5 μm.

[0133] The carbon nanotube dispersion of the present invention containing the above components has excellent dispersibility, has low viscosity of the dispersion, and has a small degree of increase in viscosity over time.

[0134] The carbon nanotube dispersion may have an initial viscosity of 1 to 10 Pa.s as measured at 25°C and 1 rpm using a viscometer (TOKISANGYO, viscometer TV-25, Rotor Code 01), for example, 1 Pa.s or more, 2 Pa.s or more, 2.5 Pa.s or more, 3 Pa.s or more, 4 Pa.s or more, or 5 Pa.s or more, and 10 Pa.s or less, 9.8 Pa.s or less, 9.5 Pa.s or less, 9 Pa.s or less, 8.5 Pa.s or less, 8 Pa.s or less, 7.5 Pa.s or less, 7 Pa.s or less, 6.5 Pa.s or less, or 6 Pa.s or less. When the carbon nanotube dispersion has an initial viscosity within the above range, an electrode slurry can be manufactured more smoothly using the same, and an electrode slurry including the carbon nanotube dispersion can have an appropriate viscosity for electrode formation.

[0135] In addition, when the carbon nanotube dispersion is left at 25°C for one week, the viscosity increase rate calculated by the following equation (1) is 15% or less, specifically 15% or less, 14.5% or less, 14% or less, 13.5% or less, 13% or less, 12.5% ​​or less, 12% or less, 11.5% or less, 11% or less, 10.5% or less, 10% or less, 9.5% or less, 9% or less, 8.5% or less, 8% or less, 7.5% or less, 7% or less, 6.5% or less, 6.1% or less, 6% or less, 5.5% or less, 5% or less, 4.5% or less, 4% or less, 3.5% or less, 3% or less, 2.5% or less, 2.4% or less, 2% or less, 1.5% or less, or 1% It could be as follows:

[0136] [Formula 1]

[0137] Viscosity increase rate (%) = {(Viscosity measured after leaving at 25℃ for 1 week - Initial viscosity) / Initial viscosity} × 100

[0138] At this time, the viscosity and initial viscosity after leaving for 1 week were measured at 25 ℃ and 1 rpm.

[0139]

[0140] Method for producing carbon nanotube dispersion

[0141] Below, a method for manufacturing a carbon nanotube dispersion is described.

[0142] The method for producing a conductive dispersion according to the present invention comprises: (1) a step of mixing carbon nanotubes, a first dispersant containing nitrogen atoms, a second dispersant containing a substituted benzopyran compound containing at least three hydroxyl groups, and a solvent to produce a carbon nanotube primary dispersion; and (2) a step of dispersing the carbon nanotube primary dispersion to produce a carbon nanotube secondary dispersion.

[0143] In step (1), a carbon nanotube primary dispersion is prepared by mixing carbon nanotubes, a first dispersant containing nitrogen atoms, a second dispersant containing a substituted benzopyran compound containing at least three hydroxyl groups, and a solvent. The step of preparing the carbon nanotube primary dispersion is performed through a wetting process in which each component is evenly mixed.

[0144] The mixing for preparing the above carbon nanotube primary dispersion may be performed using a conventional mixing method, specifically, a mixing device such as a pony mixer, a change-can mixer, a Hobert mixer, a planetary mixer, a butterfly mixer, a stone mill, a homogenizer, a bead mill, a ball mill, a basket mill, an attrition mill, a universal stirrer, a clear mixer, or a TK mixer, and may include a step of mixing at a rotation speed of 300 to 5,000 rpm for 30 minutes to 7 hours.

[0145] In addition, when mixing to prepare the primary carbon nanotube dispersion, cavitation dispersion treatment may be performed to increase the miscibility of the carbon nanotubes and the solvent, or the dispersibility of the carbon nanotubes in the solvent. The cavitation dispersion treatment is a dispersion treatment method that utilizes shock waves generated by the bursting of vacuum bubbles formed in water when high energy is applied to the liquid, and the method can disperse the carbon nanotubes without damaging the properties of the carbon nanotubes. Specifically, the cavitation dispersion treatment can be performed by ultrasonic, jet mill, or shear dispersion treatment.

