Carbon nanotube dispersion and preparation method thereof

Abstract

The present invention relates to a carbon nanotube dispersion and a method for preparing the same, the carbon nanotube dispersion comprising: carbon nanotubes; a first dispersant containing nitrogen atoms; a mixture of a second dispersant and a cation; and a solvent, in which the second dispersant contains at least one hydroxyl group and at least one carboxyl group in an aromatic ring, and the cation includes at least one selected from the group consisting of an alkali metal ion, an alkaline earth metal ion, an aluminum ion, a transition metal ion, an ammonium ion, and a sulfur # imgabs0 # ion.

Description

Technical Field

[0001] This application claims the benefit of Korean Patent Application No. 10-2023-0080140, filed on June 22, 2023, and Korean Patent Application No. 10-2024-0077176, 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] One object of the present invention is to provide a carbon nanotube dispersion comprising: carbon nanotubes; a first dispersant containing nitrogen atoms; a mixture of a second dispersant and cations; and a solvent, wherein the second dispersant contains at least one hydroxyl group and at least one carboxyl group in an aromatic ring, and the cations include ions selected from alkali metal ions, alkaline earth metal ions, aluminum ions, transition metal ions, ammonium ions, and sulfur ions. ions, 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] Still another object of the present invention is to provide a method for preparing the 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 mixture of a second dispersant and cations; and a solvent, wherein the second dispersant contains at least one hydroxyl group and at least one carboxyl group in an aromatic ring, and the cations include ions selected from alkali metal ions, alkaline earth metal ions, aluminum ions, transition metal ions, ammonium ions, and sulfur ions. At least one of the ions.

[0018] The second dispersant may have a structure not including two or more aromatic rings in the molecular structure.

[0019] The second dispersant may include a compound represented by Formula 1 below.

[0020] [Formula 1]

[0021]

[0022] In the above formula 1,

[0023] R1 to R5 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 at least one of R1 to R5 is hydroxyl,

[0024] R6 is a carboxyl group,

[0025] L is a single bond; a substituted or unsubstituted C1 to C10 alkylene group; a substituted or unsubstituted C2 to C10 alkenylene group; or a substituted or unsubstituted C2 to C10 alkynylene group.

[0026] The second dispersant may be at least one selected from the group consisting of gallic acid, protocatechuic acid, syringic acid, ferulic acid, vanillic acid, caffeic acid, p-coumaric acid, salicylic acid, 2,4-dihydroxybenzoic acid, homogentisic acid, and sinapinic acid.

[0027] The BET specific surface area of ​​carbon nanotubes can be 800 m 2 / g to 2,000m 2 / g.

[0028] 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.

[0029] The carbon nanotube dispersion may include the mixture of the second dispersant and the cation in an amount of 5 parts by weight to 250 parts by weight based on 100 parts by weight of the carbon nanotube.

[0030] The cation may be included in an amount of 2 parts by weight to 20 parts by weight based on 100 parts by weight of the second dispersant.

[0031] 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-alkylpolyimine, N-acetylpolyimine, polyacrylamide, poly-L-lysine hydrobromide, benzyl-dodecyl-dimethylammonium chloride and polyethyleneimine.

[0032] The mixture of the first dispersant and the second dispersant and the cation may be included in a weight ratio of 100:10 to 100:90.

[0033] 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.

[0034] The viscosity increase rate of the carbon nanotube dispersion represented by the following Equation 1 may be 15% or less.

[0035] [Equation 1]

[0036] Viscosity increase rate (%) = {(viscosity measured after standing at 25°C for 1 week - initial viscosity) / initial viscosity} × 100

[0037] 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 at least one hydroxyl group and at least one carboxyl group in an aromatic ring, a cationic precursor, 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.

[0038] The precursor of the cation may include a hydroxide of one or more types of cations selected from the group consisting of alkali metal ions, alkaline earth metal ions, aluminum ions, transition metal ions, ammonium ions, and sulfur ions. ion.

[0039] 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.

[0040] Beneficial Effects

[0041] Although carbon nanotubes having a large specific surface area are used, the second dispersant containing at least one hydroxyl group and at least one carboxyl group in an aromatic ring and a second dispersant selected from the group consisting of alkali metal ions, alkaline earth metal ions, aluminum ions, transition metal ions, ammonium ions and sulfur ions are used. The carbon nanotube dispersion according to the present invention has a small viscosity change over time, exhibits a relatively low viscosity, and has the characteristics of a small particle size of dispersed particles.

[0042] 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

[0043] 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.

[0044] 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.

[0045] Throughout the present specification, "%" means % by weight unless otherwise specifically stated.

[0046] 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.

[0047] 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.

[0048] In the present specification, a "precursor" may refer to a substance at a stage before becoming a specific substance in a reaction, and for example, a "cation precursor" may mean a substance that can provide a "cation" by being ionized in an aqueous solvent or the like.

