Carbon nanotube dispersion and preparation method therefor

Abstract

The present invention relates to: a carbon nanotube dispersion; a preparation method therefor; and an electrode slurry for a lithium secondary battery, comprising the carbon nanotube dispersion. The carbon nanotube dispersion comprises carbon nanotubes, a first dispersant comprising hydrogenated nitrile butadiene rubber, 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 alkanol amine-based compound, and a solvent.

Description

Carbon nanotube dispersion and method for producing the same

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

[0002] This application claims the benefit of priority to Korean Patent Application No. 10-2024-0061824, filed May 10, 2024, Korean Patent Application No. 10-2024-0073599, filed June 5, 2024, and Korean Patent Application No. 10-2025-0059846, filed May 8, 2025, the entire contents of which are incorporated herein by reference.

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

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

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

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

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

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

[0009] [Prior Art Literature]

[0010] [Patent Document]

[0011] (Patent Document 1) Chinese Patent Publication No. 117373750 (January 9, 2024)

[0012] An object of the present invention is to provide a carbon nanotube dispersion having excellent dispersibility, low viscosity of the dispersion and particle size of the dispersed particles, and little change in viscosity over time, comprising a first dispersant including carbon nanotubes, hydrogenated nitrile butadiene rubber, a second dispersant including 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 including an alkanol amine compound, and a solvent.

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

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

[0015] Another object of the present invention is to provide an electrode for a lithium secondary battery, which uses the electrode slurry composition for a lithium secondary battery and has improved bonding strength between active material particles of an electrode mixture layer formed thereby and improved adhesive strength between an electrode mixture layer and a current collector.

[0016] One embodiment of the present invention provides a carbon nanotube dispersion comprising a first dispersant including carbon nanotubes, hydrogenated nitrile butadiene rubber, a second dispersant including 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 including an alkanol amine compound, and a solvent.

[0017] 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.

[0018] The above alkanol amine compound may be a C3 to C10 linear or branched saturated hydrocarbon containing at least one hydroxyl group (-OH) and at least one amine group (-NH2).

[0019] The above 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.

[0020] The above carbon nanotube dispersion may contain 10 to 50 parts by weight of the first dispersant based on 100 parts by weight of the carbon nanotubes.

[0021] The above carbon nanotube dispersion may contain 1 to 30 parts by weight of the second dispersant based on 100 parts by weight of the carbon nanotubes.

[0022] The above carbon nanotube dispersion may contain 1 to 30 parts by weight of the third dispersant based on 100 parts by weight of the carbon nanotubes.

[0023] The total content (SOP) of the first to third dispersants relative to the carbon nanotube content of the carbon nanotube dispersion may be 20 wt% to 100 wt%.

[0024] The above carbon nanotube dispersion may have an initial viscosity of 0.1 to 10 Pa·s measured at 25°C and 1 rpm.

[0025] The above carbon nanotube dispersion may have a viscosity increase rate of 60% or less, as expressed by the following equation (1).

[0026] [Formula 1]

[0027] Viscosity increase rate (%) = {(Viscosity measured after leaving at 25 ℃ for 2 weeks - Initial viscosity) / Initial viscosity} × 100

[0028] Another embodiment of the present invention provides a method for preparing the above-described carbon nanotube dispersion, comprising the steps of (1) mixing carbon nanotubes, a first dispersant including hydrogenated nitrile butadiene rubber, a second dispersant including 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 including an alkanol amine compound, and a solvent to prepare a carbon nanotube primary dispersion, and (2) dispersing the carbon nanotube primary dispersion to prepare a carbon nanotube secondary dispersion.

[0029] Another embodiment of the present invention provides an electrode slurry composition for a lithium secondary battery comprising the above-described carbon nanotube dispersion and an electrode active material.

[0030] Another embodiment of the present invention provides an electrode for a lithium secondary battery including an electrode composite layer formed using the electrode slurry composition for a lithium secondary battery described above.

[0031] The carbon nanotube dispersion according to the present invention further comprises a third dispersant comprising an alkanol amine compound, together with a first dispersant comprising hydrogenated nitrile butadiene rubber, 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, thereby exhibiting a small change in viscosity over time, a relatively low viscosity, and having a characteristic of having a small particle size of dispersed particles by uniformly and effectively dispersing the carbon nanotubes.

[0032] Furthermore, when the carbon nanotube dispersion of the present invention is used in an electrode slurry composition, the electrode slurry composition has the characteristics of improving the bonding strength between active material particles of an electrode mixture layer for a lithium secondary battery and the adhesive strength between the electrode mixture layer and a current collector, thereby enabling the manufacture of an electrode and a secondary battery having excellent capacity characteristics and cycle characteristics.

[0033] Hereinafter, embodiments of the present invention will be described in detail. Prior to this, terms and words used in this specification and claims should not be interpreted as limited to their conventional or dictionary meanings. Rather, they should be interpreted with meanings and concepts that conform to the technical spirit of the present invention, based on the principle that the inventor can appropriately define the concept of a term to best explain his or her invention. Accordingly, the configurations described in the embodiments described in this specification are merely the most preferred embodiments of the present invention and do not represent all of the technical spirit of the present invention. Therefore, it should be understood that various equivalents and modified examples may exist as of the time of this application.

[0034] In this specification, the term "substitution" means that a hydrogen atom bonded to a carbon atom of a compound is replaced with another substituent, and the position of substitution is not limited as long as it is a position where a hydrogen atom is replaced, i.e., a position where a substituent can be replaced, and when two or more are replaced, the two or more substituents may be the same or different from each other.

[0035] Throughout this specification, whenever a part is said to 'include' a component, this does not mean that it excludes other components, but rather that it may include other components, unless otherwise specifically stated.

[0036] Throughout this specification, “%” means weight percent unless explicitly stated otherwise.

[0037] In this specification, the average particle size "D 50 " means the particle size corresponding to 50% of the volume accumulation. The above D 50 For example, it can be measured using the laser diffraction method. The laser diffraction method can generally measure particle sizes from the submicron range to several mm, and can obtain results with high reproducibility and high resolution.

[0038] In this specification, the “specific surface area” is measured by the BET method (Brunauer-Emmett-Teller Analysis), and specifically, can be calculated from the nitrogen gas adsorption amount at liquid nitrogen temperature (77 K) using BELSORP-mino II of BEL Japan.

[0039]

[0040] carbon nanotube dispersion

[0041] A carbon nanotube dispersion according to the present invention comprises carbon nanotubes, a first dispersant including hydrogenated nitrile butadiene rubber, a second dispersant including 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 including an alkanol amine compound, and a solvent. Hereinafter, each component of the carbon nanotube dispersion of the present invention will be described in detail.

[0042]

[0043] (1) Carbon nanotubes

[0044] The term 'carbon nanotube' used in the present invention refers to a secondary structure formed by assembling carbon nanotube units in a bundle shape, in whole or in part, wherein the carbon nanotube units have a graphite sheet in the shape of a cylinder with a nano-sized diameter, and sp 2 It has a bonding structure. At this time, depending on the angle and structure at which the graphite plane is rolled, it can exhibit the characteristics of a conductor or a semiconductor. The carbon nanotube unit can be classified into single-walled carbon nanotube (SWCNT, single-walled carbon nanotube), double-walled carbon nanotube (DWCNT, double-walled carbon nanotube), and multi-walled carbon nanotube (MWCNT, multi-walled carbon nanotube) depending on the number of bonds forming the wall.

[0045] The term 'bundle type' used in the present invention, unless otherwise stated, refers to a secondary shape in the form of a bundle or rope in which a plurality of carbon nanotube units are arranged in a parallel manner with their longitudinal axes substantially in the same orientation, or are arranged and then twisted or entangled. The term 'non-bundle type or entangled type' refers to a shape in which carbon nanotube units are entangled without a definite shape such as a bundle or rope.

[0046] Carbon nanotubes are highly conductive, but they tend to aggregate due to the van der Waals forces that exist between them. When the conductive material aggregates, it cannot properly form a conductive path within the electrode. Furthermore, increasing the amount of conductive material required to increase conductivity leads to a relatively small amount of active material, which can actually reduce electrode performance, such as capacity. Consequently, commercializing carbon nanotubes as a conductive material has been challenging.

[0047] The carbon nanotube dispersion according to the present invention further comprises a third dispersant comprising an alkanol amine compound, together with a first dispersant comprising hydrogenated nitrile butadiene rubber, 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, so that the initial viscosity of the carbon nanotube dispersion can be significantly reduced and the occurrence of viscosity changes over time can be suppressed, so that when applied to an electrode slurry of a lithium secondary battery, high conductivity can be exhibited due to the high conductivity of the carbon nanotubes.