[0146] The above step of preparing the primary carbon nanotube dispersion can be performed under temperature conditions in which the viscosity of the mixture and other physical properties do not change due to evaporation of the aqueous solvent. For example, it can be performed at a temperature of 50°C or lower, more specifically, from 5°C to 50°C.

[0147] The specific description of the carbon nanotubes, the first dispersant containing nitrogen atoms, the second dispersant containing a substituted benzopyran compound containing at least three hydroxyl groups, and the solvent according to the method for producing the above carbon nanotube dispersion is as described above, and therefore, a specific description will be omitted below.

[0148] In step (2), the above carbon nanotube primary dispersion is dispersed to prepare a carbon nanotube secondary dispersion.

[0149] The above stirring process can be performed by a method such as a ball mill, a bead mill, a disc mill, a basket mill, a high pressure homogenizer, etc., and more specifically, it can be performed by a milling method using a disc mill or a high pressure homogenizer.

[0150] When milling using the above disk mill, the size of the beads can be appropriately determined depending on the type and amount of carbon nanotubes and the type of dispersant, and specifically, the diameter of the beads can be 0.1 mm to 5 mm, more specifically, 0.5 mm to 4 mm. In addition, the bead milling process can be performed at a speed of 2,000 rpm to 10,000 rpm, and more specifically, can be performed at a speed of 5,000 rpm to 9,000 rpm.

[0151] Milling by the high-pressure homogenizer is achieved by pressurizing the mixture with a plunger pump of the high-pressure homogenizer, for example, and pushing it through the gap of the homogenization valve, thereby generating forces such as cavitation, shear, impact, and explosion when passing through the gap.

[0152] The above dispersion process can be performed depending on the degree of dispersion of the carbon nanotube dispersion, and specifically, can be performed under a pressure of 5,000 to 30,000 psi for 30 to 120 minutes, more specifically, 60 to 90 minutes, and the above process can be repeated 1 to 10 times.

[0153] The carbon nanotube dispersion according to the present invention may refer to the carbon nanotube secondary dispersion.

[0154]

[0155] Electrode slurry composition for lithium secondary batteries

[0156] In addition, the present invention provides an electrode slurry composition for a lithium secondary battery comprising the carbon nanotube dispersion and an electrode active material.

[0157] The above-mentioned electrode slurry composition for a lithium secondary battery may be a positive electrode slurry composition or a negative electrode slurry composition, and specifically, may be a negative electrode slurry composition.

[0158] The above-described electrode slurry composition for a lithium secondary battery may include the carbon nanotube dispersion, a positive electrode active material or a negative electrode active material as an electrode active material, a binder, a solvent, and / or other additives as needed.

[0159] As the positive electrode active material, positive electrode active materials well known in the art can be used without limitation, and for example, lithium cobalt-based oxide, lithium nickel-based oxide, lithium manganese-based oxide, lithium iron phosphate, lithium nickel manganese cobalt-based oxide, or a combination thereof can be used. Specifically, the positive electrode active material includes LiCoO2, LiNiO2, LiMn2O4, LiCoPO4, LiFePO4, and LiNiaMnbCocO. 2　 (Here, 0 < a, b, c < 1) can be used, but is not limited to this.

[0160] The above negative active materials include natural graphite, artificial graphite, carbonaceous materials; lithium-containing titanium composite oxide (LTO); metals (Me) such as Si, Sn, Li, Zn, Mg, Cd, Ce, Ni or Fe; alloys composed of the above metals (Me); oxides (MeO) of the above metals (Me). x ); and one or more types of negative electrode active materials selected from the group consisting of a complex of the above metal (Me) and carbon. The negative electrode active material may be included in an amount of 60 to 98 wt%, more preferably 70 to 98 wt%, based on the total weight of solids excluding the solvent in the negative electrode slurry.

[0161] The above binder is a component that assists in the bonding of the active material and the conductive material and the bonding 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.