[0049] Carbon Nanotube Dispersion

[0050] The carbon nanotube dispersion according to the present invention comprises: carbon nanotubes; a first dispersant containing nitrogen atoms; a second dispersant containing at least one hydroxyl group and at least one carboxyl group in an aromatic ring and an ion selected from alkali metal ions, alkaline earth metal ions, aluminum ions, transition metal ions, ammonium ions and sulfur ions. a mixture of one or more cations among the ions; and a solvent. Hereinafter, each component of the carbon nanotube dispersion of the present invention will be described in detail.

[0051] (1) Carbon nanotubes

[0052] 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 2 Bond 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).

[0053] 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.

[0054] 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.

[0055] Since the carbon nanotube dispersion according to the present invention contains a second dispersant containing at least one hydroxyl group and at least one carboxyl group in an aromatic ring and an ion selected from alkali metal ions, alkaline earth metal ions, aluminum ions, transition metal ions, ammonium ions and sulfur ions, ions, and a first dispersant containing nitrogen atoms, so that it can significantly reduce the initial viscosity of the carbon nanotube dispersion and inhibit the occurrence of viscosity changes over time, and thus when applied to electrode slurries for lithium secondary batteries, high conductivity can be achieved due to the high conductivity of carbon nanotubes.

[0056] 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.

[0057] 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.

[0058] 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.

[0059] 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.

[0060] 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, 0.7% 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.

[0061] 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.

[0062] 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.

[0063] (2) A first dispersant, and a mixture of a second dispersant and a cation

[0064] The carbon nanotube dispersion according to the present invention comprises a mixture of a second dispersant containing at least one hydroxyl group and at least one carboxyl group in an aromatic ring and a cation; and a first dispersant containing nitrogen atoms to improve the dispersibility of the carbon nanotubes.

[0065] In the carbon nanotube dispersion, the mixture of the second dispersant containing at least one hydroxyl group and at least one carboxyl group in the aromatic ring and the cation and the first dispersant containing nitrogen atoms act as dispersants that increase the dispersibility of the carbon nanotubes, so that the carbon nanotubes can be uniformly dispersed without agglomerating in the dispersion, and particularly exhibits the effect of suppressing the change in viscosity of the carbon nanotube dispersion over time.

[0066] 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.

[0067] 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.

[0068] 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.

[0069] In addition, in order to solve the problem that the viscosity of the dispersion increases with the increase of the content of carbon nanotubes in the carbon nanotube dispersion containing only the first dispersant, the carbon nanotube dispersion according to one embodiment of the present invention contains a second dispersant containing at least one hydroxyl group and at least one carboxyl group in an aromatic ring and a second dispersant selected from the group consisting of alkali metal ions, alkaline earth metal ions, aluminum ions, transition metal ions, ammonium ions and sulfur ions. ions and a first dispersant, and therefore, the carbon nanotube dispersion according to an embodiment of the present invention has excellent dispersibility compared to a carbon nanotube dispersion using only a conventional dispersant, thereby producing the effects of less particle agglomeration and lower sedimentation velocity in the slurry composition.

[0070] In one embodiment of the present invention, the second dispersant may not include two or more aromatic rings in its molecular structure.

[0071] Since the second dispersant containing at least one hydroxyl group and at least one carboxyl group in the aromatic ring does not contain two or more aromatic rings in the molecular structure, the second dispersant has a relatively low molecular weight and a small molecular size, thereby allowing it to exhibit an additional dispersing effect by adsorbing on the surface of the carbon nanotubes that is not covered by the first dispersant containing nitrogen atoms. If the carbon nanotube dispersion does not contain the second dispersant according to the present invention, the area of ​​the surface of the carbon nanotubes that is not fully covered by the dispersant may increase, and thus a stronger binding force than the appropriate binding force between the carbon nanotubes may be applied, resulting in a high dispersion viscosity due to agglomeration between the carbon nanotubes.

[0072] In addition, if the second dispersant contains a structure such as a phenol compound containing two or more aromatic rings in the molecular structure, as the molecule becomes a linear angle or forms a dense structure, it becomes unfavorable for the surface adsorption of small-diameter carbon nanotubes, especially single-walled carbon nanotubes. In addition, the pi-pi (π-π) interaction formed by the ring structure within the molecule occurs strongly, deepening the agglomeration of the dispersant, and the cations forming the mixture with the second dispersant have insufficient control over the charge, resulting in a high viscosity of the dispersion, and the viscosity of the dispersion may increase significantly over time.

[0073] In order to effectively exhibit the above characteristics, the second dispersant including a structure in which two or more independent aromatic rings in the molecular structure are connected to each other through a linking group or the like, or a structure in which two or more aromatic rings are condensed may be excluded.