[0048] Therefore, when the carbon nanotube dispersion according to the present invention is applied to the production of an electrode slurry, the carbon nanotubes are uniformly positioned between the active materials, so that even during the process of manufacturing an electrode by coating and drying the electrode slurry and then rolling, the microscopic spaces between the electrode active materials can be maintained at a constant level. In addition, since the carbon nanotubes are uniformly distributed without agglomeration, a sufficient conductive path can be formed even with a small amount of carbon nanotubes.

[0049] A carbon nanotube dispersion according to one embodiment of the present invention may include, but is not limited to, any one or more of single-walled, double-walled, and multi-walled carbon nanotubes as the carbon nanotubes, and specifically may include single-walled carbon nanotubes. Since the single-walled carbon nanotubes or double-walled carbon nanotubes have a higher specific surface area than multi-walled carbon nanotubes, they are more effective in improving cycle characteristics when applied to secondary batteries.

[0050] 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.

[0051] 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 in reducing the viscosity of the dispersion and improving the storage stability, and excellent cycle characteristics can be realized even when applied to an electrode active material.

[0052] 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.

[0053] 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 entire 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, 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 may be 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 as 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 manufactured using the carbon nanotube dispersion are excellent.

[0054] The BET surface area of ​​the above carbon nanotubes is 150 m 2 / g or more, preferably 150 m 2 / g to 2,000 m 2 / g can be 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 2 / g can be more than 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 / g or less. When carbon nanotubes having a high BET surface area as described above are used, the formation of a conductive network between electrode active materials is excellent, and thus the cycle characteristics of a secondary battery manufactured using the carbon nanotube dispersion can be improved.

[0055] The carbon nanotube dispersion according to one embodiment of the present invention can have a relatively high carbon nanotube content because the carbon nanotubes can be uniformly dispersed. When a carbon nanotube dispersion having a low carbon nanotube content is used in the production of an electrode slurry, the solid content of the produced electrode slurry decreases, so that the thickness (wet thickness) before applying and drying the electrode slurry becomes thick, and the rolling ratio measured after subsequent drying and rolling treatment increases, so that the difference in the thickness ratio before and after drying and rolling becomes large. In this way, if the rolling ratio increases, the compositions inside the slurry, including the positive electrode active material, may be damaged during the process, which may cause a problem of deterioration in the performance of the battery.

[0056]

[0057] (2) Dispersant

[0058] The carbon nanotube dispersion according to the present invention includes a dispersant to improve the dispersibility of the carbon nanotubes, and includes a first dispersant including hydrogenated nitrile butadiene rubber as the dispersant, a second dispersant including 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, and a third dispersant including an alkanol amine compound.

[0059] In the carbon nanotube dispersion, the first to third dispersants serve to increase the dispersibility of carbon nanotubes so that the carbon nanotubes can be evenly dispersed without agglomeration in the dispersion, and in particular, suppress changes in the viscosity of the carbon nanotube dispersion over time and exhibit the effect of lowering the average particle size of the dispersed particles.

[0060] In a carbon nanotube dispersion according to one specific example of the present invention, the first dispersant, hydrogenated nitrile butadiene rubber, may include repeating units represented by the following chemical formulas 1 and 2.

[0061] [Chemical Formula 1]

[0062]

[0063] [Chemical Formula 2]

[0064]

[0065] The weight average molecular weight (Mw) of the first dispersant may be 7,000 to 100,000 g / mol, and specifically, 7,000 g / mol or more, 8,000 g / mol or more, 9,000 g / mol or more, 10,000 g / mol or more, 11,000 g / mol or more, 12,000 g / mol or more, 13,000 g / mol or more, 14,000 g / mol or more, 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, 23,000 g / mol or more, 24,000 g / mol or more, 25,000 g / mol or more, 26,000 g / mol or more, 27,000 g / mol or more, 28,000 g / mol or more, 29,000 g / mol or more, 30,000 g / mol or more, 31,000 g / mol or more, 32,000 g / mol or more, 33,000 g / mol or more, 34,000 g / mol or more, 35,000 g / mol or more, 36,000 g / mol or more, 37,000 g / mol or more, 38,000 g / mol or more, 39,000 g / mol or more, 40,000 g / mol or more, 41,000 g / mol or more, 42,000 g / mol or more, 43,000 g / mol or more, 44,000 g / mol or more, 45,000 g / mol or more, 46,000 g / mol or more, 47,000 g / mol or more, 48,000 g / mol or more, 49,000 g / mol or more, 50,000 g / mol or more, 51,000 g / mol or more, 52,000 g / mol or more, or 53,000 g / mol or more, and may be 100,000 g / mol or less, 99,000 g / mol or less, 98,000 g / mol or less, 97,000 g / mol or less, 96,000 g / mol or less, 95,000 g / mol or less, 94,000 g / mol or less, 93,000 g / mol or less,92,000 g / mol or less, 91,000 g / mol or less, 90,000 g / mol or less, 89,000 g / mol or less, 88,000 g / mol or less, 87,000 g / mol or less, 86,000 g / mol or less, 85,000 g / mol or less, 84,000 g / mol or less, 83,000 g / mol or less, 82,000 g / mol or less, 81,000 g / mol or less, 80,000 g / mol or less, 79,000 g / mol or less, 78,000 g / mol or less, 77,000 g / mol or less, 76,000 g / mol or less, 75,000 g / mol or less, 74,000 g / mol or less, 73,000 g / mol or less, It may be 72,000 g / mol or less, 71,000 g / mol or less, 70,000 g / mol or less, 69,000 g / mol or less, 68,000 g / mol or less, 67,000 g / mol or less, 66,000 g / mol or less, 65,000 g / mol or less, 64,000 g / mol or less, 63,000 g / mol or less, 62,000 g / mol or less, 61,000 g / mol or less, 60,000 g / mol or less, 59,000 g / mol or less, 58,000 g / mol or less, 57,000 g / mol or less, 56,000 g / mol or less, 55,000 g / mol or less, or 54,000 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.

[0066] In addition, the hydrogenated nitrile butadiene rubber may have a polydispersity index (PDI) of 1.52.0 to 4.0 in terms of uniformly dispersing carbon nanotubes in a solvent while having the above weight average molecular weight distribution, and for example, the polydispersity index may be 2.0 or more, 2.1 or more, 2.2 or more, 2.3 or more, 2.4 or more, 2.5 or more, 2.6 or more, 2.7 or more, or 2.8 or more, and may be 3.5 or less, 3.4 or less, 3.3 or less, 3.2 or less, 3.1 or less, 3.0 or less, or 2.9 or less.

[0067] The above polydispersity index is a measure of how much the molecular weights of polymer molecules within a specific polymer differ, and is expressed as a value (Mw / Mn) obtained by dividing the weight average molecular weight (Mw) by the number average molecular weight (Mn). The weight average molecular weight (Mw) and number average molecular weight (Mn) for calculating the polydispersity index of the hydrogenated nitrile butadiene rubber according to the present invention can be measured through the polystyrene-converted molecular weight analyzed by gel permeation chromatography (GPC).

[0068] In one specific example 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, and specifically, may be included in an amount of 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, and 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. Hereinafter, it may contain 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.

[0069] 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, the dispersing effect may not be sufficient due to insufficient content of the dispersant, so that the viscosity of the dispersion may not be maintained low and may increase over time, and if it exceeds 50 parts by weight, the content of the first dispersant may be excessive, so that coagulation may occur between solids in the dispersion, causing the viscosity of the dispersion to excessively increase.

[0070] A carbon nanotube dispersion according to one embodiment of the present invention comprises, in addition to the first dispersant, 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, in order to solve the problem of the viscosity of the dispersion increasing as the content of carbon nanotubes increases in a carbon nanotube dispersion containing only the first dispersant, and thus, compared to a carbon nanotube dispersion using only a conventional dispersant, the dispersion has excellent dispersibility, reduces agglomeration of dispersion particles, and exhibits an effect of suppressing an increase in viscosity.

[0071] Among the second dispersants, polyethylene glycol, poly(1,2-propylene glycol), poly(1,3-propylene glycol), polycaprolactone, and polytetramethylene glycol are preferably used to prevent excessive increase in the viscosity of the dispersion.

[0072] The polystyrene of the second dispersant may include repeating units derived from at least one monomer selected from the group consisting of, for example, aromatic vinyl monomers such as styrene, 3-methylstyrene, 4-methylstyrene, 4-propylstyrene, 4-cyclohexylstyrene, and 4-(p-methylphenyl)styrene, and from the viewpoint of preventing excessive increase in the viscosity of the dispersion, it is preferable to use polystyrene in which the aromatic vinyl monomer is styrene.

[0073] In one specific example of the present invention, 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, and preferably, the second dispersant may include polyethylene glycol and polystyrene simultaneously.

