Carbon nanotube dispersion and preparation method therefor

Abstract

The present invention relates to a carbon nanotube dispersion and a preparation method therefor, the carbon nanotube dispersion comprising: carbon nanotubes; a first dispersant including a hydrated nitrile butadiene rubber; a second dispersant including an alkanol ammonium salt compound of a polymer containing an acidic functional group; and a solvent, wherein the weight average molecular weight of the hydrated nitrile butadiene rubber is 10,000-20,000 g / mol.

Description

Carbon nanotube dispersion and method for producing the same

[0001] This application claims the benefit of priority to Republic of Korea Patent Application No. 10-2024-0065729, dated May 21, 2024, and Republic of Korea Patent Application No. 10-2025-0063411, dated May 15, 2025, the entire contents of which are incorporated herein by reference.

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

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

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

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

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

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

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

[0009] [Prior Art Literature]

[0010] [Patent Document]

[0011] (Patent Document 1) Republic of Korea Patent Publication No. 10-2023-0149256 (October 26, 2023)

[0012] The purpose 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, hydrated nitrile butadiene rubber having a weight average molecular weight of 10,000 to 20,000 g / mol, a second dispersant including an alkylol ammonium salt compound of a polymer having an acidic functional group, and a solvent.

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

[0014] One embodiment of the present invention provides a carbon nanotube dispersion comprising carbon nanotubes, a first dispersant including hydrated nitrile butadiene rubber, a second dispersant including an alkylol ammonium salt compound of a polymer including an acidic functional group, and a solvent, wherein the hydrogenated nitrile butadiene rubber has a weight average molecular weight of 10,000 to 20,000 g / mol.

[0015] The polydispersity index (PDI) of the above hydrogenated nitrile butadiene rubber may be 2.0 to 4.0.

[0016] The above hydrogenated nitrile butadiene rubber may further include a hydroxyl group in the molecule.

[0017] The amine value of the second dispersant may be 30 to 40 mg KOH / g, and the acid value may be 20 to 30 mg KOH / g.

[0018] 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.

[0019] The above carbon nanotube dispersion may contain 5 to 40 parts by weight of the second dispersant based on 100 parts by weight of the carbon nanotubes.

[0020] The solid content of the above carbon nanotube dispersion may be 0.1 to 10 parts by weight relative to the total weight of the dispersion.

[0021] Particle size distribution D of the dispersed particles contained in the above dispersion 90 This can be 1 to 5 μm.

[0022] The above carbon nanotube dispersion may have an initial viscosity of 0.5 to 10 Pa·s measured at 25°C and 1 rpm.

[0023] Another embodiment of the present invention provides a method for preparing the above-described carbon nanotube dispersion, comprising the steps of preparing a carbon nanotube primary dispersion by mixing carbon nanotubes, a first dispersant including hydrated nitrile butadiene rubber, a second dispersant including an alkylol ammonium salt compound of a polymer including an acidic functional group, and a solvent, and the step of dispersing the carbon nanotube primary dispersion to prepare a carbon nanotube secondary dispersion.

[0024] The weight average molecular weight of the above-mentioned hydrogenated nitrile butadiene rubber may be 10,000 to 20,000 g / mol, and the polydispersity index (PDI) may be 2.0 to 4.0.

[0025] The carbon nanotube dispersion according to the present invention comprises a hydrated nitrile butadiene rubber having a weight average molecular weight of 10,000 to 20,000 g / mol as a first dispersant, and an alkylol ammonium salt compound of a polymer having an acidic functional group as a second dispersant, and in particular, satisfies that the polydispersity index (PDI) of the hydrogenated nitrile butadiene rubber is 2.0 to 4.0, so that despite using carbon nanotubes having a large specific surface area, the dispersion exhibits a small change in viscosity over time, a relatively low initial viscosity, and has the characteristic of having a small particle size of dispersed particles by uniformly and effectively dispersing the carbon nanotubes.

[0026] Figure 1 is a graph showing the particle size distribution of dispersion particles according to one embodiment and a comparative example of the present invention.

[0027] FIG. 2 shows an infrared spectroscopy (IR) spectrum for a first dispersant included in a dispersion according to one embodiment of the present invention.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] Throughout this specification, “%” means weight percent unless explicitly stated otherwise.

[0032] In this specification, "D n " means the average particle size, and means the particle size at the n% point of the cumulative distribution of the number of particles according to particle size. That is, D 50is the particle size at the 50% point of the cumulative particle number distribution according to particle size, and D 90 D is the particle size at the 90% point of the cumulative distribution of particle numbers according to particle size. 10 is the particle size at the 10% point of the cumulative particle number distribution according to particle size. Meanwhile, the average particle size can be measured using the laser diffraction method. Specifically, after the powder to be measured is dispersed in a dispersion medium, it is introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac S3500), and the difference in diffraction pattern according to particle size when the particles pass through the laser beam is measured to calculate the particle size distribution.

[0033] 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.

[0034]

[0035] carbon nanotube dispersion

[0036] A carbon nanotube dispersion according to the present invention comprises carbon nanotubes, a first dispersant comprising hydrated nitrile butadiene rubber having a weight average molecular weight of 10,000 to 20,000 g / mol, a second dispersant comprising an alkylol ammonium salt compound of a polymer having an acidic functional group, and a solvent. Hereinafter, each component of the carbon nanotube dispersion of the present invention will be described in detail.

