Carbon nanotube dispersion and preparation method thereof

Abstract

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

Description

Technical Field

[0001] This application claims the benefit of Korean Patent Application No. 10-2023-0092200 filed on July 17, 2023 and Korean Patent Application No. 10-2024-0077181 filed on June 13, 2024, which are hereby incorporated by reference in their entirety as a part of this application.

[0002] The invention relates to a carbon nanotube dispersion and a preparation method thereof. Background Art

[0003] With the development of technology and the increase in demand for mobile devices, the demand for secondary batteries as energy sources has increased rapidly. Among these secondary batteries, lithium secondary batteries with high energy density and voltage, long cycle life and low self-discharge rate have been commercialized and widely used. In addition, as an electrode for such a high-capacity lithium secondary battery, a method for improving electrode density and manufacturing an electrode with higher energy density per unit volume is being actively studied.

[0004] Typically, high-density electrodes are formed by molding electrode active material particles with a size ranging from several μm to tens of μm using a high-pressure press, and during the molding process, the particles are deformed and the space between the particles may decrease, which may reduce the permeability of the electrolyte solution.

[0005] In order to solve the above problems, when manufacturing electrodes, conductive materials with excellent electrical conductivity and strength are used. Even when the conductive material is placed between the electrode active materials and undergoes a molding process, the electrolyte solution can also be easily infiltrated by maintaining the micropores between the active material particles, and due to the excellent electrical conductivity, the resistance in the electrode can be reduced. Among these conductive materials, the use of carbon nanotubes (conductive materials based on fiber carbon) is increasing, and the carbon nanotubes can further reduce the resistance of the electrode by forming a conductive path in the electrode.

[0006] Carbon nanotubes (a type of fine carbon fiber) are tubular carbon fibers with a diameter of 1 μm or less, and have high electrical conductivity, tensile strength, and heat resistance due to their specific structure, and are therefore expected to be used and commercialized in various fields. However, carbon nanotubes have problems of low dispersibility and agglomeration due to strong van der Waals attraction between them caused by their high specific surface area.

[0007] In order to solve these problems, a method of dispersing carbon nanotubes in a dispersion medium by mechanical dispersion treatment such as ultrasonic treatment has been proposed. However, in the case of the mechanical dispersion treatment method, there is a problem that the carbon nanotubes agglomerate as soon as the ultrasonic irradiation ends, or they agglomerate again over time after dispersion.

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

[0009] [Prior art literature]

[0010] [Patent Document]

[0011] (Patent Document 1) Chinese Patent Publication No. 110128784 (2019.08.16). Summary of the invention

[0012] Technical issues

[0013] An object 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 and thus has excellent dispersibility, so that the viscosity of the dispersion and the particle size of the dispersed particles are low, and the change in viscosity over time is small.

[0014] Another object of the present invention is to provide an electrode slurry composition for a lithium secondary battery, which comprises the carbon nanotube dispersion.

[0015] Yet another object of the present invention is to provide a method for preparing a carbon nanotube dispersion.

[0016] Technical Solution

[0017] One embodiment of the present invention provides 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.

[0018] The second dispersant may include a compound represented by the following Formula 1:

[0019] [Formula 1]

[0020]

[0021] In the above formula 1,

[0022] is a single bond or a double bond;

[0023] A1 to A6 are the same as or different from each other and are each independently hydrogen; deuterium; halogen; cyano; hydroxyl; carboxyl; substituted or unsubstituted C1 to C10 alkyl; substituted or unsubstituted C2 to C10 alkenyl; substituted or unsubstituted C2 to C10 alkynyl; substituted or unsubstituted C1 to C10 alkoxy; substituted or unsubstituted C3 to C10 cycloalkyl; substituted or unsubstituted C2 to C10 heterocycloalkyl; or a substituent represented by the following Formula 2, wherein at least one of A1 to A6 is represented by the following Formula 2,

[0024] [Formula 2]

[0025]

[0026] In the above formula 2,

[0027] B1 to B5 are the same as or different from each other and are each independently hydrogen; deuterium; halogen; cyano; hydroxyl; carboxyl; substituted or unsubstituted C1 to C10 alkyl; substituted or unsubstituted C2 to C10 alkenyl; substituted or unsubstituted C2 to C10 alkynyl; substituted or unsubstituted C1 to C10 alkoxy; substituted or unsubstituted C3 to C10 cycloalkyl; or substituted or unsubstituted C2 to C10 heterocycloalkyl,

[0028] wherein the substituents among A1 to A6 in Formula 1 that are not represented by Formula 2 and at least three of B1 to B5 in Formula 2 are hydroxyl groups.

[0029] The second dispersant may include a compound represented by any one of the following Formulae 3 to 5:

[0030] [Formula 3]

[0031]

[0032] [Formula 4]

[0033]

[0034] [Formula 5]

[0035]

[0036] In the above formulas 3 to 5,

[0037] A1 to A5 and B1 to B5 are the same as or different from each other and are each independently hydrogen; deuterium; halogen; cyano; hydroxyl; carboxyl; substituted or unsubstituted C1 to C10 alkyl; substituted or unsubstituted C2 to C10 alkenyl; substituted or unsubstituted C2 to C10 alkynyl; substituted or unsubstituted C1 to C10 alkoxy; substituted or unsubstituted C3 to C10 cycloalkyl; or substituted or unsubstituted C2 to C10 heterocycloalkyl,

[0038] At least three of A1 to A5 and B1 to B5 in Formula 1 are hydroxyl groups.

[0039] The second dispersant may be at least one selected from the group consisting of luteolin, quercetin, kaempferol, myricetin, fisetin, morin, hesperidin, naringenin, and eriodictyol.

[0040] The BET specific surface area of ​​carbon nanotubes can be 800 m 2 / g to 2,000m 2 / g.

[0041] The carbon nanotube dispersion may include the first dispersant in an amount of 25 parts by weight to 450 parts by weight based on 100 parts by weight of the carbon nanotube.

[0042] The carbon nanotube dispersion may include the second dispersant in an amount of 5 parts by weight to 250 parts by weight based on 100 parts by weight of the carbon nanotube.

[0043] The first dispersant may be at least one selected from the group consisting of polyvinyl pyrrolidone, polyacrylic acid hydrazide, poly-N-vinyl-5-methyl Oxazolidinone, N-alkyl polyimine, N-acetyl polyimine, polyacrylamide, poly-L-lysine hydrobromide, benzyl-dodecyl-dimethylammonium chloride and polyethyleneimine.

[0044] The first dispersant and the second dispersant may be included in a weight ratio of 100:10 to 100:90.

[0045] The initial viscosity of the carbon nanotube dispersion as measured at 25° C. and 1 rpm may be 1 Pa·s to 10 Pa·s.

[0046] The viscosity increase rate of the carbon nanotube dispersion represented by the following Equation 1 may be 15% or less.

[0047] [Equation 1]

[0048] Viscosity increase rate (%) = {(viscosity measured after standing at 25°C for 1 week - initial viscosity) / initial viscosity} × 100

[0049] Another embodiment of the present invention provides a method for preparing a carbon nanotube dispersion, the method comprising the steps of: (1) mixing carbon nanotubes, a first dispersant containing nitrogen atoms, a second dispersant containing a substituted benzopyran-based compound containing at least three or more hydroxyl groups, and a solvent to prepare a primary dispersion of carbon nanotubes, and (2) dispersing the primary dispersion of carbon nanotubes to prepare a secondary dispersion of carbon nanotubes.

[0050] Another embodiment of the present invention provides an electrode slurry composition for a lithium secondary battery, which includes the carbon nanotube dispersion and an electrode active material.