[0074] At this time, when one polymer selected from the group consisting of polyethylene glycol, poly(1,2-propylene glycol), poly(1,3-propylene glycol), polycaprolactone and polytetramethylene glycol is included together with polystyrene as the second dispersant, the content of polystyrene may be included as 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 and 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.

[0075] The second dispersant may be included in the dispersion in the form of a solution in which a polymer such as polyethylene glycol, poly(1,2-propylene glycol), poly(1,3-propylene glycol), polycaprolactone, polytetramethylene glycol, and polystyrene is dissolved in an organic solvent such as N-methyl pyrrolidone (NMP) so that it can be well dissolved in the carbon nanotube dispersion of the present invention.

[0076] In one specific example 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, and the content of the second dispersant here means the sum of the content of 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 polystyrene.

[0077] 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.

[0078] When the second dispersant is included in the carbon nanotube dispersion within the above content range, it can exhibit an additional dispersing effect by adsorbing to the surface of the carbon nanotube that the first dispersant was not able to cover, and can prevent aggregation of the remaining dispersants by reducing the content of the remaining dispersant that was not effectively adsorbed to the surface of the carbon nanotube.

[0079] 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 alkanol amine compound. By including the third dispersant, the dispersion has the property of uniformly and effectively dispersing carbon nanotubes, thereby maintaining a lower viscosity of the dispersion and further suppressing an increase in viscosity over time.

[0080] In one specific embodiment of the present invention, the alkanol amine compound may be a C3 to C10 linear or branched saturated hydrocarbon containing at least one hydroxyl group (-OH) and at least one amine group (-NH2). In particular, since the alkanol amine compound, which is the third dispersant, contains a hydroxyl group and at least one amine group in the molecule, it can form a hydrogen bond with the solvent in the dispersion, thereby allowing the 'carbon nanotube-dispersant' complex to stably maintain a dispersed state in the solvent.

[0081] The above alkanol amine 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 formulae 3 to 6.

[0082] [Chemical Formula 3] [Chemical Formula 4]

[0083]

[0084] [Chemical Formula 5] [Chemical Formula 6]

[0085]

[0086] In one specific embodiment of the present invention, the third 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, and specifically, 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, 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, It may be included in amounts of 17 parts by weight or less or 16 parts by weight or less.

[0087] When the third dispersant is included in the carbon nanotube dispersion within the above content range, it can exhibit an additional dispersing effect by adsorbing to the surface of the carbon nanotubes that the first dispersant and the second dispersant could not wrap, and by reducing the content of the excess dispersant that was not effectively adsorbed to the surface of the carbon nanotubes, aggregation of the remaining dispersants can be prevented, thereby suppressing a strong bonding force between carbon nanotubes that is more than an appropriate level, thereby maintaining a low viscosity of the carbon nanotube dispersion. Furthermore, the bonding force between active material particles of the electrode mixture layer for a lithium secondary battery formed using the electrode slurry composition for a lithium secondary battery including the dispersion and the electrode active material and the adhesive force between the electrode mixture layer and the current collector can be effectively improved.

[0088] From this point of view, in order to improve the bonding force between the active materials of the electrode for a lithium secondary battery formed using the dispersion and the adhesive force between the active material and the current collector, and to maintain low viscosity of the dispersion, the content (Solid On Powder, SOP) of the first to third dispersants in relation to the carbon nanotube content of the carbon nanotube dispersion may be 20 to 100 wt%, for example, 20 to 80 wt%, 20 to 50 wt%, and preferably 30 to 35 wt%.

[0089]

[0090] (3) Solvent

[0091] The solvent of the carbon nanotube dispersion according to one embodiment of the present invention is a dispersion medium for dispersing the carbon nanotubes and the first to third dispersants, and is used to supply the carbon nanotube dispersion by pre-dispersing the carbon nanotubes to prevent agglomeration when using the powdered carbon nanotubes directly in the manufacture of an electrode slurry composition.

[0092] The solvent may be an organic solvent containing one or more heteroatoms selected from the group consisting of, for example, nitrogen atoms (N) and oxygen atoms (O) having unshared electron pairs.

[0093] Specifically, the dispersion medium may be an amide polar organic solvent such as dimethylformamide (DMF), diethyl formamide, dimethyl acetamide (DMAc), N-methyl pyrrolidone (NMP); an alcohol 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; a glycol such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, 1,3-propanediol, 1,3-butanediol, 1,5-pentanediol, or hexylene glycol; Examples thereof include polyhydric alcohols such as glycerin, trimethylolpropane, pentaerythritol, or sorbitol; 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, methyl propyl ketone, or cyclopentanone; and esters such as ethyl acetate, γ-butyl lactone, and ε-propiolactone, and any one of these or a mixture of two or more thereof may be used.

[0094]

[0095] The carbon nanotube dispersion according to one embodiment of the present invention can reduce the average particle size distribution of dispersed particles included in the dispersion, such as a composite of carbon nanotubes and each dispersant, by enabling the first to third dispersants to uniformly disperse carbon nanotubes in a solvent as described above.

[0096] Accordingly, the carbon nanotube dispersion may have an initial viscosity of 0.1 to 10 Pa·s as measured at 25°C and 1 rpm using a viscometer (TOKISANGYO, viscometer TV-25, Rotor Code 01), for example, 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 It can be 4.7 Pa·s or more, 4.8 Pa·s or more, 4.9 Pa·s or more, or 5.0 Pa·s or more, and 10.0 Pa·s or less, 9.9 Pa·s or less, 9.8 Pa·s or less, 9.7 Pa·s or less, 9.6 Pa·s or less, 9.5 Pa·s or less, 9.4 Pa·s or less, 9.3 Pa·s or less, 9.2 Pa·s or less, 9.1 Pa·s or less, 9.0 Pa·s or less, 8.9 Pa·s or less, 8.8 Pa·s or less, 8.7 Pa·s or less, 8.6 Pa·s or less, 8.5 Pa·s or less, 8.4 Pa·s or less, 8.3 Pa·s or less, 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, It may be 5.7 Pa·s or less, 5.6 Pa·s or less, 5.5 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. When the carbon nanotube dispersion has an initial viscosity in the above range, an electrode slurry can be manufactured more smoothly using it, and an electrode slurry including the carbon nanotube dispersion can have an appropriate viscosity for electrode formation.

[0097] In addition, the particle size distribution D of the dispersed particles included in the dispersion according to one specific example of the present invention 50 This may be 5 to 15 ㎛, for example, 5 ㎛ or more, 6 ㎛ or more, 7 ㎛ or more, 8 ㎛ or more, or 9 ㎛ or more, 15 ㎛ or less, 14 ㎛ or less, 13 ㎛ or less, 12 ㎛ or less, 11 ㎛ or less, or 10 ㎛ or less, and preferably, the particle size distribution can be kept low at 8 to 11 ㎛.

[0098] In addition, when the carbon nanotube dispersion according to one specific example of the present invention is left at 25°C for 2 weeks, the viscosity increase rate calculated by the following equation (1) may be 60% or less, for example, 10% or more and 60% 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, or 28% or more, and 60% or less, 59% or less, 58% or less, 57% or less, 56% or less, 55% or less, 54% or less, 53% or less, 52% or less, 51% It may be less than, 50% or less, 49% or less, 48% or less, 47% or less, 46% or less, 45% or less, 44% or less, 43% or less, 42% or less, 41% or less, 40% or less, 39% or less, 38% or less, 37% or less, 36% or less, 35% or less, 34% or less, 33% or less, 32% or less, 31% or less, 30% or less, or 29% or less.

[0099] [Formula 1]

[0100] Viscosity increase rate (%) = {(Viscosity measured after leaving at 25 ℃ for 2 weeks - Initial viscosity) / Initial viscosity} × 100

[0101] At this time, the viscosity and initial viscosity after 2 weeks of standing were measured at 25 ℃ and 1 rpm.

[0102]

[0103] Method for producing carbon nanotube dispersion

[0104] Hereinafter, a method for producing a carbon nanotube dispersion according to one embodiment of the present invention will be described.

[0105] The method for producing a carbon nanotube dispersion according to the present invention comprises: (1) mixing a first dispersant including hydrogenated nitrile butadiene rubber, a second dispersant including 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 including an alkanol amine compound, and a solvent to produce a carbon nanotube primary dispersion; and (2) a step of dispersing the carbon nanotube primary dispersion to produce a carbon nanotube secondary dispersion. Therefore, the carbon nanotube dispersion according to the present invention may refer to a carbon nanotube secondary dispersion produced by the above-described production method.

[0106] In step (1), a carbon nanotube primary dispersion is prepared by mixing a first dispersant including hydrogenated nitrile butadiene rubber, a second dispersant including 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 including an alkanol amine compound, and a solvent. The step of preparing the carbon nanotube primary dispersion is performed by a wetting process in which each component is evenly mixed.