[0037]

[0038] (1) Carbon nanotubes

[0039] 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.

[0040] 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.

[0041] 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.

[0042] The carbon nanotube dispersion according to the present invention comprises a first dispersant including hydrated nitrile butadiene rubber having a weight average molecular weight of 10,000 to 20,000 g / mol and a second dispersant including an alkylol ammonium salt compound of a polymer having an acidic functional group, so that the initial viscosity of the carbon nanotube dispersion can be significantly reduced, and the occurrence of viscosity change over time can be suppressed, while maintaining a low particle size of the dispersed particles. Therefore, when applied to an electrode slurry of a lithium secondary battery, the carbon nanotube dispersion can exhibit high conductivity due to the high conductivity of the carbon nanotubes.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] 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 implemented even when applied to an electrode active material. At this time, the average diameter of the carbon nanotubes can be measured by photographing a carbon nanotube powder with a scanning electron microscope, and the average length of the carbon nanotubes can be measured by photographing a carbon nanotube dispersion with a scanning electron microscope.

[0047] The carbon nanotubes may be included in an amount of 0.1 to 10 parts by weight based on the total weight of the 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 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, 7.4 parts by weight or less, 7.It may be included in an amount of 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 cycle characteristics of the secondary battery manufactured using the carbon nanotube dispersion are excellent.

[0048] 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.

[0049] 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.

[0050]

[0051] (2) First dispersant and second dispersant

[0052] The carbon nanotube dispersion according to the present invention comprises a first dispersant including hydrated nitrile butadiene rubber having a weight average molecular weight of 10,000 to 20,000 g / mol, in order to improve the dispersibility of the carbon nanotubes, and a second dispersant including an alkylol ammonium salt compound of a polymer including an acidic functional group.

[0053] In the above carbon nanotube dispersion, the first dispersant and the second dispersant serve to increase the dispersibility of the carbon nanotubes so that the carbon nanotubes can be evenly dispersed without agglomeration in the dispersion, and in particular, 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.

[0054] In a carbon nanotube dispersion according to one specific example of the present invention, the hydrated nitrile butadiene rubber may include repeating units represented by the following chemical formulas 1 to 3.

[0055] [Chemical Formula 1]

[0056]

[0057] [Chemical Formula 2]

[0058]

[0059] [Chemical Formula 3]

[0060]

[0061] In the above chemical formulas 1 to 3,

[0062] * is the connecting part.

[0063] In one specific example of the present invention, the hydrogenated nitrile butadiene rubber may contain a repeating unit represented by the chemical formula 1 and a repeating unit represented by the chemical formula 2 in a molar ratio of 82:18 to 50:50.

[0064] Additionally, in one specific example of the present invention, the hydrogenated nitrile butadiene rubber may contain 0.1 to 2.0 mol % of the repeating unit represented by the chemical formula 3 relative to the total molar number of the repeating unit represented by the chemical formula 1.

[0065] In one specific example of the present invention, the weight average molecular weight (Mw) of the hydrogenated nitrile butadiene rubber may be 10,000 to 20,000 g / mol, specifically, may be 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, or 15,000 g / mol or more, and may be 20,000 g / mol or less, 19,000 g / mol or less, 18,000 g / mol or less, 17,000 g / mol or less, or 16,000 g / mol or less.

[0066] In addition, in the case of the hydrogenated nitrile butadiene rubber according to one specific example of the present invention, it may have the weight average molecular weight distribution and satisfy a polydispersity index (PDI) of 2.0 to 4.0, 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, 4.0 or less, 3.9 or less, 3.8 or less, 3.7 or less, 3.6 or less, 3.5 or less, 3.4 or less, 3.3 or less, 3.2 or less, 3.1 or less, 3.0 or less, 2.9 or less, 2.8 or less, 2.7 or less, or 2.6 or less, and preferably, the polydispersity index may be 2.5 to 3.0.

[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] As described above, the hydrogenated nitrile butadiene rubber, which is a first dispersing agent according to one specific example of the present invention, can maintain low viscosity of the dispersion and exhibit an effect in which viscosity changes little over time due to a low weight average molecular weight (Mw) distribution of 10,000 to 20,000 g / mol. In addition, the hydrogenated nitrile butadiene rubber, which is a first dispersing agent according to one specific example of the present invention, can exhibit the weight average molecular weight of the above distribution and at the same time have a low polydispersity index of 2.0 to 4.0. Therefore, the hydrogenated nitrile butadiene rubber exhibiting the narrow molecular weight distribution as described above can uniformly surround carbon nanotubes, thereby imparting a characteristic in which the average particle size of the carbon nanotube dispersion particles is lowered.

[0069] Accordingly, the particle size distribution D of the dispersed particles included in the dispersion according to one specific example of the present invention 90 It may be 1 to 5 ㎛, for example, 1 ㎛ or more, 1.1 ㎛ or more, 1.2 ㎛ or more, 1.3 ㎛ or more, 1.4 ㎛ or more, 1.5 ㎛ or more, 1.6 ㎛ or more, 1.7 ㎛ or more, 1.8 ㎛ or more, 1.9 ㎛ or more, 2 ㎛ 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, 2.8 ㎛ or more, 2.9 ㎛ or more or 3 ㎛ or more, 5 ㎛ or less, 4.9 ㎛ or less, 4.8 ㎛ or less, 4.7 ㎛ or less, 4.6 ㎛ or less, 4.5 ㎛ or less, 4.4 ㎛ or less, 4.3 ㎛ or less, It may be 4.2 ㎛ or less, 4.1 ㎛ or less, 4 ㎛ or less, 3.9 ㎛ or less, 3.8 ㎛ or less, 3.7 ㎛ or less, 3.6 ㎛ or less, 3.5 ㎛ or less, 3.4 ㎛ or less, 3.3 ㎛ or less, 3.2 ㎛ or less, or 3.1 ㎛ or less, and preferably, the particle size distribution can be kept low at 2.5 to 4.0 ㎛.