[0074] In one embodiment of the present invention, the second dispersant may include a compound represented by Formula 1 below.

[0075] [Formula 1]

[0076]

[0077] In the above formula 1,

[0078] R1 to R5 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 at least one of R1 to R5 is hydroxyl,

[0079] R6 is a carboxyl group,

[0080] L is a single bond; a substituted or unsubstituted C1 to C10 alkylene group; a substituted or unsubstituted C2 to C10 alkenylene group; or a substituted or unsubstituted C2 to C10 alkynylene group.

[0081] As shown in Formula 1 above, since the second dispersant simultaneously includes at least one hydroxyl group and a carboxyl group in the aromatic ring, the pi-pi (π-π) interaction between the carbon nanotubes in the dispersion and the aromatic ring of the second dispersant and the interaction through hydrogen bonding between the nitrogen atoms included in the first dispersant and the hydroxyl group and the carboxyl group 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.

[0082] In Formula 1, R1 to R5 are the same as or different from each other and are each independently hydrogen; deuterium; 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 one of R1 to R5 may be hydroxyl.

[0083] In Formula 1, R1 to R5 are the same as or different from each other, and are each independently hydrogen; deuterium; hydroxyl; or carboxyl, wherein at least one of R1 to R5 may be a hydroxyl.

[0084] In Formula 1, at least two of R1 to R5 may be hydroxyl groups.

[0085] In Formula 1, at least three of R1 to R5 may be hydroxyl groups.

[0086] In Formula 1, L may be a single bond; a substituted or unsubstituted C1 to C5 alkylene group; a substituted or unsubstituted C2 to C5 alkenylene group; or a substituted or unsubstituted C2 to C5 alkynylene group.

[0087] In Formula 1 above, L may be a single bond; a substituted or unsubstituted C1 to C5 alkylene group; or a substituted or unsubstituted C2 to C5 alkenylene group.

[0088] In one embodiment of the present invention, specific examples of the second dispersant may be at least one selected from the following: gallic acid, protocatechuic acid, syringic acid, ferulic acid, vanillic acid, caffeic acid, p-coumaric acid, salicylic acid, 2,4-dihydroxybenzoic acid, homogentisic acid and sinapinic acid, as shown in Table 1 below, and it may not be limited to the above types, as long as it can increase the dispersibility of the carbon nanotubes while containing at least one hydroxyl group and at least one carboxyl group in the aromatic ring.

[0089] [Table 1]

[0090]

[0091]

[0092] In one embodiment of the present invention, the carbon nanotube dispersion may include a mixture of a second dispersant and a cation in an amount of 5 to 250 parts by weight, based on 100 parts by weight of the carbon nanotubes, and may include, 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 may include 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. or less, 150 parts by weight or less, 160 parts by weight or less, 170 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.

[0093] If the content of the mixture of the second dispersant and the cation is less than 5 parts by weight based on 100 parts by weight of the carbon nanotubes, there may be a problem that the first dispersant does not form sufficient hydrogen bonds with the mixture of the second dispersant and the cation, and thus does not show an effective dispersing effect, and thus the viscosity of the dispersion may not be low and the viscosity increases over time. If the content of the mixture of the second dispersant and the cation 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 mixture of the second dispersant and the cation, resulting in a high viscosity of the dispersion.

[0094] In one embodiment of the present invention, the mixture of the first dispersant, the second dispersant and the cation in the carbon nanotube dispersion may be contained in a weight ratio of 100:10 to 100:90, and for example, the mixture of the first dispersant, the second dispersant and the cation may be contained 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. The first dispersant and the mixture of the second dispersant and the cation may be contained 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, 100:60 or less, 100:55 or less, 100:50 or less, 100:45 or less, or 100:40 or less. If the content of the first dispersant and the mixture of the second dispersant and the cation in the carbon nanotube dispersion is 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.

[0095] In one embodiment of the present invention, the cations included with the second dispersant to form a mixture include cations selected from the group consisting of alkali metal ions, alkaline earth metal ions, aluminum ions, transition metal ions, ammonium ions, and sulfur ions. ions, and since the cations are contained in the carbon nanotube dispersion as a mixture together with the second dispersant, the terminal of the dispersant becomes negatively charged, thereby increasing the surface charge, and allowing the cations to remain in the dispersant, the electrostatic repulsion between the carbon nanotubes increases, thereby showing the characteristic of suppressing agglomeration.

[0096] The ammonium ions may be ammonium ions in which one, two, three or all four hydrogen atoms are replaced by hydrogen or the same or different radicals in C1-C5-alkyl, or tertiary aliphatic or heteroaliphatic ammonium ions, or heterocyclic ammonium cations, and may be, for example, in each case protonated pyridine, quinoline, quinoxaline, 1,2-dimethylimidazole, 1,3-dimethylimidazole, Methyl sulfate.