[0051] Beneficial Effects

[0052] Although carbon nanotubes having a large specific surface area are used, by uniformly and effectively dispersing the carbon nanotubes through the use of a second dispersant containing a substituted benzopyran-based compound containing at least three or more hydroxyl groups and a first dispersant containing nitrogen atoms, the carbon nanotube dispersion according to the present invention has a small viscosity change over time, shows a relatively low viscosity, and has the characteristic that the particle size of dispersed particles is small.

[0053] Furthermore, by using the carbon nanotube dispersion of the present invention in an electrode slurry composition, an electrode and a secondary battery having excellent capacity characteristics and cycle characteristics can be manufactured. DETAILED DESCRIPTION

[0054] Hereinafter, embodiments of the present invention will be described in detail. Prior to this, the terms or words used in this specification and claims should not be interpreted as being limited to their ordinary meanings or dictionary meanings, but should be interpreted as meanings and concepts consistent with the technical concept of the present invention based on the principle that the inventor can appropriately define terms to describe his invention in the best possible way. Therefore, since the configuration described in the embodiments of this specification is only one of the most preferred embodiments of the present invention, and does not represent the entire technical concept of the present invention, it should be understood that when submitting this application, there may be various equivalents and modifications that can replace it.

[0055] As used herein, the term "substituted" means that a hydrogen atom bonded to a carbon atom of a compound is replaced by another substituent, and the position to be substituted is not limited as long as it is a position where a hydrogen atom is replaced (i.e., a position where a substituent can replace), and when substituted by two or more substituents, the two or more substituents may be the same as or different from each other.

[0056] As used herein, the term "substituted or unsubstituted" means substituted or unsubstituted with one or more substituents selected from the following: deuterium; cyano; straight or branched C1 to C60 alkyl; straight or branched C2 to C60 alkenyl; straight or branched C2 to C60 alkynyl; monocyclic or polycyclic C3 to C60 cycloalkyl; monocyclic or polycyclic C2 to C60 heterocycloalkyl; monocyclic or polycyclic C6 to C60 aryl; monocyclic or polycyclic C2 to C60 heteroaryl; -SiRR'R"; -P(=O)RR'; C1 to C20 alkylamine; monocyclic or polycyclic C6 to C60 arylamine; and monocyclic or polycyclic C2 to C60 heteroarylamine, or substituted or unsubstituted with substituents selected from the substituents exemplified above connected with two or more substituents.

[0057] Throughout the present specification, when a part is referred to as “comprising” a certain constituent element, unless explicitly described otherwise, this means that other constituent elements are not excluded and may further be included.

[0058] Throughout the present specification, "%" means % by weight unless otherwise specifically stated.

[0059] In this specification, the average particle size "D 50 " means the particle size corresponding to 50% of the cumulative volume. 50 The measurement can be performed using, for example, laser diffraction, which is generally capable of measuring particle sizes in the submicron region to several millimeters, and can obtain highly reproducible and high-resolution results.

[0060] In this specification, the "specific surface area" is measured by the BET method (Brunauer-Emmett-Teller analysis), and can be specifically calculated from the amount of nitrogen adsorption at liquid nitrogen temperature (77K) using BELSORP-mino II from BEL Japan.

[0061] Carbon Nanotube Dispersion

[0062] The carbon nanotube dispersion according to the present invention comprises carbon nanotubes, a first dispersant containing nitrogen atoms, a second dispersant containing a substituted benzopyran-based compound containing at least three or more hydroxyl groups, and a solvent. Hereinafter, each component of the carbon nanotube dispersion of the present invention will be described in detail.

[0063] (1) Carbon nanotubes

[0064] The term "carbon nanotube" used in the present invention is a secondary structure formed by completely or partially aggregating carbon nanotube units into a bundle type, wherein the carbon nanotube units have a graphene sheet in a cylindrical shape having a nanometer-sized diameter and have sp 2Bond structure. In this case, depending on the angle and structure of the graphite surface winding, it can exhibit conductor or semiconductor properties. According to the number of bonds forming the wall, carbon nanotube units can be divided into single-walled carbon nanotubes (SWCNT), double-walled carbon nanotubes (DWCNT) and multi-walled carbon nanotubes (MWCNT).

[0065] Unless otherwise specified, the term "bundle type" used in the present invention refers to a secondary shape in the form of a bundle or rope in which a plurality of carbon nanotube units are arranged side by side with the longitudinal axes of the units being substantially in the same direction, or are arranged and then twisted or tangled. "Non-bundle type or tangled type" refers to a form in which carbon nanotube units are tangled without a definite shape such as a bundle or rope form.

[0066] Carbon nanotubes have high electrical conductivity, but have high agglomeration characteristics due to the van der Waals forces that occur between carbon nanotubes. If the conductive material agglomerates, the conductive path cannot be properly formed, and relatively more conductive material is used, so the amount of active material is reduced, and the performance of the electrode may actually be deteriorated. Therefore, there are difficulties in commercializing carbon nanotubes as conductive materials.

[0067] Since the carbon nanotube dispersion according to the present invention contains: a second dispersant containing a substituted benzopyran-based compound containing at least three or more hydroxyl groups and a first dispersant containing nitrogen atoms, it can significantly reduce the initial viscosity of the carbon nanotube dispersion and inhibit the occurrence of viscosity changes over time, and therefore when applied to electrode slurry for lithium secondary batteries, high conductivity can be achieved due to the high conductivity of carbon nanotubes.

[0068] Therefore, when the carbon nanotube dispersion according to the present invention is applied to the manufacture of electrode slurry, since the carbon nanotubes are uniformly positioned between the active materials, the micro spaces between the electrode active materials can be kept constant even during the manufacture of the electrode by coating and drying the electrode slurry and then rolling it. In addition, since the carbon nanotubes are uniformly distributed without agglomeration, a conductive path can be fully formed even with a small amount of carbon nanotubes.

[0069] The 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 carbon nanotubes, double-walled carbon nanotubes and multi-walled carbon nanotubes, and may specifically include single-walled carbon nanotubes. Since single-walled carbon nanotubes or double-walled carbon nanotubes have a higher specific surface area than multi-walled carbon nanotubes, when applied to secondary batteries, they are more effective in improving cycle characteristics.

[0070] At the same time, the average diameter of the carbon nanotubes can be, for example, 0.6nm to 10nm, preferably 0.8nm to 5nm, more preferably 0.8nm to 3nm, and can be 0.8nm or more, 0.9nm or more, 1.0nm or more, 1.1nm or more, 1.2nm or more, 1.3nm or more, 1.4nm or more, 1.5nm or more, 1.6nm or more, 1.7nm or more, 1.8nm or more, or 1.9nm or more, and can be 3.0nm or less, 2.9nm or less, 2.8nm or less, 2.7nm or less, 2.6nm or less, 2.5nm or less, 2.4nm or less, 2.3nm or less, 2.2nm or less, 2.1nm or less, or 2.0nm or less.

[0071] In addition, the average length of the carbon nanotubes can be 0.5 μm to 20 μm, preferably 1 μm to 20 μm, more preferably 5 μm to 20 μm, and can 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 can be 20 μm or less, 18 μm or less, 16 μm or less, or 14 μm or less. If the average diameter and average length of the carbon nanotubes meet the above range, it is effective in reducing the viscosity of the dispersion and improving storage stability, and when applied to electrode active materials, excellent cycle characteristics can be achieved. In this case, the average diameter of the carbon nanotubes can be measured by photographing the 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.

[0072] Based on the total weight of the carbon nanotube dispersion, the carbon nanotubes may be included in an amount of 0.1% to 5% by weight, preferably 0.1% to 3% by weight, and more preferably 0.5% to 2% by weight, and may be included in an amount of 0.1% by weight or more, 0.3% by weight or more, 0.5% by weight or more, 0.6% by weight or more, 0.7% by weight or more, 0.9% by weight or more, 1.0% by weight, 1.1% by weight or more, or 1.3% by weight or more, and may be included in an amount of 2% by weight or less, 1.8% by weight or less, 1.6% by weight or less, or 1.4% by weight or less. If 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 the secondary battery are excellent.

