Carbon nanotube dispersions and methods for making the same

Abstract

This invention relates to carbon nanotube dispersions and methods for preparing them, the carbon nanotube dispersions comprising: carbon nanotubes; a first dispersant comprising hydrogenated nitrile butadiene rubber; a second dispersant comprising an alkanoic acid ammonium salt compound of a polymer containing acidic functional groups; and a solvent, wherein the hydrogenated nitrile butadiene rubber has a weight-average molecular weight of 10,000 g / mol to 20,000 g / mol.

Description

Technical Field

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

[0002] This invention relates to carbon nanotube dispersions and methods for preparing them. Background Technology

[0003] With technological advancements and increasing demands for mobile devices, the need for secondary batteries as an energy source is rapidly growing. Among these secondary batteries, lithium-ion batteries, characterized by high energy density and voltage, long cycle life, and low self-discharge rate, have been commercialized and are widely used. Furthermore, research is actively underway on methods to improve electrode density and thus manufacture electrodes with higher energy density per unit volume for use in such high-capacity lithium-ion batteries.

[0004] Typically, high-density electrodes are formed by pressing electrode active material particles with a size of several μm to tens of μm using high pressure. However, during the forming process, the particles may deform and the space between the particles may decrease, which can easily reduce the permeability of the electrolyte solution.

[0005] To address the above issues, conductive materials with excellent conductivity and strength are used in electrode manufacturing. The conductive material is positioned between the electrode active materials, thus maintaining the micropores between the active material particles even during the molding process. This allows for easy permeation of the electrolyte solution and provides excellent conductivity, thereby reducing the resistance within the electrode. Among these conductive materials, the use of carbon nanotubes, fibrous carbon-based conductive materials that can further reduce electrode resistance by forming conductive pathways within the electrode, is increasing.

[0006] Carbon nanotubes (a type of fine carbon fiber) are tubular carbon fibers with a diameter of 1 μm or less. Due to their high electrical conductivity, tensile strength, and heat resistance resulting from their unique structure, carbon nanotubes are expected to be applied and commercialized in multiple fields. However, a problem with carbon nanotubes is that they exhibit low dispersibility and a tendency to aggregate due to the strong van der Waals attraction between them caused by their high specific surface area.

[0007] To address these issues, mechanical dispersion methods, such as ultrasonic treatment, have been proposed to disperse carbon nanotubes in a dispersion medium. However, with mechanical dispersion methods, there is a problem that the carbon nanotubes aggregate once the ultrasonic radiation ends, or re-aggregate over time after dispersion.

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

[0009] [Existing technical documents]

[0010] [Patent Literature]

[0011] (Patent Document 1) Korean Patent Publication No. 10-2023-0149256 (October 26, 2023) Summary of the Invention

[0012] Technical issues

[0013] One object of the present invention is to provide a carbon nanotube dispersion comprising: carbon nanotubes; a first dispersant comprising hydrogenated nitrile butadiene rubber having a weight-average molecular weight of 10,000 g / mol to 20,000 g / mol; a second dispersant comprising an alkanoic acid ammonium salt compound of a polymer containing acidic functional groups; and a solvent, wherein the carbon nanotube dispersion exhibits excellent dispersibility, low viscosity of the dispersion, small particle size of the dispersed particles, and minimal viscosity change over time.

[0014] Another object of the present invention is to provide a method for preparing carbon nanotube dispersions.

[0015] Technical solution

[0016] One embodiment of the present invention provides a carbon nanotube dispersion comprising: carbon nanotubes; a first dispersant comprising hydrogenated nitrile butadiene rubber; a second dispersant comprising an alkanoic acid ammonium salt compound of a polymer containing acidic functional groups; and a solvent, wherein the hydrogenated nitrile butadiene rubber has a weight-average molecular weight of 10,000 g / mol to 20,000 g / mol.

[0017] The polydispersity index (PDI) of hydrogenated nitrile butadiene rubber can range from 2.0 to 4.0.

[0018] Hydrogenated nitrile butadiene rubber can also contain hydroxyl groups within the molecule.

[0019] The second dispersant may have an amine value of 30 mg KOH / g to 40 mg KOH / g and an acid value of 20 mg KOH / g to 30 mg KOH / g.

[0020] Based on 100 parts by weight of carbon nanotubes, the carbon nanotube dispersion may contain 10 to 50 parts by weight of a first dispersant.

[0021] Based on 100 parts by weight of carbon nanotubes, the carbon nanotube dispersion may contain 5 to 40 parts by weight of a second dispersant.

[0022] The solid content of the dispersion can be from 0.1 parts by weight to 10 parts by weight relative to the total weight of the carbon nanotube dispersion.

[0023] The particle size distribution D of the dispersed particles contained in the dispersion 90 It can range from 1 μm to 5 μm.

[0024] The initial viscosity of carbon nanotube dispersions, as measured at 25°C and 1 rpm, can range from 0.5 Pa·s to 10 Pa·s.

[0025] Another embodiment of the present invention provides a method for preparing a carbon nanotube dispersion, the method comprising the steps of: mixing carbon nanotubes, a first dispersant comprising hydrogenated nitrile rubber, a second dispersant comprising an alkanoic acid ammonium salt compound containing an acidic functional group, and a solvent to prepare a primary dispersion of carbon nanotubes, and dispersing the primary dispersion of carbon nanotubes to prepare a secondary dispersion of carbon nanotubes.

[0026] The weight-average molecular weight of hydrogenated nitrile butadiene rubber can be from 10,000 g / mol to 20,000 g / mol, and the polydispersity index (PDI) can be from 2.0 to 4.0.