[0097] In one embodiment of the present invention, the cation may be included in an amount of 2 to 20 parts by weight, and for example, may be included in an amount of 2 parts by weight or more, 3 parts by weight or more, 3.5 parts by weight or more, 4 parts by weight or more, 5 parts by weight or more, 6 parts by weight or more, 7 parts by weight or more, 8 parts by weight or more, 9 parts by weight or more, or 10 parts by weight or more, and may be included in an amount of 20 parts by weight or less, 19 parts by weight or less, 18 parts by weight or less, 17 parts by weight or less, 16 parts by weight or less, 15 parts by weight or less, 14 parts by weight or less, 13 parts by weight or less, 12 parts by weight or less, or 11 parts by weight or less.

[0098] If the content of the cation is less than 2 parts by weight based on 100 parts by weight of the second dispersant in total, there may be a problem that the carbon nanotubes agglomerate due to lack of repulsion between the carbon nanotubes and low viscosity of the dispersion cannot be ensured. If the content of the cation exceeds 20 parts by weight, there may be a problem that the surface charge of the carbon nanotubes is too high and thus reaches a level that destroys electrostatic stability, causing the dispersion to become highly viscous or the stability of the dispersion to decrease and thus cause the viscosity to increase over time.

[0099] (3) Solvent

[0100] The solvent used for the carbon nanotube dispersion according to one embodiment of the present invention is used to dissolve the carbon nanotubes, the first dispersant, the second dispersant, and the ions selected from alkali metal ions, alkaline earth metal ions, aluminum ions, transition metal ions, ammonium ions, and sulfur ions. The present invention relates to a dispersion medium in which at least one cation among ions is dispersed, 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.

[0101] The solvent can separate the carbon nanotubes, the first dispersant, the second dispersant, and the ions selected from alkali metal ions, alkaline earth metal ions, aluminum ions, transition metal ions, ammonium ions, and sulfur ions. At least one cation among the ions is dissolved or dispersed above a certain level. The aqueous solvent may be, for example, water, and may be included in an amount that allows the electrode slurry composition to have an appropriate viscosity in consideration of coating properties of the electrode slurry composition manufactured using the carbon nanotube dispersion, etc.

[0102] In the case of a carbon nanotube dispersion according to one embodiment of the present invention, since the first dispersant, the second dispersant and the cation 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.

[0103] 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.

[0104] 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.

[0105] 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 Corporation) 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, 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, 9.6 Pa.s or less, 9.3 Pa.s or less, 9 Pa.s or less, 8.8 Pa.s or less, 8 Pa.s or less, 7.7 Pa.s or less, 7 Pa.s or less, or 6 Pa.s or less. 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.

[0106] 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 can be 15% or less, specifically 15% or less, 14% or less, 13% or less, 12% or less, 11% or less, 10% or less, 9% or less, 8.9% or less, 8.3% or less, 8% or less, 7% or less, 6.8% or less, 6% or less, 5.4% or less, 5% or less, 4% or less, 3% or less, 2.6% or less, 2% or less, or 1% or less.

[0107] [Equation 1]

[0108] Viscosity increase rate (%) = {(viscosity measured after standing at 25°C for 1 week - initial viscosity) / initial viscosity} × 100

[0109] In this case, the viscosity after standing for one week and the initial viscosity were measured at 25° C. and 1 rpm.

[0110] Method for preparing carbon nanotube dispersion

[0111] Hereinafter, a method for preparing a carbon nanotube dispersion will be described. 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 at least one hydroxyl group and at least one carboxyl group in an aromatic ring, a cationic precursor, 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.

[0112] In step (1), a primary dispersion of carbon nanotubes is prepared by mixing carbon nanotubes, a first dispersant containing nitrogen atoms, a second dispersant containing at least one hydroxyl group and at least one carboxyl group in an aromatic ring, a cationic precursor, 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.

[0113] 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.

[0114] 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.

[0115] In the method for preparing a carbon nanotube dispersion according to one embodiment of the present invention, the precursor of the cation may include a hydroxide of one or more cations selected from the group consisting of alkali metal ions, alkaline earth metal ions, aluminum ions, transition metal ions, ammonium ions, and sulfur ions. ion.

[0116] 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.

[0117] In the preparation method of the carbon nanotube dispersion, since the detailed description of the carbon nanotubes, the first dispersant containing nitrogen atoms, the second dispersant containing at least one hydroxyl group and at least one carboxyl group in the aromatic ring, the cationic precursor, and the solvent are the same as described above, the detailed description will be omitted below.

[0118] In step (2), a secondary dispersion of carbon nanotubes is prepared by dispersing a primary dispersion of carbon nanotubes.