[0107] The specific description of the carbon nanotubes according to the method for producing the above carbon nanotube dispersion, the first dispersant including hydrogenated nitrile butadiene rubber, the second dispersant including 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, the third dispersant including an alkanol amine compound, and the solvent is as described above, and therefore, the specific description will be omitted below.

[0108] The mixing for preparing the above carbon nanotube primary dispersion may be performed using a conventional mixing method, specifically, a mixing device such as a pony mixer, a change-can mixer, a Hobert mixer, a planetary mixer, a butterfly mixer, a stone mill, a homogenizer, a bead mill, a ball mill, a basket mill, an attrition mill, a universal stirrer, a clear mixer, or a TK mixer, and may include a step of mixing at a rotation speed of 300 to 5,000 rpm for 30 minutes to 7 hours.

[0109] In addition, when mixing to prepare the primary carbon nanotube dispersion, cavitation dispersion treatment may be performed to increase the miscibility of the carbon nanotubes and the solvent, or the dispersibility of the carbon nanotubes in the solvent. The cavitation dispersion treatment is a dispersion treatment method that utilizes shock waves generated by the bursting of vacuum bubbles formed in water when high energy is applied to the liquid, and the method can disperse the carbon nanotubes without damaging the properties of the carbon nanotubes. Specifically, the cavitation dispersion treatment can be performed by ultrasonic, jet mill, or shear dispersion treatment.

[0110] The step of preparing the above carbon nanotube primary dispersion may be performed under temperature conditions in which the viscosity of the mixture and other physical properties do not change due to evaporation of the solvent. For example, it may be performed at a temperature of 50°C or lower, more specifically, from 5°C to 50°C.

[0111] In step (2), the above carbon nanotube primary dispersion is dispersed to prepare a carbon nanotube secondary dispersion.

[0112] The process for producing the above carbon nanotube secondary dispersion can be performed by a method such as a ball mill, a bead mill, a disc mill, a basket mill, a high pressure homogenizer, etc., and more specifically, it can be performed by a dispersion method using a high pressure homogenizer.

[0113] Dispersion by the high-pressure disperser is achieved by pressurizing the mixture with a plunger pump of the high-pressure disperser, for example, and pushing it through the gap of the dispersion valve, thereby generating forces such as cavitation, shear, impact, and explosion when passing through the gap.

[0114] The above dispersion process can be performed depending on the degree of dispersion of the carbon nanotube dispersion, and specifically, can be performed under a pressure of 5,000 to 30,000 psi for 30 to 120 minutes, more specifically, 60 to 90 minutes, and the above process can be repeated 1 to 10 times.

[0115]

[0116] Electrode slurry composition for lithium secondary batteries and electrode for lithium secondary batteries

[0117] In addition, the present invention provides an electrode slurry composition for a lithium secondary battery comprising the carbon nanotube dispersion and an electrode active material.

[0118] The above-mentioned electrode slurry composition for a lithium secondary battery may be a positive electrode slurry composition or a negative electrode slurry composition, and specifically, may be a positive electrode slurry composition.

[0119] The above-described electrode slurry composition for a lithium secondary battery may include the carbon nanotube dispersion, a positive electrode active material or a negative electrode active material as an electrode active material, a binder, and other additives such as a solvent and / or viscosity modifier and a filler as needed.

[0120] As the positive electrode active material, positive electrode active materials well known in the art can be used without limitation, and for example, lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium iron phosphate, lithium nickel manganese cobalt oxide, or a combination thereof can be used. Specifically, the positive electrode active material includes LiCoO2, LiNiO2, LiMn2O4, LiCoPO4, LiFePO4, and LiNi a Mn b Co c O 2　 (Here, 0 < a, b, c < 1) can be used, but is not limited to this.

[0121] The above negative active materials include natural graphite, artificial graphite, carbonaceous materials; lithium-containing titanium composite oxide (LTO); metals (Me) such as Si, Sn, Li, Zn, Mg, Cd, Ce, Ni or Fe; alloys composed of the above metals (Me); oxides (MeO) of the above metals (Me). x); and one or more types of negative electrode active materials selected from the group consisting of a complex of the above metal (Me) and carbon. The negative electrode active material may be included in an amount of 60 to 98 wt%, more preferably 70 to 98 wt%, based on the total weight of solids excluding the solvent in the negative electrode slurry.

[0122] The above binder is a component that assists in the bonding of the active material and the conductive material and the bonding to the current collector, and is typically added in an amount of 1 to 30 wt% based on the total weight of the mixture including the electrode active material. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluororubber, and various copolymers.

[0123] The solvents mentioned above include organic solvents such as N-methyl pyrrolidone (NMP), dimethyl formamide (DMF), acetone, dimethyl acetamide, etc., or water, and these solvents may be used alone or in combination of two or more. The amount of solvent used is sufficient to dissolve and disperse the electrode active material, binder, and conductive agent, taking into account the coating thickness and manufacturing yield of the electrode slurry.

[0124] The above viscosity modifier may be carboxymethylcellulose, polyacrylic acid, or the like, and by adding it, the viscosity of the electrode slurry can be adjusted to facilitate the manufacturing of the electrode slurry and the application process on the electrode current collector.

[0125] The above filler is optionally used as a component that suppresses expansion of the electrode, and is not particularly limited as long as it is a fibrous material that does not cause chemical changes in the battery. For example, olefin-based polymers such as polyethylene and polypropylene; fibrous materials such as glass fiber and carbon fiber are used.

[0126] When the above electrode slurry composition is a composition of a positive electrode slurry for forming a positive electrode, the positive electrode can be manufactured by applying the composition of the positive electrode slurry onto a positive electrode current collector, followed by drying and rolling. Alternatively, the positive electrode slurry can be manufactured by casting the positive electrode slurry onto a separate support, and then laminating the film obtained by peeling it off from the support onto the positive electrode current collector.

[0127] The thickness of the positive electrode active material layer formed by the positive electrode slurry may vary depending on the loading amount, loading speed, etc. for applying the positive electrode slurry.

[0128] In the case of an electrode for a lithium secondary battery according to the present invention, it is formed using an electrode slurry composition for a lithium secondary battery, and the electrode slurry composition includes the carbon nanotube dispersion and the electrode active material according to the present invention, and the carbon nanotube dispersion includes a first dispersant including carbon nanotubes and hydrogenated nitrile butadiene rubber, a second dispersant including 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, and in particular, a third dispersant including an alkanol amine compound, thereby making it possible to manufacture an electrode and a secondary battery having excellent capacity characteristics and cycle characteristics.

[0129] The above-described positive electrode current collector generally has a thickness of 3 μm to 500 μm. The positive electrode current collector is not particularly limited as long as it has high conductivity and does not cause chemical changes in the battery. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. can be used. In addition, the surface of the positive electrode current collector may be formed with fine irregularities to strengthen the bonding strength of the positive electrode active material, and it can be used in various forms such as a film, sheet, foil, net, porous body, foam, or non-woven fabric.

[0130] When the above electrode slurry composition is a composition of a negative electrode slurry for forming a negative electrode, the negative electrode can be manufactured by applying the composition of the negative electrode slurry onto a negative electrode current collector, followed by drying and rolling. Alternatively, the negative electrode slurry can be manufactured by casting the negative electrode slurry onto a separate support, and then laminating the resulting film onto the negative electrode current collector by peeling it off from the support.

[0131] The thickness of the negative electrode active material layer formed by the above negative electrode slurry may vary depending on the loading amount, loading speed, etc. for applying the negative electrode slurry.

[0132] The above negative electrode current collector generally has a thickness of 3 ㎛ to 500 ㎛. The negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloy, etc. can be used. In addition, like the negative electrode current collector, the bonding strength of the negative electrode active material can be strengthened by forming fine unevenness on the surface, and can be used in various forms such as a film, sheet, foil, net, porous body, foam, non-woven fabric, etc.

[0133]

[0134] lithium secondary battery

[0135] A lithium secondary battery includes a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and an electrolyte. The positive electrode and the negative electrode are the same as those described above, so a detailed description thereof will be omitted.

[0136] The above separator separates the negative electrode and the positive electrode and provides a passage for lithium ions to move. Any separator commonly used in lithium secondary batteries can be used without any particular restrictions, and in particular, one having low resistance to ion movement of the electrolyte and excellent electrolyte moisture absorption capacity is preferable. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof, may be used. In addition, a conventional porous nonwoven fabric, for example, a nonwoven fabric made of high-melting-point glass fiber, polyethylene terephthalate fiber, etc. may be used. In addition, a coated separator containing a ceramic component or a polymer material to secure heat resistance or mechanical strength may be used, and may optionally be used in a single-layer or multi-layer structure.