[0027] Beneficial effects

[0028] The carbon nanotube dispersion according to the present invention comprises hydrogenated nitrile butadiene rubber with a weight-average molecular weight of 10,000 g / mol to 20,000 g / mol as a first dispersant, and comprises an alkanol ammonium salt compound of a polymer containing acidic functional groups as a second dispersant, and particularly satisfies that the polydispersity index (PDI) of the hydrogenated nitrile butadiene rubber is 2.0 to 4.0. Therefore, despite the use of carbon nanotubes with a large specific surface area, the carbon nanotube dispersion also has the characteristics of small viscosity change over time, relatively low initial viscosity, and small particle size of dispersed particles due to the uniform and effective dispersion of carbon nanotubes. Attached Figure Description

[0029] Figure 1 A graph illustrating the particle size distribution of dispersed particles in the dispersions of embodiments and comparative examples according to the present invention.

[0030] Figure 2 The infrared (IR) spectrum of a first dispersant contained in a dispersion according to an embodiment of the present invention is shown. Detailed Implementation

[0031] The embodiments of the invention will be described in more detail below. Prior to this, the terms or words used in this specification and claims should not be construed as limited to their ordinary or dictionary meanings, but should be interpreted in a meaning and concept consistent with the technical concept of the invention, based on the principle that the inventor can appropriately define the concepts of the terms to describe his invention in the best possible way. Therefore, it should be understood that the configurations described in the embodiments described in this specification are only the most preferred embodiments of the invention and do not represent all the technical concepts of the invention. Thus, various equivalents and modifications may exist at the time of filing this application.

[0032] As used herein, the term “substituted” means that a hydrogen atom bonded to a carbon atom of a compound is replaced by another substituent, and there are no restrictions on the position to be substituted, as long as the position is where the hydrogen atom is substituted (i.e., the position where the substituent can be substituted), and if two or more substituents are substituted, the two or more substituents can be the same as or different from each other.

[0033] Throughout this specification, when a portion is referred to as "containing" a certain component, unless otherwise specifically stated, this means that it may also contain other components, without excluding other components.

[0034] Throughout this specification, unless otherwise expressly stated, “%” means weight.

[0035] In this specification, "D" n "This refers to the average particle size, and specifically, the particle size at the n% point of the cumulative distribution of the number of particles based on particle size. That is, D..." 50 D is the particle size at the 50% point of the cumulative distribution of particle number based on particle size. 90 The particle size at the 90% point of the cumulative distribution of particle number based on particle size, and D 10 This refers to the particle size at the 10% point of the cumulative distribution of particle number based on particle size. Simultaneously, the average particle size can be measured using laser diffraction. Specifically, the target powder for measurement is dispersed in a dispersion medium and then introduced into a commercially available laser diffraction particle size measurement device (e.g., Microtrac S3500). The particle size distribution is calculated by measuring the differences in the diffraction pattern based on the particle size as the particles pass through the laser beam.

[0036] In this specification, "specific surface area" is measured by the Brunauer-Emmett-Teller analysis (BET) method, and specifically, it can be calculated by the amount of nitrogen adsorbed at liquid nitrogen temperature (77 K) using the BELSORP-mino II from BEL Japan.

[0037] carbon nanotube dispersions

[0038] The carbon nanotube dispersion according to the present invention comprises: carbon nanotubes; a first dispersant comprising hydrogenated nitrile butadiene rubber having a weight-average molecular weight of 10,000 g / mol to 20,000 g / mol; a second dispersant comprising an alkanoic acid ammonium salt compound of a polymer containing acidic functional groups; and a solvent. The components of the carbon nanotube dispersion of the present invention will be described in detail below.

[0039] (1) Carbon nanotubes

[0040] As used in this invention, the term "carbon nanotube" refers to a secondary structure formed by assembling carbon nanotube units into a bundle, either wholly or partially, wherein the carbon nanotube units have graphite sheets in the shape of cylinders with nanometer-sized diameters and possess sp... 2 Bonded structure. In this case, depending on the angle and structure of the graphite sheet being pressed, it can exhibit conductive or semiconductor properties. Based on the number of bonds forming the walls, carbon nanotube units can be classified into single-walled carbon nanotubes (SWCNTs), double-walled carbon nanotubes (DWCNTs), and multi-walled carbon nanotubes (MWCNTs).

[0041] Unless otherwise stated, the term "bundle" as used in this invention refers to a secondary shape in which a plurality of carbon nanotube units are arranged parallel to each other with their longitudinal axes in substantially the same orientation, or are twisted or entangled after arrangement. The term "non-bundle or entangled" refers to a form in which carbon nanotube units are entangled but do not have a specific shape such as bundle or rope.

[0042] Carbon nanotubes possess high electrical conductivity, but they are also highly cohesive due to van der Waals forces between them. If conductive materials aggregate, it may prevent the proper formation of conductive pathways within the electrode, and the amount of active material is relatively reduced due to the use of more conductive material to increase conductivity, potentially degrading electrode performance such as capacity. Therefore, it is difficult to commercialize carbon nanotubes as conductive materials.

[0043] The carbon nanotube dispersion according to the present invention comprises: a second dispersant comprising an alkanoic acid ammonium salt compound containing a polymer containing acidic functional groups; and a first dispersant comprising hydrogenated nitrile butadiene rubber having a weight-average molecular weight of 10,000 g / mol to 20,000 g / mol. Therefore, the initial viscosity of the carbon nanotube dispersion can be significantly reduced, the viscosity change over time can be suppressed, and the low particle size of the dispersed particles can be maintained at the same time, so that when applied to the electrode slurry of lithium secondary batteries, it can exhibit high conductivity due to the high conductivity of carbon nanotubes.

