Carbon nanotube dispersion and preparation method therefor

Abstract

The present invention relates to: a carbon nanotube dispersion comprising carbon nanotubes, a first dispersant containing nitrogen atoms, a second dispersant comprising at least one polymer selected from the group consisting of polyethylene glycol, poly(1,2-propylene glycol), poly(1,3-propylene glycol), polycaprolactone, polytetramethylene glycol, and polystyrene, a third dispersant comprising an alkanolamine-based compound, and a solvent; a preparation method for the carbon nanotube dispersion; and an electrode slurry for a lithium secondary battery, comprising the carbon nanotube dispersion.

Description

Carbon nanotube dispersion and method for preparing the same

[0001] The present invention relates to a carbon nanotube dispersion and a method for preparing the same.

[0002] The present application claims the benefit of priority based on Korean Patent Application No. 10-2024-0130417 filed September 26, 2024 and Korean Patent Application No. 10-2025-0138578 filed September 25, 2025, and includes all contents disclosed in the documents of said Korean patent applications as part of this specification.

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

[0004] Generally, high-density electrodes are formed by molding electrode active material particles with a size of several µm to tens of µm using a high-pressure press. During the molding process, the particles may be deformed and the space between the particles may be reduced, which can easily lead to a decrease in electrolyte permeability.

[0005] To address the aforementioned problems, conductive materials possessing excellent electrical conductivity and strength are used during the manufacture of electrodes. Even when positioned between electrode active materials and subjected to a molding process, these conductive materials maintain micropores between active material particles, allowing the electrolyte to penetrate easily, and their excellent electrical conductivity can reduce resistance within the electrode. Among such conductive materials, the use of carbon nanotubes, which are fibrous carbon-based conductive materials capable of further reducing electrode resistance by forming electrical conduction pathways within the electrode, is increasing.

[0006] Carbon nanotubes, a type of fine carbon fiber, are tubular carbon fibers with a diameter of 1 μm or less. Due to their high conductivity, tensile strength, and heat resistance resulting from their unique structure, they are expected to be applied and commercialized in various fields. However, carbon nanotubes have a problem of low dispersibility and aggregation due to strong van der Waals forces between them caused by their high specific surface area.

[0007] To address these issues, methods have been proposed to disperse carbon nanotubes in a dispersion medium using mechanical dispersion treatments such as ultrasonic treatment. However, mechanical dispersion methods have problems, such as the carbon nanotubes aggregating immediately after the ultrasonic irradiation ends or re-aggregating over time after dispersion.

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

[0009] [Prior Art Literature]

[0010] [Patent Literature]

[0011] (Patent Document 1) Korean Published Patent Application No. 2021-0003144 (January 11, 2021)

[0012] The objective of the present invention is to provide a carbon nanotube dispersion that comprises a carbon nanotube, a first dispersant containing nitrogen atoms, a second dispersant containing one or more polymers selected from the group consisting of polyethylene glycol, poly(1,2-propylene glycol), poly(1,3-propylene glycol), polycaprolactone, polytetramethylene glycol, and polystyrene, a third dispersant containing an alkanolamine-based compound, and a solvent, which has excellent dispersibility, low viscosity of the dispersion and particle size of the dispersed particles, and low change in viscosity over time.

[0013] Another objective of the present invention is to provide a method for preparing the carbon nanotube dispersion.

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

[0015] One embodiment of the present invention provides a carbon nanotube dispersion comprising a carbon nanotube, a first dispersant comprising a nitrogen atom, a second dispersant comprising one or more polymers selected from the group consisting of polyethylene glycol, poly(1,2-propylene glycol), poly(1,3-propylene glycol), polycaprolactone, polytetramethylene glycol, and polystyrene, a third dispersant comprising an alkanolamine-based compound, and a solvent.

[0016] The second dispersant may include polystyrene and one polymer selected from the group consisting of polyethylene glycol, poly(1,2-propylene glycol), poly(1,3-propylene glycol), polycaprolactone and polytetramethylene glycol.

[0017] The above alkanolamine compound may be a linear or branched C3 to C10 saturated hydrocarbon comprising at least one hydroxyl group (-OH) and at least one amine group (-NH2).

[0018] The carbon nanotubes may be included in an amount of 0.1 to 10 parts by weight based on 100 parts by weight of the dispersion.

[0019] The carbon nanotube dispersion may contain 10 to 50 parts by weight of the first dispersant based on 100 parts by weight of the carbon nanotube.

[0020] The carbon nanotube dispersion may contain 1 to 30 parts by weight of the second dispersant based on 100 parts by weight of the carbon nanotube.

[0021] The carbon nanotube dispersion may contain 1 to 50 parts by weight of the third dispersant based on 100 parts by weight of the carbon nanotube.

[0022] The above carbon nanotube dispersion may have an initial viscosity of 0.1 to 10 Pa·s measured at 25 ℃ and 1 rpm.

[0023] The above carbon nanotube dispersion may have a viscosity increase rate of 60% or less, as indicated by the following formula (1).

[0024] [Equation 1]

[0025] Viscosity increase rate (%) = {(Viscosity measured after leaving at 25 ℃ for 1 week - Initial viscosity) / Initial viscosity} × 100

[0026] Another embodiment of the present invention provides a method for preparing a carbon nanotube dispersion described above, comprising the steps of: (1) preparing a carbon nanotube primary dispersion by mixing a carbon nanotube, a first dispersant containing a nitrogen atom, a second dispersant containing one or more polymers selected from the group consisting of polyethylene glycol, poly(1,2-propylene glycol), poly(1,3-propylene glycol), polycaprolactone, polytetramethylene glycol, and polystyrene, a third dispersant containing an alkanolamine-based compound, and a solvent; and (2) preparing a carbon nanotube secondary dispersion by dispersing the carbon nanotube primary dispersion.

[0027] Another embodiment of the present invention provides an electrode slurry composition for a lithium secondary battery comprising the carbon nanotube dispersion and electrode active material described above.

[0028] The carbon nanotube dispersion according to the present invention further comprises a first dispersant containing nitrogen atoms, a second dispersant containing one or more polymers selected from the group consisting of polyethylene glycol, poly(1,2-propylene glycol), poly(1,3-propylene glycol), polycaprolactone, polytetramethylene glycol, and polystyrene, and a third dispersant containing an alkanolamine-based compound. As a result, despite using carbon nanotubes with a large specific surface area, the change in viscosity over time is small, and the viscosity is relatively low. Furthermore, as the carbon nanotubes are dispersed uniformly and effectively, the dispersion has the characteristic of having a small particle size of dispersed particles.

[0029] Furthermore, if the carbon nanotube dispersion of the present invention is used in an electrode slurry composition, an electrode and a secondary battery having excellent capacity and cycle characteristics can be manufactured.

[0030] Embodiments of the present invention will be described in detail below. Prior to this, terms and words used in this specification and claims should not be interpreted as being limited to their ordinary or dictionary meanings. Instead, based on the principle that the inventor can appropriately define the concepts of terms to best describe their invention, they should be interpreted in a meaning and concept consistent with the technical spirit of the present invention. Therefore, the configurations described in the embodiments of this specification are merely one preferred embodiment of the present invention and do not represent all aspects of the technical spirit of the present invention. It should be understood that various equivalents and modifications capable of replacing them may exist at the time of filing this application.

[0031] In this specification, the term "substitution" means that a hydrogen atom bonded to a carbon atom of a compound is replaced with another substituent, and the substitution location is not limited to the location where the hydrogen atom is substituted, that is, any location where a substituent can be substituted, and in the case of two or more substitutions, the two or more substituents may be the same or different from each other.

[0032] Throughout this specification, when a part is described as 'comprising' a certain component, it means that, unless specifically stated otherwise, it does not exclude other components but may include additional components.

[0033] Throughout this specification, "%" means weight percent unless otherwise explicitly indicated.

[0034] In this specification, average particle size "D 50 " refers to a particle size corresponding to a volume accumulation of 50%. The above D 50 For example, it can be measured using the laser diffraction method. The laser diffraction method generally enables the measurement of particle sizes ranging from the submicron range to several mm, and can obtain results with high reproducibility and high resolution.

[0035] In this specification, "specific surface area" is measured by the BET method (Brunauer-Emmett-Teller Analysis), and specifically, can be calculated from the amount of nitrogen gas adsorbed at liquid nitrogen temperature (77K) using BELSORP-mino II of BEL Japan.