[0070] In one specific embodiment of the present invention, the hydrogenated nitrile butadiene rubber may further include a hydroxyl group (-OH) in the molecule.

[0071] The above hydrogenated nitrile-butadiene rubber is produced by low-temperature emulsion polymerization of acrylonitrile and butadiene to produce a nitrile-butadiene copolymer, and then adding hydrogen to the carbon-carbon double bonds contained in the nitrile-butadiene copolymer using a transition metal catalyst such as platinum (Pt). Therefore, by controlling the input amounts of the reactants acrylonitrile and butadiene and the polymerization reaction time, nitrile-butadiene copolymers having various weight-average molecular weights can be produced.

[0072] However, some carbon-carbon double bonds may remain even after the hydrogenation reaction of the nitrile-butadiene copolymer, and when the weight average molecular weight of the nitrile-butadiene copolymer increases, the number of remaining carbon-carbon double bonds may further increase.

[0073] The carbon nanotube dispersion according to the present invention can maintain low viscosity of the dispersion, and can provide the effect of not significantly changing viscosity over time, as well as the characteristic of lowering the average particle size of carbon nanotube dispersion particles.

[0074] These properties can be achieved by applying a hydrogenated nitrile butadiene rubber having a low weight average molecular weight (Mw) distribution of 10,000 to 20,000 g / mol and a low polydispersity index of 2.0 to 4.0 as a first dispersant of a carbon nanotube dispersion, and by subjecting the hydrogenated nitrile butadiene rubber having a relatively high weight average molecular weight to ozonolysis, the hydrogenated nitrile butadiene rubber can have the low weight average molecular weight and polydispersity index.

[0075] Although not limited to a specific theory, the carbon-carbon double bonds remaining in the hydrogenated nitrile butadiene copolymer are cleaved by the ozonolysis reaction, and thus a polymer having a relatively large weight average molecular weight can be produced as a hydrogenated nitrile butadiene rubber having a low weight average molecular weight (Mw) distribution of 10,000 to 20,000 g / mol and a low polydispersity index of 2.0 to 4.0. In addition, since the carbon-carbon double bonds remaining after the hydrogenation reaction of the nitrile butadiene rubber are cleaved by the ozonolysis reaction, the degree of hydrogenation of the hydrogenated nitrile butadiene rubber having a low weight average molecular weight, which is an ozonolysis product, can further increase.

[0076] In one specific example of the present invention, a hydroxyl group may be introduced at the position where the carbon-carbon double bond of the product of the ozonolysis reaction of the hydrogenated nitrile butadiene rubber as described above is broken, and this result is, for example, the infrared spectroscopy (IR) measurement result of the ozonolysis reaction product, which appears at 3,200 to 3,600 cm -1 It can be confirmed from the detection of a broad peak.

[0077] In one specific embodiment of the present invention, the first dispersant may be included in an amount of 10 to 50 parts by weight based on 100 parts by weight of carbon nanotubes in the carbon nanotube dispersion, and specifically, may be 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 50 parts by weight or less, 49 parts by weight or less, 48 ​​parts by weight or less, 47 parts by weight or less, 46 parts by weight or less, 45 parts by weight or less, It may 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.

[0078] 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, and thus the viscosity of the dispersion may not be formed low and may increase over time, and if it exceeds 50 parts by weight, the content of the first dispersant may be excessive, and thus coagulation between solids in the dispersion may occur, resulting in a problem of high viscosity of the dispersion.

[0079] In addition, the carbon nanotube dispersion according to one embodiment of the present invention includes, in order to solve the problem of the viscosity of the dispersion increasing as the content of carbon nanotubes increases in the carbon nanotube dispersion containing only the first dispersant, a second dispersant including an alkylol ammonium salt compound of a polymer containing an acidic functional group together with the first dispersant, and thus, compared to a carbon nanotube dispersion using only a conventional dispersant, the dispersion has excellent dispersibility, and can exhibit the effects of less particle agglomeration of the slurry composition and a low sedimentation rate.

[0080] The polymer alkylol ammonium salt compound including the acidic functional group may have a weight average molecular weight of 1,000 to 3,000 g / mol, specifically 1,000 g / mol or more, 1,100 g / mol or more, 1,200 g / mol or more, 1,300 g / mol or more, 1,400 g / mol or more, 1,500 g / mol or more, 1,600 g / mol or more, 1,700 g / mol or more, 1,800 g / mol or more, 1,900 g / mol or more, or 2,000 g / mol or more, 3,000 g / mol or less, 2,900 g / mol or less, 2,800 g / mol or less, 2,700 g / mol or less, 2,600 g / mol or less, 2,500 g / mol or less, 2,400 g / mol It may be less than, 2,300 g / mol or less, 2,200 g / mol or less, or 2,100 g / mol or less.