[0162] The solvents mentioned above include organic solvents such as N-methyl pyrrolidone (NMP), dimethyl formamide (DMF), acetone, dimethyl acetamide, etc., or water, and these solvents may be used alone or in combination of two or more. The amount of solvent used is sufficient to dissolve and disperse the electrode active material, binder, and conductive agent, taking into account the coating thickness of the slurry and the manufacturing yield.

[0163] The above viscosity modifier may be carboxymethylcellulose, polyacrylic acid, or the like, and by adding it, the viscosity of the electrode slurry can be adjusted to facilitate the manufacturing of the electrode slurry and the application process on the electrode current collector.

[0164] The above filler is optionally used as a component that suppresses 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, olefin-based polymers such as polyethylene and polypropylene; fibrous materials such as glass fiber and carbon fiber are used.

[0165] When the above electrode slurry composition is a composition of a positive electrode slurry for forming a positive electrode, the positive electrode can be manufactured by applying the composition of the positive electrode slurry onto a positive electrode current collector, followed by drying and rolling. Alternatively, the positive electrode slurry can be manufactured by casting the positive electrode slurry onto a separate support, and then laminating the film obtained by peeling it off from the support onto the positive electrode current collector.

[0166] The thickness of the positive electrode active material layer formed by the positive electrode slurry may vary depending on the loading amount, loading speed, etc. for applying the positive electrode slurry.

[0167] The above-described positive electrode current collector generally has a thickness of 3 μm to 500 μm. The positive electrode current collector is not particularly limited 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 surface-treated with carbon, nickel, titanium, silver, etc. can be used. In addition, the surface of the positive electrode current collector may be formed with fine irregularities to strengthen the bonding strength of the positive electrode active material, and the positive electrode current collector can be used in various forms such as a film, sheet, foil, net, porous body, foam, or non-woven fabric.

[0168] When the above electrode slurry composition is a composition of a negative electrode slurry for forming a negative electrode, the negative electrode can be manufactured by applying the composition of the negative electrode slurry onto a negative electrode current collector, followed by drying and rolling. Alternatively, the negative electrode slurry can be manufactured by casting the negative electrode slurry onto a separate support, and then laminating the resulting film onto the negative electrode current collector by peeling it off from the support.

[0169] The thickness of the negative electrode active material layer formed by the above negative electrode slurry may vary depending on the loading amount, loading speed, etc. for applying the negative electrode slurry.

[0170] The above negative electrode current collector generally has a thickness of 3 ㎛ to 500 ㎛. The negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloy, etc. can be used. In addition, like the negative electrode current collector, the bonding strength of the negative electrode active material can be strengthened by forming fine unevenness on the surface, and can be used in various forms such as a film, sheet, foil, net, porous body, foam, non-woven fabric, etc.

[0171]

[0172] lithium secondary battery

[0173] A 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, so a detailed description thereof will be omitted.

[0174] The above separator separates the negative electrode and the positive electrode and provides a passage for lithium ions to move. Any separator commonly used in lithium secondary batteries can be used without any particular restrictions, and in particular, one having low resistance to ion movement of the electrolyte and excellent electrolyte moisture absorption capacity is preferable. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof, may be used. In addition, a conventional porous nonwoven fabric, for example, a nonwoven fabric made of high-melting-point glass fiber, polyethylene terephthalate fiber, etc. may be used. In addition, a coated separator containing a ceramic component or a polymer material to secure heat resistance or mechanical strength may be used, and may optionally be used in a single-layer or multi-layer structure.

[0175] The electrolyte may be, but is not limited to, an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel-type polymer electrolyte, a solid inorganic electrolyte, a molten inorganic electrolyte, etc. that can be used in the manufacture of a lithium secondary battery. Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0176] The organic solvent may be used without any particular limitation as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the organic solvent may 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; Carbonate solvents such as dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (wherein R is a C2 to C20 linear, branched, or cyclic hydrocarbon group, and may include a double-bonded aromatic ring or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes can be used. Among these, a carbonate solvent is preferable, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate, etc.) having high ionic conductivity and high dielectric constant that can improve the charge / discharge performance of the battery and a linear carbonate compound having low viscosity (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate, etc.) is more preferable.In this case, the performance of the electrolyte may be excellent when the cyclic carbonate and the chain carbonate are mixed and used in a volume ratio of about 1:1 to about 1:9.