[0036]

[0037] carbon nanotube dispersion

[0038] The carbon nanotube dispersion according to the present invention comprises carbon nanotubes, a first dispersant containing nitrogen atoms, a second dispersant containing one or more polymers selected from the group consisting of polyethylene glycol, poly(1,2-propylene glycol), poly(1,3-propylene glycol), polycaprolactone, polytetramethylene glycol, and polystyrene, a third dispersant containing an alkanolamine-based compound, and a solvent. Hereinafter, each component of the carbon nanotube dispersion of the present invention will be described in detail.

[0039]

[0040] (1) Carbon nanotube

[0041] The term 'carbon nanotube' as used in the present invention refers to a secondary structure formed by assembling carbon nanotube units, either wholly or partially, into a bundle, wherein the carbon nanotube units are graphite sheets having a cylindrical shape with a nano-sized diameter, and sp 2 It has a bonded structure. At this time, depending on the angle and structure in which the graphite plane is rolled, it can exhibit conductive or semiconductor properties. The carbon nanotube monomers can be classified into single-walled carbon nanotubes (SWCNT), double-walled carbon nanotubes (DWCNT), and multi-walled carbon nanotubes (MWCNT) depending on the number of bonds forming the walls.

[0042] The term 'bundle type' as 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 in parallel with the axes along the length direction of the units in substantially the same orientation, or are twisted or entangled after arrangement. 'Non-bundle type' or 'entangled type' refers to a shape in which carbon nanotube units are entangled without a specific shape such as a bundle or rope.

[0043] Carbon nanotubes have high conductivity, but they exhibit high aggregation due to van der Waals forces generated between them. When conductive materials aggregate, they cannot properly form conductive pathways within the electrode. Furthermore, using more conductive material to increase conductivity results in a relatively smaller amount of active material, which can actually degrade performance, such as electrode capacity. Therefore, there have been difficulties in commercializing carbon nanotubes as conductive materials.

[0044] The carbon nanotube dispersion according to the present invention further comprises a third dispersant comprising an alkanolamine-based compound, along with a first dispersant comprising a nitrogen atom, a second dispersant comprising one or more polymers selected from the group consisting of polyethylene glycol, poly(1,2-propylene glycol), poly(1,3-propylene glycol), polycaprolactone, polytetramethylene glycol, and polystyrene. This allows for a significant reduction in the initial viscosity of the carbon nanotube dispersion and suppression of viscosity changes over time, thereby enabling high conductivity due to the high conductivity of the carbon nanotubes when applied to an electrode slurry of a lithium secondary battery.

[0045] Accordingly, when the carbon nanotube dispersion according to the present invention is applied to the manufacture of an electrode slurry, the carbon nanotubes are uniformly positioned between the active materials, so that the microspace between the electrode active materials can be consistently maintained even during the manufacture of the electrode by coating, drying, and rolling the electrode slurry. In addition, since the carbon nanotubes are uniformly distributed without aggregation, a sufficient conductive path can be formed even with a small amount of carbon nanotubes.

[0046] A carbon nanotube dispersion according to one embodiment of the present invention may include one or more of single-wall, double-wall, and multi-wall carbon nanotubes as the carbon nanotubes, but is not limited thereto, and specifically may include single-wall carbon nanotubes. Since the single-wall carbon nanotubes or double-wall carbon nanotubes have a higher specific surface area compared to multi-wall carbon nanotubes, they are more effective in improving cycle characteristics when applied to a secondary battery.

[0047] Meanwhile, the average diameter of the carbon nanotube may be, for example, 0.6 to 10 nm, preferably 0.8 to 5 nm, more preferably 0.8 to 3 nm, and may be 0.8 nm or more, 0.9 nm or more, 1.0 nm or more, 1.1 nm or more, 1.2 nm or more, 1.3 nm or more, 1.4 nm or more, 1.5 nm or more, 1.6 nm or more, 1.7 nm or more, 1.8 nm or more, or 1.9 nm or more, and may be 3.0 nm or less, 2.9 nm or less, 2.8 nm or less, 2.7 nm or less, 2.6 nm or less, 2.5 nm or less, 2.4 nm or less, 2.3 nm or less, 2.2 nm or less, 2.1 nm or less, or 2.0 nm or less.

[0048] In addition, the carbon nanotubes may have an average length of 0.5 to 20 μm, preferably 1 to 20 μm, more preferably 5 to 20 μm, and may be 5 μm or more, 7 μm or more, 9 μm or more, 11 μm or more, or 13 μm or more, and may be 20 μm or less, 18 μm or less, 16 μm or less, or 14 μm or less. When the average diameter and average length of the carbon nanotubes satisfy the above ranges, it is effective for reducing the viscosity of the dispersion and improving storage stability, and excellent cycle characteristics can be achieved even when applied as an electrode active material.

[0049] At this time, 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.

[0050] The carbon nanotubes may be included in an amount of 0.1 to 10 parts by weight based on 100 parts by weight of the total carbon nanotube dispersion, and may be 0.1 parts by weight or more, 0.2 parts by weight or more, 0.3 parts by weight or more, 0.4 parts by weight or more, 0.5 parts by weight or more, 0.6 parts by weight or more, 0.7 parts by weight or more, 0.8 parts by weight or more, 0.9 parts by weight or more, 1.0 parts by weight or more, 1.1 parts by weight or more, 1.2 parts by weight or more, 1.3 parts by weight or more, 1.4 parts by weight or more, 1.5 parts by weight or more, 1.6 parts by weight or more, 1.7 parts by weight or more, 1.8 parts by weight or more, 1.9 parts by weight or more, 2.0 parts by weight or more, 2.1 parts by weight or more, 2.2 parts by weight or more, 2.3 parts by weight or more, 2.4 parts by weight or more, 2.5 parts by weight or more, 2.6 parts by weight or more, It may be 2.7 parts by weight or more, 2.8 parts by weight or more, 2.9 parts by weight or more, 3.0 parts by weight or more, 3.1 parts by weight or more, 3.2 parts by weight or more, 3.3 parts by weight or more, 3.4 parts by weight or more, 3.5 parts by weight or more, 3.6 parts by weight or more, 3.7 parts by weight or more, 3.8 parts by weight or more, 3.9 parts by weight or more, 4.0 parts by weight or more, 4.1 parts by weight or more, 4.2 parts by weight or more, 4.3 parts by weight or more, 4.4 parts by weight or more, 4.5 parts by weight or more, 4.6 parts by weight or more, 4.7 parts by weight or more, 4.8 parts by weight or more, 4.9 parts by weight or more, or 5.0 parts by weight or more, and 10.0 parts by weight or less, 9.9 parts by weight or less, 9.8 parts by weight or less, 9.7 parts by weight or less, 9.6 parts by weight or less, 9.5 parts by weight or less, 9.4 parts by weight or less, 9.3 parts by weight or less, 9.2 parts by weight or less, 9.1 parts by weight or less, 9.0 parts by weight or less, 8.9 parts by weight or less, 8.8 parts by weight or less, 8.7 parts by weight or less, 8.6 parts by weight or less, 8.5 parts by weight or less, 8.4 parts by weight or less, 8.3 parts by weight or less, 8.2 parts by weight or less, 8.1 parts by weight or less, 8.0 parts by weight or less, 7.9 parts by weight or less, 7.8 parts by weight or less, 7.7 parts by weight or less, 7.6 parts by weight or less, 7.5 parts by weight or less, 7.It may be included in an amount of 4 parts by weight or less, 7.3 parts by weight or less, 7.2 parts by weight or less, 7.1 parts by weight or less, 7.0 parts by weight or less, 6.9 parts by weight or less, 6.8 parts by weight or less, 6.7 parts by weight or less, 6.6 parts by weight or less, 6.5 parts by weight or less, 6.4 parts by weight or less, 6.3 parts by weight or less, 6.2 parts by weight or less, 6.1 parts by weight or less, 6.0 parts by weight or less, 5.9 parts by weight or less, 5.8 parts by weight or less, 5.7 parts by weight or less, 5.6 parts by weight or less, 5.5 parts by weight or less, 5.4 parts by weight or less, 5.3 parts by weight or less, 5.2 parts by weight or less, or 5.1 parts by weight or less. When the content of carbon nanotubes satisfies the above range, the effect of improving the viscosity of the dispersion and the effect of improving the conductivity of the secondary battery produced through the carbon nanotube dispersion are excellent.