[0081] The amine value of the alkylol ammonium salt compound of the polymer containing the acidic functional group may be 30 to 40 mg KOH / g, and specifically, may be 30 mg KOH / g or more, 31 mg KOH / g or more, 32 mg KOH / g or more, 33 mg KOH / g or more, 34 mg KOH / g or more, or 35 mg KOH / g or more, and may be 40 mg KOH / g or less, 39 mg KOH / g or less, 38 mg KOH / g or less, 37 mg KOH / g or less, or 36 mg KOH / g or less.

[0082] In addition, the acid value of the alkylol ammonium salt compound of the polymer containing an acidic functional group may be 20 to 30 mg KOH / g, specifically 20 mg KOH / g or more, 21 mg KOH / g or more, 22 mg KOH / g or more, 23 mg KOH / g or more, 24 mg KOH / g or more, or 25 mg KOH / g or more, and 30 mg KOH / g or less, 29 mg KOH / g or less, 28 mg KOH / g or less, 27 mg KOH / g or less, or 26 mg KOH / g or less.

[0083] It is preferable to use an alkylol ammonium salt compound of a polymer containing the above acidic functional group that has both an amine value and an acid value within the above range.

[0084] In one specific example of the present invention, the second dispersant may be included in an amount of 5 to 40 parts by weight based on 100 parts by weight of carbon nanotubes in the carbon nanotube dispersion, and specifically, may be 5 parts by weight or more, 6 parts by weight or more, 7 parts by weight or more, 8 parts by weight or more, 9 parts by weight or more, 10 parts by weight or more, 11 parts by weight or more, 12 parts by weight or more, 13 parts by weight or more, 14 parts by weight or more, 15 parts by weight or more, 16 parts by weight or more, 17 parts by weight or more, 18 parts by weight or more, 19 parts by weight or more, 20 parts by weight or more, 21 parts by weight or more, or 22 parts by weight or more, and may be 40 parts by weight or less, 39 parts by weight or less, 38 parts by weight or less, 37 parts by weight or less, 36 parts by weight or less, 35 parts by weight or less, 34 parts by weight or less, 33 parts by weight or less, 32 parts by weight or less, 31 parts by weight. It may contain 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, or 23 parts by weight or less.

[0085] If the content of the second dispersant is less than 5 parts by weight based on 100 parts by weight of carbon nanotubes, the effective dispersing effect of the first and second dispersants may not be achieved, and as a result, the viscosity of the dispersion may not be formed low, and there may be a problem in that the viscosity increases over time. If it exceeds 40 parts by weight, the content of the second dispersant is excessive, so that coagulation between solids in the dispersion may occur, and there may be a problem in that the viscosity of the dispersion is formed high.

[0086] In one specific embodiment of the present invention, the solid content of the carbon nanotube dispersion may be 0.1 to 10 parts by weight relative to the total weight of the dispersion, for example, 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 or 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 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.It may be included in an amount of 5 parts by weight or less, 7.4 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.

[0087] Here, the solid content may mean the total content of carbon nanotubes, the first dispersant, and the second dispersant included in the carbon nanotube dispersion.

[0088] When the solid content of the carbon nanotube dispersion satisfies the above range, the initial viscosity of the carbon nanotube dispersion can be effectively reduced, and the particle size of the dispersed particles can be maintained low.

[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, the first dispersant, and the second dispersant, and is used to supply the carbon nanotube dispersion by pre-dispersing it to prevent agglomeration when using the carbon nanotubes in a powdered state directly in the manufacture of an electrode slurry composition.

[0092] The solvent is capable of dissolving or dispersing the carbon nanotubes, the first dispersant, and the second dispersant to a certain level or higher. The solvent may be an organic solvent containing one or more heteroatoms selected from the group consisting of 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] A carbon nanotube dispersion according to one embodiment of the present invention can reduce the average particle size distribution of dispersed particles included in the dispersion, such as a composite of carbon nanotubes and each dispersant, by enabling the first dispersant and the second dispersant to uniformly disperse carbon nanotubes in a solvent as described above.

[0095] The carbon nanotube dispersion may have an initial viscosity of 0.5 to 10 Pa.s as measured at 25°C and 1 rpm using a viscometer (TOKISANGYO, viscometer TV-25, Rotor Code 01), for example, 0.5 Pa.s or more, 0.6 Pa.s or more, 0.8 Pa.s or more, 1 Pa.s or more, 1.1 Pa.s or more, 1.5 Pa.s or more, 2 Pa.s or more, 2.5 Pa.s or more, 3 Pa.s or more, 3.5 Pa.s or more, 4 Pa.s or more, 4.5 Pa.s or more, or 5 Pa.s or more, and 10 Pa.s or less, 9.5 Pa.s or less, 9 Pa.s or less, 8.9 Pa.s or less, 8.5 Pa.s or less, 8 Pa.s or less, 7.5 Pa.s or less, or 7 Pa.s or less. It can be less than 6.5 Pa.s, 6 Pa.s or less than 5.5 Pa.s.

[0096] More specifically, the carbon nanotube dispersion may have an initial viscosity measured at 25°C and 1 rpm using a viscometer (TOKISANGYO, viscometer TV-25, Rotor Code 01) of 0.5 to 1.0 Pa.s when the solid content of the dispersion is 0.1 to 3.5 parts by weight relative to the total weight of the dispersion, and may have an initial viscosity of 1.1 to 10 Pa.s when the solid content of the dispersion is 3.6 to 10 parts by weight relative to the total weight of the dispersion.