[0044] Therefore, when the carbon nanotube dispersion according to the invention is applied to a slurry for manufacturing electrodes, the carbon nanotubes are uniformly positioned between the active materials, such that even during the process of manufacturing electrodes by coating and drying the slurry and then pressing, the microspace between the electrode active materials can be maintained at a constant level. Furthermore, since the carbon nanotubes are uniformly distributed and do not agglomerate, conductive pathways can be sufficiently formed even with a small amount of carbon nanotubes.

[0045] The carbon nanotube dispersion according to one embodiment of the present invention may comprise, but is not limited to, any or more of single-walled carbon nanotubes, double-walled carbon nanotubes, and multi-walled carbon nanotubes as carbon nanotubes, and specifically may comprise single-walled carbon nanotubes. Since single-walled 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.

[0046] Meanwhile, the average diameter of the carbon nanotubes can be, for example, 0.6 nm to 10 nm, preferably 0.8 nm to 5 nm, and more preferably 0.8 nm to 3 nm, and can be 0.8 nm or greater, 0.9 nm or greater, 1.0 nm or greater, 1.1 nm or greater, 1.2 nm or greater, 1.3 nm or greater, 1.4 nm or greater, 1.5 nm or greater, 1.6 nm or greater, 1.7 nm or greater, 1.8 nm or greater, or 1.9 nm or greater, and can 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.

[0047] Furthermore, carbon nanotubes can have an average length of 0.5 μm to 20 μm, preferably 1 μm to 20 μm, more preferably 5 μm to 20 μm, and can have an average length of 5 μm or greater, 7 μm or greater, 9 μm or greater, 11 μm or greater, or 13 μm or greater, and 20 μm or less, 18 μm or less, 16 μm or less, or 14 μm or less. If the average diameter and average length of the carbon nanotubes meet the above ranges, they are effective in reducing the viscosity of the dispersion and improving storage stability, and can also achieve excellent cycling characteristics when used as an electrode active material. In this case, the average diameter of the carbon nanotubes can be measured by scanning electron microscopy of the carbon nanotube powder, and the average length of the carbon nanotubes can be measured by scanning electron microscopy of the carbon nanotube dispersion.

[0048] Based on the total weight of the carbon nanotube dispersion, carbon nanotubes can be included in amounts from 0.1 parts by weight to 10 parts by weight, and can be in quantities of 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 or more parts by weight, 2.3 or more parts by weight, 2.4 or more parts by weight, 2.5 or more parts by weight, 2.6 or more parts by weight, 2.7 or more parts by weight, 2.8 or more parts by weight, 2.9 or more parts by weight, 3.0 or more parts by weight, 3.1 or more parts by weight, 3.2 or more parts by weight, 3.3 or more parts by weight, 3.4 or more parts by weight, 3.5 or more parts by weight, 3.6 or more parts by weight, 3.7 or more parts by weight, 3.8 or more parts by weight, 3.9 or more parts by weight, 4.0 or more parts by weight, 4.1 or more parts by weight, 4.2 or more parts by weight, 4.3 or more parts by weight, 4.4 or more parts by weight, 4.5 or more parts by weight, 4.6 or more parts by weight It may be contained in amounts of 4.7 or more, 4.8 or more, 4.9 or more, or 5.0 or more, and may also be contained in amounts of 10.0 or less, 9.9 or less, 9.8 or less, 9.7 or less, 9.6 or less, 9.5 or less, 9.4 or less, 9.3 or less, 9.2 or less, 9.1 or less, 9.0 or less, 8.9 or less, 8.8 or less, 8.7 or less, 8.6 or less, 8.5 or less, 8.4 or less, 8.3 or less, 8.2 or less, 8... 0.1 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, 7.3 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.The amounts included are 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 carbon nanotube content meets the above ranges, the effect of improving the viscosity of the dispersion and the effect of improving the cycle characteristics of secondary batteries manufactured by the carbon nanotube dispersion are excellent.

[0049] The BET surface area of ​​carbon nanotubes can be 150 m². 2 / g or greater, preferably 150 m 2 / g to 2,000 m 2 / g, and can be 150 m 2 / g or greater, 200 m 2 / g or greater, 250 m 2 / g or greater, 300 m 2 / g or greater, 350 m 2 / g or greater, 400 m 2 / g or greater, 450 m 2 / g or greater, 500 m 2 / g or greater, 550 m 2 / g or greater, 600 m 2 / g or greater, 650 m 2 / g or greater, 700 m 2 / g or greater, 750 m 2 / g or greater, 800 m 2 / g or greater, 850 m 2 / g or greater, 900 m 2 / g or greater, 950 m 2 / g or greater, 1000 m 2 / g or greater, or 1050 m 2 / g or greater, and can be 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. If carbon nanotubes with high BET surface area as described above are used, the formation of a conductive network between the electrode active materials is excellent, which makes it possible to improve the cycle characteristics of secondary batteries manufactured by carbon nanotube dispersions.

[0050] The carbon nanotube dispersion according to one embodiment of the invention can have a relatively high carbon nanotube content because the carbon nanotubes can be uniformly dispersed. If a carbon nanotube dispersion with a low carbon nanotube content is used to manufacture an electrode slurry, the thickness (wet thickness) of the electrode slurry before application and drying becomes thicker due to the reduced solids content, and the pressing ratio measured after subsequent drying and rolling processes becomes higher, resulting in a larger difference in the thickness ratio before and after drying and rolling. In this way, if the pressing ratio becomes high, the components inside the slurry (including the positive electrode active material) may be damaged during the process, which may lead to problems with reduced battery performance.

[0051] (2) First dispersant and second dispersant

[0052] The carbon nanotube dispersion according to the present invention comprises: a second dispersant comprising an alkanoic acid ammonium salt compound containing a polymer containing acidic functional groups; and a first dispersant comprising hydrogenated nitrile butadiene rubber having a weight-average molecular weight of 10,000 g / mol to 20,000 g / mol, to improve the dispersibility of carbon nanotubes.