[0051] The BET specific surface area of ​​the above carbon nanotube is 150 m² 2 / g or more, preferably 150 m 2 / g to 2,000 m 2 It can be / g, and 150 m 2 / g or more, 200 m 2 / g or more, 250 m 2 / g or more, 300 m 2 / g or more, 350 m 2 / g or more, 400 m 2 / g or more, 450 m 2 / g or more, 500 m 2 / g or more, 550 m 2 / g or more, 600 m 2 / g or more, 650 m 2 / g or more, 700 m 2 / g or more, 750 m 2 / g or more, 800 m 2 / g or more, 850 m 2 / g or more, 900 m 2 / g or more, 950 m 2 / g or more, 1000 m 2 / g or more or 1050 m 2It can be more than / g, and 2000 m 2 / g or less, 1950 m 2 / g or less, 1900 m 2 / g or less, 1850 m 2 / g or less, 1800 m 2 / g or less, 1750 m 2 / g or less, 1700 m 2 / g or less, 1650 m 2 / g or less, 1600 m 2 / g or less, 1550 m 2 / g or less, 1500 m 2 / g or less, 1450 m 2 / g or less, 1400 m 2 / g or less, 1350 m 2 / g or less, 1300 m 2 / g or less, 1250 m 2 / g or less, 1200 m 2 / g or less, 1150 m 2 / g or less or 1100 m 2 It may be less than / g. When carbon nanotubes having a high BET specific surface area as described above are used, excellent formation of a conductive network between electrode active materials is achieved, thereby improving the cycle characteristics of the secondary battery manufactured using the carbon nanotube dispersion.

[0052] A carbon nanotube dispersion according to one embodiment of the present invention can have a relatively high carbon nanotube content because carbon nanotubes can be uniformly dispersed. When a carbon nanotube dispersion with a low carbon nanotube content is used in the manufacture of an electrode slurry, the solid content of the manufactured electrode slurry decreases, and the thickness (wetting thickness) before applying and drying the electrode slurry becomes thicker. Consequently, the rolling rate measured after subsequent drying and rolling treatments increases, leading to a larger difference in the thickness ratio before and after drying and rolling. As such, if the rolling rate increases, the compositions inside the slurry, including the positive electrode active material, may be damaged during the process, and problems such as a decrease in battery performance may occur.

[0053]

[0054] (2) Dispersant

[0055] The carbon nanotube dispersion according to the present invention comprises a dispersant to improve the dispersibility of the carbon nanotube, and together with the dispersant, a first dispersant comprising a nitrogen atom, a second dispersant comprising one or more polymers selected from the group consisting of polyethylene glycol, poly(1,2-propylene glycol), poly(1,3-propylene glycol), polycaprolactone, polytetramethylene glycol, and polystyrene, and a third dispersant comprising an alkanolamine-based compound.

[0056] In the carbon nanotube dispersion, the first to third dispersants play a role in increasing the dispersibility of carbon nanotubes so that the carbon nanotubes can be evenly dispersed without aggregating within the dispersion, and in particular, they suppress changes in the viscosity of the carbon nanotube dispersion over time and have the effect of lowering the average particle size of the dispersed particles.

[0057] In a carbon nanotube dispersion according to one embodiment of the present invention, the first dispersant containing the nitrogen atom may be one or more selected from the group consisting of, for example, polyvinylpyrrolidone, polyacrylic acid hydrazide, poly-N-vinyl-5-methoxazolidon, N-alkyl polyimine, N-acetyl polyimine, polyacrylamide, poly-L-lysine hydrobromide, benzyl-dodecyl-dimethylammonium chloride, and polyethylenimine, and preferably polyvinylpyrrolidone may be used. According to one embodiment of the present invention, a carbon nanotube dispersion may exhibit an effect of improving the viscosity of the dispersion and an effect of suppressing changes in viscosity over time by including a first dispersant containing the nitrogen atom.

[0058] The weight-average molecular weight (Mw) of the first dispersant may be 15,000 to 30,000 g / mol, specifically 15,000 g / mol or more, 16,000 g / mol or more, 17,000 g / mol or more, 18,000 g / mol or more, 19,000 g / mol or more, 20,000 g / mol or more, 21,000 g / mol or more, 22,000 g / mol or more, or 23,000 g / mol or more, and 30,000 g / mol or less, 29,000 g / mol or less, 28,000 g / mol or less, 27,000 g / mol or less, 26,000 g / mol or less, 25,000 g / mol or less, or 24,000 g / mol or less. When the first dispersant has the above weight-average molecular weight range, carbon nanotubes can be uniformly dispersed in the solvent.

[0059] In one embodiment of the present invention, the first dispersant may be included in an amount of 10 to 50 parts by weight based on 100 parts by weight of carbon nanotubes in the carbon nanotube dispersion, specifically 10 parts by weight or more, 11 parts by weight or more, 12 parts by weight or more, 13 parts by weight or more, 14 parts by weight or more, 15 parts by weight or more, 16 parts by weight or more, 17 parts by weight or more, 18 parts by weight or more, 19 parts by weight or more, 20 parts by weight or more, 21 parts by weight or more, 22 parts by weight or more, 23 parts by weight or more, 24 parts by weight or more, 25 parts by weight or more, 26 parts by weight or more, 27 parts by weight or more, 28 parts by weight or more, 29 parts by weight or more, or 30 parts by weight or more, 50 parts by weight or less, 49 parts by weight or less, 48 ​​parts by weight or less, 47 parts by weight or less, 46 parts by weight or less, 45 parts by weight or less, It may be included in an amount of 44 parts by weight or less, 43 parts by weight or less, 42 parts by weight or less, 41 parts by weight or less, 40 parts by weight or less, 39 parts by weight or less, 38 parts by weight or less, 37 parts by weight or less, 36 parts by weight or less, 35 parts by weight or less, 34 parts by weight or less, 33 parts by weight or less, 32 parts by weight or less, or 31 parts by weight or less. Preferably, the first dispersant may be included in an amount of 25 to 35 parts by weight based on 100 parts by weight of carbon nanotubes in the carbon nanotube dispersion.

[0060] If the first dispersant is included in an amount of less than 10 parts by weight based on 100 parts by weight of carbon nanotubes in the carbon nanotube dispersion, a sufficient dispersion effect is not achieved due to the insufficient content of the dispersant, and there may be a problem in that the viscosity of the dispersion is not maintained at a low level and increases over time; if it exceeds 50 parts by weight, there may be a problem in that aggregation between solid components in the dispersion proceeds due to the excessive content of the first dispersant, causing the viscosity of the dispersion to increase excessively.

[0061] A carbon nanotube dispersion according to one embodiment of the present invention comprises, in order to solve the problem that the viscosity of the dispersion increases as the carbon nanotube content increases in a carbon nanotube dispersion containing only the first dispersant, a second dispersant comprising one or more polymers selected from the group consisting of polyethylene glycol, poly(1,2-propylene glycol), poly(1,3-propylene glycol), polycaprolactone, polytetramethylene glycol, and polystyrene together with the first dispersant, and accordingly, compared to a carbon nanotube dispersion using only a conventional dispersant, it has excellent dispersibility, resulting in less clumping of dispersion particles and an effect of suppressing the increase in viscosity.

[0062] Among the second dispersants mentioned above, in the case of polyethylene glycol, poly(1,2-propylene glycol), poly(1,3-propylene glycol), polycaprolactone, and polytetramethylene glycol, it is preferable to use polyethylene glycol to prevent an excessive increase in the viscosity of the dispersion.

[0063] The polystyrene of the second dispersant above may include one or more monomer-derived repeating units selected from the group consisting of, for example, styrene, 3-methylstyrene, 4-methylstyrene, 4-propylstyrene, 4-cyclohexylstyrene, and 4-(p-methylphenyl)styrene, which are aromatic vinyl monomers, and it is preferable to use polystyrene in which the aromatic vinyl monomer is styrene in order to prevent the viscosity of the dispersion from increasing excessively.

[0064] In one embodiment of the present invention, the second dispersant may comprise polystyrene and one polymer selected from the group consisting of polyethylene glycol, poly(1,2-propylene glycol), poly(1,3-propylene glycol), polycaprolactone and polytetramethylene glycol, and preferably, the second dispersant may comprise polyethylene glycol and polystyrene simultaneously.