[0119] 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, or the like, and more specifically, may be performed by a grinding method using a disc mill or a high-pressure homogenizer.

[0120] 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.

[0121] 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.

[0122] 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.

[0123] The carbon nanotube dispersion according to the present invention may mean a secondary dispersion of carbon nanotubes.

[0124] Electrode slurry composition for lithium secondary battery

[0125] 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.

[0126] The electrode paste composition for a lithium secondary battery can be a positive electrode paste composition or a negative electrode paste composition, and specifically can be a negative electrode paste composition.

[0127] The electrode paste composition for a lithium secondary battery can 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.

[0128] 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.

[0129] 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 (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 paste, the negative electrode active material can be included in an amount of 60% to 98% by weight, more preferably 70% to 98% by weight.

[0130] 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.

[0131] 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 paste application and the preparation yield.

[0132] The viscosity modifier may be carboxymethyl cellulose, polyacrylic acid, etc., and by adding it, the viscosity of the electrode slurry may be adjusted to facilitate the preparation of the electrode slurry and the application process on the electrode current collector.

[0133] 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 and carbon fiber.

[0134] 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.

[0135] 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.

[0136] 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 whose surface is 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.

[0137] 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.

[0138] 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.

[0139] 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, foils, nets, porous bodies, foams, and non-woven fabrics.

[0140] Lithium secondary battery

[0141] 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.

[0142] 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.

[0143] 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.

[0144] 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.

[0145] 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.

[0146] 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.

[0147] 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).

[0148] 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.

[0149] 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.

[0150] Embodiments of the invention

[0151] 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.

[0152] Example

[0153] Example 1

[0154] (1) 5.625 g (1.125 wt % relative to a total of 100 parts by weight of the carbon nanotube dispersion) of polyvinyl pyrrolidone (PVP, manufactured by Zhangzhou Huafu Chemical Co., Ltd.) as a first dispersant containing nitrogen atoms, 1.69 g of gallic acid (manufactured by Sigma-Aldrich Co., Ltd.) and 8.28 g of a 1N (3.8 wt %) aqueous NaOH solution (manufactured by Daejung Chemicals & Metals Co., Ltd.) (0.375 wt % relative to a total of 100 parts by weight of the carbon nanotube dispersion is obtained, which is a mixture of gallic acid and NaOH, a second dispersant containing at least one hydroxyl group and at least one carboxyl group in an aromatic ring, and containing 11 parts by weight of NaOH relative to 100 parts by weight of gallic acid) were mixed.+ ions), and 479.4 g of water as a solvent to prepare 495 g of a mixed solution, and the obtained mixed solution was put into a dissolution tank (dissolver, Dispermat-CA, manufactured by VMA-GETZMANN Company) equipped with an impeller and a container and stirred and mixed at 400 rpm for 10 minutes.

[0155] 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 ) was 5 μm single-walled carbon nanotubes (SWCNT, TUBALL, produced by OCSiAl Corporation) and stirred at 8,000 rpm for 60 minutes to prepare a primary dispersion of 500 g of carbon nanotubes in total.

[0156] (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.

[0157] Example 2

[0158] 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 1.275 wt % relative to a total of 100 parts by weight of the carbon nanotube dispersion, and 13 parts by weight of Na 2 SO 4 NH 4 3 ... + The mixture of ions was 0.225 wt%.

[0159] Example 3

[0160] A carbon nanotube dispersion was prepared in the same manner as in Example 1 above, except that in Example 1 above, LiOH (prepared by Sigma-Aldrich) was added instead of NaOH so that LiOH was 100 parts by weight of gallic acid. + ions are 3.5 parts by weight.

[0161] Example 4

[0162] A carbon nanotube dispersion was prepared in the same manner as in Example 1 above, except that in Example 1 above, KOH (prepared by Sigma-Aldrich) was added instead of NaOH so that KOH was 0.1% by weight relative to 100 parts by weight of gallic acid. + The ions are 17 parts by weight.

[0163] Example 5

[0164] A carbon nanotube dispersion was prepared in the same manner as in Example 1 above, except that in Example 1 above, tetramethylammonium hydroxide (manufactured by Sigma-Aldrich) was added so that the tetramethylammonium ion was 19 parts by weight relative to 100 parts by weight of gallic acid.

[0165] Example 6

[0166] A carbon nanotube dispersion was prepared in the same manner as in Example 1 above, except that in Example 1 above, as the first dispersant, 5.625 g (1.125 wt % relative to a total of 100 parts by weight of the carbon nanotube dispersion) of polyethyleneimine (PEI, produced by Zhangzhou Huafu Chemical Co., Ltd.) was added instead of polyvinyl pyrrolidone.