[0053] In the carbon nanotube dispersion, the first and second dispersants are used to increase the dispersibility of the carbon nanotubes, so that the carbon nanotubes can be uniformly dispersed in the dispersion without agglomeration, and in particular, to suppress the viscosity of the carbon nanotube dispersion over time and exhibit the effect of reducing the average particle size of the dispersed particles.

[0054] In a carbon nanotube dispersion according to one embodiment of the present invention, hydrogenated nitrile rubber may contain repeating units represented by the following formulas 1 to 3.

[0055] [Formula 1]

[0056]

[0057] [Equation 2]

[0058]

[0059] [Formula 3]

[0060]

[0061] In equations 1 to 3,

[0062] * indicates a connecting part.

[0063] In one embodiment of the invention, the hydrogenated nitrile rubber may comprise repeating units represented by Formula 1 and repeating units represented by Formula 2 in a molar ratio of 82:18 to 50:50.

[0064] Furthermore, in one embodiment of the invention, hydrogenated nitrile butadiene rubber may contain repeating units represented by Formula 3 at a rate of 0.1 mol% to 2.0 mol% relative to the total molar of repeating units represented by Formula 1.

[0065] In one embodiment of the invention, the weight-average molecular weight (Mw) of the hydrogenated nitrile butadiene rubber can be from 10,000 g / mol to 20,000 g / mol, and specifically, it can be 10,000 g / mol or greater, 11,000 g / mol or greater, 12,000 g / mol or greater, 13,000 g / mol or greater, 14,000 g / mol or greater, or 15,000 g / mol or greater, and can 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] Furthermore, in the case of hydrogenated nitrile butadiene rubber according to one embodiment of the present invention, it may have the weight-average molecular weight distribution as described above, and at the same time, the polydispersity index (PDI) may be between 2.0 and 4.0, and for example, the polydispersity index may be 2.0 or greater, 2.1 or greater, 2.2 or greater, 2.3 or greater, 2.4 or greater, 2.5 or greater, and may be 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 between 2.5 and 3.0.

[0067] The polydispersity index is a measure of the degree of difference in molecular weight among polymer molecules within a particular polymer, 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) used to calculate the polydispersity index of the hydrogenated nitrile butadiene rubber according to the present invention can be measured by the molecular weight converted from polystyrene analyzed by gel permeation chromatography (GPC).

[0068] As described above, the hydrogenated nitrile butadiene rubber (NBR) with the first dispersant according to one embodiment of the present invention exhibits a low weight-average molecular weight (Mw) distribution of 10,000 g / mol to 20,000 g / mol, thus maintaining a low viscosity of the dispersion and exhibiting the effect that the viscosity does not change significantly over time. Furthermore, the hydrogenated NBR with the first dispersant according to one embodiment of the present invention can exhibit the aforementioned weight-average molecular weight distribution and simultaneously has a low polydispersity index of 2.0 to 4.0. Therefore, the hydrogenated NBR exhibiting the narrow molecular weight distribution described above can uniformly surround carbon nanotubes, thereby also imparting the property of reducing the average particle size of the dispersed carbon nanotube particles.

[0069] Therefore, the particle size distribution D of the dispersed particles contained in the dispersion according to one embodiment of the present invention 90 It can be from 1 μm to 5 μm, and for example, it can be 1 μm or larger, 1.1 μm or larger, 1.2 μm or larger, 1.3 μm or larger, 1.4 μm or larger, 1.5 μm or larger, 1.6 μm or larger, 1.7 μm or larger, 1.8 μm or larger, 1.9 μm or larger, 2 μm or larger, 2.1 μm or larger, 2.2 μm or larger, 2.3 μm or larger, 2.4 μm or larger, 2.5 μm or larger, 2.6 μm or larger, 2.7 μm or larger, 2.8 μm or larger, 2.9 μm or larger, or 3 μm or larger, and can be 5 μm or smaller, 4.9 μm or smaller, 4.8 μm or smaller, 4.7 μm or smaller, 4.6 μm or smaller, 4.5 μm or smaller, 4.4 μm or smaller, 4.3 μm or smaller, 4.2 μm or smaller. The particle size distribution can be maintained at a low level of 2.5 μm to 4.0 μm, or smaller, 4 μm or smaller, 3.9 μm or smaller, 3.8 μm or smaller, 3.7 μm or smaller, 3.6 μm or smaller, 3.5 μm or smaller, 3.4 μm or smaller, 3.3 μm or smaller, 3.2 μm or smaller, or 3.1 μm or smaller, and preferably, the particle size distribution can be maintained at a low level of 2.5 μm to 4.0 μm.

[0070] In one embodiment of the present invention, hydrogenated nitrile rubber may also contain hydroxyl groups (-OH) in the molecule.

[0071] Hydrogenated nitrile butadiene rubber is a rubber obtained by producing a nitrile butadiene copolymer via low-temperature emulsion polymerization of acrylonitrile and butadiene, followed by hydrogen addition 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 reactants (acrylonitrile and butadiene) and the polymerization reaction time, nitrile butadiene copolymers with various weight-average molecular weights can be produced.

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

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

[0074] These properties can be achieved by using hydrogenated nitrile butadiene rubber with a low weight-average molecular weight (Mw) distribution of 10,000 g / mol to 20,000 g / mol and a low polydispersity index of 2.0 to 4.0 as the first dispersant for carbon nanotube dispersions, and by subjecting hydrogenated nitrile butadiene rubber with a relatively high weight-average molecular weight to a decomposition reaction (ozone decomposition) through the addition of ozone, thereby giving hydrogenated nitrile butadiene rubber a low weight-average molecular weight and a low polydispersity index.