[0065] At this time, when polystyrene is included together with one polymer selected from the group consisting of polyethylene glycol, poly(1,2-propylene glycol), poly(1,3-propylene glycol), polycaprolactone, and polytetramethylene glycol as the second dispersant, the content of polystyrene may be included in an amount of 10 to 50 parts by weight based on 100 parts by weight of the total second dispersant, for example, 10 parts by weight or more, 11 parts by weight or more, 12 parts by weight or more, 13 parts by weight or more, 14 parts by weight or more, 15 parts by weight or more, 16 parts by weight or more, 17 parts by weight or more, 18 parts by weight or more, 19 parts by weight or more, 20 parts by weight or more, 21 parts by weight or more, 22 parts by weight or more, 23 parts by weight or more, 24 parts by weight or more, 25 parts by weight or more, 26 parts by weight or more, 27 parts by weight or more, 28 parts by weight or more, 29 parts by weight or more, or 30 parts by weight or more. It may be included in an amount of 50 parts by weight or less, 49 parts by weight or less, 48 ​​parts by weight or less, 47 parts by weight or less, 46 parts by weight or less, 45 parts by weight or less, 44 parts by weight or less, 43 parts by weight or less, 42 parts by weight or less, 41 parts by weight or less, 40 parts by weight or less, 39 parts by weight or less, 38 parts by weight or less, 37 parts by weight or less, 36 parts by weight or less, 35 parts by weight or less, 34 parts by weight or less, 33 parts by weight or less, 32 parts by weight or less, or 31 parts by weight or less.

[0066] The second dispersant may be included in the dispersion in the form of a solution in which polymers such as polyethylene glycol, poly(1,2-propylene glycol), poly(1,3-propylene glycol), polycaprolactone, polytetramethylene glycol, and polystyrene are dissolved in an organic solvent such as N-methylpyrrolidone (NMP) so as to be well dissolved in the carbon nanotube dispersion of the present invention.

[0067] In one embodiment of the present invention, the second dispersant may be included in an amount of 1 to 30 parts by weight based on 100 parts by weight of carbon nanotubes in the carbon nanotube dispersion, wherein the content of the second dispersant refers to the total content of polystyrene and one polymer selected from the group consisting of polyethylene glycol, poly(1,2-propylene glycol), poly(1,3-propylene glycol), polycaprolactone and polytetramethylene glycol.

[0068] Specifically, the second dispersant may be included in an amount of 1 part by weight or more, 2 parts by weight or more, 3 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, 10 parts by weight or more, 11 parts by weight or more, 12 parts by weight or more, 13 parts by weight or more, 14 parts by weight or more, or 15 parts by weight or more, based on 100 parts by weight of carbon nanotubes in the carbon nanotube dispersion, and may be included in an amount of 30 parts by weight or less, 29 parts by weight or less, 28 parts by weight or less, 27 parts by weight or less, 26 parts by weight or less, 25 parts by weight or less, 24 parts by weight or less, 23 parts by weight or less, 22 parts by weight or less, 21 parts by weight or less, 20 parts by weight or less, 19 parts by weight or less, 18 parts by weight or less, 17 parts by weight or less, or 16 parts by weight or less. Preferably, the second dispersant may be included in an amount of 2.5 to 15 parts by weight based on 100 parts by weight of carbon nanotubes in the carbon nanotube dispersion.

[0069] When the second dispersant is included in the carbon nanotube dispersion within the above content range, it can be adsorbed onto the carbon nanotube surface that was not covered by the first dispersant to provide an additional dispersion effect, and the amount of excess dispersant that was not effectively adsorbed onto the carbon nanotube surface can be reduced, thereby preventing aggregation of the remaining dispersants.

[0070] A carbon nanotube dispersion according to one embodiment of the present invention comprises, in addition to the first and second dispersants, a third dispersant comprising an alkanolamine-based compound. As the dispersion comprises the third dispersant, the carbon nanotubes are dispersed uniformly and effectively, thereby maintaining a lower viscosity of the dispersion and further suppressing the increase in viscosity over time.

[0071] In one embodiment of the present invention, the alkanolamine compound may be a linear or branched saturated hydrocarbon of C3 to C10 containing at least one hydroxyl group (-OH) and at least one amine group (-NH2). In particular, since the alkanolamine compound, which is the third dispersant, contains a hydroxyl group and at least one amine group within the molecule, it may form hydrogen bonds with the solvent in the dispersion, thereby enabling the 'carbon nanotube-dispersant' conjugate to maintain a stable dispersed state in the solvent.

[0072] The above alkanolamine-based compound may be a C3 linear saturated hydrocarbon containing at least one hydroxyl group (-OH) and at least one amine group (-NH2), a C4 linear or branched saturated hydrocarbon, a C5 linear or branched saturated hydrocarbon, a C6 linear or branched saturated hydrocarbon, a C7 linear or branched saturated hydrocarbon, a C8 linear or branched saturated hydrocarbon, a C9 linear or branched saturated hydrocarbon, or a C10 linear or branched saturated hydrocarbon, and specifically may be a compound represented by the following chemical formulas 1 to 4.

[0073] [Chemical Formula 1] [Chemical Formula 2]

[0074]

[0075] [Chemical Formula 3] [Chemical Formula 4]

[0076]

[0077] In one embodiment of the present invention, the third dispersant may be included in an amount of 1 to 50 parts by weight based on 100 parts by weight of carbon nanotubes in the carbon nanotube dispersion, specifically 1 part by weight or more, 2 parts by weight or more, 3 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, 10 parts by weight or more, 11 parts by weight or more, 12 parts by weight or more, 13 parts by weight or more, 14 parts by weight or more, 15 parts by weight or more, 16 parts by weight or more, 17 parts by weight or more, 18 parts by weight or more, 19 parts by weight or more, 20 parts by weight or more, 21 parts by weight or more, 22 parts by weight or more, 23 parts by weight or more, 24 parts by weight or more, or 25 parts by weight or more, and 50 parts by weight or less, 49 parts by weight or less, 48 ​​parts by weight or less, 47 It may be included in an amount of 46 parts by weight or less, 45 parts by weight or less, 44 parts by weight or less, 43 parts by weight or less, 42 parts by weight or less, 41 parts by weight or less, 40 parts by weight or less, 39 parts by weight or less, 38 parts by weight or less, 37 parts by weight or less, 36 parts by weight or less, 35 parts by weight or less, 34 parts by weight or less, 33 parts by weight or less, 32 parts by weight or less, 31 parts by weight or less, 30 parts by weight or less, 29 parts by weight or less, 28 parts by weight or less, 27 parts by weight or less, or 26 parts by weight or less. Preferably, the third dispersant may be included in an amount of 5 to 50 parts by weight based on 100 parts by weight of carbon nanotubes in the carbon nanotube dispersion.

[0078] When the above-mentioned third dispersant is included in the carbon nanotube dispersion within the above-mentioned content range, it can adsorb onto the carbon nanotube surface that was not covered by the first and second dispersants to exhibit an additional dispersion effect, and by reducing the content of excess dispersant that was not effectively adsorbed onto the carbon nanotube surface, it is possible to prevent aggregation among the remaining dispersants, thereby suppressing strong bonding forces between carbon nanotubes beyond an appropriate level and maintaining a low viscosity of the carbon nanotube dispersion.

[0079]

[0080] (3) solvent

[0081] The solvent of the carbon nanotube dispersion according to one embodiment of the present invention is a dispersion medium for dispersing the carbon nanotube and the first to third dispersants, and is used to pre-disperse the carbon nanotube to prevent aggregation when the carbon nanotube in powder form is used directly in the preparation of an electrode slurry composition, and to supply it as a carbon nanotube dispersion.

[0082] The above solvent may be an organic solvent comprising one or more heteroatoms selected from the group consisting of nitrogen atoms (N) and oxygen atoms (O) having non-covalent electron pairs.