[0137] The electrolyte may be, but is not limited to, an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel-type polymer electrolyte, a solid inorganic electrolyte, a molten inorganic electrolyte, etc. that can be used in the manufacture of a lithium secondary battery. Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0138] The organic solvent may be used without any particular limitation as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the organic solvent may include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; Carbonate solvents such as dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (wherein R is a C2 to C20 linear, branched, or cyclic hydrocarbon group, and may include a double-bonded aromatic ring or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes can be used. Among these, a carbonate solvent is preferable, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate, etc.) having high ionic conductivity and high dielectric constant that can improve the charge / discharge performance of the battery and a linear carbonate compound having low viscosity (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate, etc.) is more preferable.In this case, the performance of the electrolyte may be excellent when the cyclic carbonate and the chain carbonate are mixed and used in a volume ratio of about 1:1 to about 1:9.

[0139] The lithium salt may be used without any particular limitation as long as it is a compound capable of providing lithium ions used in a lithium secondary battery. Specifically, the lithium salt may include LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAl04, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2. LiCl, LiI, or LiB(C2O4)2. It is preferable that the concentration of the lithium salt be used within the range of 0.1M to 2.0M. When the concentration of the lithium salt is within the above range, the electrolyte can exhibit excellent electrolyte performance because it has appropriate conductivity and viscosity, and lithium ions can move effectively.

[0140] In addition to the electrolyte components, the electrolyte may further include one or more additives, such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, cyclic ethers, ethylene diamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, for the purpose of improving the life characteristics of the battery, suppressing battery capacity decrease, and improving the discharge capacity of the battery. At this time, the additives may be included in an amount of 0.1 wt% to 5 wt% based on the total weight of the electrolyte.

[0141] 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 reduce the content thereof compared to a case where a conductive material such as conventional carbon black is included, thereby stably exhibiting excellent discharge capacity and output characteristics. As a result, the lithium secondary battery can be usefully used in portable devices such as mobile phones, laptop computers, and digital cameras, and electric vehicles such as hybrid electric vehicles (HEVs).

[0142] Accordingly, according to another embodiment of the present invention, the lithium secondary battery, a battery module including the lithium secondary battery as a unit cell, and a battery pack including the same can be provided.

[0143] The above battery module or battery pack can be used as a power source for one or more medium- to large-sized devices, such as a power tool; an electric vehicle (EV), a hybrid electric vehicle, and a plug-in hybrid electric vehicle (PHEV); or a power storage system.

[0144]

[0145] Below, specific embodiments of the present invention are presented. However, the embodiments described below are intended solely to specifically illustrate or explain the present invention and are not intended to limit the scope of the invention. Furthermore, any details not described herein are technically feasible to those skilled in the art and thus are omitted.

[0146]

[0147] Example 1: Viscosity Evaluation of Carbon Nanotube Dispersions

[0148]

[0149] Example 1.1

[0150] (1) Butterfly mixer (BTM-2K, KM Tech Co.), with a specific surface area of ​​250 m based on 100 parts by weight of the total dispersion. 2 / g multi-walled carbon nanotubes (MWCNT, LG Chem) 3.3 parts by weight, hydrogenated nitrile butadiene rubber (HNBR) (Mw 70,000, PDI 2.5) as a first dispersant (corresponding to 22.5 parts by weight with respect to 100 parts by weight of carbon nanotubes, and the hydrogenated nitrile butadiene rubber was dissolved in N-methyl pyrrolidone (NMP) solvent and introduced as a solution with a concentration of 20 wt%), 0.25 parts by weight of a mixture of polyethylene glycol (Sigma Aldrich, Mw=750) and polystyrene (Sigma Aldrich, Mw=3,000) in a weight ratio of 60 to 80:20 to 40 as a second dispersant (corresponding to 7.5 parts by weight with respect to 100 parts by weight of carbon nanotubes, and the polyethylene glycol and polystyrene were each added in N-methyl pyrrolidone A primary carbon nanotube dispersion was prepared by adding 0.165 parts by weight of 2-amino-2-methyl-1-propanol (5 parts by weight based on 100 parts by weight of carbon nanotubes) as a third dispersant (dissolved in a pyrrolidone (NMP) solvent and introduced as a 20 wt% concentration solution) and the remainder of N-methylpyrrolidone (NMP) as a solvent, and mixing at 5,000 rpm for 5 hours.

[0151] The weight average molecular weight of the hydrogenated nitrile butadiene rubber, which is the first dispersant, was measured using GPC (Gel permeation chromatography) under the following conditions. When measuring the molecular weight, DMF was used as the solvent. In the dispersion state, the molecular weight of the supernatant can be measured by centrifugation, and in the electrode and battery state, the molecular weight can be measured by scraping the electrode and extracting the partially hydrogenated nitrile rubber using THF.

[0152] - Device: Alliance 2695 from Waters

[0153] - Detector: Viscotek TDA 302 RID from Malvern

[0154] - Column: 2 PLgel Olexis and 1 PLgel mixed C from Agilent

[0155] - Solvent: THF

[0156] - Column temperature: 40 ℃

[0157] - Flow rate: 1 ml / min

[0158] - Sample concentration: 1 mg / mL, 100 μl injection

[0159] - Standard sample: Polystyrene (Mp: 3900000, 723000, 316500, 70950, 31400, 8450, 3940, 485)

[0160] The analysis program used Malvern's OmmiSEC, and after obtaining the weight-average molecular weight (Mw) and number-average molecular weight (Mn) by GPC, the molecular weight distribution (PDI) was calculated from the weight-average molecular weight / number-average molecular weight (Mw / Mn).

[0161] (2) The carbon nanotube primary dispersion was homogeneously dispersed five times at a pressure of 10,000 psi using a high-pressure disperser (PICOMAX, manufactured by Micronox) to prepare a carbon nanotube secondary dispersion.

[0162]

[0163] Example 1.2

[0164] In the above Example 1.1, except that the content of carbon nanotubes was 4.2 parts by weight based on 100 parts by weight of the total dispersion, the content of the first dispersant was 0.95 parts by weight (corresponding to 22.5 parts by weight based on 100 parts by weight of carbon nanotubes), the content of the second dispersant was 0.32 parts by weight (corresponding to 7.5 parts by weight based on 100 parts by weight of carbon nanotubes), and the content of the third dispersant was 0.21 parts by weight (corresponding to 5 parts by weight based on 100 parts by weight of carbon nanotubes), a carbon nanotube dispersion was prepared in the same manner as in the above Example 1.1.

[0165]

[0166] Example 1.3

[0167] In the above Example 1.1, except that the content of carbon nanotubes was 5.2 parts by weight based on 100 parts by weight of the total dispersion, the content of the first dispersant was 1.17 parts by weight (corresponding to 22.5 parts by weight based on 100 parts by weight of carbon nanotubes), the content of the second dispersant was 0.39 parts by weight (corresponding to 7.5 parts by weight based on 100 parts by weight of carbon nanotubes), and the content of the third dispersant was 0.26 parts by weight (corresponding to 5 parts by weight based on 100 parts by weight of carbon nanotubes), a carbon nanotube dispersion was prepared in the same manner as in the above Example 1.1.

[0168]

[0169] Example 1.4

[0170] In the above Example 1.1, except that the content of carbon nanotubes was 7.0 parts by weight based on 100 parts by weight of the total dispersion, the content of the first dispersant was 1.58 parts by weight (corresponding to 22.5 parts by weight based on 100 parts by weight of carbon nanotubes), the content of the second dispersant was 0.53 parts by weight (corresponding to 7.5 parts by weight based on 100 parts by weight of carbon nanotubes), and the content of the third dispersant was 0.35 parts by weight (corresponding to 5 parts by weight based on 100 parts by weight of carbon nanotubes), a carbon nanotube dispersion was prepared in the same manner as in the above Example 1.1.

[0171]

[0172] Example 1.5

[0173] A carbon nanotube dispersion was prepared in the same manner as in Example 1.1, except that 2-amino-1-ethanol was used as the third dispersant.

[0174]

[0175] Example 1.6

[0176] A carbon nanotube dispersion was prepared in the same manner as in Example 1.2, except that 2-amino-1-ethanol was used as the third dispersant.

[0177]

[0178] Example 1.7

[0179] A carbon nanotube dispersion was prepared in the same manner as in Example 1.3, except that 2-amino-1-ethanol was used as the third dispersant.

[0180]

[0181] Example 1.8

[0182] A carbon nanotube dispersion was prepared in the same manner as in Example 1.4, except that 2-amino-1-ethanol was used as the third dispersant.

[0183]

[0184] Comparative Example 1.1

[0185] In the above Example 1.1, a carbon nanotube dispersion was prepared in the same manner as in the above Example 1.1, except that the third dispersant was not added.

[0186]

[0187] Comparative Example 1.2

[0188] In the above Example 1.2, a carbon nanotube dispersion was prepared in the same manner as in the above Example 1.1, except that the third dispersant was not added.