[0177] The lithium salt may be used without any particular limitation as long as it is a compound capable of providing lithium ions used in a lithium secondary battery. Specifically, the lithium salt may include LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAl04, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2. LiCl, LiI, or LiB(C2O4)2. It is preferable that the concentration of the lithium salt be used within the range of 0.1M to 2.0M. When the concentration of the lithium salt is within the above range, the electrolyte can exhibit excellent electrolyte performance because it has appropriate conductivity and viscosity, and lithium ions can move effectively.

[0178] In addition to the electrolyte components, the electrolyte may further include one or more additives, such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, cyclic ethers, ethylene diamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinone imine 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 the life characteristics of the battery, suppressing battery capacity decrease, and improving the discharge capacity of the battery. At this time, the additives may be included in an amount of 0.1 wt% to 5 wt% based on the total weight of the electrolyte.

[0179] A lithium secondary battery comprising an electrode manufactured using a carbon nanotube dispersion according to the present invention, specifically a lithium secondary battery comprising an anode manufactured using a carbon nanotube dispersion, has carbon nanotubes uniformly dispersed within the anode, and can reduce the content thereof compared to a case where a conductive material such as conventional carbon black is included, thereby stably exhibiting excellent discharge capacity and output characteristics. As a result, the lithium secondary battery can be usefully used in portable devices such as mobile phones, laptop computers, and digital cameras, and electric vehicles such as hybrid electric vehicles (HEVs).

[0180] 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.

[0181] The above battery module or battery pack can be used as a power source for one or more medium- to large-sized devices, such as a power tool; an electric vehicle (EV), a hybrid electric vehicle, and a plug-in hybrid electric vehicle (PHEV); or a power storage system.

[0182] Below, specific embodiments of the present invention are presented. However, the embodiments described below are intended solely to specifically illustrate or explain the present invention and are not intended to limit the scope of the invention. Furthermore, any details not described herein are technically feasible to those skilled in the art and thus are omitted.

[0183]

[0184] Example

[0185]

[0186] Example 1

[0187] (1) 5.625 g of polyvinylpyrrolidone (PVP, manufactured by Zhangzhou Huafu Chemical) as a first dispersant containing nitrogen atoms (1.125 wt% based on 100 wt% of the total carbon nanotube dispersion), 1.875 g of luteolin (manufactured by INDOFINE Chemical) as a second dispersant containing a substituted benzopyran compound containing at least three hydroxyl groups (0.375 wt% based on 100 wt% of the total carbon nanotube dispersion), and 487.5 g of water as a solvent are mixed to prepare a 495 g mixed solution, which is then placed in a dissolution tank equipped with an impeller and a container (dissolver, Dispermat-CA, manufactured by VMA-GETZMANN) and stirred at 400 rpm for 10 minutes to mix.

[0188] The above 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 wt parts of the total carbon nanotube dispersion) of 5 ㎛ single-walled carbon nanotubes (SWCNT, TUBALL, manufactured by OCSiAl) is additionally added and stirred at 8,000 rpm for 60 minutes to prepare a total of 500 g of a primary carbon nanotube dispersion.

[0189] (3) The carbon nanotube primary dispersion was homogeneously dispersed 7 times at a pressure of 20,000 psi using a high-pressure disperser (PICOMAX, manufactured by Micronox) to prepare a carbon nanotube secondary dispersion.

[0190]

[0191] Example 2

[0192] In the above Example 1, a carbon nanotube dispersion was prepared in the same manner as in the above Example 1, except that the content of the first dispersant was 1.000 wt% based on 100 parts by weight of the total carbon nanotube dispersion, and the content of the second dispersant was 0.5 wt% based on 100 parts by weight of the total carbon nanotube dispersion.