[0083] Specifically, the dispersion medium is an amide-based polar organic solvent such as dimethylformamide (DMF), diethylformamide, dimethylacetamide (DMAc), or N-methylpyrrolidone (NMP); alcohols such as methanol, ethanol, 1-propanol, 2-propanol (isopropyl alcohol), 1-butanol (n-butanol), 2-methyl-1-propanol (isobutanol), 2-butanol (sec-butanol), 1-methyl-2-propanol (tert-butanol), pentanol, hexanol, heptanol, or octanol; glycols such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, 1,3-propanediol, 1,3-butanediol, 1,5-pentanediol, or hexylene glycol; and polyhydric alcohols such as glycerin, trimethylolpropane, pentaerythritol, or sorbitol. Examples include glycol ethers such as ethylene glycol monomethyl ether, diethylene glycol monomethyl ether, triethylene glycol monomethyl ether, tetraethylene glycol monomethyl ether, ethylene glycol monoethyl ether, diethylene glycol monoethyl ether, triethylene glycol monoethyl ether, tetraethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, or tetraethylene glycol monobutyl ether; ketones such as acetone, methyl ethyl ketone, methylpropyl ketone, or cyclopentanone; esters such as ethyl acetate, γ-butyl lactone, and ε-propiolactone, and any one or a mixture of two or more of these may be used.

[0084]

[0085] A carbon nanotube dispersion according to one embodiment of the present invention allows the first to third dispersants to uniformly disperse carbon nanotubes in a solvent as described above, thereby enabling a reduction in the average particle size distribution of dispersed particles contained in the dispersion, such as carbon nanotubes and composites of each dispersant.

[0086] Accordingly, the carbon nanotube dispersion may have an initial viscosity of 0.1 to 10 Pa·s measured at 25 ℃ and 1 rpm using a viscometer (Brookfield RV-4), for example, 0.1 Pa·s or more, 0.2 Pa·s or more, 0.3 Pa·s or more, 0.4 Pa·s or more, 0.5 Pa·s or more, 0.6 Pa·s or more, 0.7 Pa·s or more, 0.8 Pa·s or more, 0.9 Pa·s or more, 1.0 Pa·s or more, 1.1 Pa·s or more, 1.2 Pa·s or more, 1.3 Pa·s or more, 1.4 Pa·s or more, 1.5 Pa·s or more, 1.6 Pa·s or more, 1.7 Pa·s or more, 1.8 Pa·s or more, 1.9 Pa·s or more, 2.0 Pa·s or more, 2.1 Pa·s or more, 2.2 Pa·s or more, 2.3 Pa·s or more, 2.4 Pa·s or more, 2.5 Pa·s or more, 2.6 Pa·s or more, 2.7 Pa·s or more, 2.8 Pa·s or more, 2.9 Pa·s or more, 3.0 Pa·s or more, 3.1 Pa·s or more, 3.2 Pa·s or more, 3.3 Pa·s or more, 3.4 Pa·s or more, 3.5 Pa·s or more, 3.6 Pa·s or more, 3.7 Pa·s or more, 3.8 Pa·s or more, 3.9 Pa·s or more, 4.0 Pa·s or more, 4.1 Pa·s or more, 4.2 Pa·s or more, 4.3 Pa·s or more, 4.4 Pa·s or more, 4.5 Pa·s or more, 4.6 Pa·s or more, 4.7 Pa·s or more, 4.8 Pa·s or more, It may be 4.9 Pa·s or higher or 5.0 Pa·s or higher, and 10.0 Pa·s or lower, 9.9 Pa·s or lower, 9.8 Pa·s or lower, 9.7 Pa·s or lower, 9.6 Pa·s or lower, 9.5 Pa·s or lower, 9.4 Pa·s or lower, 9.3 Pa·s or lower, 9.2 Pa·s or lower, 9.1 Pa·s or lower, 9.0 Pa·s or lower, 8.9 Pa·s or lower, 8.8 Pa·s or lower, 8.7 Pa·s or lower, 8.6 Pa·s or lower, 8.5 Pa·s or lower, 8.4 Pa·s or lower, 8.3 Pa·s or lower, 8.2 Pa·s or less, 8.1 Pa·s or less, 8.0 Pa·s or less, 7.9 Pa·s or less, 7.8 Pa·s or less, 7.7 Pa·s or less, 7.6 Pa·s or less, 7.5 Pa·s or less, 7.4 Pa·s or less, 7.3 Pa·s or less, 7.2 Pa·s or less, 7.1 Pa·s or less, 7.0 Pa·s or less, 6.9 Pa·s or less, 6.8 Pa·s or less, 6.7 Pa·s or less, 6.6 Pa·s or less, 6.5 Pa·s or less, 6.4 Pa·s or less, 6.3 Pa·s or less, 6.2 Pa·s or less, 6.1 Pa·s or less, 6.0 Pa·s or less, 5.9 Pa·s or less, 5.8 Pa·s or less, 5.7 Pa·s or less, 5.6 Pa·s or less, 5.5 It may be Pa·s or less, 5.4 Pa·s or less, 5.3 Pa·s or less, 5.2 Pa·s or less, or 5.1 Pa·s or less. If the carbon nanotube dispersion has an initial viscosity within the above range, an electrode slurry can be prepared more smoothly using it, and the electrode slurry containing the carbon nanotube dispersion can have a viscosity suitable for electrode formation.

[0087] In addition, particle size distribution D of the dispersed particles included in the dispersion liquid according to one embodiment of the present invention 50 This can be 5 to 15 μm, for example, 5 μm or more, 6 μm or more, 7 μm or more, 8 μm or more, or 9 μm or more, 15 μm or less, 14 μm or less, 13 μm or less, 12 μm or less, 11 μm or less, or 10 μm or less, and preferably the particle size distribution can be maintained low at 8 to 11 μm.

[0088] In addition, when a carbon nanotube dispersion according to one embodiment of the present invention is left at 25°C for one week, the increase rate of viscosity calculated by the following formula (1) may be 100% or less, for example, 10% or more and 100% or less, and specifically 10% or more, 11% or more, 12% or more, 13% or more, 14% or more, 15% or more, 16% or more, 17% or more, 18% or more, 19% or more, 20% or more, 21% or more, 22% or more, 23% or more, 24% or more, 25% or more, 26% or more, 27% or more, 28% or more, 29% or more, 30% or more, 31% or more, 32% or more, 33% or more, 34% or more, 35% or more, 36% or more, 37% or more, 38% or more, 39 % or more, 40% or more, 41% or more, 42% or more, 43% or more, 44% or more, 45% or more, 46% or more, 47% or more, 48% or more, 49% or more, 50% or more, 51% or more, 52% or more, 53% or more, 54% or more, or 55% or more, may be 100% or less, 99% or less, 98% or less, 97% or less, 96% or less, 95% or less, 94% or less, 93% or less, 92% or less, 91% or less, 90% or less, 89% or less, 88% or less, 87% or less, 86% or less, 85% or less, 84% or less, 83% or less, 82% or less, 81% or less, 80% or less, 79% or less, 78% or less, 77% It may be 69% or less, 76% or less, 75% or less, 74% or less, 73% or less, 72% or less, 71% or less, 70% or less, 69% or less, 68% or less, 67% or less, 66% or less, 65% or less, 64% or less, 63% or less, 62% or less, 61% or less, 60% or less, 59% or less, 58% or less, 57% or less, or 56% or less.

[0089] [Equation 1]

[0090] Viscosity increase rate (%) = {(Viscosity measured after leaving at 25 ℃ for 1 week - Initial viscosity) / Initial viscosity} × 100

[0091] At this time, the viscosity after leaving for one week and the initial viscosity were measured at 25 ℃ and 1 rpm.

[0092]

[0093] Method for preparing a carbon nanotube dispersion

[0094] Hereinafter, a method for preparing a carbon nanotube dispersion according to one embodiment of the present invention will be described.

[0095] A method for preparing a carbon nanotube dispersion according to the present invention comprises: (1) a step of preparing a primary carbon nanotube dispersion by mixing a first dispersant containing a nitrogen atom, a second dispersant containing one or more polymers selected from the group consisting of polyethylene glycol, poly(1,2-propylene glycol), poly(1,3-propylene glycol), polycaprolactone, polytetramethylene glycol, and polystyrene, a third dispersant containing an alkanolamine-based compound, and a solvent; and (2) a step of preparing a secondary carbon nanotube dispersion by dispersing the primary carbon nanotube dispersion. Accordingly, the carbon nanotube dispersion according to the present invention may refer to a secondary carbon nanotube dispersion prepared by the above-described method.

[0096] In step (1), a carbon nanotube primary dispersion is prepared by mixing a carbon nanotube, a first dispersant containing nitrogen atoms, a second dispersant containing one or more polymers selected from the group consisting of polyethylene glycol, poly(1,2-propylene glycol), poly(1,3-propylene glycol), polycaprolactone, polytetramethylene glycol, and polystyrene, a third dispersant containing an alkanolamine-based compound, and a solvent. The step of preparing the carbon nanotube primary dispersion is carried out as a wetting process to evenly mix each component.