[0073] The BET specific surface area of ​​carbon nanotubes can be 800 m 2 / g or more, preferably 800m 2 / g to 5,000m 2 / g, more preferably 800m 2 / g to 2,000m 2 / g, and can be 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 can be 2,000m 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 When the carbon nanotubes having a high BET specific surface area as above are used, formation of a conductive network between electrode active materials is excellent, thereby having an effect of improving cycle characteristics of a secondary battery.

[0074] The carbon nanotube dispersion according to one embodiment of the present invention can have a relatively high content of carbon nanotubes because the carbon nanotubes can be uniformly dispersed. If a carbon nanotube dispersion with a low content of carbon nanotubes is used to manufacture an electrode slurry, the thickness (wet thickness) before applying and drying the electrode slurry is thick due to the reduction in the solid content of the manufactured electrode slurry, and thereafter, the calendering rate measured after the drying and calendering process increases, so the difference in the thickness ratio before and after drying and calendering increases. Therefore, if the calendering rate increases, the composition (including the positive electrode active material) in the slurry may be destroyed during the process, and there may be a problem of a corresponding reduction in battery performance.

[0075] (2) First dispersant and second dispersant

[0076] The carbon nanotube dispersion according to the present invention includes: a second dispersant including a substituted benzopyran-based compound including at least three or more hydroxyl groups, and a first dispersant including nitrogen atoms to improve dispersibility of the carbon nanotubes.

[0077] In a carbon nanotube dispersion, a first dispersant containing nitrogen atoms and a second dispersant containing a substituted benzopyran-based compound containing at least three or more hydroxyl groups are used to increase the dispersibility of the carbon nanotubes so that the carbon nanotubes can be uniformly dispersed without agglomerating in the dispersion, and particularly exhibit an effect of suppressing the change in viscosity of the carbon nanotube dispersion over time.

[0078] In the carbon nanotube dispersion according to one embodiment of the present invention, the first dispersant containing nitrogen atoms may be dissolved in an aqueous solvent to be described later, and may be, for example, at least one selected from the group consisting of polyvinyl pyrrolidone, polyacrylic acid hydrazide, poly-N-vinyl-5-methyl The carbon nanotube dispersion according to one embodiment of the present invention includes the first dispersant containing nitrogen atoms, which can show the effect of improving the viscosity of the dispersion and the effect of suppressing the change of viscosity over time.

[0079] In one embodiment of the present invention, the carbon nanotube dispersion may include the first dispersant in an amount of 25 to 450 parts by weight, based on 100 parts by weight of the carbon nanotubes, and for example, may include in the following amounts: 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, 120 parts by weight or more, 130 parts by weight or more, 140 parts by weight or more, 150 parts by weight or more, 160 parts by weight or more, 170 parts by weight or more, 180 parts by weight or more, 190 parts by weight or more, 200 parts by weight or more, 210 parts by weight or more, 220 parts by weight or more, 230 parts by weight or more, 240 parts by weight or more, 250 parts by weight or more, 260 parts by weight or more, 270 parts by weight or more, 280 parts by weight or more, 290 parts by weight or more, 300 parts by weight or more, 310 parts by weight or more, 320 parts by weight or more, 330 parts by weight or more, 340 parts by weight or more The amount of the present invention may be 12.5 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 may be 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, 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, 25 0 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.

[0080] If the content of the first dispersant is less than 25 parts by weight based on 100 parts by weight of the carbon nanotubes, there may be a problem that a sufficient dispersing effect cannot be achieved due to insufficient content of the dispersant, and thus the viscosity of the dispersion cannot be made low and the viscosity increases over time. If the content of the first dispersant exceeds 450 parts by weight, there may be a problem that solids in the dispersion coagulate due to excessive content of the first dispersant, resulting in high viscosity of the dispersion.

[0081] Furthermore, in order to solve the problem that, for a carbon nanotube dispersion containing only a first dispersant, the viscosity of the dispersion increases as the content of carbon nanotubes increases, a carbon nanotube dispersion according to one embodiment of the present invention comprises: a second dispersant comprising a substituted benzopyran-based compound containing at least three or more hydroxyl groups, and a first dispersant, and therefore, compared with a carbon nanotube dispersion using only a conventional dispersant, the carbon nanotube dispersion according to one embodiment of the present invention has excellent dispersibility, thereby producing the effects of less particle agglomeration and lower sedimentation velocity in the slurry composition.

[0082] Since the substituted benzopyran-based compound contained 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, thereby allowing it to exhibit an additional dispersing effect by adsorbing on the surface of the carbon nanotube that is not covered by the first dispersant containing nitrogen atoms. In addition, in the case of the benzopyran structure contained in the second dispersant, the pi-pi (π-π) interaction with the carbon nanotube occurs stably in a local area, thereby ensuring sufficient bonding strength between the dispersant and the carbon nanotube, and by reducing the content of the remaining dispersant that is not effectively adsorbed on the surface of the carbon nanotube, the agglomeration of the remaining dispersant can be prevented. In addition, at least three hydroxyl groups contained in the substituted benzopyran-based compound contained in the second dispersant form hydrogen bonds with the solvent in the dispersion, thereby maintaining a stable dispersion state of the "carbon nanotube-dispersant" combination in the solvent.

[0083] If the carbon nanotube dispersion does not include the second dispersant according to the present invention, the area of ​​the surface of the carbon nanotubes that is not sufficiently covered by the dispersant may increase, and thus, stronger bonding forces than an appropriate level occur between the carbon nanotubes, and agglomeration occurs between the carbon nanotubes, and thus the viscosity of the dispersion may become high.

[0084] In addition, if the second dispersant contains, for example, three or more aromatic rings in the molecular structure, small-diameter carbon nanotubes, especially single-walled carbon nanotubes, are not conducive to surface adsorption because the molecules become linear angles or form a dense structure. In addition, since strong pi-pi (π-π) interactions occur between non-adsorbed dispersants, thereby aggravating the agglomeration of the dispersants, the viscosity of the dispersion is formed to be high, and the viscosity of the dispersion may increase significantly due to its change over time.

[0085] Furthermore, if the substituted benzopyran-based compound contained in the second dispersant contains more than 6 hydroxyl groups, such as tannic acid or epigallocatechin gallate (EGCG), there is a problem that when these are applied to a carbon nanotube dispersion together with a first dispersant containing a nitrogen atom, very strong hydrogen bonds are formed between the dispersants, and thus a hydrogel or an insoluble combination may be formed, which may cause the viscosity of the dispersion to become too high.

[0086] In order to effectively express the above characteristics, if the substituted benzopyran-based compound included in the second dispersant contains three or more aromatic rings in the molecular structure or has a structure including more than six hydroxyl groups, it may be excluded.

[0087] In one embodiment of the present invention, the second dispersant may include a compound represented by Formula 1 below.