[0075] Although not limited to a specific theory, the decomposition reaction induced by ozone in hydrogenated nitrile butadiene rubber (NBR) breaks the residual carbon-carbon double bonds in the hydrogenated NBR copolymer, thereby producing a polymer with a relatively high weight-average molecular weight (Mw) distribution of 10,000 g / mol to 20,000 g / mol and a low polydispersity index of 2.0 to 4.0. Furthermore, since the decomposition reaction induced by ozone breaks the residual carbon-carbon double bonds after the hydrogenation of the NBR, the degree of hydrogenation of the hydrogenated NBR (which is a product of the ozone-induced decomposition reaction) with a low weight-average molecular weight can be further increased.

[0076] In one embodiment of the invention, as described above, by adding ozone to hydrogenated nitrile butadiene rubber, hydroxyl groups can be introduced at the carbon-carbon double bond breaking sites in the products of the decomposition reaction, and this result can be detected, for example, by infrared spectroscopy (IR) measurements of the products of the decomposition reaction with added ozone at 3,200 cm⁻¹. -1 Up to 3,600 cm -1The broad peak at that location is used for confirmation.

[0077] In one embodiment of the invention, based on 100 parts by weight of carbon nanotubes in the carbon nanotube dispersion, the first dispersant may be included in an amount of 10 to 50 parts by weight, and specifically, may be in amounts 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. It may be included in quantities of 28 or more, 29 or more, or 30 or more, and may also be included in quantities of 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, or 31 or less.

[0078] If the first dispersant is included in an amount of less than 10 parts by weight of carbon nanotubes in a carbon nanotube dispersion (100 parts by weight), insufficient dispersant content may lead to inadequate dispersion, resulting in failure to maintain a low viscosity and an increase in viscosity over time. If the first dispersant exceeds 50 parts by weight, excessive content of the first dispersant may cause agglomeration of solids in the dispersion, leading to an increase in viscosity.

[0079] Furthermore, in order to address the problem that the viscosity of a carbon nanotube dispersion increases with increasing carbon nanotube content in a carbon nanotube dispersion containing only a first dispersant, a carbon nanotube dispersion according to an embodiment of the present invention, in addition to the first dispersant, also contains a second dispersant: an alkanol ammonium salt compound comprising a polymer containing acidic functional groups. Therefore, compared with conventional carbon nanotube dispersions using only a dispersant, it has excellent dispersibility, and thus can exhibit the effect of less particle agglomeration and lower sedimentation rate in the slurry composition.

[0080] The weight-average molecular weight of the alkanoic ammonium salt compounds of polymers containing acidic functional groups can be from 1,000 g / mol to 3,000 g / mol, and specifically, the weight-average molecular weight can be 1,000 g / mol or greater, 1,100 g / mol or greater, 1,200 g / mol or greater, 1,300 g / mol or greater, 1,400 g / mol or greater, 1,500 g / mol or greater, 1,600 g / mol or greater, 1,700 g / mol or greater, 1,800 g / mol or greater, 1,900 g / mol or greater, or 2,000 g / mol or greater, and can be 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 or less, or less than 3,000 g / mol, 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, or less than 2,400 g / mol. g / mol or less, 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 alkanoic ammonium salt compound of the polymer containing acidic functional groups can be from 30 mg KOH / g to 40 mg KOH / g, and specifically can be 30 mg KOH / g or greater, 31 mg KOH / g or greater, 32 mg KOH / g or greater, 33 mg KOH / g or greater, 34 mg KOH / g or greater, or 35 mg KOH / g or greater, and can 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] Furthermore, the acid value of the alkanoic ammonium salt compound of the polymer containing acidic functional groups can be from 20 mg KOH / g to 30 mg KOH / g, and specifically can be 20 mg KOH / g or greater, 21 mg KOH / g or greater, 22 mg KOH / g or greater, 23 mg KOH / g or greater, 24 mg KOH / g or greater, or 25 mg KOH / g or greater, and can be 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 preferred to use an alkanoic ammonium salt compound containing an acidic functional group of an amine value and an acid value within the above-mentioned range.

[0084] In one embodiment of the invention, based on 100 parts by weight of carbon nanotubes in the carbon nanotube dispersion, the second dispersant may be included in an amount of 5 to 40 parts by weight, and specifically may be in the form of 5 or more parts by weight, 6 or more parts by weight, 7 or more parts by weight, 8 or more parts by weight, 9 or more parts by weight, 10 or more parts by weight, 11 or more parts by weight, 12 or more parts by weight, 13 or more parts by weight, 14 or more parts by weight, 15 or more parts by weight, 16 or more parts by weight, 17 or more parts by weight, 18 or more parts by weight, 19 or more parts by weight, 20 or more parts by weight, or... More, 21 or more, or 22 or more parts by weight are included, and may be included in amounts of 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, 29 or less, 28 or less, 27 or less, 26 or less, 25 or less, 24 or less, or 23 or less.

[0085] If, based on 100 parts by weight of carbon nanotubes, the content of the second dispersant is less than 5 parts by weight, no effective dispersion effect caused by the first and second dispersants will occur, and as a result, the viscosity of the dispersion may not be able to remain low and may increase over time. If the content of the second dispersant exceeds 40 parts by weight, agglomeration of solids in the dispersion may occur due to the excessive content of the second dispersant, resulting in a high viscosity in the dispersion.

[0086] In one embodiment of the invention, the solid content of the dispersion can be from 0.1 parts by weight to 10 parts by weight relative to the total weight of the carbon nanotube dispersion, and for example, it can 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, 7.4 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, solid content can refer to the total content of carbon nanotubes, the first dispersant, and the second dispersant contained in the carbon nanotube dispersion.