[0097] As the specific description of the carbon nanotube according to the method for preparing the carbon nanotube dispersion above, the first dispersant containing a nitrogen atom, the second dispersant containing one or more polymers selected from the group consisting of polyethylene glycol, poly(1,2-propylene glycol), poly(1,3-propylene glycol), polycaprolactone, polytetramethylene glycol, and polystyrene, the third dispersant containing an alkanolamine-based compound, and the solvent is as described above, the specific description below will be omitted.

[0098] The mixing for preparing the above carbon nanotube primary dispersion can be performed using a conventional mixing method, specifically using a mixing device such as a Pony mixer, Change-can mixer, Hobart mixer, Planetary mixer, Butterfly mixer, Stone mill, Homogenizer, Beads mill, Ball mill, Basket mill, Attrition mill, Universal stirrer, Clear mixer, or TK mixer, and may include a step of mixing for 30 minutes to 7 hours at a rotational speed of 300 to 5,000 rpm.

[0099] In addition, when mixing to prepare the primary dispersion of carbon nanotubes, cavitation dispersion treatment may be performed to improve the miscibility between carbon nanotubes and the solvent, or the dispersibility of carbon nanotubes in the solvent. The cavitation dispersion treatment is a dispersion method that utilizes shock waves generated by the rupture of vacuum bubbles formed in water when high energy is applied to the liquid, and can disperse carbon nanotubes without damaging their properties. Specifically, the cavitation dispersion treatment may be performed by ultrasonic, jet mill, or shear dispersion treatment.

[0100] The step of preparing the above-mentioned primary dispersion of carbon nanotubes can be performed under temperature conditions where physical properties, such as the viscosity of the mixture, do not change due to the evaporation of the solvent. For example, it can be performed at a temperature of 50°C or lower, more specifically at a temperature of 5°C to 50°C.

[0101] In step (2), the carbon nanotube primary dispersion is dispersed to prepare a carbon nanotube secondary dispersion.

[0102] The process of preparing the above carbon nanotube secondary dispersion can be carried out by methods such as a ball mill, bead mill, disc mill or basket mill, or a high-pressure disperser (high-pressure homogenizer), and more specifically, by a dispersion method using a high-pressure disperser (high-pressure homogenizer).

[0103] Dispersion by the above-mentioned high-pressure disperser is achieved by pressurizing the mixture with, for example, the plunger pump of the high-pressure disperser and pushing it through the gap of the dispersion valve, and by forces such as cavitation, shear, impact, and explosion when passing through the gap.

[0104] The above dispersion process can be performed according to the degree of dispersion of the carbon nanotube dispersion, specifically, under a pressure of 5,000 to 30,000 psi for 30 to 120 minutes, more specifically for 60 to 90 minutes, and the above process can be repeated 1 to 10 times.

[0105]

[0106] Electrode slurry composition for lithium secondary batteries and electrode for lithium secondary batteries

[0107] In addition, the present invention provides an electrode slurry composition for a lithium secondary battery comprising the carbon nanotube dispersion and the electrode active material.

[0108] The above electrode slurry composition for a lithium secondary battery may be an anode slurry composition or a cathode slurry composition, and specifically may be an anode slurry composition.

[0109] The above electrode slurry composition for a lithium secondary battery may include the carbon nanotube dispersion, a positive or negative active material as an electrode active material, a binder, and other additives such as a solvent and / or viscosity modifier, and a filler, as needed.

[0110] As the above-mentioned cathode active material, cathode active materials well known in the relevant technical field may be used without limitation. For example, lithium cobalt-based oxides, lithium nickel-based oxides, lithium manganese-based oxides, lithium iron phosphate, lithium nickel manganese cobalt-based oxides, or combinations thereof may be used. Specifically, as the above-mentioned cathode active material, LiCoO2, LiNiO2, LiMn2O4, LiCoPO4, LiFePO4, and LiNi a Mn b Co c O 2　 (Here, 0 < a, b, c < 1) etc. may be used, but are not limited thereto.

[0111] The above-mentioned negative electrode active material includes natural graphite, artificial graphite, carbonaceous material; lithium-containing titanium composite oxide (LTO); metals (Me) such as Si, Sn, Li, Zn, Mg, Cd, Ce, Ni, or Fe; alloys composed of the above-mentioned metals (Me); and oxides (MeO) of the above-mentioned metals (Me). xExamples include one or more cathode active materials selected from the group consisting of metals (Me) and composites of carbon. The cathode active material may be included in an amount of 60 to 98 weight%, more preferably 70 to 98 weight%, based on the total weight of the solids excluding the solvent in the cathode slurry.

[0112] The above binder is a component that assists in the bonding of the active material and the conductive material, and in the bonding to the current collector, and is typically added in an amount of 1 to 30 weight percent based on the total weight of the mixture containing the electrode active material. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluororubber, and various copolymers.

[0113] The above solvents include organic solvents such as N-methylpyrrolidone (NMP), dimethylformamide (DMF), acetone, and dimethylacetamide, or water, and these solvents may be used alone or in a mixture of two or more. The amount of solvent used is sufficient if it is sufficient to dissolve and disperse the electrode active material, binder, and conductive material, taking into account the coating thickness of the electrode slurry and the manufacturing yield.

[0114] The above viscosity modifier may be carboxymethylcellulose or polyacrylic acid, and the viscosity of the electrode slurry can be controlled by adding it to facilitate the preparation of the electrode slurry and the coating process on the electrode current collector.

[0115] The above-mentioned filler is optionally used as a component to inhibit the expansion of the electrode, and is not particularly limited as long as it is a fibrous material that does not cause chemical changes in the battery; for example, olivine-based polymers such as polyethylene and polypropylene; and fibrous materials such as glass fibers and carbon fibers are used.

[0116] If the above electrode slurry composition is a composition of an anode slurry for forming an anode, the anode can be manufactured by applying the above anode slurry composition onto an anode current collector, followed by drying and rolling. Alternatively, the anode can be manufactured by casting the above anode slurry onto a separate support and then laminating the film obtained by peeling it off from the support onto the above anode current collector.

[0117] The thickness of the anode active material layer formed by the anode slurry may vary depending on the loading amount, loading speed, etc., for applying the anode slurry.

[0118] In the case of an electrode for a lithium secondary battery according to the present invention, the electrode slurry composition for a lithium secondary battery is formed using the electrode slurry composition, and the electrode slurry composition comprises the carbon nanotube dispersion and the electrode active material according to the present invention, wherein the carbon nanotube dispersion comprises a first dispersant comprising carbon nanotubes and nitrogen atoms, and a second dispersant comprising one or more polymers selected from the group consisting of polyethylene glycol, poly(1,2-propylene glycol), poly(1,3-propylene glycol), polycaprolactone, polytetramethylene glycol, and polystyrene, and further comprises a third dispersant comprising an alkanolamine-based compound, thereby enabling the manufacture of an electrode and a secondary battery having excellent capacity characteristics and cycle characteristics.

[0119] The above positive current collector generally has a thickness of 3 μm to 500 μm. Such a positive 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 surface-treated with carbon, nickel, titanium, silver, etc. may be used. In addition, fine irregularities may be formed on the surface of the positive current collector to strengthen the bonding strength of the positive active material, and it may be used in various forms such as films, sheets, foils, nets, porous bodies, foams, and nonwoven fabrics.

[0120] In the case where the above electrode slurry composition is a composition of a cathode slurry for forming a cathode, the cathode can be manufactured by applying the composition of the cathode slurry onto a cathode current collector, followed by drying and rolling. Alternatively, the cathode can be manufactured by casting the cathode slurry onto a separate support and then laminating the film obtained by peeling it off from the support onto the cathode current collector.

[0121] The thickness of the cathode active material layer formed by the above cathode slurry may vary depending on the loading amount, loading speed, etc., for applying the cathode slurry.

[0122] The above-mentioned negative current collector generally has a thickness of 3 μm to 500 μm. Such a negative current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface treated with carbon, nickel, titanium, silver, etc., or aluminum-cadmium alloy may be used. In addition, similar to the negative current collector, fine irregularities may be formed on the surface to strengthen the bonding strength of the negative active material, and it may be used in various forms such as films, sheets, foils, nets, porous bodies, foams, and nonwoven fabrics.