[0097] When the carbon nanotube dispersion has an initial viscosity within the above range, an electrode slurry can be manufactured more smoothly using the same, and an electrode slurry including the carbon nanotube dispersion can have an appropriate viscosity for electrode formation.

[0098]

[0099] Method for producing carbon nanotube dispersion

[0100] Below, a method for manufacturing a carbon nanotube dispersion is described.

[0101] The method for producing a carbon nanotube dispersion according to the present invention comprises: (1) mixing carbon nanotubes, a first dispersant including hydrated nitrile butadiene rubber, a second dispersant including an alkylol ammonium salt compound of a polymer including an acidic functional group, and a solvent to produce a carbon nanotube primary dispersion; and (2) 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.

[0102] In step (1), a carbon nanotube primary dispersion is prepared by mixing carbon nanotubes, a first dispersant including hydrated nitrile butadiene rubber, a second dispersant including an alkylol ammonium salt compound of a polymer including an acidic functional group, 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.

[0103] In one specific example of the present invention, the weight average molecular weight of the hydrated nitrile butadiene rubber may be 10,000 to 20,000 g / mol, and the polydispersity index (PDI) may be 2.0 to 4.0.

[0104] Mixing for preparing the above carbon nanotube primary dispersion can be performed using a conventional mixing method, specifically, a mixing device such as a homogenizer, bead mill, ball mill, basket mill, attrition mill, universal stirrer, clear mixer or TK mixer, and can include a step of stirring at 300 to 5,000 rpm for 30 minutes to 3 hours.

[0105] In addition, when mixing to prepare the above carbon nanotube primary dispersion, cavitation dispersion treatment may be performed to increase the mixing property of the carbon nanotubes and the dispersion medium, or the dispersibility of the carbon nanotubes in the dispersion medium. 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.

[0106] 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.

[0107] In step (2), the above carbon nanotube primary dispersion is dispersed to prepare a carbon nanotube secondary dispersion.

[0108] 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, can be performed by a milling method using a disc mill or a high pressure homogenizer.

[0109] Milling by the high-pressure homogenizer is achieved by pressurizing the mixture with a plunger pump of the high-pressure homogenizer, for example, and pushing it through the gap of the homogenization valve, thereby generating forces such as cavitation, shear, impact, and explosion when passing through the gap.

[0110] The above milling process can be performed depending on the degree of dispersion of the carbon nanotube dispersion, and can be performed specifically for 30 to 120 minutes, more specifically for 60 to 90 minutes.

[0111] The particle size distribution D of the carbon nanotube secondary dispersion of the present invention manufactured by the above method 90 can be 1 to 5 μm.

[0112]

[0113] Electrode slurry composition for lithium secondary batteries

[0114] 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.

[0115] 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.

[0116] The above-described electrode slurry composition for a lithium secondary battery may include the carbon nanotube dispersion, a positive electrode active material or a negative electrode active material as an electrode active material, a binder, a solvent, and / or other additives as needed.

[0117] As the positive electrode active material, positive electrode active materials well known in the art can be used without limitation, and for example, lithium cobalt-based oxide, lithium nickel-based oxide, lithium manganese-based oxide, lithium iron phosphate, lithium nickel manganese cobalt-based oxide, or a combination thereof can be used. Specifically, the positive electrode active material includes LiCoO2, LiNiO2, LiMn2O4, LiCoPO4, LiFePO4, and LiNiaMnbCocO. 2　 (Here, 0 < a, b, c < 1) can be used, but is not limited to this.

[0118] 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.

[0119] 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.

[0120] The solvents mentioned above include organic solvents such as N-methyl pyrrolidone (NMP), dimethyl formamide (DMF), acetone, dimethyl acetamide, etc., or water, and these solvents may be used alone or in combination of two or more. The amount of solvent used is sufficient to dissolve and disperse the electrode active material, binder, and conductive agent, taking into account the coating thickness of the slurry and the manufacturing yield.

[0121] 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.

[0122] 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.

[0123] 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.

[0124] 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.

[0125] The above-described positive electrode current collector generally has a thickness of 3 μm to 500 μm. The positive electrode current collector is not particularly limited as long as it has high conductivity and does not cause chemical changes in the battery. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. can be used. In addition, the surface of the positive electrode current collector may be formed with fine irregularities to strengthen the bonding strength of the positive electrode active material, and the positive electrode current collector can be used in various forms such as a film, sheet, foil, net, porous body, foam, or non-woven fabric.

[0126] 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.

[0127] 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.

[0128] 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.

[0129]

[0130] lithium secondary battery

[0131] 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.

[0132] 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.

[0133] 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.

[0134] 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.

[0135] 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.

[0136] 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.

[0137] A lithium secondary battery comprising an electrode manufactured using a carbon nanotube dispersion according to the present invention, specifically a lithium secondary battery comprising a cathode manufactured using a carbon nanotube dispersion, has carbon nanotubes uniformly dispersed within the cathode, 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).

[0138] 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.

[0139] 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.

[0140]

[0141] 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.