[0088] If the solid content of the carbon nanotube dispersion meets 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 kept low.

[0089] (3) Solvent

[0090] According to one embodiment of the invention, the solvent of the carbon nanotube dispersion is a dispersion medium for dispersing carbon nanotubes, a first dispersant, and a second dispersant, and is used to supply the carbon nanotube dispersion by pre-dispersing the carbon nanotubes in powder form to prevent them from immediately agglomerating when used to prepare an electrode slurry composition.

[0091] The solvent is a solvent that can dissolve or disperse the carbon nanotubes, the first dispersant, and the second dispersant to a certain level or higher. The solvent can be an organic solvent containing one or more heteroatoms selected from, for example, nitrogen (N) and oxygen (O) atoms having non-shared electron pairs.

[0092] Specifically, the dispersion medium may comprise: an amide-based polar organic solvent, such as dimethylformamide (DMF), diethylformamide, dimethylacetamide (DMAc), or N-methylpyrrolidone (NMP); alcohols, such as methanol, ethanol, 1-propanol, 2-propanol (isopropanol), 1-butanol (n-butanol), 2-methyl-1-propanol (isobutanol), 2-butanol (sec-butanol), 1-methyl-2-propanol (tert-butanol), pentanol, hexanol, heptanol, or octanol; and diols, such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, 1,3-propanediol, 1,3-butanediol ... 5-Pentanediol or hexanediol; polyols, such as glycerol, 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; esters, such as ethyl acetate, γ-butyrolactone, and ε-propiolactone, etc., and mixtures of one, two, or more of these may be used.

[0093] As described above, by enabling the first and second dispersants to uniformly disperse carbon nanotubes in a solvent, the carbon nanotube dispersion according to one embodiment of the present invention can reduce the average particle size distribution of the dispersed particles (e.g., a complex of carbon nanotubes and various dispersants) contained in the dispersion.

[0094] Carbon nanotube dispersions can have initial viscosities ranging from 0.5 Pa·s to 10 Pa·s, as measured using a viscometer (manufactured by TOKISANGYO, viscometer TV-25, rotor code 01) at 25°C and 1 rpm. For example, they can have initial viscosities of 0.5 Pa·s or greater, 0.6 Pa·s or greater, 0.8 Pa·s or greater, 1 Pa·s or greater, 1.1 Pa·s or greater, 1.5 Pa·s or greater, 2 Pa·s or greater, 2.5 Pa·s or greater, 3 Pa·s or greater, 3.5 Pa·s or greater, 4 Pa·s or greater, 4.5 Pa·s or greater, or 5 Pa·s or greater. They can also have initial viscosities of 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, 7 Pa·s or less, 6.5 Pa·s or less, etc. Initial viscosity of Pa·s or less, 6 Pa·s, or 5.5 Pa·s or less.

[0095] More specifically, when the solid content of the dispersion is 0.1 parts by weight to 3.5 parts by weight relative to the total weight of the dispersion, the carbon nanotube dispersion can have an initial viscosity of 0.5 Pa·s to 1.0 Pa·s, as measured using a viscometer (manufactured by TOKISANGYO, viscometer TV-25, rotor code 01) at 25°C and 1 rpm; and when the solid content of the dispersion is 3.6 parts by weight to 10 parts by weight relative to the total weight of the dispersion, the carbon nanotube dispersion can have an initial viscosity of 1.1 Pa·s to 10 Pa·s.

[0096] If the carbon nanotube dispersion has an initial viscosity within the above range, it can be used to prepare electrode slurries more smoothly, and the electrode slurry containing the carbon nanotube dispersion can have a suitable viscosity for forming the electrode.

[0097] Methods for preparing carbon nanotube dispersions

[0098] The method for preparing carbon nanotube dispersions will be described below.

[0099] The method for preparing a carbon nanotube dispersion according to the present invention comprises the following steps: (1) mixing carbon nanotubes, a first dispersant comprising hydrogenated nitrile rubber, a second dispersant comprising an alkanoic acid ammonium salt compound containing an acidic functional group, and a solvent to prepare a primary dispersion of carbon nanotubes; and (2) dispersing the primary dispersion of carbon nanotubes to prepare a secondary dispersion of carbon nanotubes. Therefore, the carbon nanotube dispersion according to the present invention can refer to a secondary dispersion of carbon nanotubes prepared by the above-described preparation method.

[0100] In step (1), carbon nanotubes, a first dispersant comprising hydrogenated nitrile butadiene rubber, a second dispersant comprising an alkanoic acid ammonium salt compound containing an acidic functional group, and a solvent are mixed to prepare a primary dispersion of carbon nanotubes. The step of preparing the primary dispersion of carbon nanotubes is carried out using a wet process to uniformly mix the components.

[0101] In one embodiment of the present invention, the weight-average molecular weight of the hydrogenated nitrile rubber can be from 10,000 g / mol to 20,000 g / mol, and the polydispersity index (PDI) can be from 2.0 to 4.0.

[0102] The mixing of the primary dispersion used to prepare carbon nanotubes can be carried out using conventional mixing methods, specifically using mixing devices (such as homogenizers, bead mills, ball mills, basket mills, grinders, general-purpose stirrers, transparent mixers, or TK mixers), and can include a step of stirring at 300 rpm to 5,000 rpm for 30 minutes to 3 hours.

[0103] Furthermore, when mixing to prepare a primary dispersion of carbon nanotubes, cavitation dispersion treatment can be performed to improve the miscibility of carbon nanotubes and the dispersion medium, or the dispersibility of carbon nanotubes in the dispersion medium. Cavitation dispersion is a dispersion method that utilizes the shock waves generated by the collapse of vacuum bubbles formed in water when high energy is applied to the liquid. This method allows carbon nanotubes to be dispersed without damaging their properties. Specifically, cavitation dispersion can be performed through ultrasonic treatment, jet milling, or shear dispersion.