[0088] [Formula 1]

[0089]

[0090] In the above formula 1,

[0091] is a single bond or a double bond;

[0092] A1 to A6 are the same as or different from each other and are each independently hydrogen; deuterium; halogen; cyano; hydroxyl; carboxyl; substituted or unsubstituted C1 to C10 alkyl; substituted or unsubstituted C2 to C10 alkenyl; substituted or unsubstituted C2 to C10 alkynyl; substituted or unsubstituted C1 to C10 alkoxy; substituted or unsubstituted C3 to C10 cycloalkyl; substituted or unsubstituted C2 to C10 heterocycloalkyl; or a substituent represented by the following Formula 2, wherein at least one of A1 to A6 is represented by the following Formula 2,

[0093] [Formula 2]

[0094]

[0095] In the above formula 2,

[0096] B1 to B5 are the same as or different from each other and are each independently hydrogen; deuterium; halogen; cyano; hydroxyl; carboxyl; substituted or unsubstituted C1 to C10 alkyl; substituted or unsubstituted C2 to C10 alkenyl; substituted or unsubstituted C2 to C10 alkynyl; substituted or unsubstituted C1 to C10 alkoxy; substituted or unsubstituted C3 to C10 cycloalkyl; or substituted or unsubstituted C2 to C10 heterocycloalkyl,

[0097] wherein the substituents among A1 to A6 in Formula 1 that are not represented by Formula 2 and at least three of B1 to B5 in Formula 2 are hydroxyl groups.

[0098] Since the second dispersant includes a substituted benzopyran-based compound containing a benzopyran mother core represented by Formula 1 and a benzene ring represented by Formula 2, and at least three of the substituents of the substituted benzopyran-based compound are replaced by hydroxyl groups, the pi-pi (π-π) interaction between the carbon nanotubes in the dispersion and the aromatic rings of the second dispersant and the interaction through hydrogen bonding between the nitrogen atoms contained in the first dispersant and the hydroxyl groups of the second dispersant are properly balanced, and thus the effect of reducing the viscosity of the carbon nanotube dispersion and suppressing the increase in viscosity due to time change can be further improved.

[0099] In Formula 1, A1 to A6 are the same as or different from each other and are each independently hydrogen; deuterium; halogen; cyano; hydroxyl; carboxyl; substituted or unsubstituted C1 to C5 alkyl; substituted or unsubstituted C2 to C5 alkenyl; substituted or unsubstituted C2 to C5 alkynyl; substituted or unsubstituted C1 to C5 alkoxy; substituted or unsubstituted C3 to C5 cycloalkyl; substituted or unsubstituted C2 to C5 heterocycloalkyl; or a substituent represented by Formula 2 above, wherein at least one of A1 to A6 is represented by Formula 2 above,

[0100] In Formula 2, B1 to B5 are the same as or different from each other and are each independently hydrogen; deuterium; halogen; cyano; hydroxyl; carboxyl; substituted or unsubstituted C1 to C5 alkyl; substituted or unsubstituted C2 to C5 alkenyl; substituted or unsubstituted C2 to C5 alkynyl; substituted or unsubstituted C1 to C5 alkoxy; substituted or unsubstituted C3 to C5 cycloalkyl; or substituted or unsubstituted C2 to C5 heterocycloalkyl, wherein the substituents in A1 to A6 in Formula 1 that are not represented by Formula 2 and at least three of B1 to B5 in Formula 2 may be hydroxyl groups.

[0101] In Formula 1, A1 to A6 are the same as or different from each other and are each independently hydrogen; deuterium; hydroxyl; substituted or unsubstituted C1 to C5 alkoxy; or a substituent represented by Formula 2 above, wherein at least one of A1 to A6 is represented by Formula 2 above.

[0102] In Formula 2, B1 to B5 are the same as or different from each other and are each independently hydrogen; deuterium; hydroxyl; or a substituted or unsubstituted C1 to C5 alkoxy group, provided that the substituents in A1 to A6 in Formula 1 that are not represented by Formula 2 and at least three of B1 to B5 in Formula 2 can be hydroxyl groups.

[0103] In Formula 1, at least two of A1 to A6 may be hydroxyl groups.

[0104] In Formula 2, at least one of B1 to B5 may be a hydroxyl group.

[0105] In one embodiment of the present invention, the second dispersant may include a compound represented by any one of the following Formulae 3 to 5:

[0106] [Formula 3]

[0107]

[0108] [Formula 4]

[0109]

[0110] [Formula 5]

[0111]

[0112] In the above formulas 3 to 5,

[0113] A1 to A5 and B1 to B5 are the same as or different from each other and are each independently hydrogen; deuterium; halogen; cyano; hydroxyl; carboxyl; substituted or unsubstituted C1 to C10 alkyl; substituted or unsubstituted C2 to C10 alkenyl; substituted or unsubstituted C2 to C10 alkynyl; substituted or unsubstituted C1 to C10 alkoxy; substituted or unsubstituted C3 to C10 cycloalkyl; or substituted or unsubstituted C2 to C10 heterocycloalkyl,

[0114] At least three of A1 to A5 and B1 to B5 in Formula 1 are hydroxyl groups.

[0115] In Formulae 3 to 5, A1 to A5 and B1 to B5 are the same as or different from each other and are each independently hydrogen; deuterium; halogen; cyano; hydroxyl; carboxyl; substituted or unsubstituted C1 to C5 alkyl; substituted or unsubstituted C2 to C5 alkenyl; substituted or unsubstituted C2 to C5 alkynyl; substituted or unsubstituted C1 to C5 alkoxy; substituted or unsubstituted C3 to C5 cycloalkyl; or substituted or unsubstituted C2 to C5 heterocycloalkyl, wherein at least three of A1 to A5 and B1 to B5 in Formula 1 are hydroxyl groups.

[0116] In Formulae 3 to 5, A1 to A5 and B1 to B5 are the same as or different from each other and are each independently hydrogen; deuterium; hydroxyl; or a substituted or unsubstituted C1 to C5 alkoxy group, wherein at least three of A1 to A5 and B1 to B5 in Formula 1 may be hydroxyl groups.

[0117] In Formulae 3 to 5, at least two of A1 to A5 may be a hydroxyl group, and at least one of B1 to B5 may be a hydroxyl group.

[0118] In one embodiment of the present invention, specific examples of the second dispersant may be at least one selected from the following: luteolin, quercetin, kaempferol, myricetin, fisetin, morin, hesperidin, naringenin and eriodictyol, as shown in Table 1, and specific examples of the second dispersant are substituted benzopyran-based compounds, and may not be limited to the above types, as long as it contains at least three hydroxyl groups in the molecule and can improve the dispersibility of the carbon nanotubes.

[0119] [Table 1]

[0120]

[0121]

[0122] In one embodiment of the present invention, the carbon nanotube dispersion may include the second dispersant in an amount of 5 to 250 parts by weight, based on 100 parts by weight of the carbon nanotubes, and for example, may include it in an amount of 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 include it in an amount of 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, 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.

[0123] If the content of the second dispersant is less than 5 parts by weight based on 100 parts by weight of the carbon nanotubes, there may be a problem that the viscosity of the dispersion may not be low and the viscosity increases over time because the first dispersant and the second dispersant do not form sufficient hydrogen bonds and thus do not produce an effective dispersion effect. If the content of the second dispersant exceeds 250 parts by weight, there may be a problem that the solids in the dispersion agglomerate with each other due to the excessive content of the second dispersant, resulting in a high viscosity of the dispersion.

[0124] In one embodiment of the present invention, the first dispersant and the second dispersant in the carbon nanotube dispersion may be included in a weight ratio of 100:10 to 100:90, and for example, the first dispersant and 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, 100:34.33 or more, 100:35.33 or more, 100:36.33 or more, 100:37.33 or more, 100:38.33 or more, 100:39.34 or more, 100:40.35 or more, 100:41.36 or more, 100:42.36 or more, 100:43.33 or more, 100:44.33 or more, 100:45.33 or more, 100:46.33 or more, 100:47.33 or more, 100:48.33 or more, 100:49.34 or more, 100:40.35 or more, 100:49.35 or more, 100:41.33 or more, 100:49 ... The first dispersant and the second dispersant may be included in a weight ratio of 100:35 or more, 100:40 or more, 100:45 or more, 100:50 or more, or 100:55 or more, and the first dispersant and 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 100:60 or less.