[0142]

[0143] Example

[0144]

[0145] Example 1

[0146] (1) In a homogenous mixer, the specific surface area is 250 m 2 / g multi-walled carbon nanotubes (MWCNT, BT1001M, LG Chemical), 1 part by weight of hydrated nitrile butadiene rubber (HNBR) (Mw 19,000, PDI 2.8) as a first dispersant, 0.5 part by weight of an alkylol ammonium salt compound of a polymer containing an acidic functional group (BYK, product name: BYK-ET 3001, amine value 37 mg KOH / g, acid value 29 mg KOH / g) as a second dispersant, and 93.5 parts by weight of methylpyrrolidone (N-Methyl-2-pyrrolidone, NMP) as a solvent were added so that the solid content was 5 parts by weight based on the total weight of the carbon nanotube primary dispersion, and then stirred and mixed at 5,000 rpm for 1 hour to prepare a carbon nanotube primary dispersion. At this time, the first dispersant used was hydrogenated nitrile butadiene rubber (Mw 270,000, degree of hydrogenation 84.5%) obtained through ozonolysis for 3 hours.

[0147] 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.

[0148] - Device: Alliance e2695 from Waters

[0149] - Detector: Waters 2414 RID

[0150] - Column: Use 1 PKgel MiniMIX-B

[0151] - Solvent: THF (stabilized)

[0152] - Column temperature: 40 ℃

[0153] - Flow rate: 0.3 ml / min

[0154] - Sample concentration: 1 mg / mL, 20 μl injection

[0155] - Standard sample: Polystyrene (Mp: 4230000, 1270000, 327000, 113300, 31420, 9600, 3790, 580)

[0156] 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).

[0157] (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.

[0158]

[0159] Example 2

[0160] A carbon nanotube dispersion was prepared in the same manner as in Example 1, except that hydrated nitrile butadiene rubber (HNBR) (Mw 12,000, PDI 2.7) was used as the first dispersant.

[0161]

[0162] Example 3

[0163] In the above Example 1, 3.3 parts by weight of carbon nanotubes, 0.66 parts by weight of hydrated nitrile butadiene rubber (HNBR) (Mw 19,000, PDI 2.8) as a first dispersant, and 0.33 parts by weight of a second dispersant were used, so that the solid content relative to the total weight of the carbon nanotube primary dispersion was 3.3 parts by weight, and a carbon nanotube dispersion was prepared in the same manner as in Example 1.

[0164]

[0165] Example 4

[0166] In the above Example 1, 3.3 parts by weight of carbon nanotubes, 0.66 parts by weight of hydrated nitrile butadiene rubber (HNBR) (Mw 12,000, PDI 2.7) as a first dispersant, and 0.33 parts by weight of a second dispersant were used, so that the solid content relative to the total weight of the carbon nanotube primary dispersion was 3.3 parts by weight, and a carbon nanotube dispersion was prepared in the same manner as in Example 1.

[0167]

[0168] Example 5

[0169] In the above Example 1, 3.3 parts by weight of carbon nanotubes, 0.66 parts by weight of hydrated nitrile butadiene rubber (HNBR) (Mw 15,000, PDI 2.6) as a first dispersant, and 0.33 parts by weight of a second dispersant were used, so that the solid content relative to the total weight of the carbon nanotube primary dispersion was 3.3 parts by weight, and a carbon nanotube dispersion was prepared in the same manner as in Example 1.

[0170]

[0171] Example 6

[0172] In the above Example 1, 3.3 parts by weight of carbon nanotubes, 0.66 parts by weight of hydrated nitrile butadiene rubber (HNBR) (Mw 15,000, PDI 2.8) as a first dispersant, and 0.33 parts by weight of a second dispersant were used, so that the solid content relative to the total weight of the carbon nanotube primary dispersion was 3.3 parts by weight, and a carbon nanotube dispersion was prepared in the same manner as in Example 1.

[0173]

[0174] Example 7

[0175] In the above Example 1, 3.3 parts by weight of carbon nanotubes, 0.66 parts by weight of hydrated nitrile butadiene rubber (HNBR) (Mw 13,000, PDI 2.8) as a first dispersant, and 0.33 parts by weight of a second dispersant were used, so that the solid content relative to the total weight of the carbon nanotube primary dispersion was 3.3 parts by weight, and a carbon nanotube dispersion was prepared in the same manner as in Example 1.

[0176]

[0177] Comparative Example 1

[0178] A carbon nanotube dispersion was prepared in the same manner as in Example 1, except that hydrated nitrile butadiene rubber (HNBR) (Mw 19,000, PDI 4.3) was used as the first dispersant.

[0179]

[0180] Comparative Example 2

[0181] A carbon nanotube dispersion was prepared in the same manner as in Example 1, except that hydrated nitrile butadiene rubber (HNBR) (Mw 19,000, PDI 4.6) was used as the first dispersant.

[0182]

[0183] Comparative Example 3

[0184] A carbon nanotube dispersion was prepared in the same manner as in Example 1, except that hydrated nitrile butadiene rubber (HNBR) (Mw 8,200, PDI 1.9) was used as the first dispersant.

[0185]

[0186] Comparative Example 4

[0187] In the above Example 1, 3.3 parts by weight of carbon nanotubes, 0.66 parts by weight of hydrated nitrile butadiene rubber (HNBR) (Mw 19,000, PDI 4.6) as a first dispersant, and 0.33 parts by weight of a second dispersant were used, and the solid content was set to 3.3 parts by weight relative to the total weight of the carbon nanotube primary dispersion, and a carbon nanotube dispersion was prepared in the same manner as in Example 1.