[0189]

[0190] Comparative Example 1.3

[0191] In the above Example 1.3, a carbon nanotube dispersion was prepared in the same manner as in the above Example 1.1, except that the third dispersant was not added.

[0192]

[0193] Comparative Example 1.4

[0194] In the above Example 1.4, a carbon nanotube dispersion was prepared in the same manner as in the above Example 1.1, except that the third dispersant was not added.

[0195]

[0196] Comparative Example 1.5

[0197] A carbon nanotube dispersion was prepared in the same manner as in Example 1.3, except that (Hydroxypropyl)methyl cellulose was used instead of 2-amino-2-methyl-1-propanol as the third dispersant.

[0198]

[0199] Comparative Example 1.6

[0200] A carbon nanotube dispersion was prepared in the same manner as in Example 1.3, except that methyl cellulose was used instead of 2-amino-2-methyl-1-propanol as the third dispersant.

[0201]

[0202] Comparative Example 1.7

[0203] A carbon nanotube dispersion was prepared in the same manner as in Example 1.3, except that polyvinylpyrrolidone was used instead of 2-amino-2-methyl-1-propanol as the third dispersant.

[0204]

[0205] Comparative Example 1.8

[0206] In the above Example 1.3, a carbon nanotube dispersion was prepared in the same manner as in the above Example 1.3, except that the second dispersant was not used.

[0207]

[0208] Comparative Example 1.9

[0209] In the above Example 1.7, a carbon nanotube dispersion was prepared in the same manner as in the above Example 1.7, except that the second dispersant was not used.

[0210]

[0211] Comparative Example 1.10

[0212] A carbon nanotube dispersion was prepared in the same manner as in Example 1.3, except that polyethylene glycol monoethyl ether was used as the second dispersant.

[0213]

[0214] Comparative Example 1.11

[0215] A carbon nanotube dispersion was prepared in the same manner as in Example 1.3, except that only 0.16 parts by weight of the second dispersant was used as the dispersant.

[0216]

[0217] The conditions for manufacturing the carbon nanotube dispersions of Examples 1.1 to 1.8 and Comparative Examples 1.1 to 1.11 are shown in Table 1 below.

[0218]

[0219] CNT content (parts by weight) First dispersant (parts by weight) Second dispersant (parts by weight) Third dispersant type Content (parts by weight) Example 1.1 3.3 0.74 0.25 2-Amino-2-methyl-1-propanol 0.165 Example 1.24 20.95 0.32 2-Amino-2-methyl-1-propanol 0.21 Example 1.35 21.17 0.39 2-Amino-2-methyl-1-propanol 0.26 Example 1.47 01.58 0.53 2-Amino-2-methyl-1-propanol 0.35 Example 1.5 3.3 0.74 0.25 2-Amino-1-ethanol 0.165 Example 1.6 4.20.95 0.32 2-Amino-1-ethanol 0.21 Example 1.75.21.170.39 2-Amino-1-ethanol 0.26 Example 1.87.0 1.58 0.53 2-Amino-1-ethanol 0.35 Comparative Example 1.13.3 0.74 0.25-0 Comparative Example 1.24.20.95 0.32-0 Comparative Example 1.35.21.170.39-0 Comparative Example 1.47.0 1.58 0.53-0 Comparative Example 1.55.21.170.39 (Hydroxypropyl) methyl cellulose 0.26 Comparative Example 1.65.21.170.39 Methyl cellulose 0.26 Comparative Example 1.75.21.170.39 Polyvinylpyrrolidone 0.26 Comparative Example 1.85.21.1702-Amino-2-methyl-1-propanol0.26Comparative Example 1.95.21.1702-Amino-1-ethanol0.26Comparative Example 1.105.21.170.39(mPEG * )2-Amino-2-methyl-1-propanol0.26Comparative example 1.115.200.16-0 * mPEG: polyethylene glycol monomethyl ether

[0220]

[0221] Experimental Example 1

[0222] The viscosity of the carbon nanotube dispersions of Examples 1.1 to 1.8 and Comparative Examples 1.1 to 1.11 was measured, and the viscosity was measured again after leaving them at 25°C for two weeks, and the results are shown in Table 2 below.

[0223] Viscosity was measured using a viscometer (TOKI SANGYO, viscometer TV-25, 3.83 / s shear rate) at 25°C and 1 rpm after 3 minutes, and the initial viscosity was taken as the value.

[0224]

[0225] ViscosityInitial viscosity(Pa·s)After 1 weekAfter 2 weeksViscosity(Pa·s)Increase rate(%)Viscosity(Pa·s)Increase rate(%)Example 1.10.6630.924391.03857Example 1.21.1762.484412.74756Example 1.32.5353.260293.42035Example 1.47.69011.044411.5851Example 1.50.6800.911341.04053Example 1.61.3351.995492.12959Example 1.72.3703.340413.64054Example 1.87.34010.3604111.37455Comparative Example 1.11.1581.956692.470113Comparative Example 1.21.9554.5401325.378175Comparative Example 1.33.1304.630485.03061Comparative Example 1.410.33017.8807818.98084Comparative Example 1.53.6266.205716.32074Comparative Example 1.63.1365.140645.42073Comparative Example 1.73.6706.064656.70083Comparative Example 1.85.6419.5637011.580105Comparative Example 1.95.2847.8424810.24294Comparative example 1.1011.58017.0144721.05082Comparative example 1.1115.54823.9305429.33189

[0226]

[0227] Referring to Table 2 above, it can be confirmed that the carbon nanotube dispersions of Examples 1.1 to 1.8, which include a first dispersant including hydrogenated nitrile butadiene rubber, a second dispersant including 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, and a third dispersant including an alkanol amine compound, have a low initial viscosity immediately after dispersing carbon nanotubes in an aqueous solvent, and in particular, the increase in viscosity of the carbon nanotube dispersion over time is very effectively suppressed.

[0228] On the other hand, in the case of the carbon nanotube dispersions according to Comparative Examples 1.1 to 1.4, since the third dispersant including an alkanol amine compound is not included as in the present invention, the initial viscosity immediately after dispersing the carbon nanotubes in the solvent is high, and as the carbon nanotube content in the dispersion increases, the effect of suppressing the viscosity increase of the carbon nanotube dispersion over time is not observed.

[0229] As in Comparative Examples 1.5 to 1.7, when a dispersant containing a hydroxyl group and an amine group in the molecule is not included in the dispersion, the tendency of the carbon nanotube-dispersant complex to form hydrogen bonds with the solvent is reduced compared to the carbon nanotube dispersions according to Examples 1.1 to 1.8, making it difficult to maintain a stable dispersion state in the solvent, so the initial viscosity of the dispersion is low, and it can be seen that the viscosity of the dispersion increases rapidly over time.

[0230] In the case of the carbon nanotube dispersions according to Comparative Examples 1.8 and 1.9, since the second dispersant including 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 is not included, it can be seen that the initial viscosity immediately after dispersing the carbon nanotubes in the solvent is high, and as the carbon nanotube content in the dispersion increases, the effect of suppressing the viscosity increase of the carbon nanotube dispersion over time is not exhibited.

[0231] In the case of the carbon nanotube dispersion according to Comparative Example 1.10, it can be seen that the initial viscosity immediately after dispersing the carbon nanotubes in the solvent is high due to the use of polyethylene glycol monoethyl ether as the second dispersant, and that the effect of suppressing the viscosity increase of the carbon nanotube dispersion over time is not exhibited as the carbon nanotube content in the dispersion increases.

[0232] In the case of the carbon nanotube dispersion according to Comparative Example 1.11, since only the second dispersant including 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 is included, it can be seen that the initial viscosity immediately after dispersing the carbon nanotubes in the solvent is high, and as the carbon nanotube content in the dispersion increases, the effect of suppressing the viscosity increase of the carbon nanotube dispersion over time is not exhibited.

[0233]

[0234] Example 2

[0235]

[0236] Example 2.1

[0237] (1) Butterfly mixer (BTM-2K, KM Tech Co.), with a specific surface area of ​​250 m based on 100 parts by weight of the total dispersion. 2 / g, average particle size (D50 ) 3.3 parts by weight of multi-walled carbon nanotubes (MWCNT, TUBALL, OCSiAl Co.) with a diameter of 5 μm, 0.64 parts by weight of hydrogenated nitrile butadiene rubber (HNBR) (Mw 70,000, PDI 1.5) as a first dispersant, 0.21 parts by weight of a mixture of polyethylene glycol (Sigma Aldrich Co., Mw=750) and polystyrene (Sigma Aldrich Co., Mw=3,000) in a weight ratio of 60 to 80:20 to 40 as a second dispersant, 0.14 parts by weight of 2-amino-2-methyl-1-propanol as a third dispersant, and the remainder of methylpyrrolidone (N-Methyl-2-pyrrolidone, NMP) as a solvent, to obtain a solid content relative to the carbon nanotube content in the dispersion. The content (SOP, solid on powder) was adjusted to 30 wt%, and then mixed at 5,000 rpm for 5 hours to prepare a primary carbon nanotube dispersion.