[0125] If the contents of the first dispersant and the second dispersant in the carbon nanotube dispersion are in the above weight ratio, since the carbon nanotubes are uniformly dispersed in the carbon nanotube dispersion, the viscosity can be maintained at a constant level over time while having a low viscosity.

[0126] (3) Solvent

[0127] The solvent used in 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 pre-disperse the carbon nanotubes in a powder state to prevent them from agglomerating, and is supplied to the carbon nanotube dispersion when it is directly used in the production of the electrode slurry composition.

[0128] The solvent can dissolve or disperse the carbon nanotubes, the first dispersant, and the second dispersant to a certain level. The aqueous solvent can be, for example, water, and can be contained in an amount that allows the electrode slurry composition to have an appropriate viscosity, taking into account the coating properties of the electrode slurry composition manufactured using the carbon nanotube dispersion, etc.

[0129] In the case of a carbon nanotube dispersion according to one embodiment of the present invention, since the first dispersant and the second dispersant allow the carbon nanotubes to be uniformly dispersed in the solvent as described above, the average particle size distribution of the dispersed particles contained in the dispersion (e.g., a composite of the carbon nanotubes and each dispersant) can be reduced.

[0130] The average particle size distribution (D 50 ) can be, for example, 0.5 μm to 10 μm, 1 μm to 10 μm, 1 μm to 8 μm, preferably 1 μm to 5 μm.

[0131] The carbon nanotube dispersion of the present invention including the components described above has excellent dispersibility, low viscosity, and small increase in viscosity over time.

[0132] The initial viscosity of the carbon nanotube dispersion measured at 25° C. and 1 rpm using a viscometer (viscometer TV-25, rotor number 01, manufactured by TOKISANGYO) may be 1 to 10 Pa.s, and for example, the initial viscosity may be 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 the initial viscosity may be 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. If the carbon nanotube dispersion has an initial viscosity within the above range, an electrode slurry may be more smoothly manufactured using it, and the electrode slurry containing the carbon nanotube dispersion may have an appropriate viscosity for forming an electrode.

[0133] In addition, when the carbon nanotube dispersion is left at 25° C. for 1 week, the viscosity increase rate calculated by the following equation (1) may be 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% or less.

[0134] [Equation 1]

[0135] Viscosity increase rate (%) = {(viscosity measured after standing at 25°C for 1 week - initial viscosity) / initial viscosity} × 100

[0136] In this case, the viscosity after standing for one week and the initial viscosity were measured at 25° C. and 1 rpm.

[0137] Method for preparing carbon nanotube dispersion

[0138] Hereinafter, a method for preparing a carbon nanotube dispersion will be described.

[0139] The method for preparing a conductive material dispersion according to the present invention comprises the following steps: (1) mixing carbon nanotubes, a first dispersant containing nitrogen atoms, a second dispersant containing a substituted benzopyran-based compound containing at least three or more hydroxyl groups, and a solvent to prepare a primary dispersion of carbon nanotubes; and (2) dispersing the primary dispersion of carbon nanotubes to prepare a secondary dispersion of carbon nanotubes.

[0140] 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 a substituted benzopyran-based compound containing at least three or more hydroxyl groups, and a solvent. The step of preparing the primary dispersion of carbon nanotubes is performed in a wet method in which the components are uniformly mixed.

[0141] Mixing to produce a primary dispersion of carbon nanotubes can be carried out by a conventional mixing method, specifically using 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, a grinding mill, a universal agitator, a clear mixer or a TK mixer, etc., and can include a step of mixing at a rotation speed of 300 rpm to 5,000 rpm for 30 minutes to 7 hours.

[0142] In addition, when mixing to produce a primary dispersion of carbon nanotubes, a cavitation dispersion treatment may also be performed to increase the miscibility of the carbon nanotubes with 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 collapse of vacuum bubbles formed in water when high energy is applied to the liquid. By the above method, the carbon nanotubes can be dispersed without damaging their characteristics. Specifically, the cavitation dispersion treatment can be performed by ultrasonic, jet milling or shear dispersion treatment.

[0143] The step of preparing the primary dispersion of carbon nanotubes can be performed at a temperature under which the physical properties of the mixture, including viscosity, do not change due to evaporation of the aqueous solvent. For example, it can be performed at 50°C or lower, more specifically 5°C to 50°C.

[0144] In the preparation method of the carbon nanotube dispersion, since the detailed descriptions of the carbon nanotubes, the first dispersant containing nitrogen atoms, the second dispersant containing a substituted benzopyran-based compound containing at least 3 or more hydroxyl groups, and the solvent are the same as described above, the detailed description will be omitted below.

[0145] In step (2), a secondary dispersion of carbon nanotubes is prepared by dispersing a primary dispersion of carbon nanotubes.

[0146] The stirring process may be performed by a method using a ball mill, a bead mill, a disc mill or a basket mill, a high-pressure homogenizer, etc. More specifically, it may be performed by a grinding method using a disc mill or a high-pressure homogenizer.

[0147] When grinding by a disc mill, the size of the beads can be appropriately determined according to the type and amount of the carbon nanotubes and the type of the dispersant. Specifically, the diameter of the beads can be 0.1 mm to 5 mm, and 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.

[0148] Grinding by a high pressure homogenizer pressurizes the mixture, for example, with a plunger pump of the high pressure homogenizer and pushes it through the gap of a homogenizing valve, and thus is achieved by forces such as cavitation, shearing, impact and explosion when passing through the gap.

[0149] The dispersion process may be performed according to the dispersion degree of the carbon nanotube dispersion, and specifically may be performed at a pressure of 5,000 psi to 30,000 psi for 30 to 120 minutes, more specifically 60 to 90 minutes, and the process may be repeated 1 to 10 times.

[0150] The carbon nanotube dispersion according to the present invention may mean a secondary dispersion of carbon nanotubes.

[0151] Electrode slurry composition for lithium secondary battery

[0152] In addition, the present invention provides an electrode slurry composition for a lithium secondary battery, which includes a carbon nanotube dispersion and an electrode active material.

[0153] The 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.

[0154] The electrode slurry composition for a lithium secondary battery may include a carbon nanotube dispersion, a positive electrode active material or a negative electrode active material as an electrode active material, a binder, and, if necessary, a solvent and / or other additives.

[0155] As the positive electrode active material, positive electrode active materials known in the art can be used without limitation. For example, lithium cobalt-based oxides, lithium nickel-based oxides, lithium manganese-based oxides, lithium iron phosphate, lithium nickel manganese cobalt-based oxides, or combinations thereof can be used. Specifically, as the positive electrode active material, LiCoO2, LiNiO2, LiMn2O4, LiCoPO4, LiFePO4, LiNiaMnbCocO2 (where 0 < a, b, c < 1), etc. can be used, but are not limited thereto.

[0156] The negative electrode active material can include one or two or more negative electrode active materials selected from the following: natural graphite, artificial graphite, carbon-containing materials; lithium-containing titanium composite oxides (LTO), metals (Me) (which are Si, Sn, Li, Zn, Mg, Cd, Ce, Ni, or Fe); alloys composed of the above metals (Me); oxides of the above metals (MeO x ); and composites of the above metals (Me) and carbon. Based on the total weight of the solids excluding the solvent in the negative electrode slurry, the negative electrode active material can be included in an amount of 60% to 98% by weight, more preferably 70% to 98% by weight.

[0157] The binder is a component that helps the adhesion between the active material and the conductive material, etc., and the adhesion to the current collector, and is usually added in an amount of 1% to 30% by weight based on the total weight of the mixture containing the electrode active material. Examples of such binders can 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, various copolymers, etc.