[0167] Example 7

[0168] A carbon nanotube dispersion was prepared in the same manner as in Example 1 above, except that in Example 1 above, as a second dispersant containing at least one hydroxyl group and at least one carboxyl group in an aromatic ring, 1.69 g of protocatechuic acid (manufactured by Sigma-Aldrich) and 8.28 g of a 1N (3.8 wt %) NaOH aqueous solution (manufactured by Daejung Chemicals & Metals) were added instead of the mixture of gallic acid and NaOH, so that with respect to a total of 100 parts by weight of the carbon nanotube dispersion, 11 parts by weight of NaOH were contained with respect to 100 parts by weight of protocatechuic acid. + The mixture of ions was 0.375 wt%.

[0169] Example 8

[0170] A carbon nanotube dispersion was prepared in the same manner as in Example 1 above, except that in Example 1 above, as a second dispersant containing at least one hydroxyl group and at least one carboxyl group in an aromatic ring, 1.69 g of protocatechuic acid (manufactured by Sigma-Aldrich) and 8.28 g of a 1N (3.8 wt %) KOH aqueous solution (manufactured by Daejung Chemicals & Metals) were added instead of the mixture of gallic acid and NaOH, so that with respect to a total of 100 parts by weight of the carbon nanotube dispersion, 11 parts by weight of KOH were contained with respect to 100 parts by weight of protocatechuic acid. + The mixture of ions was 0.375 wt%.

[0171] Example 9

[0172] A carbon nanotube dispersion was prepared in the same manner as in Example 1 above, except that in Example 1 above, as a second dispersant containing at least one hydroxyl group and at least one carboxyl group in an aromatic ring, 1.69 g of syringic acid (manufactured by Sigma-Aldrich) and 8.28 g of a 1N (3.8 wt %) aqueous NaOH solution (manufactured by Daejung Chemicals & Metals) were added instead of the mixture of gallic acid and NaOH, so that NaOH was 0.1% by weight relative to a total of 100 parts by weight of the carbon nanotube dispersion. + The content of ions in a mixture of 11 parts by weight of syringic acid per 100 parts by weight is 0.375% by weight.

[0173] Example 10

[0174] A carbon nanotube dispersion was prepared in the same manner as in Example 1 above, except that in Example 1 above, as a second dispersant containing at least one hydroxyl group and at least one carboxyl group in an aromatic ring, 1.69 g of 2,4-dihydroxybenzoic acid (manufactured by Sigma-Aldrich) and 8.28 g of a 1N (3.8 wt %) NaOH aqueous solution (manufactured by Daejung Chemicals & Metals) were added instead of the mixture of gallic acid and NaOH, so that with respect to a total of 100 parts by weight of the carbon nanotube dispersion, 11 parts by weight of NaOH were contained with respect to 100 parts by weight of 2,4-dihydroxybenzoic acid. + The mixture of ions was 0.375 wt%.

[0175] Comparative Example 1

[0176] A carbon nanotube dispersion was prepared in the same manner as in Example 1 above, except that in Example 1 above, the mixture of the second dispersant and NaOH was not added.

[0177] Comparative Example 2

[0178] A carbon nanotube dispersion was prepared in the same manner as in Example 1 above, except that in Example 1 above, the carbon nanotubes were set to 0.6 wt % relative to a total of 100 parts by weight of the carbon nanotube dispersion, polyvinyl pyrrolidone as the first dispersant was set to 0.9 wt % relative to a total of 100 parts by weight of the carbon nanotube dispersion, and the mixture of the second dispersant and NaOH was not added.

[0179] Comparative Example 3

[0180] A carbon nanotube dispersion was prepared in the same manner as in Example 1 above, except that in Example 1 above, NaOH was not added, and gallic acid as a second dispersant was added at 0.375 wt % relative to a total of 100 parts by weight of the carbon nanotube dispersion.

[0181] Comparative Example 4

[0182] A carbon nanotube dispersion was prepared in the same manner as in Example 1 above, except that in Example 1 above, polyvinyl pyrrolidone as the first dispersant was not added, and as a mixture of gallic acid and NaOH (which was the second dispersant), 11 parts by weight of NaOH was added relative to 100 parts by weight of gallic acid relative to a total of 100 parts by weight of the carbon nanotube dispersion. + The ion mixture was added at 1.0 wt%.

[0183] Comparative Example 5

[0184] A carbon nanotube dispersion was prepared in the same manner as in Example 1 above, except that in Example 1 above, polyvinyl pyrrolidone as the first dispersant was set to 0.045 wt % relative to a total of 100 parts by weight of the carbon nanotube dispersion, and as a mixture of gallic acid and NaOH (which was the second dispersant), 11 parts by weight of NaOH relative to 100 parts by weight of gallic acid was set to 0.045 wt % relative to a total of 100 parts by weight of the carbon nanotube dispersion. + The mixture of ions was added at 1.455 wt%.