[0238] The weight average molecular weight of the hydrogenated nitrile butadiene rubber, which is the first dispersant, was measured using GPC (Gel permeation chromatography) under the following conditions. When measuring the molecular weight, DMF was used as the solvent. In the dispersion state, the molecular weight of the supernatant can be measured by centrifugation, and in the electrode and battery state, the molecular weight can be measured by scraping the electrode and extracting the partially hydrogenated nitrile rubber using THF.

[0239] - Device: Alliance 2695 from Waters

[0240] - Detector: Viscotek TDA 302 RID from Malvern

[0241] - Column: 2 PLgel Olexis and 1 PLgel mixed C from Agilent

[0242] - Solvent: THF

[0243] - Column temperature: 40 ℃

[0244] - Flow rate: 1 ml / min

[0245] - Sample concentration: 1 mg / mL, 100 μl injection

[0246] - Standard sample: Polystyrene (Mp: 3900000, 723000, 316500, 70950, 31400, 8450, 3940, 485)

[0247] The analysis program used Malvern's OmmiSEC, and after obtaining the weight-average molecular weight (Mw) and number-average molecular weight (Mn) by GPC, the molecular weight distribution (PDI) was calculated from the weight-average molecular weight / number-average molecular weight (Mw / Mn).

[0248] (2) The carbon nanotube primary dispersion was homogeneously dispersed five times at a pressure of 20,000 psi using a high-pressure disperser (PICOMAX, manufactured by Micronox) to prepare a carbon nanotube secondary dispersion.

[0249]

[0250] Example 2.2

[0251] In the above Example 2.1, a carbon nanotube dispersion was prepared in the same manner as in the above Example 2.1, except that the first dispersant was added in an amount of 0.75 parts by weight, the second dispersant in an amount of 0.25 parts by weight, and the third dispersant in an amount of 0.16 parts by weight, and the solid content (SOP, solid on powder) in the dispersion was set to 35% by weight.

[0252]

[0253] Example 2.3

[0254] A carbon nanotube dispersion was prepared in the same manner as in Example 2.1, except that 2-amino-1-ethanol was used as the third dispersant.

[0255]

[0256] Comparative Example 2.1

[0257] In the above Example 2.1, 0.74 parts by weight of the first dispersant was added, and 0.25 parts by weight of hydroxypropyl methylcellulose (HPMC) was added instead of the second and third dispersants, so that the solid content (SOP, solid on powder) in the dispersion was 30% by weight, and a carbon nanotube dispersion was prepared in the same manner as in the above Example 2.1.

[0258]

[0259] Comparative Example 2.2

[0260] In the above Example 2.1, a carbon nanotube dispersion was prepared in the same manner as in the above Example 2.1, except that 0.85 parts by weight of the first dispersant was added, the second dispersant was not added, and 0.14 parts by weight of the third dispersant was added so that the solid content (SOP, solid on powder) in the dispersion was 30% by weight relative to the carbon nanotube content.

[0261]

[0262] Comparative Example 2.3

[0263] A carbon nanotube dispersion was prepared in the same manner as in Example 2.1, except that polyethylene glycol monoethyl ether was used as the second dispersant.

[0264]

[0265] Comparative Example 2.4

[0266] A carbon nanotube dispersion was prepared in the same manner as in Example 2.1, except that 0.99 parts by weight of polyethylene glycol monoethyl ether was used as the first and second dispersants.

[0267]

[0268] The conditions for manufacturing the carbon nanotube dispersions of Examples 2.1 to 2.3 and Comparative Examples 2.1 to 2.4 are shown in Table 3 below.

[0269]

[0270] CNT content (parts by weight) 1st dispersant (parts by weight) 2nd dispersant (parts by weight) 3rd dispersant SOP (%) Type Content (parts by weight) Example 2.13.30.640.21 2-amino-2-methyl-1-propanol 0.1430 Example 2.23.30.750.25 2-amino-2-methyl-1-propanol 0.1635 Example 2.33.30.640.21 2-amino-1-ethanol 0.1430 Comparative example 2.13.30.740.25 (hydroxypropyl methylcellulose) 30 Comparative example 2.23.30.850 2-amino-2-methyl-1-propanol 0.1430 Comparative example 2.33.30.640.21 (mPEG * )2-Amino-2-methyl-1-propanol0.1430Comparative Example 2.43.300.99-030 * mPEG: polyethylene glycol monomethyl ether

[0271]

[0272] Experimental Example 2: Evaluation of Adhesion of Positive Electrode for Lithium Secondary Battery

[0273]

[0274] Manufacturing Example 2.1

[0275] LiNi, a nickel-cobalt-manganese-aluminum series cathode active material 0.88 Co 0.05 Mn 0.05 Al 0.02O2 (nickel: cobalt: manganese: aluminum = 88: 5: 5: 2, LG Chemical, HN803), the carbon nanotube dispersion according to Example 2.1 as a conductive material, and polyvinylidene fluoride (PVDF, product name: KF9700, manufacturer: Kureha) as a binder were mixed with the solvent N-methyl-2-pyrrolidone (NMP) at a weight ratio of 97.74: 0.91: 1.35 (however, in the case of the carbon nanotube dispersion, the content of carbon nanotubes contained in the dispersion) to prepare a cathode slurry. The cathode slurry was coated on aluminum foil to a thickness of 20 μm to form a thin electrode plate, and then dried at 135°C for 3 hours or more to prepare a cathode for a lithium secondary battery.

[0276]

[0277] Manufacturing Example 2.2

[0278] In the above Manufacturing Example 2.1, a positive electrode was manufactured in the same manner as in the above Manufacturing Example 2.1, except that the positive electrode slurry was coated on aluminum foil to form a thin plate, dried at 135°C for 3 hours or more, and then pressed.

[0279]

[0280] Manufacturing Example 2.3

[0281] In the above Manufacturing Example 2.1, a positive electrode was manufactured in the same manner as in the above Manufacturing Example 2.1, except that 97.70 parts by weight of the positive electrode active material was used, and 1.35 parts by weight of the carbon nanotube dispersion according to the above Example 2.2 was used as the conductive material.

[0282]

[0283] Manufacturing Example 2.4

[0284] In the above Manufacturing Example 2.3, a positive electrode was manufactured in the same manner as in the above Manufacturing Example 2.3, except that the positive electrode slurry was coated on aluminum foil to form a thin plate, dried at 135°C for 3 hours or more, and then pressed.

[0285]

[0286] Manufacturing Example 2.5

[0287] In the above manufacturing example 2.1, LiNi, a nickel-cobalt-manganese-aluminum series cathode active material, is used as the cathode active material. 0.89 Co 0.06 Mn 0.04 Al 0.01 A positive electrode was manufactured using the same method as Manufacturing Example 2.1, except that 97.74 parts by weight of O2 (nickel: cobalt: manganese: aluminum = 89:6:4:1, LG Chemical, HN856A) was used.

[0288]

[0289] Manufacturing Example 2.6

[0290] In the above Manufacturing Example 2.5, a positive electrode was manufactured in the same manner as in the above Manufacturing Example 2.5, except that the positive electrode slurry was coated on aluminum foil to form a thin plate, dried at 135°C for 3 hours or more, and then pressed.

[0291]

[0292] Manufacturing Example 2.7

[0293] In the above Manufacturing Example 2.1, a positive electrode was manufactured in the same manner as in the above Manufacturing Example 2.1, except that 97.70 parts by weight of the positive electrode active material was used, and 1.35 parts by weight of the carbon nanotube dispersion according to the above Example 2.2 was used as the conductive material.

[0294]

[0295] Manufacturing Example 2.8

[0296] In the above Manufacturing Example 2.7, a positive electrode was manufactured in the same manner as in Manufacturing Example 2.8, except that the positive electrode slurry was coated on aluminum foil to form a thin plate, dried at 135°C for 3 hours or more, and then pressed.

[0297]

[0298] Manufacturing Example 2.9

[0299] In the above Manufacturing Example 2.5, the positive electrode was manufactured in the same manner as in the above Manufacturing Example 2.5, except that Example 2.3 was used as the conductive material.

[0300]

[0301] Manufacturing Example 2.10

[0302] In the above Manufacturing Example 2.6, the positive electrode was manufactured in the same manner as in the above Manufacturing Example 2.6, except that Example 2.3 was used as the conductive material.