[0193]

[0194] Example 3

[0195] In the above Example 1, a carbon nanotube dispersion was prepared in the same manner as in the above Example 1, except that the content of carbon nanotubes was 0.6 wt% based on 100 parts by weight of the entire carbon nanotube dispersion, the content of the first dispersant was 0.675 wt% based on 100 parts by weight of the entire carbon nanotube dispersion, and the content of the second dispersant was 0.225 wt% based on 100 parts by weight of the entire carbon nanotube dispersion.

[0196]

[0197] Example 4

[0198] In the above Example 1, a carbon nanotube dispersion was prepared in the same manner as in the above Example 1, except that the content of the second dispersant was set to 0.113 wt% based on 100 wt% of the total carbon nanotube dispersion.

[0199]

[0200] Example 5

[0201] In the above Example 1, a carbon nanotube dispersion was prepared in the same manner as in the above Example 1, except that the content of the first dispersant was 2.500 wt% based on 100 parts by weight of the total carbon nanotube dispersion, and the content of the second dispersant was 2.250 wt% based on 100 parts by weight of the total carbon nanotube dispersion.

[0202]

[0203] Example 6

[0204] In the above Example 1, a carbon nanotube dispersion was prepared in the same manner as in the above Example 1, except that 1.875 g (0.375 wt% based on 100 wt parts of the total carbon nanotube dispersion) of quercetin (manufactured by INDOFINE Chemical) was used instead of luteolin as the second dispersant including a substituted benzopyran compound having at least three hydroxyl groups.

[0205]

[0206] Example 7

[0207] In the above Example 1, a carbon nanotube dispersion was prepared in the same manner as in the above Example 1, except that 1.875 g (0.375 wt% based on 100 wt parts of the total carbon nanotube dispersion) of Myricetin (manufactured by INDOFINE Chemical) was used instead of luteolin as the second dispersant including a substituted benzopyran compound having at least three hydroxyl groups.

[0208]

[0209] Comparative Example 1

[0210] In the above Example 1, a carbon nanotube dispersion was prepared in the same manner as in the above Example 1, except that the second dispersant was not added.

[0211]

[0212] Comparative Example 2

[0213] In the above Example 1, the content of carbon nanotubes was 0.6 wt% based on 100 parts by weight of the total carbon nanotube dispersion, the content of the first dispersant was 0.900 wt% based on 100 parts by weight of the total carbon nanotube dispersion, and the content of the second dispersant was not added, except that a carbon nanotube dispersion was prepared in the same manner as in the above Example 1.

[0214]

[0215] Comparative Example 3

[0216] In the above Example 1, a carbon nanotube dispersion was prepared in the same manner as in the above Example 1, except that the content of the second dispersant was added in an amount of 1.500 wt% relative to 100 wt% of the total carbon nanotube dispersion, and the first dispersant was not added.

[0217]

[0218] Comparative Example 4

[0219] In the above Example 1, a carbon nanotube dispersion was prepared in the same manner as in the above 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, the content of the first dispersant was used in an amount of 0.675 wt% based on 100 parts by weight of the total carbon nanotube dispersion, and tristyrylphenol ethoxylate was used instead of luteolin as the second dispersant in an amount of 0.225 wt% based on 100 parts by weight of the total carbon nanotube dispersion.

[0220]

[0221] Comparative Example 5

[0222] In the above Example 1, a carbon nanotube dispersion was prepared in the same manner as in the above Example 1, except that the carbon nanotubes were used in an amount of 0.6 wt% based on 100 wt% of the total carbon nanotube dispersion, the content of the first dispersant was used in an amount of 0.675 wt% based on 100 wt% of the total carbon nanotube dispersion, and the content of the second dispersant was used in an amount of 0.225 wt% based on 100 wt% of the total carbon nanotube dispersion, instead of luteolin.

[0223]

[0224] Comparative Example 6

[0225] In the above Example 1, a carbon nanotube dispersion was prepared in the same manner as in the above Example 1, except that 0.375 wt% of tannic acid was added as a second dispersant instead of luteolin based on 100 wt% of the total carbon nanotube dispersion.