[0158] The solvent can be an organic solvent such as N-methylpyrrolidone (NMP), dimethylformamide (DMF), acetone, and dimethylacetamide, or water, and these solvents can be used alone or as a mixture of two or more types. The amount of the solvent used is sufficient as long as it can dissolve and disperse the electrode active material, binder, and conductive material considering the thickness of the slurry application and the preparation yield.

[0159] The viscosity regulator can be carboxymethyl cellulose, polyacrylic acid, etc., and by adding it, the viscosity of the electrode slurry can be adjusted to facilitate the preparation of the electrode slurry and the application process on the electrode current collector.

[0160] The filler is selectively used as a component for suppressing electrode expansion and is not particularly limited as long as it is a fiber material that does not cause chemical changes in the battery, and includes, for example, olefin polymerizers such as polyethylene and polypropylene; fiber materials such as glass fiber or carbon fiber.

[0161] If the electrode slurry composition is a positive electrode slurry composition for forming a positive electrode, the positive electrode can be manufactured by applying the positive electrode slurry composition to a positive electrode current collector, and then drying and rolling it. Alternatively, it can also be manufactured by casting the positive electrode slurry on a separate support, and then laminating the film obtained by peeling off the support on the positive electrode current collector.

[0162] The thickness of the positive electrode active material layer formed from the positive electrode slurry may vary depending on the loading amount, loading speed, etc. of applying the positive electrode slurry.

[0163] The thickness of the positive electrode current collector is generally 3 μm to 500 μm. This positive electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel with a surface treated with carbon, nickel, titanium, silver, etc. can be used. In addition, by forming fine irregularities on the surface of the positive electrode current collector, the bonding strength of the positive electrode active material can be enhanced, and it can be used in various forms such as films, sheets, foils, nets, porous bodies, foams, and non-woven fabrics.

[0164] If the electrode slurry composition is a negative electrode slurry composition for forming a negative electrode, the negative electrode can be manufactured by applying the negative electrode slurry composition to a negative electrode current collector, and then drying and rolling it. In addition, it can also be manufactured by casting the negative electrode slurry on a separate support, and then laminating the film obtained by peeling off the support on the negative electrode current collector.

[0165] The thickness of the negative electrode active material layer formed from the negative electrode slurry may vary according to the loading amount, loading speed, etc. of applying the negative electrode slurry.

[0166] The thickness of the negative electrode current collector is generally 3 μm to 500 μm. This negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, or copper or stainless steel treated with carbon, nickel, titanium, silver, etc., or aluminum-cadmium alloy can be used. In addition, with respect to the negative electrode current collector, the bonding strength of the negative electrode active material can be enhanced by forming fine irregularities on the surface, and it can be used in various forms such as films, sheets, meshes, foils, porous bodies, foams, and non-woven fabrics.

[0167] Lithium secondary battery

[0168] The lithium secondary battery includes a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte solution. Since the positive electrode and the negative electrode are the same as described above, a detailed description is omitted.

[0169] The separator separates the negative electrode and the positive electrode, and provides a channel for lithium ion movement. The separator can be used without any particular restrictions, as long as it is commonly used as a separator in a lithium secondary battery. As a separator, it is particularly preferred to have low resistance to the movement of electrolyte ions and excellent electrolyte solution impregnation ability. Specifically, a porous polymer film can be used, such as a porous polymer film made of a polyolefin-based polymer (such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, ethylene / methacrylate copolymer, etc.) or a laminated structure of two or more layers thereof. In addition, conventional porous nonwoven fabrics can also be used, such as nonwoven fabrics made of high melting point glass fiber, polyethylene terephthalate fiber, etc. In addition, a coated separator comprising a ceramic component or a polymer material can be used to ensure heat resistance or mechanical strength, and the separator can be selectively used with a single layer or multilayer structure.

[0170] The electrolyte includes, but is not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the manufacture of lithium secondary batteries. Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0171] The organic solvent can be used without any particular limitation, as long as it can act as a medium through which ions participating in the electrochemical reaction of the battery can move. Specifically, the organic solvent can be an ester-based solvent, such as methyl acetate, ethyl acetate, γ-butyrolactone or ε-caprolactone; an ether-based solvent, such as dibutyl ether or tetrahydrofuran; a ketone-based solvent, such as cyclohexanone; an aromatic hydrocarbon-based solvent, such as benzene or fluorobenzene; a carbonate-based solvent, such as dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), propylene carbonate (PC); an alcohol-based solvent, such as ethanol or isopropanol; a nitrile, such as R-CN (R is a C2 to C20 linear, branched or cyclic hydrocarbon group, and may contain a double bond aromatic ring or an ether bond); an amide, such as dimethylformamide; a dioxolane, such as 1,3-dioxolane; or cyclopentane sulfone. Among them, carbonate-based solvents are preferred, and a mixture of cyclic carbonates (e.g., ethylene carbonate or propylene carbonate, etc.) with high ionic conductivity and high dielectric constant that can improve the charge / discharge performance of the battery and a linear carbonate-based compound (e.g., ethyl methyl carbonate, dimethyl carbonate or diethyl carbonate, etc.) with low viscosity is more preferred. In this case, when the cyclic carbonate and the chain carbonate are mixed in a volume ratio of about 1:1 to about 1:9, the performance of the electrolyte solution can be excellent.

[0172] Lithium salts can be used without particular limitation, as long as they are compounds that can provide lithium ions for lithium secondary batteries. Specifically, the lithium salt can be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2, etc. The concentration of the lithium salt is preferably used in the range of 0.1M to 2.0M. If the concentration of the lithium salt is within the above range, since the electrolyte has suitable conductivity and viscosity, it can exhibit excellent electrolyte performance, and lithium ions can be effectively moved.

[0173] In the electrolyte, in addition to the above-mentioned electrolyte components, for the purpose of improving the life characteristics of the battery, suppressing the reduction of the battery capacity and improving the discharge capacity of the battery, for example, one or more additives may be included, such as halogenated alkylene carbonate-based compounds such as difluoroethylene carbonate; pyridine; triethyl phosphite; triethanolamine; cyclic ether; ethylenediamine; n-glyme; hexaphosphoric acid triamide; nitrobenzene derivatives; sulfur, quinone imine dyes; N-substituted Oxazolidinone; N,N-substituted imidazolidine; ethylene glycol dialkyl ether; ammonium salt; pyrrole; 2-methoxyethanol or aluminum trichloride. In this case, the additive may be included in an amount of 0.1 wt % to 5 wt % based on the total weight of the electrolyte.

[0174] A lithium secondary battery including an electrode manufactured using a carbon nanotube dispersion according to the present invention, specifically, a lithium secondary battery including a negative electrode manufactured using the carbon nanotube dispersion has carbon nanotubes uniformly distributed in the negative electrode, and its content can be reduced compared to conventional conductive materials such as carbon black, so it can stably exhibit excellent discharge capacity and output characteristics. Therefore, it can be effectively used in portable devices such as mobile phones, notebook computers, digital cameras and electric vehicles, such as hybrid electric vehicles (HEV).

[0175] Therefore, according to another embodiment of the present invention, the present invention provides a battery module including the lithium secondary battery as a unit battery and a battery pack including the same.

[0176] The battery module or battery pack can be used as a power source for any one or more of the following medium and large devices: power tools; electric vehicles, including electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); or power storage systems, etc.

[0177] Embodiments of the invention

[0178] Hereinafter, specific embodiments of the present invention are given. However, the following embodiments are only used to describe or explain the present invention in detail, but not to limit the present invention. In addition, since those skilled in the art can fully infer the contents not described herein from a technical point of view, the description thereof is omitted.