[0303]

[0304] Comparative Manufacturing Example 2.1

[0305] LiNi, a nickel-cobalt-manganese-aluminum series cathode active material 0.88 Co 0.05 Mn 0.05 Al 0.02 O2 (nickel: cobalt: manganese: aluminum = 88: 5: 5: 2, LG Chemical, HN803), the carbon nanotube dispersion according to Comparative Example 2.1 as a conductive material, and polyvinylidene fluoride (PVDF, product name: KF9700, manufacturer: Kureha) as a binder were mixed with the solvent N-methyl-2-pyrrolidone (NMP) at a weight ratio of 97.74: 0.91: 1.35 (however, in the case of the carbon nanotube dispersion, the content of carbon nanotubes contained in the dispersion) to prepare a cathode slurry. The cathode slurry was coated on aluminum foil to a thickness of 20 ㎛ to form a thin electrode plate, and then dried at 135°C for 3 hours or more to prepare a cathode for a lithium secondary battery.

[0306]

[0307] Comparative Manufacturing Example 2.2

[0308] In the above comparative manufacturing example 2.1, the positive electrode was manufactured in the same manner as in manufacturing example 2.1, except that the positive electrode slurry was coated on aluminum foil to form a thin plate, dried at 135°C for 3 hours or more, and then pressed.

[0309]

[0310] Comparative Manufacturing Example 2.3

[0311] In the above Manufacturing Example 2.5, the positive electrode was manufactured in the same manner as in the above Manufacturing Example 2.5, except that Comparative Example 2.2 was used as the conductive material.

[0312]

[0313] Comparative Manufacturing Example 2.4

[0314] In the above Manufacturing Example 2.6, the positive electrode was manufactured in the same manner as in the above Manufacturing Example 2.6, except that Comparative Example 2.2 was used as the conductive material.

[0315]

[0316] Comparative Manufacturing Example 2.5

[0317] In the above Manufacturing Example 2.5, the positive electrode was manufactured in the same manner as in the above Manufacturing Example 2.5, except that Comparative Example 2.3 was used as the conductive material.

[0318]

[0319] Comparative Manufacturing Example 2.6

[0320] In the above Manufacturing Example 2.6, an anode was manufactured in the same manner as in the above Manufacturing Example 2.6, except that Comparative Example 2.3 was used as a conductive material.

[0321]

[0322] Comparative Manufacturing Example 2.7

[0323] In the above Manufacturing Example 2.5, an anode was manufactured in the same manner as in the above Manufacturing Example 2.5, except that Comparative Example 2.4 was used as a conductive material.

[0324]

[0325] Comparative Manufacturing Example 2.8

[0326] In the above Manufacturing Example 2.6, the positive electrode was manufactured in the same manner as in the above Manufacturing Example 2.6, except that Comparative Example 2.4 was used as the conductive material.

[0327]

[0328] In the positive electrodes for lithium secondary batteries of the above Manufacturing Examples 2.1 to 2.10 and Comparative Manufacturing Examples 2.1 to 2.8, the bonding strength between the active materials and the adhesive strength between the active materials and the current collector were measured, and the results were shown in Table 4 below, with Examples 2.1 to 2.10 and Comparative Examples 2.1 to 2.8, respectively.

[0329] Measurement of the bonding strength between the above active materials and the adhesive strength between the active materials and the current collector,

[0330] 1) The surface of the positive electrode for lithium secondary batteries according to Manufacturing Examples 2.1 to 2.10 and Comparative Manufacturing Examples 2.1 and 2.8 was cut and fixed on a slide glass, and then the aluminum foil as the current collector was peeled off at a peeling speed of 0.3 m / min, and the 90-degree peel strength was measured using TAXT Plus (MHK Corporation) (Experiment 1)

[0331]

[0332] 2) Using SAICAS (surface and Interfacial Measuring Analysis System), the bonding strength of the positive electrode active material and the adhesion between the active material and the current collector were measured (Experiment 2).

[0333] It was carried out in this way.

[0334] The measurement through SAICAS of the above 2) was performed using SAICAS (EN-EX, Daipla Wintes, JAPAN) under the conditions of a clearance angle of 10 degrees, a rake angle of 20 degrees, a shear angle of 45 degrees, and a horizontal velocity of 4 ㎛ / s using a diamond blade with a width of 1 mm to measure the bonding force. Specifically, a constant-velocity analysis was performed on the bonding force between the active materials on the surface of the positive electrodes for lithium secondary batteries of Examples 2.1 to 2.10 and Comparative Examples 2.1 and 2.2 to the aluminum foil, and the blade was moved horizontally along the surface of the positive electrode current collector to remove the positive electrode active material layer, and a constant-velocity analysis was performed on the adhesion between the active material and the current collector.

[0335] The measurement results of 1) and 2) above are shown in Table 4 below.

[0336]

[0337] Experiment 1 Experiment 2 Peeling strength (gf / cm) Active material-collector adhesion (MPa) Active material-active material bonding strength (MPa) Manufacturing example 2.1 27.8 1.5 34.42 Manufacturing example 2.2 24.9 8.95 11.93 Manufacturing example 2.3 18.5 1.39 3.76 Manufacturing example 2.4 16.7 6.9 7 9.02 Manufacturing example 2.5 27.2 1.8 23.34 Manufacturing example 2.6 23.9 9.01 10.64 Manufacturing example 2.7 19.01 75 3.11 Manufacturing example 2.8 17.4 7.46 8.78 Manufacturing example 2.9 28.7 1.7 23.50 Manufacturing example 2.10 22.7 8.5 10.37 Comparative manufacturing example 2.113.70.951.67Comparative Manufacturing Example 2.29.46.596.52Comparative Manufacturing Example 2.313.0Not MeasuredNot MeasuredComparative Manufacturing Example 2.410.6Not MeasuredNot MeasuredComparative Manufacturing Example 2.517.0Not MeasuredNot MeasuredComparative Manufacturing Example 2.915.5Not MeasuredNot MeasuredComparative Manufacturing Example 2.78.9Not MeasuredNot MeasuredComparative Manufacturing Example 2.86.9Not MeasuredNot Measured

[0338]

[0339] Referring to Table 4 above, in Experiments 1 and 2, it can be confirmed that the bonding strength between the active materials of the positive electrodes for lithium secondary batteries of Examples 2.1 to 2.10 manufactured using the carbon nanotube dispersions according to the present invention and the adhesive strength between the active materials and the current collector are higher than those of Comparative Examples 2.1 and 2.8. This can be understood to mean that the carbon nanotube dispersions according to the present invention further include an alkanol amine-based compound as a third dispersant, thereby improving the bonding strength between the active materials in the positive electrodes for lithium secondary batteries formed therefrom and increasing the adhesive strength with the current collector.

[0340]

[0341] Although the preferred embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements made by those skilled in the art using the basic concept of the present invention defined in the following claims also fall within the scope of the present invention.

Claims

1. Carbon nanotubes; A first dispersant comprising hydrogenated nitrile butadiene rubber; 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), polytetramethylene glycol, polycaprolactone, and polystyrene; A third dispersant comprising an alkanol amine 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 alkanol amine compound is a C3 to C10 linear or branched saturated hydrocarbon containing 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 above carbon nanotube dispersion contains 10 to 50 parts by weight of the first dispersant based on 100 parts by weight of the carbon nanotubes. Carbon nanotube dispersion.

6. In paragraph 1, The above carbon nanotube dispersion contains 1 to 30 parts by weight of the second dispersant based on 100 parts by weight of the carbon nanotubes. Carbon nanotube dispersion.

7. In paragraph 1, The above carbon nanotube dispersion contains 1 to 30 parts by weight of the third dispersant based on 100 parts by weight of the carbon nanotubes. Carbon nanotube dispersion.

8. In paragraph 1, The total content (SOP) of the first to third dispersants relative to the carbon nanotube content of the carbon nanotube dispersion is 20 wt% to 100 wt%, Carbon nanotube dispersion.

9. In paragraph 1, The above carbon nanotube dispersion has an initial viscosity of 0.1 to 10 Pa·s measured at 25°C and 1 rpm. Carbon nanotube dispersion.

10. In paragraph 1, The above carbon nanotube dispersion has a viscosity increase rate of 60% or less, as expressed by the following formula (1). Carbon nanotube dispersions: [Formula 1] Viscosity increase rate (%) = {(Viscosity measured after leaving at 25 ℃ for 2 weeks - Initial viscosity) / Initial viscosity} × 100 11.(1) A step of preparing a carbon nanotube primary dispersion by mixing a first dispersant including carbon nanotubes, hydrogenated nitrile butadiene rubber, a second dispersant including 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 including an alkanol amine compound, and a solvent; and (2) A step of preparing a carbon nanotube secondary dispersion by dispersing the carbon nanotube primary dispersion; A method for producing a carbon nanotube dispersion according to claim 1, comprising:

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

13. An electrode for a lithium secondary battery comprising an electrode composite layer formed using an electrode slurry composition for a lithium secondary battery according to Article 12.

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