[0226]

[0227] Comparative Example 7

[0228] In the above Example 1, a carbon nanotube dispersion was prepared in the same manner as in the above Example 1, except that epigallocatechin gallate was added as the second dispersant instead of luteolin at 0.375 wt% based on 100 wt% of the total carbon nanotube dispersion.

[0229]

[0230] Comparative Example 8

[0231] In the above Example 1, a carbon nanotube dispersion was prepared in the same manner as in the above Example 1, except that the content of the first dispersant was 0.250 wt% based on 100 parts by weight of the total carbon nanotube dispersion, and the content of the second dispersant was 0.025 wt% based on 100 parts by weight of the total carbon nanotube dispersion.

[0232]

[0233] Comparative Example 9

[0234] In the above Example 1, a carbon nanotube dispersion was prepared in the same manner as in the above Example 1, except that the content of the first dispersant was 3.056 wt% based on 100 parts by weight of the total carbon nanotube dispersion, and the content of the second dispersant was 2.750 wt% based on 100 parts by weight of the total carbon nanotube dispersion.

[0235]

[0236] Comparative Example 10

[0237] In the above Example 1, a carbon nanotube dispersion was prepared in the same manner as in the above Example 1, except that the content of the first dispersant was 2.600 wt% based on 100 parts by weight of the total carbon nanotube dispersion, and the content of the second dispersant was 2.600 wt% based on 100 parts by weight of the total carbon nanotube dispersion.

[0238]

[0239] Experimental example

[0240] The viscosity of the carbon nanotube dispersions of Examples 1 to 7 and Comparative Examples 1 to 10 was measured, and the viscosity was measured again after leaving them at 25°C for one week, and the results are shown in Table 2 below.

[0241] Viscosity was measured at 25°C and 1 rpm using a viscometer (TOKI SANGYO, viscometer TV-25, Rotor Code 01).

[0242] CNT content (weight%) 1st dispersant 2nd dispersant Viscosity Type Content (weight%) Type Content (weight%) After dispersion (Pa·s) After 1 week (Pa·s) Increase rate (%) Example 11 PVP 1.125 Luteolin 0.37 5 8.5 8.7 2.4 Example 21 PVP 1.000 Luteolin 0.50 0 9.8 1 0.4 6.1 Example 30.6 PVP 0.675 Luteolin 0.22 5 2.5 2.5 5 2.0 Example 41 PVP 1.125 Luteolin 0.1 1 3 9.9 1 1.3 1 4.1 Example 51 PVP 2.500 Luteolin 2.25 0 9.7 1 0.14.1 Example 61PVP1.125Quercetin0.3758.910.113.4Example 71PVP1.125Myricetin0.3759.310.29.7Comparative Example 11PVP1.125--24.030.025.0Comparative Example 20.6PVP0.900--12.014.621.7Comparative Example 31--Luteolin1.500Viscosity not measurableViscosity not measurableViscosity not measurableComparative Example 40.6PVP0.675Tristyrylphenol ethoxylate0.22518.424.533.2Comparative Example 50.6PVP0.675Styrene maleic acid copolymer0.2259.717.075.3Comparative Example 61PVP1.125Tannin acid0.37513.215.618.2Comparative example 71PVP1.125Epigallocatechin gallate0.37515.118.321.2Comparative example 81PVP0.250Luteolin0.025Viscosity not measurableViscosity not measurableViscosity not measurableComparative example 91PVP3.056Luteolin2.75019.927.739.3Comparative example 101PVP2.600Luteolin2.60018.123.429.2

[0243] (* The contents of CNT, first dispersant, and second dispersant are based on 100 wt% of the total carbon nanotube dispersion)

[0244]

[0245] Referring to Table 2 above, it can be confirmed that the carbon nanotube dispersions of Examples 1 to 7, which include a first dispersant and a second dispersant including a substituted benzopyran-based compound having at least three hydroxyl groups in a specific amount, have a low initial viscosity immediately after dispersing carbon nanotubes in an aqueous solvent, and in particular, the increase in viscosity of the carbon nanotube dispersion over time is very effectively suppressed.