[0188]

[0189] Comparative Example 5

[0190] In the above Example 1, 3.3 parts by weight of carbon nanotubes, 0.66 parts by weight of hydrated nitrile butadiene rubber (HNBR) (Mw 26,000, PDI 4.8) as a first dispersant, and 0.33 parts by weight of a second dispersant were used, and the solid content was set to 3.3 parts by weight relative to the total weight of the carbon nanotube primary dispersion, and a carbon nanotube dispersion was prepared in the same manner as in the above Example 1.

[0191]

[0192] Comparative Example 6

[0193] In the above Example 1, 3.3 parts by weight of carbon nanotubes, 0.66 parts by weight of hydrated nitrile butadiene rubber (HNBR) (Mw 39,000, PDI 5.5) as a first dispersant, and 0.33 parts by weight of a second dispersant were used, and the solid content was set to 3.3 parts by weight relative to the total weight of the carbon nanotube primary dispersion, and a carbon nanotube dispersion was prepared in the same manner as in Example 1.

[0194]

[0195] Comparative Example 7

[0196] In the above Example 1, 3.3 parts by weight of carbon nanotubes, 0.66 parts by weight of hydrated nitrile butadiene rubber (HNBR) (Mw 170,000, PDI 3.7) as a first dispersant, and 0.33 parts by weight of a second dispersant were used, and a carbon nanotube dispersion was prepared in the same manner as in Example 1, except that the solid content was set to 3.3 parts by weight relative to the total weight of the carbon nanotube primary dispersion.

[0197]

[0198] Experimental example

[0199]

[0200] Experimental Example 1: Measurement of viscosity and particle size of carbon nanotube dispersion

[0201] The viscosity and particle size of the carbon nanotube dispersions of Examples 1 to 7 and Comparative Examples 1 to 7 were measured, and the results are shown in Tables 1 to 3 below.

[0202] Specifically, Table 1 below shows the viscosity and particle size measurement results of the first dispersions of carbon nanotube dispersions according to Examples 1 and 2 and Comparative Examples 1 to 3, Table 2 shows the viscosity and particle size measurement results of the second dispersions of carbon nanotube dispersions according to Examples 1 and 2 and Comparative Examples 1 to 3 (however, the solid content of the carbon nanotube dispersions of each Example and Comparative Example was 5% (5 parts by weight of solid content relative to the total weight of the dispersion)), and Table 3 shows the viscosity and particle size measurement results of the second dispersions of carbon nanotube dispersions according to Examples 3 to 7 and Comparative Examples 4 to 7 (however, the solid content of the carbon nanotube dispersions of each Example and Comparative Example was 3.3% (3.3 parts by weight of solid content relative to the total weight of the dispersion)).

[0203] Viscosity was measured at 25°C and 1 rpm using a viscometer (TOKI SANGYO, viscometer TV-25, Rotor Code 01).

[0204] Particle size was measured at 2,000 rpm using a laser diffraction scattering particle size distribution measuring device Mastersizer (Malvern Panalytical). The particle size at 50% by volume was D 50 , and the particle size at 90% of the volume is D 90 It was done as follows.

[0205]

[0206] (Carbon nanotube primary dispersion) Solid content concentration (%) Primary dispersant viscosity (Pa·s) Particle size (D 90)Weight average molecular weight (g / mol)PDIExample 15.019,0002.813.17.4Example 25.012,0002.714.110.4Comparative example 15.019,0004.39.226.5Comparative example 25.019,0004.612.519.2Comparative example 35.08,2001.910.214.5

[0207]

[0208] (Carbon nanotube secondary dispersion) Solid content concentration (%) First dispersant viscosity (Pa·s) Particle size (D 90 )Weight average molecular weight (g / mol)PDIExample 15.019,0002.88.93.4Example 25.012,0002.78.03.2Comparative example 15.019,0004.312.46.1Comparative example 25.019,0004.614.75.6Comparative example 35.08,2001.914.95.2

[0209]

[0210] (Carbon nanotube secondary dispersion) Solid content concentration (%) First dispersant viscosity (Pa·s) Particle size (D 90 )Weight average molecular weight (g / mol)PDIExample 33.319,0002.80.62.8Example 43.312,0002.70.83.8Example 53.315,0002.60.83.5Example 63.315,0002.80.63.4Example 73.313,0002.80.63.2Comparative Example 43.319,0004.61.15.5Comparative Example 53.326,0004.81.36.5Comparative Example 63.339,0005.51.87.9Comparative Example 73.3170,0003.75.68.0

[0211]

[0212] Referring to Table 1 above, in the case of Examples 1 and 2, when hydrated nitrile butadiene rubber having a weight average molecular weight of 10,000 to 20,000 g / mol and a polydispersity index (PDI) of 2.0 to 4.0 was used as the first dispersant, it was confirmed that the viscosity of the carbon nanotube primary dispersion and the particle size of the dispersed particles were maintained low. On the other hand, in the case of Comparative Examples 1 and 2, when hydrated nitrile butadiene rubber having a polydispersity index exceeding 4.0 was used as the first dispersant, it was confirmed that the particle size of the carbon nanotube primary dispersion increased. In addition, in the case of Comparative Example 3, it can be seen that when hydrogenated nitrile butadiene rubber having a weight average molecular weight of less than 10,000 g / mol and a polydispersity index of less than 2.0 was used as the first dispersant, the particle size of the dispersed particles of the carbon nanotube primary dispersion actually increased.