[0104] The preparation of primary dispersions of carbon nanotubes can be carried out at temperatures in which the physical properties of the mixture (including viscosity) are not altered by solvent evaporation. For example, it can be carried out at 50°C or lower, more specifically, at temperatures between 5°C and 50°C.

[0105] In step (2), a secondary dispersion of carbon nanotubes is prepared by dispersing the primary dispersion of carbon nanotubes.

[0106] The process for preparing the secondary dispersion of carbon nanotubes can be carried out by methods such as a ball mill, a bead mill, a disc mill, a basket mill, or a high-pressure homogenizer, and more specifically, it can be carried out by a grinding method using a disc mill or a high-pressure homogenizer.

[0107] The grinding method using a high-pressure homogenizer is achieved, for example, by pressurizing the mixture with a plunger pump of the high-pressure homogenizer and forcing it through the gap of a homogenizing valve, thus generating forces such as cavitation, shearing, impact and explosion when the mixture passes through the gap.

[0108] The grinding process can be carried out according to the dispersion degree of the carbon nanotube dispersion, and specifically, it can be carried out for 30 minutes to 120 minutes, more specifically, 60 minutes to 90 minutes.

[0109] The particle size distribution D of the secondary dispersion of carbon nanotubes of the present invention prepared by the above method 90 may be 1 μm to 5 μm.

[0110] Electrode slurry composition for lithium secondary batteries

[0111] Furthermore, the present invention provides an electrode slurry composition for lithium secondary batteries comprising a carbon nanotube dispersion and an electrode active material.

[0112] The electrode slurry composition for lithium secondary batteries may be a slurry composition for a positive electrode or a slurry composition for a negative electrode, and specifically, it may be a slurry composition for a positive electrode.

[0113] The electrode slurry composition for lithium secondary batteries may comprise the carbon nanotube dispersion, a positive electrode active material or a negative electrode active material serving as the electrode active material, a binder, a solvent and / or other optional additives.

[0114] As the positive electrode active material, any positive electrode active material well known in the art can be used without limitation. For example, lithium cobalt-based oxides, lithium nickel-based oxides, lithium manganese-based oxides, lithium iron phosphate, lithium nickel manganese cobalt-based oxides, or combinations thereof can be used. Specifically, the positive electrode active material may be LiCoO2, LiNiO2, LiMn2O4, LiCoPO4, LiFePO4 and LiNi a Mn b Co c O2 (wherein 0<a, b, c<1), but is not limited thereto.

[0115] The negative electrode active material may include one or more of the following: natural graphite, artificial graphite, carbonaceous materials; lithium-containing titanium oxide (LTO); metals (Me) such as Si, Sn, Li, Zn, Mg, Cd, Ce, Ni, or Fe; alloys composed of the above metals (Me); oxides of the above metals (MeO). x ); and complexes of the above metal (Me) and carbon. Based on the total weight of solids other than solvent in the negative electrode slurry, the negative electrode active material may be included in an amount of 60% to 98% by weight, more preferably 70% to 98% by weight.

[0116] The binder is a component that facilitates the bonding of the active and conductive materials, as well as the bonding with the current collector, and is typically added in an amount of 1% to 30% by weight based on the total weight of the mixture containing the electrode active materials. Examples of such binders may include polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluororubber, and various copolymers.

[0117] Solvents may include organic solvents such as N-methylpyrrolidone (NMP), dimethylformamide (DMF), acetone, dimethylacetamide, etc., or water, and these solvents may be used alone or in combination of both or more thereof. Considering the coating thickness and preparation yield of the slurry, the amount of solvent used is sufficient as long as it can dissolve and disperse the electrode active material, binder, and conductive material.

[0118] Viscosity modifiers can be carboxymethyl cellulose, polyacrylic acid, etc., and by adding viscosity modifiers, the viscosity of electrode slurry can be adjusted to facilitate the preparation of electrode slurry and its application to electrode current collectors.

[0119] Fillers may be used as components to suppress electrode expansion, and there are no particular limitations on the fillers, as long as they are fibrous materials that do not cause chemical changes in the battery, such as olefin polymers such as polyethylene and polypropylene; and fibrous materials such as glass fibers and carbon fibers.

[0120] If the electrode slurry composition is a positive electrode slurry composition for forming a positive electrode, the positive electrode slurry composition can be applied to a positive electrode current collector, followed by drying and pressing to manufacture the positive electrode. Alternatively, the positive electrode can be manufactured by casting the positive electrode slurry onto a separate support, and then laminating a film obtained by peeling the support onto the positive electrode current collector.

[0121] The thickness of the positive electrode active material layer formed by the positive electrode slurry can be varied depending on the loading amount and loading speed of the positive electrode slurry applied.

[0122] The thickness of the positive electrode current collector typically ranges from 3 μm to 500 μm. There are no particular limitations on the positive electrode current collector, as long as it has high conductivity and does not cause chemical changes in the battery. For example, stainless steel; aluminum; nickel; titanium; sintered carbon; or aluminum or stainless steel with a surface treated with carbon, nickel, titanium, silver, etc., can be used. Furthermore, the positive electrode current collector can have minute irregularities formed on its surface to enhance its bonding with the positive electrode active material, and it can be formed in various forms such as films, sheets, foils, meshes, porous bodies, foams, nonwoven fabrics, etc.