[0246] 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 the effect of suppressing the viscosity increase of the dispersion over time was not exhibited because the second dispersing agent including a substituted benzopyran-based compound including at least three hydroxyl groups was not included compared to Examples 1 to 3.

[0247] In the case of the carbon nanotube dispersion of Comparative Example 3, since the first dispersant was not included compared to the carbon nanotube dispersions of Examples 1 to 3, the carbon nanotubes could not be completely dispersed in the aqueous solvent, and coagulation of the dispersion occurred, making it impossible to measure the viscosity.

[0248] In the case of the carbon nanotube dispersions of Comparative Examples 4 and 5, since a substance that does not include a substituted benzopyran-based compound having at least three or more hydroxyl groups is not used as a second dispersant compared to the carbon nanotube dispersions of Examples 1 to 3, it can be seen that the initial viscosity immediately after dispersing the carbon nanotubes in the aqueous solvent is high (Comparative Example 4), and the effect of suppressing the viscosity increase of the carbon nanotube dispersion over time is not expressed (Comparative Examples 4 and 5).

[0249] In the case of the carbon nanotube dispersions of Comparative Examples 6 and 7, since the compound used as the second dispersant contained more than 6 hydroxyl groups compared to the carbon nanotube dispersions of Examples 1 to 3, the excessive amount of hydroxyl groups resulted in excessive hydrogen bonding with the first dispersant and the solvent, which resulted in the formation of a hydrogel being intensified, resulting in a high initial viscosity immediately after dispersing the carbon nanotubes, and the effect of suppressing the increase in viscosity of the carbon nanotube dispersion over time was not exhibited.

[0250] In the case of the carbon nanotube dispersion of Comparative Example 8, since the second dispersant was included in a content range below a certain level compared to the carbon nanotube dispersions of Examples 1 to 3, the carbon nanotubes could not be completely dispersed in the aqueous solvent, and coagulation of the dispersion occurred, making it impossible to measure the viscosity.

[0251] In the case of the carbon nanotube dispersion of Comparative Example 9, it can be seen that the initial viscosity immediately after dispersing the carbon nanotubes in the aqueous solvent is high because the second dispersant is excessively included compared to the carbon nanotube dispersions of Examples 1 to 3, and the effect of suppressing the increase in viscosity of the carbon nanotube dispersion over time is not exhibited.

[0252] In the case of the carbon nanotube dispersion of Comparative Example 10, since the contents of the first dispersant and the second dispersant did not satisfy a certain ratio compared to the carbon nanotube dispersions of Examples 1 to 3, it can be seen that the initial viscosity immediately after dispersing the carbon nanotubes in the aqueous solvent was high, and the effect of suppressing the increase in viscosity of the carbon nanotube dispersion over time was not expressed.

[0253]

[0254] Accordingly, it was confirmed that the carbon nanotube dispersion, in which carbon nanotubes are dispersed in an aqueous solvent, exhibits low viscosity and can suppress viscosity increase over time only when the carbon nanotube dispersion comprises a first dispersant containing nitrogen atoms and a second dispersant, wherein the second dispersant comprises a substituted benzopyran-based compound containing at least three hydroxyl groups at a certain weight ratio.

[0255]

[0256] 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 comprising a nitrogen atom; A second dispersant comprising a substituted benzopyran compound; and Contains a solvent, The substituted benzopyran compound contained in the second dispersant contains at least three hydroxyl groups. Carbon nanotube dispersion.