[0185] Comparative Example 6

[0186] A carbon nanotube dispersion was prepared in the same manner as in Example 1 above, except that in Example 1 above, 30 parts by weight of Na 2 O 4 0.5 N 2 O 4 0.6 N 2 O 4 0.7 N 2 O 4 0.8 N 2 O 4 0.9 N 2 O 5 0.9 N 2 O 6 0.8 N 2 O 8 0.9 N 2 O 9 0.9 N 2 O 10 ... + The mixture of ions was 0.375 wt%.

[0187] Comparative Example 7

[0188] 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 1.455 wt % relative to a total of 100 parts by weight of the carbon nanotube dispersion, and 13 parts by weight of Na 2 SO 4 NH 4 3 ... + The mixture of ions was 0.045 wt%.

[0189] Comparative Example 8

[0190] A carbon nanotube dispersion was prepared in the same manner as in Example 1 above, except that in Example 1 above, the carbon nanotubes were 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 tristyrylphenol ethoxylate was used at 0.225 wt % relative to a total of 100 parts by weight of the carbon nanotube dispersion instead of gallic acid and NaOH as the second dispersant.

[0191] Comparative Example 9

[0192] A carbon nanotube dispersion was prepared in the same manner as in Example 1 above, except that in Example 1 above, the carbon nanotubes were 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 styrene maleic acid copolymer was used at 0.225 wt % relative to a total of 100 parts by weight of the carbon nanotube dispersion instead of gallic acid and NaOH as the second dispersant.

[0193] Comparative Example 10

[0194] A carbon nanotube dispersion was prepared in the same manner as in Example 1 above, except that in Example 1 above, instead of a mixture of gallic acid and NaOH as the second dispersant containing at least one hydroxyl group and at least one carboxyl group in an aromatic ring, 1.69 g of protocatechuic acid (manufactured by Sigma-Aldrich) and 22.58 g of a 1N (3.8 wt %) NaOH aqueous solution (manufactured by Daejung Chemicals & Metals) were added so that, relative to a total of 100 parts by weight of the carbon nanotube dispersion, 30 parts by weight of NaOH were contained relative to 100 parts by weight of protocatechuic acid. + The mixture of ions was 0.375 wt%.

[0195] Comparative Example 11

[0196] A carbon nanotube dispersion was prepared in the same manner as in Example 1 above, except that in Example 1 above, instead of a mixture of gallic acid and NaOH as the second dispersant containing at least one hydroxyl group and at least one carboxyl group in an aromatic ring, 1.69 g of epigallocatechin gallate (manufactured by Sigma-Aldrich) and 8.28 g of a 1N (3.8 wt %) NaOH aqueous solution (manufactured by Daejung Chemicals & Metals) were added so that, relative to a total of 100 parts by weight of the carbon nanotube dispersion, 11 parts by weight of NaOH were contained relative to 100 parts by weight of epigallocatechin gallate.+ The mixture of ions was 0.375 wt%.

[0197] Experimental example

[0198] The viscosity of the carbon nanotube dispersions of Examples 1 to 10 and Comparative Examples 1 to 11 was measured, and the viscosity was measured again after leaving them at 25° C. for one week, and the results are shown in Table 2 below.

[0199] The viscosity is measured using a viscometer (Viscometer TV-25, rotor No. 01, manufactured by TOKI SANGYO CORPORATION) at 25°C and 1 rpm.

[0200] [Table 2]

[0201]

[0202]

[0203]

[0204] *TMAH: Tetramethylammonium hydroxide

[0205] *TMA: Tetramethylammonium

[0206] *PEI: Polyethyleneimine

[0207] Referring to Table 2 above, it can be seen that, compared with the carbon nanotube dispersion of Comparative Example 1 containing only polyvinyl pyrrolidone as the first dispersant, the carbon nanotube dispersions of Examples 1 to 10 containing a mixture of a first dispersant, a second dispersant and a cation have a low initial viscosity immediately after dispersing the carbon nanotubes in an aqueous solvent, and in particular, an increase in the viscosity of the carbon nanotube dispersion over time is very effectively suppressed.

[0208] 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 the 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 contain a mixture of a second dispersant and a cation compared with Examples 1 to 10, the effect of suppressing the increase in the viscosity of the dispersion due to changes over time is not observed.

[0209] In the case of the carbon nanotube dispersion in Comparative Example 3, it can be seen that since it contains only the second dispersant instead of a mixture of the second dispersant and cations compared to the carbon nanotube dispersions of Examples 1 to 10, the initial viscosity immediately after dispersing the carbon nanotubes is relatively high, and the effect of suppressing the increase in the viscosity of the dispersion due to changes over time is not observed.