[0179] Example

[0180] Example 1

[0181] (1) 5.625 g (1.125 wt % relative to a total of 100 parts by weight of the carbon nanotube dispersion) of polyvinylpyrrolidone (PVP, manufactured by Zhangzhou Huafu Chemical Co., Ltd.) as a first dispersant containing nitrogen atoms, 1.875 g (0.375 wt % relative to a total of 100 parts by weight of the carbon nanotube dispersion) of luteolin (manufactured by INDOFINE Chemical Co., Ltd.) (which is a second dispersant containing a substituted benzopyran-based compound containing at least three or more hydroxyl groups) and 487.5 g of water as a solvent were mixed to prepare 495 g of a mixed solution, and the obtained mixed solution was put into a dissolving tank (dissolver, Dispermat-CA, manufactured by VMA-GETZMANN Co., Ltd.) equipped with an impeller and a container and stirred and mixed at 400 rpm for 10 minutes.

[0182] To the above mixture was further added 5.0 g (1.0 wt % relative to a total of 100 parts by weight of the carbon nanotube dispersion) of a carbon nanotube having a specific surface area of ​​1,160 m 2 / g and the average particle size (D 50 ) with a single-walled carbon nanotube (SWCNT, TUBALL, produced by OCSiAl Corporation) having a size of 5 μm, and stirred at 8,000 rpm for 60 minutes to produce a primary dispersion of 500 g of carbon nanotubes in total.

[0183] (3) The primary dispersion of carbon nanotubes was uniformly dispersed seven times using a high-pressure disperser (PICOMAX, manufactured by Micronox Corporation) at a pressure of 20,000 psi to prepare a secondary dispersion of carbon nanotubes.

[0184] Example 2

[0185] A carbon nanotube dispersion was prepared in the same manner as in Example 1 above, except that in Example 1 above, the content of the first dispersant was set to 1.000 wt % relative to a total of 100 parts by weight of the carbon nanotube dispersion, and the content of the second dispersant was set to 0.5 wt % relative to a total of 100 parts by weight of the carbon nanotube dispersion.

[0186] Example 3

[0187] A carbon nanotube dispersion was prepared in the same manner as in Example 1 above, except that in Example 1 above, the content of the carbon nanotubes was set to 0.6 wt % relative to a total of 100 parts by weight of the carbon nanotube dispersion, the content of the first dispersant was set to 0.675 wt % relative to a total of 100 parts by weight of the carbon nanotube dispersion, and the content of the second dispersant was set to 0.225 wt % relative to a total of 100 parts by weight of the carbon nanotube dispersion.

[0188] Example 4

[0189] A carbon nanotube dispersion was prepared in the same manner as in Example 1 above, except that in Example 1 above, the content of the second dispersant was set to 0.113 wt % relative to a total of 100 parts by weight of the carbon nanotube dispersion.

[0190] Example 5

[0191] A carbon nanotube dispersion was prepared in the same manner as in Example 1 above, except that in Example 1 above, the content of the first dispersant was set to 2.500 wt % relative to a total of 100 parts by weight of the carbon nanotube dispersion, and the content of the second dispersant was set to 2.250 wt % relative to a total of 100 parts by weight of the carbon nanotube dispersion.

[0192] Example 6

[0193] A carbon nanotube dispersion was prepared in the same manner as in Example 1 above, except that in Example 1 above, 1.875 g (0.375 wt % relative to a total of 100 parts by weight of the carbon nanotube dispersion) of quercetin (produced by INDOFINE Chemical Co., Ltd.) was used instead of luteolin as the second dispersant including a substituted benzopyran-based compound containing at least three hydroxyl groups.

[0194] Example 7

[0195] A carbon nanotube dispersion was prepared in the same manner as in Example 1 above, except that in Example 1 above, 1.875 g (0.375 wt % relative to a total of 100 parts by weight of the carbon nanotube dispersion) of myricetin (prepared by INDOFINE Chemical) was used instead of luteolin as the second dispersant comprising a substituted benzopyran-based compound containing at least three hydroxyl groups.

[0196] Comparative Example 1

[0197] A carbon nanotube dispersion was prepared in the same manner as in Example 1 above, except that in Example 1 above, the second dispersant was not added.

[0198] Comparative Example 2

[0199] A carbon nanotube dispersion was prepared in the same manner as in Example 1 above, except that in Example 1 above, the content of the carbon nanotubes was set to 0.6 wt % relative to a total of 100 parts by weight of the carbon nanotube dispersion, and the content of the first dispersant was set to 0.900 wt % relative to a total of 100 parts by weight of the carbon nanotube dispersion, and the second dispersant was not added.

[0200] Comparative Example 3

[0201] A carbon nanotube dispersion was prepared in the same manner as in Example 1 above, except that in Example 1 above, the content of the second dispersant was set to 1.500 wt % with respect to a total of 100 parts by weight of the carbon nanotube dispersion, and the first dispersant was not added.

[0202] Comparative Example 4

[0203] A carbon nanotube dispersion was prepared in the same manner as in Example 1 above, except that in Example 1 above, the content of the carbon nanotubes was set to 0.6 wt % relative to a total of 100 parts by weight of the carbon nanotube dispersion, the content of the first dispersant was set to 0.675 wt % relative to a total of 100 parts by weight of the carbon nanotube dispersion, and the content of the second dispersant, which was tristyrylphenol ethoxylate instead of luteolin, was set to 0.225 wt % relative to a total of 100 parts by weight of the carbon nanotube dispersion.

[0204] Comparative Example 5

[0205] A carbon nanotube dispersion was prepared in the same manner as in Example 1 above, except that in Example 1 above, the content of the carbon nanotubes was set to 0.6 wt % relative to a total of 100 parts by weight of the carbon nanotube dispersion, the content of the first dispersant was set to 0.675 wt % relative to a total of 100 parts by weight of the carbon nanotube dispersion, and the content of the second dispersant, which was a styrene maleic acid copolymer instead of luteolin, was set to 0.225 wt % relative to a total of 100 parts by weight of the carbon nanotube dispersion.

[0206] Comparative Example 6

[0207] A carbon nanotube dispersion was prepared in the same manner as in Example 1 above, except that in Example 1 above, tannic acid was added as the second dispersant in an amount of 0.375 wt % instead of luteolin, relative to a total of 100 parts by weight of the carbon nanotube dispersion.

[0208] Comparative Example 7

[0209] A carbon nanotube dispersion was prepared in the same manner as in Example 1 above, except that in Example 1 above, epigallocatechin gallate was added as the second dispersant in an amount of 0.375 wt % instead of luteolin, relative to a total of 100 parts by weight of the carbon nanotube dispersion.

[0210] Comparative Example 8

[0211] A carbon nanotube dispersion was prepared in the same manner as in Example 1 above, except that in Example 1 above, the content of the first dispersant was set to 0.250 wt % relative to a total of 100 parts by weight of the carbon nanotube dispersion, and the content of the second dispersant was set to 0.025 wt % relative to a total of 100 parts by weight of the carbon nanotube dispersion.

[0212] Comparative Example 9

[0213] A carbon nanotube dispersion was prepared in the same manner as in Example 1 above, except that in Example 1 above, the content of the first dispersant was set to 3.056 wt % relative to a total of 100 parts by weight of the carbon nanotube dispersion, and the content of the second dispersant was set to 2.750 wt % relative to a total of 100 parts by weight of the carbon nanotube dispersion.

[0214] Comparative Example 10

[0215] A carbon nanotube dispersion was prepared in the same manner as in Example 1 above, except that in Example 1 above, the content of the first dispersant was set to 2.600 wt % relative to a total of 100 parts by weight of the carbon nanotube dispersion, and the content of the second dispersant was set to 2.600 wt % relative to a total of 100 parts by weight of the carbon nanotube dispersion.

[0216] Experimental example

[0217] 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.

[0218] The viscosity is measured using a viscometer (Viscometer TV-25, rotor No. 01, manufactured by TOKI SANGYO CORPORATION) at 25°C and 1 rpm.