[0123]

[0124] lithium secondary battery

[0125] A lithium secondary battery comprises a positive electrode, a negative electrode, a separator disposed between the positive and negative electrodes, and an electrolyte. Since the positive and negative electrodes are identical to those described above, a detailed description is omitted.

[0126] The above separator separates the negative electrode and the positive electrode and provides a pathway for the movement of lithium ions. It can be used without special restrictions as long as it is typically used as a separator in a lithium secondary battery, and it is particularly desirable that it has low resistance to the movement of electrolyte ions and excellent electrolyte wettability. Specifically, a porous polymer film, such as a porous polymer film made of a polyolefin-based polymer like ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof may be used. In addition, a conventional porous nonwoven fabric, such as a nonwoven fabric made of high-melting-point glass fiber or polyethylene terephthalate fiber, may be used. Furthermore, a coated separator containing ceramic components or polymer materials may be used to ensure heat resistance or mechanical strength, and it may optionally be used in a single-layer or multi-layer structure.

[0127] The above electrolyte may be an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel-type polymer electrolyte, a solid inorganic electrolyte, a molten inorganic electrolyte, etc., which can be used in the manufacture of a lithium secondary battery, but is not limited to these. Specifically, the above electrolyte may include an organic solvent and a lithium salt.

[0128] The above organic solvent may be used without special restrictions as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the above organic solvent may include ester-based solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether-based solvents such as dibutyl ether or tetrahydrofuran; ketone-based solvents such as cyclohexanone; and aromatic hydrocarbon-based solvents such as benzene and fluorobenzene. Carbonate-based solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol-based solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (where R is a straight-chain, branched, or cyclic hydrocarbon group having C2 to C20 structures and may include a double bond, a directional ring, or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes may be used. Among these, a carbonate-based solvent is preferred, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate, etc.) having high ionic conductivity and high dielectric constant that can improve the charge / discharge performance of the battery, and a low-viscosity linear carbonate-based compound (e.g., ethylmethyl carbonate, dimethyl carbonate or diethyl carbonate, etc.) is more preferred.In this case, using a mixture of cyclic carbonate and chain carbonate in a volume ratio of about 1:1 to about 1:9 can result in excellent performance of the electrolyte.

[0129] The above lithium salt can be used without special restrictions as long as it is a compound capable of providing lithium ions used in lithium secondary batteries. Specifically, the lithium salt may be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2. The above lithium salt may be used within the range of 0.1M to 2.0M. When the concentration of the lithium salt falls within the above range, the electrolyte has appropriate conductivity and viscosity, so it can exhibit excellent electrolyte performance and allow lithium ions to move effectively.

[0130] In addition to the above electrolyte components, the above electrolyte may further include one or more additives for the purpose of improving the lifespan characteristics of the battery, suppressing the decrease in battery capacity, and improving the discharge capacity of the battery, such as, for example, haloalkylene carbonate-based compounds such as difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, triamide hexaphosphate, nitrobenzene derivative, sulfur, quinone imine dye, 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% to 5% by weight based on the total weight of the electrolyte.

[0131] A lithium secondary battery comprising an electrode manufactured using a carbon nanotube dispersion according to the present invention, specifically a lithium secondary battery comprising an electrode manufactured using a carbon nanotube dispersion, has carbon nanotubes uniformly dispersed within the electrode and can stably exhibit excellent discharge capacity and output characteristics by reducing the content of conductive materials such as conventional carbon black compared to cases containing such materials. As a result, it can be usefully applied in fields such as portable devices like mobile phones, laptop computers, and digital cameras, and electric vehicles such as hybrid electric vehicles (HEVs).

[0132] Accordingly, according to another embodiment of the present invention, the lithium secondary battery, the battery module including the lithium secondary battery as a unit cell, and the battery pack including the same may be provided.

[0133] The above battery module or battery pack can be used as a power source for one or more medium-to-large devices, including a power tool; an electric vehicle (EV), a hybrid electric vehicle, and a plug-in hybrid electric vehicle (PHEV); or a power storage system.

[0134] Specific embodiments of the present invention are presented below. However, the embodiments described below are merely for the purpose of specifically illustrating or explaining the present invention and do not limit the present invention. Furthermore, details not described herein can be sufficiently technically inferred by a person skilled in the art, so their description is omitted.

[0135]

[0136] Examples

[0137]

[0138] Example 1

[0139] (1) In a butterfly mixer (BTM-2K, KM Tech), a specific surface area of ​​250 m² is added relative to 100 parts by weight of the total dispersion. 2 4.2 parts by weight of multi-walled carbon nanotubes (MWCNT, LG Chem) with a weight of / g; 1.47 parts by weight of polyvinylpyrrolidone (PVP) powder (PVP K30, manufactured by Zhangzhou Huafu Chemical) (Mw 40,000 g / mol) as a first dispersant (corresponding to 35 parts by weight relative to 100 parts by weight of carbon nanotubes); 0.105 parts by weight of a mixture of polyethylene glycol (Sigma Aldrich, Mw=750 g / mol) and polystyrene (Sigma Aldrich, Mw=3,000 g / mol) in a weight ratio of 60 to 80:20 to 40 as a second dispersant (polyethylene glycol and polystyrene are each dissolved in N-methylpyrrolidone (NMP) solvent and added as a 20 wt% solution, corresponding to 2.5 parts by weight relative to 100 parts by weight of carbon nanotubes); and a third dispersant 0.21 parts by weight of 2-amino-2-methyl-1-propanol (corresponding to 5.0 parts by weight per 100 parts by weight of carbon nanotubes) and the remainder of N-methylpyrrolidone (NMP) as a solvent were added and mixed at 5,000 rpm for 3 hours to prepare a primary dispersion of carbon nanotubes.

[0140] (2) The above carbon nanotube primary dispersion was homogeneously dispersed five times at a pressure of 20,000 psi using a high-pressure disperser (PICOMAX, Micronox) to prepare a carbon nanotube secondary dispersion.

[0141]

[0142] Example 2

[0143] In the above Example 1, a carbon nanotube dispersion was prepared in the same manner as in Example 1, except that 1.26 parts by weight of the first dispersant (corresponding to 30 parts by weight of carbon nanotubes) were added relative to 100 parts by weight of the total dispersion, 0.21 parts by weight of the second dispersant (corresponding to 5 parts by weight of carbon nanotubes) were added relative to 100 parts by weight of the total dispersion, and 2.1 parts by weight of the third dispersant (corresponding to 50 parts by weight of carbon nanotubes) were added relative to 100 parts by weight of the total dispersion.

[0144]

[0145] Comparative Example 1

[0146] A carbon nanotube dispersion was prepared in the same manner as in Example 1, except that in Example 1, the second dispersant was not added, and ethanolamine (CAS No. 141-43-5) was added as the third dispersant at a rate of 0.315 parts by weight (corresponding to 7.5 parts by weight per 100 parts by weight of carbon nanotubes) per 100 parts by weight of the total dispersion.

[0147]

[0148] Comparative Example 2

[0149] In the above Example 1, a carbon nanotube dispersion was prepared in the same manner as in Example 1, except that the second and third dispersants were not added.

[0150]

[0151] Comparative Example 3

[0152] In the above Example 2, a carbon nanotube dispersion was prepared in the same manner as in Example 2, except that the third dispersant was not added.

[0153]

[0154] Comparative Example 4

[0155] In the above Example 1, a carbon nanotube dispersion was prepared in the same manner as in Example 1, except that only 0.42 parts by weight of the first dispersant (corresponding to 10 parts by weight relative to 100 parts by weight of carbon nanotubes) was added, and the second and third dispersants were not added.

[0156]

[0157] Comparative Example 5

[0158] In the above Example 1, a carbon nanotube dispersion was prepared in the same manner as in Example 1, except that only 2.1 parts by weight of the first dispersant (corresponding to 50 parts by weight relative to 100 parts by weight of carbon nanotubes) was added, and the second and third dispersants were not added.

[0159]

[0160] Comparative Example 6

[0161] In the above Example 1, a carbon nanotube dispersion was prepared in the same manner as in Example 1, except that 0.42 parts by weight of the first dispersant (corresponding to 10 parts by weight per 100 parts by weight of carbon nanotubes) was added, the second dispersant was not added, and 0.42 parts by weight of the third dispersant (corresponding to 10 parts by weight per 100 parts by weight of carbon nanotubes) was added.