[0213]

[0214] Referring to Table 2 and FIG. 1 above, in the case of Examples 1 and 2, when hydrated nitrile butadiene rubber having a weight average molecular weight of 10,000 to 20,000 g / mol and a polydispersity index (PDI) of 2.0 to 4.0 was used as the first dispersant, it was confirmed that the viscosity of the carbon nanotube secondary dispersion and the particle size of the dispersed particles were also maintained low. On the other hand, in the case of Comparative Examples 1 and 2, when hydrated nitrile butadiene rubber having a polydispersity index exceeding 4.0 was used as the second dispersant, it was confirmed that both the viscosity of the carbon nanotube secondary dispersion and the particle size of the dispersed particles increased. In addition, in the case of Comparative Example 3, it can be seen that when hydrogenated nitrile butadiene rubber having a weight average molecular weight of less than 10,000 g / mol and a polydispersity index of less than 2.0 was used as the first dispersant, the viscosity of the carbon nanotube secondary dispersion and the particle size of the dispersed particles actually increased.

[0215]

[0216] Referring to Table 3 above, it can be confirmed that in the carbon nanotube dispersions according to Examples 3 to 7, which maintained a lower solid content compared to Examples 1 and 2 of Table 2 above, the viscosity of the carbon nanotube secondary dispersion and the particle size of the dispersed particles were also maintained low when using hydrated nitrile butadiene rubber having a weight average molecular weight of 10,000 to 20,000 g / mol and a polydispersity index (PDI) of 2.0 to 4.0 as the first dispersant. In contrast, in the case of the carbon nanotube dispersions according to Comparative Examples 4 to 6, it can be confirmed that the particle size of the dispersed particles of the carbon nanotube secondary dispersion significantly increases when the polydispersity index of the hydrogenated nitrile butadiene rubber, which is the first dispersing agent, exceeds 4.0 (Comparative Example 4) or the weight average molecular weight of the hydrogenated nitrile butadiene rubber exceeds 20,000 g / mol (Comparative Examples 5 and 6). In addition, in the case of the carbon nanotube dispersion according to Comparative Example 7, it can be confirmed that the viscosity of the carbon nanotube secondary dispersion and the particle size of the dispersed particles significantly increase when the polydispersity index of the hydrogenated nitrile butadiene rubber, which is the first dispersing agent, exceeds 2.0 to 4.0 or the weight average molecular weight exceeds 20,000 g / mol.

[0217]

[0218] Experimental Example 2: Determination of the presence of hydroxyl functional groups in hydrogenated nitrile butadiene.

[0219] Regarding the first dispersant used in Example 1, hydrated nitrile butadiene rubber (HNBR) (Mw 19,000, PDI 2.8), the presence or absence of a hydroxyl group (-OH) was measured using infrared spectroscopy, and the results are shown in Fig. 2.

[0220] Referring to Figure 2, 3,200 to 3,600 cm -1 Through the observation of a wide spectrum in the region, it can be confirmed that the first dispersant, hydrated nitrile butadiene rubber (HNBR), used in Example 1, contains a hydroxyl group in the molecule as a result of the ozonolysis reaction so that it can have a low weight average molecular weight and polydispersity index.

[0221]

[0222] 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 hydrated nitrile butadiene rubber; A second dispersant comprising an alkylol ammonium salt compound of a polymer containing an acidic functional group; and Contains a solvent, The weight average molecular weight of the above hydrogenated nitrile butadiene rubber is 10,000 to 20,000 g / mol. Carbon nanotube dispersion.

2. In paragraph 1, The polydispersity index (PDI) of the above hydrogenated nitrile butadiene rubber is 2.0 to 4.0, Carbon nanotube dispersion.

3. In paragraph 1, The above hydrogenated nitrile butadiene rubber further contains a hydroxyl group in the molecule. Carbon nanotube dispersion.

4. In paragraph 1, The amine value of the second dispersant is 30 to 40 mg KOH / g, and the acid value is 20 to 30 mg KOH / g. 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 5 to 40 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 solid content of the above carbon nanotube dispersion is 0.1 to 10 parts by weight relative to the total weight of the dispersion. Carbon nanotube dispersion.

8. In paragraph 1, Particle size distribution D of the dispersed particles contained in the above dispersion 90 This is 1 to 5 μm, Carbon nanotube dispersion.

9. In paragraph 1, The above carbon nanotube dispersion has an initial viscosity of 0.5 to 10 Pa·s measured at 25°C and 1 rpm. Carbon nanotube dispersion.

10. A step of preparing a carbon nanotube primary dispersion by mixing carbon nanotubes, a first dispersant including hydrated nitrile butadiene rubber, a second dispersant including an alkylol ammonium salt compound of a polymer including an acidic functional group, and a solvent; and A step of preparing a carbon nanotube secondary dispersion by dispersing the above carbon nanotube primary dispersion; A method for producing a carbon nanotube dispersion according to claim 1, comprising:

11. In paragraph 10, The weight average molecular weight of the above-mentioned hydrogenated nitrile butadiene rubber is 10,000 to 20,000 g / mol, and the polydispersity index (PDI) is 2.0 to 4.

0. Method for preparing carbon nanotube dispersion.

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