[0219] [Table 2]

[0220]

[0221]

[0222] (*The contents of CNT, the first dispersant and the second dispersant are based on a total of 100 wt% of the carbon nanotube dispersion)

[0223] Referring to Table 2 above, it can be seen that the carbon nanotube dispersions of Examples 1 to 7 containing the first dispersant and the second dispersant containing a substituted benzopyran-based compound containing at least 3 or more hydroxyl groups in specific amounts have low initial viscosities immediately after dispersing the carbon nanotubes in an aqueous solvent, and in particular, increase in viscosity of the carbon nanotube dispersion over time is very effectively suppressed, compared to the carbon nanotube dispersion of Comparative Example 1 containing only polyvinyl pyrrolidone as the first dispersant.

[0224] In the case of the carbon nanotube dispersion in Comparative Example 2, it can be seen that since the content of carbon nanotubes is reduced compared with the carbon nanotube dispersion in Comparative Example 1, the initial viscosity immediately after dispersing the carbon nanotubes in an aqueous solvent is reduced compared with the carbon nanotube dispersion in Comparative Example 1, but like the carbon nanotube dispersion of Comparative Example 1, since it does not include the second dispersant containing a substituted benzopyran-based compound containing at least 3 or more hydroxyl groups compared with Examples 1 to 3, the effect of suppressing the increase in the viscosity of the dispersion due to changes over time is not observed.

[0225] In the case of the carbon nanotube dispersion in Comparative Example 3, since the first dispersant was not included compared with the carbon nanotube dispersions in Examples 1 to 3, the carbon nanotubes could not be completely dispersed in the aqueous solvent, and agglomeration of the dispersion occurred, making viscosity measurement impossible.

[0226] In the case of the carbon nanotube dispersions in Comparative Examples 4 and 5, it can be seen that since a material containing a substituted benzopyran-based compound containing at least 3 or more hydroxyl groups is not used compared to the carbon nanotube dispersions in Examples 1 to 3, the initial viscosity immediately after dispersing the carbon nanotubes in an aqueous solution is high (Comparative Example 4), and the effect of suppressing the increase in the viscosity of the dispersion due to changes over time is not observed (Comparative Examples 4 and 5).

[0227] In the case of the carbon nanotube dispersions in Comparative Examples 6 and 7, it can be seen that since the compound used as the second dispersant contains more than six hydroxyl groups compared to the carbon nanotube dispersions in Examples 1 to 3, excessive hydrogen bonding with the first dispersant and the solvent occurs due to the excessive hydroxyl groups, and as a result, the formation of hydrogel is intensified, and the initial viscosity immediately after dispersing the carbon nanotubes is high, and the effect of suppressing the increase in the viscosity of the dispersion due to time change is not observed.

[0228] In the case of the carbon nanotube dispersion in Comparative Example 8, since the second dispersant was included at a content lower than a certain range compared with the carbon nanotube dispersions in Examples 1 to 3, the carbon nanotubes could not be completely dispersed in the aqueous solvent, and agglomeration of the dispersion occurred, making viscosity measurement impossible.

[0229] In the case of the carbon nanotube dispersion in Comparative Example 9, it can be seen that since the second dispersant is contained in excess compared to the carbon nanotube dispersions in Examples 1 to 3, the initial viscosity immediately after dispersing the carbon nanotubes in the aqueous solution is high, and the effect of suppressing the increase in the viscosity of the dispersion due to changes over time is not observed.

[0230] In the case of the carbon nanotube dispersion in Comparative Example 10, it can be seen that since the contents of the first dispersant and the second dispersant do not satisfy a certain ratio compared to the carbon nanotube dispersions in Examples 1 to 3, the initial viscosity immediately after dispersing the carbon nanotubes in the aqueous solution is high, and the effect of suppressing the increase in the viscosity of the dispersion due to changes over time is not observed.

[0231] Therefore, it was determined that only when a carbon nanotube dispersion obtained by dispersing carbon nanotubes in an aqueous solvent contained a first dispersant containing nitrogen atoms and a second dispersant at a certain weight ratio, and the second dispersant contained a substituted benzopyran-based compound containing at least 3 or more hydroxyl groups, the carbon nanotube dispersion exhibited low viscosity and an increase in viscosity due to time-dependent changes could be suppressed.

[0232] Although the preferred embodiments of the present invention have been described in detail above, the scope of rights 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 appended claims also fall within the scope of rights of the present invention.

Claims

1. A carbon nanotube dispersion comprising: Carbon nanotubes; a first dispersant containing nitrogen atoms; a second dispersant comprising a substituted benzopyran-based compound; and Solvents, The substituted benzopyran-based compound included in the second dispersant contains at least three hydroxyl groups.

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

3. The carbon nanotube dispersion according to claim 1, wherein the second dispersant comprises a compound represented by any one of the following Formulas 3 to 5: [Formula 3] [Formula 4] [Formula 5] In the above formulas 3 to 5, A1 to A5 and B1 to B5 are the same as or different from each other and are each independently hydrogen; deuterium; halogen; cyano; hydroxyl; carboxyl; substituted or unsubstituted C1 to C10 alkyl; substituted or unsubstituted C2 to C10 alkenyl; substituted or unsubstituted C2 to C10 alkynyl; substituted or unsubstituted C1 to C10 alkoxy; substituted or unsubstituted C3 to C10 cycloalkyl; or substituted or unsubstituted C2 to C10 heterocycloalkyl, At least three of A1 to A5 and B1 to B5 in Formula 1 are hydroxyl groups. 4 . The carbon nanotube dispersion according to claim 1 , wherein the second dispersant is at least one selected from the group consisting of luteolin, quercetin, kaempferol, myricetin, fisetin, morin, hesperidin, naringenin, and eriodictyol.

5. The carbon nanotube dispersion according to claim 1, wherein the carbon nanotubes have a BET specific surface area of ​​800 m 2 / g to 2,000m 2 / g. 6 . The carbon nanotube dispersion according to claim 1 , wherein the carbon nanotube dispersion comprises the first dispersant in an amount of 25 parts by weight to 450 parts by weight based on 100 parts by weight of the carbon nanotubes. 7 . The carbon nanotube dispersion according to claim 1 , wherein the carbon nanotube dispersion comprises the second dispersant in an amount of 5 parts by weight to 250 parts by weight based on 100 parts by weight of the carbon nanotubes.

8. The carbon nanotube dispersion according to claim 1, wherein the first dispersant is at least one selected from the group consisting of polyvinyl pyrrolidone, polyacrylic acid hydrazide, poly-N-vinyl-5-methyl Oxazolidinone, N-alkylpolyimine, N-acetylpolyimine, polyacrylamide, poly-L-lysine hydrobromide, benzyl-dodecyl-dimethylammonium chloride and polyethyleneimine. 9 . The carbon nanotube dispersion according to claim 1 , wherein the first dispersant and the second dispersant are included in a weight ratio of 100:10 to 100:

90. 10 . The carbon nanotube dispersion according to claim 1 , wherein the carbon nanotube dispersion has an initial viscosity of 1 to 10 Pa·s as measured at 25° C. and 1 rpm.

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

12. A method for preparing the carbon nanotube dispersion according to claim 1, comprising: (1) mixing carbon nanotubes, a first dispersant containing nitrogen atoms, a second dispersant containing a substituted benzopyran-based compound containing at least three hydroxyl groups, and a solvent to prepare a primary dispersion of carbon nanotubes; as well as (2) dispersing the primary dispersion of carbon nanotubes to prepare a secondary dispersion of carbon nanotubes. 13 . An electrode slurry composition for a lithium secondary battery, comprising the carbon nanotube dispersion according to claim 1 and an electrode active material.

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