[0162]

[0163] Comparative Example 7

[0164] In the above Example 1, a carbon nanotube dispersion was prepared in the same manner as in Example 1, except that 0.42 parts by weight of the first dispersant (corresponding to 10 parts by weight per 100 parts by weight of carbon nanotubes) was added, the second dispersant was not added, and 0.21 parts by weight of the third dispersant (corresponding to 5 parts by weight per 100 parts by weight of carbon nanotubes) was added.

[0165]

[0166] Comparative Example 8

[0167] In Example 2 above, a carbon nanotube dispersion was prepared in the same manner as in Example 2, except that the first and second dispersants were not added, and 1.26 parts by weight of the third dispersant (corresponding to 30 parts by weight relative to 100 parts by weight of carbon nanotubes) was added.

[0168]

[0169] Experimental Example

[0170] The viscosity of the carbon nanotube dispersions of Examples 1 and 2 and Comparative Examples 1 to 8 was measured, and the viscosity was measured again after leaving them at 25°C for one week, and the results are shown in Table 1 below.

[0171] The viscosity was measured using a viscometer (Brookfield RV-4) at 25°C and 40 rpm for 3 minutes as the initial viscosity.

[0172] CNT Content (parts by weight) 1st Dispersant Content (parts by weight) 2nd Dispersant Content (parts by weight) 3rd Dispersant Content (parts by weight) Viscosity Initial Viscosity (Pa·s) Viscosity After 1 Week (Pa·s) Growth Rate (%) Example 14.21.47 0.10 50.21 0.10 20.19 591 Example 24.21.26 0.21 2.10.34 50.56 664 Comparative Example 14.21.47 -0.31 50.33 00.62 589 Comparative Example 24.21.47 -1.62 53.56 119 Comparative Example 34.21.26 0.21 -0.69 01.53 2122 Comparative Example 44.20.42 001.82 6.00 2228 Comparative Example 54.22.1001.1662.845144 Comparative Example 64.20.4200.420.891.63884 Comparative Example 74.20.4200.210.650.7617 Comparative Example 84.2001.262.474.2873

[0173] (However, the content of CNT, the first dispersant, the second dispersant, and the third dispersant is based on 100 parts by weight of the dispersion.)

[0174] Referring to Table 1 above, it can be seen that the carbon nanotube dispersions of Examples 1 and 2, which include a first dispersant containing nitrogen atoms, a second dispersant containing polyethylene glycol and polystyrene, and a third dispersant containing an alkanolamine-based compound, have a low initial viscosity immediately after dispersing carbon nanotubes in a solvent, and in particular, the increase in viscosity of the carbon nanotube dispersion over time is very effectively suppressed.

[0175] On the other hand, in the case of the carbon nanotube dispersion according to Comparative Example 1, the effect of suppressing the increase in viscosity of the carbon nanotube dispersion over time shows a similar trend to that of the carbon nanotube dispersion according to Example 1, but as it does not include a second dispersant containing polyethylene glycol and polystyrene as in the present invention, it can be seen that the initial viscosity immediately after dispersing carbon nanotubes in a solvent is about 3 times higher.

[0176] In addition, as in Comparative Example 2, when the carbon nanotube dispersion does not contain a third dispersant including an alkanolamine-based compound as well as a second dispersant, the tendency for the carbon nanotube-dispersant complex to form hydrogen bonds with the solvent is reduced compared to the carbon nanotube dispersion according to Example 1, making it difficult to maintain a stable dispersed state in the solvent. Consequently, it can be seen that the initial viscosity of the dispersion is low and the viscosity of the dispersion increases rapidly over time.

[0177] In particular, when the amount of the third dispersant added in Example 2 is increased to 50 parts by weight relative to 100 parts by weight of carbon nanotubes compared to Example 1, it can be confirmed that the initial viscosity of the dispersion is lower and exhibits excellent change over time compared to the dispersion of Comparative Example 3, in which the conditions of the first and second dispersants are the same as those of Example 2 and only the third dispersant is not added.

[0178] In the case of Comparative Example 4, since only a small amount of the first dispersant is included and the second and third dispersants are not included at all, it can be seen that not only is the viscosity formed high from the beginning of dispersion, but the increase in viscosity over time is also extreme, making it difficult to maintain a stable dispersion state.

[0179] In the case of Comparative Example 5, since only the first dispersant is included in large quantities and the second and third dispersants are not included, the initial dispersibility is significantly reduced compared to the example, so stable dispersion in the solvent is not achieved, and it can be seen that the increase in viscosity over time is also clearly evident.

[0180] Comparative Example 6 includes both the first and third dispersants but lacks the second dispersant, so the initial viscosity is still formed at a high level, and the increase in viscosity over time is not suppressed, making it difficult to obtain a stable dispersion effect like that of the example.

[0181] In the case of Comparative Example 7, the increase in viscosity over time was relatively suppressed because the first and third dispersants were included together; however, since the initial viscosity was already higher than that of the example, it can be confirmed that the overall dispersion stability did not reach that of the example.

[0182] Finally, in Comparative Example 8, since only the third dispersant is included and the first and second dispersants are not included, the initial viscosity is formed higher than that of the example, and it can be confirmed that the dispersion stability is significantly reduced as the viscosity increases rapidly over time.

[0183] Although preferred embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements by those skilled in the art using the basic concept of the present invention as defined in the following claims also fall within the scope of the present invention.

Claims

1. Carbon nanotubes; A first dispersant containing nitrogen atoms; A second dispersant comprising one or more polymers selected from the group consisting of polyethylene glycol, poly(1,2-propylene glycol), poly(1,3-propylene glycol), polytetramethylene glycol, polycaprolactone, and polystyrene; A third dispersant comprising an alkanolamine-based compound; and containing a solvent Carbon nanotube dispersion.

2. In Paragraph 1, The second dispersant comprises polystyrene and one polymer selected from the group consisting of polyethylene glycol, poly(1,2-propylene glycol), poly(1,3-propylene glycol), polycaprolactone, and polytetramethylene glycol. Carbon nanotube dispersion.

3. In Paragraph 1, The above alkanolamine compound is a linear or branched C3 to C10 saturated hydrocarbon comprising at least one hydroxyl group (-OH) and at least one amine group (-NH2). Carbon nanotube dispersion.

4. In Paragraph 1, The carbon nanotubes are included in an amount of 0.1 to 10 parts by weight based on 100 parts by weight of the dispersion. Carbon nanotube dispersion.

5. In Paragraph 1, The carbon nanotube dispersion comprises 10 to 50 parts by weight of the first dispersant based on 100 parts by weight of the carbon nanotube. Carbon nanotube dispersion.

6. In Paragraph 1, The carbon nanotube dispersion comprises 1 to 30 parts by weight of the second dispersant based on 100 parts by weight of the carbon nanotube. Carbon nanotube dispersion.

7. In Paragraph 1, The carbon nanotube dispersion comprises 1 to 50 parts by weight of the third dispersant based on 100 parts by weight of the carbon nanotube. Carbon nanotube dispersion.

8. In Paragraph 1, The carbon nanotube dispersion has an initial viscosity of 0.1 to 10 Pa·s measured at 25 ℃ and 1 rpm, Carbon nanotube dispersion.

9. In Paragraph 1, The above carbon nanotube dispersion is one in which the viscosity increase rate represented by the following formula (1) is 100% or less, Carbon nanotube dispersion: [Equation 1] Viscosity increase rate (%) = {(Viscosity measured after leaving at 25 ℃ for 1 week - Initial viscosity) / Initial viscosity} × 100 10. (1) A step of preparing a carbon nanotube primary dispersion by mixing a carbon nanotube, a first dispersant containing nitrogen atoms, a second dispersant containing one or more polymers selected from the group consisting of polyethylene glycol, poly(1,2-propylene glycol), poly(1,3-propylene glycol), polycaprolactone, polytetramethylene glycol, and polystyrene, a third dispersant containing an alkanolamine-based compound, and a solvent; and (2) A step of preparing a carbon nanotube secondary dispersion by dispersing the carbon nanotube primary dispersion above; A method for preparing a carbon nanotube dispersion according to claim 1, comprising 11. An electrode slurry composition for a lithium secondary battery comprising a carbon nanotube dispersion and an electrode active material according to claim 1.

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