[0210] In the case of the carbon nanotube dispersions in Comparative Examples 4 and 5, it can be seen that since they do not contain the first dispersant (Comparative Example 4) or contain the first dispersant in a small amount other than a certain content ratio (Comparative Example 5) compared with the carbon nanotube dispersions of Examples 1 to 10, the carbon nanotubes cannot be completely dispersed in the aqueous solvent.

[0211] In the case of the carbon nanotube dispersions in Comparative Examples 6 and 10, it can be seen that since the cations included together with the second dispersant are included in excess exceeding a certain content ratio compared with the carbon nanotube dispersions of Examples 1 to 10, the initial viscosity immediately after dispersing the carbon nanotubes in the aqueous solvent is high, and the effect of suppressing the increase in viscosity of the carbon nanotube dispersion over time is not observed.

[0212] Furthermore, in the case of the carbon nanotube dispersion in Comparative Example 7, it can be seen that, since the mixture of the second dispersant and the cation is contained in a small amount other than a certain content ratio compared to the carbon nanotube dispersions of Examples 1 to 10, the initial viscosity immediately after dispersing the carbon nanotubes in the aqueous solvent is high, and the effect of suppressing the increase in the viscosity of the carbon nanotube dispersion over time is not observed.

[0213] In the case of the carbon nanotube dispersions in Comparative Examples 8 and 9, it can be seen that since a material that does not contain at least one hydroxyl group and at least one carboxyl group in an aromatic ring is used as the second dispersant and does not contain cations such as alkali metal cations compared to the carbon nanotube dispersions of Examples 1 to 10, the initial viscosity immediately after dispersing the carbon nanotubes in an aqueous solvent is high (Comparative Example 8), and the effect of suppressing the increase in viscosity of the carbon nanotube dispersion over time is not observed (Comparative Examples 8 and 9).

[0214] In the case of the carbon nanotube dispersion in Comparative Example 11, it can be seen that, compared with the carbon nanotube dispersions of Examples 1 to 10, epigallocatechin gallate as the second dispersant contains two or more aromatic rings in its molecular structure, and thus the molecule forms a linear angle or a dense structure, and the pi-pi (π-π) interaction formed by the ring structure within the molecule also occurs strongly, deepening the agglomeration of the dispersant, and the cation forming a mixture with the second dispersant has insufficient control over the charge, resulting in a high viscosity of the dispersion, and thus the initial viscosity immediately after dispersing the carbon nanotubes in an aqueous solvent is high, and the effect of suppressing the increase in viscosity of the carbon nanotube dispersion over time is not observed. Therefore, it was determined that only when the carbon nanotube dispersion obtained by dispersing the carbon nanotubes in an aqueous solvent contains the first dispersant containing nitrogen atoms and a mixture of the second dispersant and the cation in a certain weight ratio, wherein the second dispersant contains at least one hydroxyl group and at least one carboxyl group in the aromatic ring, and wherein the cation contains a group selected from alkali metal ions, alkaline earth metal ions, aluminum ions, transition metal ions, ammonium ions, and sulfur When at least one of the ions is contained, the carbon nanotube dispersion exhibits low viscosity and the increase in viscosity due to time change can be suppressed.

[0215] 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 mixture of a second dispersant and a cation; and Solvents, wherein the second dispersant contains at least one hydroxyl group and at least one carboxyl group in an aromatic ring, and The cations include alkali metal ions, alkaline earth metal ions, aluminum ions, transition metal ions, ammonium ions and sulfur ions. At least one of the ions. 2 . The carbon nanotube dispersion according to claim 1 , wherein the second dispersant has a structure not including two or more aromatic rings in its molecular structure.

3. 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, R1 to R5 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 at least one of R1 to R5 is hydroxyl, R6 is a carboxyl group, and L is a single bond; a substituted or unsubstituted C1 to C10 alkylene group; a substituted or unsubstituted C2 to C10 alkenylene group; or a substituted or unsubstituted C2 to C10 alkynylene group.

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

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 mixture of the second dispersant and the cation in an amount of 5 to 250 parts by weight based on 100 parts by weight of the carbon nanotube. 8 . The carbon nanotube dispersion according to claim 1 , wherein the cation is included in an amount of 2 parts by weight to 20 parts by weight based on 100 parts by weight of the second dispersant.

9. 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. 10 . The carbon nanotube dispersion according to claim 1 , wherein the mixture of the first dispersant and the second dispersant and the cation is included in a weight ratio of 100:10 to 100:

90. 11 . 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.

12. 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.

13. 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 at least one hydroxyl group and at least one carboxyl group in an aromatic ring, a cationic precursor, 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.

14. The method for preparing a carbon nanotube dispersion according to claim 13, wherein the precursor of the cation comprises a hydroxide of one or more cations selected from the group consisting of alkali metal ions, alkaline earth metal ions, aluminum ions, transition metal ions, ammonium ions, and sulfur ions. ion. 15 . 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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