2. In paragraph 1, The second dispersant comprises a compound represented by the following chemical formula 1: Carbon nanotube dispersions: [Chemical Formula 1] In the above chemical formula 1, is a single or double bond; A1 to A6 are the same as or different from each other, and each independently represent hydrogen; deuterium; halogen; cyano group; hydroxy group; carboxyl group; substituted or unsubstituted C1 to C10 alkyl group; substituted or unsubstituted C2 to C10 alkenyl group; substituted or unsubstituted C2 to C10 alkynyl group; substituted or unsubstituted C1 to C10 alkoxy group; substituted or unsubstituted C3 to C10 cycloalkyl group; substituted or unsubstituted C2 to C10 heterocycloalkyl group; or a substituent represented by the following chemical formula 2, wherein at least one of A1 to A6 is represented by the following chemical formula 2, [Chemical Formula 2] In the above chemical formula 2, B1 to B5 are the same or different and are each independently hydrogen; deuterium; halogen; cyano group; hydroxy group; carboxyl group; substituted or unsubstituted C1 to C10 alkyl group; substituted or unsubstituted C2 to C10 alkenyl group; substituted or unsubstituted C2 to C10 alkynyl group; substituted or unsubstituted C1 to C10 alkoxy group; substituted or unsubstituted C3 to C10 cycloalkyl group; or substituted or unsubstituted C2 to C10 heterocycloalkyl group, Among A1 to A6 of the above chemical formula 1, at least three or more substituents not represented by the above chemical formula 2 and among B1 to B5 of the above chemical formula 2 are hydroxy groups.

3. In paragraph 1, The second dispersant comprises a compound represented by any one of the following chemical formulas 3 to 5: Carbon nanotube dispersions: [Chemical Formula 3] [Chemical Formula 4] [Chemical Formula 5] In the above chemical formulas 3 to 5, A1 to A5 and B1 to B5 are the same as or different from each other, and each independently represent hydrogen; deuterium; halogen; cyano group; hydroxy group; carboxyl group; substituted or unsubstituted C1 to C10 alkyl group; substituted or unsubstituted C2 to C10 alkenyl group; substituted or unsubstituted C2 to C10 alkynyl group; substituted or unsubstituted C1 to C10 alkoxy group; substituted or unsubstituted C3 to C10 cycloalkyl group; or substituted or unsubstituted C2 to C10 heterocycloalkyl group, At least three of A1 to A5 and B1 to B5 in the above chemical formula 1 are hydroxy groups.

4. In paragraph 1, The second dispersant is at least one selected from the group consisting of luteolin, quercetin, kaempferol, myricetin, fisetin, morin, hesperetin, naringenin, and eriodictyol. Carbon nanotube dispersion.

5. In paragraph 1, The BET surface area of ​​the above carbon nanotubes is 800 to 2,000 m 2 / g is, Carbon nanotube dispersion.

6. In paragraph 1, The above carbon nanotube dispersion contains 25 to 450 parts by weight of the first dispersant based on 100 parts by weight of the carbon nanotubes. Carbon nanotube dispersion.

7. In paragraph 1, The above carbon nanotube dispersion contains 5 to 250 parts by weight of the second dispersant based on 100 parts by weight of the carbon nanotubes. Carbon nanotube dispersion.

8. In paragraph 1, The first dispersant is at least one 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 polyethylenimine. Carbon nanotube dispersion.

9. In paragraph 1, The first dispersant and the second dispersant are included in a weight ratio of 100:10 to 100:

90. Carbon nanotube dispersion.

10. In paragraph 1, The above carbon nanotube dispersion has an initial viscosity of 1 to 10 Pa·s measured at 25°C and 1 rpm. Carbon nanotube dispersion.

11. In paragraph 1, The above carbon nanotube dispersion has a viscosity increase rate of 15% or less, as expressed by the following formula (1). Carbon nanotube dispersions: [Formula 1] Viscosity increase rate (%) = {(Viscosity measured after leaving at 25 ℃ for 1 week - Initial viscosity) / Initial viscosity} × 100. 12.(1) A step of preparing a carbon nanotube primary dispersion by mixing carbon nanotubes, a first dispersant containing nitrogen atoms, a second dispersant containing a substituted benzopyran compound containing at least three hydroxyl groups, and a solvent; and (2) A step of preparing a carbon nanotube secondary dispersion by dispersing the above carbon nanotube primary dispersion. A method for producing a carbon nanotube dispersion according to claim 1, comprising:

13. An electrode slurry composition for a lithium secondary battery comprising a carbon nanotube dispersion according to Article 1 and an electrode active material.

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