[0123] If the electrode slurry composition is a negative electrode slurry composition for forming a negative electrode, the negative electrode can be manufactured by applying the negative electrode slurry composition onto a negative electrode current collector, followed by drying and pressing it. Alternatively, the negative electrode can be manufactured by casting the negative electrode slurry onto a separate support, and then laminating a film obtained by peeling the support onto the negative electrode current collector.

[0124] The thickness of the negative electrode active material layer formed by the negative electrode slurry can be varied depending on the loading amount and loading speed of the negative electrode slurry.

[0125] The thickness of the negative electrode current collector typically ranges from 3 μm to 500 μm. There are no particular limitations on the negative electrode current collector, as long as it has high conductivity and does not cause chemical changes in the battery. For example, copper; stainless steel; aluminum; nickel; titanium; sintered carbon; or copper or stainless steel with a surface treated with carbon, nickel, titanium, silver, etc.; or aluminum-cadmium alloys can be used. Furthermore, similar to the positive electrode current collector, the negative electrode current collector can have minute irregularities formed on its surface to enhance the bonding force with the negative electrode active material, and can be formed in various forms such as films, sheets, foils, meshes, porous bodies, foams, nonwoven fabrics, etc.

[0126] Lithium secondary batteries

[0127] A lithium secondary battery includes a positive electrode, a negative electrode, a separator disposed between the positive and negative electrodes, and an electrolyte solution. Since the positive and negative electrodes are the same as those described above, detailed descriptions are omitted.

[0128] The separator separates the negative and positive electrodes and provides a channel for lithium-ion movement. The separator can be used without any particular limitations, as long as it is typically used as a separator in a lithium secondary battery, and is particularly preferably characterized by low resistance to ion movement in the electrolyte and excellent electrolyte solution impregnation capability. Specifically, porous polymer membranes can be used, such as porous polymer membranes made from polyolefin-based polymers such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, ethylene / methacrylate copolymers, etc., or laminated structures of two or more layers thereof. Alternatively, conventional porous nonwoven fabrics can be used, such as nonwoven fabrics made from high-melting-point glass fibers, polyethylene terephthalate fibers, etc. Furthermore, coated separators containing ceramic components or polymer materials can be used to ensure heat resistance or mechanical strength, and the separator can be selectively used in single-layer or multi-layer structures.

[0129] Electrolytes include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used to manufacture lithium secondary batteries. Specifically, the electrolyte may contain organic solvents and lithium salts.

[0130] Organic solvents can be used without any particular restrictions, as long as they can serve as a medium through which the ions involved in the electrochemical reactions of the battery can move. Specifically, organic solvents can be ester-based solvents, such as methyl acetate, ethyl acetate, γ-butyrolactone, or ε-caprolactone; ether-based solvents, such as dibutyl ether or tetrahydrofuran; ketone-based solvents, such as cyclohexanone; aromatic hydrocarbon-based solvents, such as benzene or fluorobenzene; carbonate-based solvents, such as dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol-based solvents, such as ethanol or isopropanol; nitriles, such as R-CN (where R is a C2 to C20 linear, branched, or cyclic hydrocarbon group and may contain a double bond, aromatic ring, or ether bond); amides, such as dimethylformamide; dioxolane, such as 1,3-dioxolane; or sulfolane. Among these, a carbonate-based solvent is preferred, and a mixture of cyclic carbonates (e.g., ethylene carbonate or propylene carbonate, etc.) with high ionic conductivity and high dielectric constant, which can improve the charge / discharge performance of the battery, and a compound based on linear carbonates (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate, etc.) with low viscosity is even more preferred. In this case, when the cyclic carbonate and linear carbonate are mixed in a volume ratio of about 1:1 to about 1:9, the performance of the electrolyte can be excellent.

[0131] Lithium salts can be used without particular restrictions, as long as they are compounds capable of providing lithium ions for use in lithium secondary batteries. Specifically, lithium salts can be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2, etc. The concentration of the lithium salt is preferably used in the range of 0.1 M to 2.0 M. If the concentration of the lithium salt is within this range, the electrolyte exhibits excellent electrolyte performance due to its suitable conductivity and viscosity, and lithium ions can move efficiently.

[0132] In addition to the electrolyte components mentioned above, the electrolyte may contain one or more additives for the purpose of improving battery life characteristics, suppressing battery capacity reduction, and improving battery discharge capacity. These additives may include, for example, compounds based on alkyl halogenated carbonates (e.g., ethylene difluorocarbonate), pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glycol dimethyl ether, triammonium hexaphosphate, nitrobenzene derivatives, sulfur, quinone imine dyes, and N-substituted compounds. Alzolidinediones, N,N-substituted imidazolidinediols, ethylene glycol dialkyl ethers, ammonium salts, pyrroles, 2-methoxyethanol, or aluminum trichloride. In this case, the additive may be included in an amount from 0.1% to 5% by weight, based on the total weight of the electrolyte.

[0133] Lithium-ion secondary batteries, including those using electrodes manufactured using the carbon nanotube dispersion according to the invention, specifically those including a positive electrode manufactured using the carbon nanotube dispersion, can stably exhibit excellent discharge capacity and output characteristics because the carbon nanotubes are uniformly dispersed within the positive electrode, and their content can be reduced compared to cases containing conductive materials such as conventional carbon black. As a result, they can be usefully used in portable devices such as cell phones, laptops, and digital cameras, as well as electric vehicles such as hybrid electric vehicles (HEVs).

[0134] Therefore, according to another embodiment of the present invention, it can provide a lithium secondary battery, a battery module including the lithium secondary battery as a unit battery, and a battery pack including the same.

[0135] Battery modules or battery packs can be used as a power source for one or more of the following medium-sized and large devices: power tools; electric vehicles, including electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); or energy storage systems.

[0136] Invention Embodiments

[0137] Specific embodiments of the invention are presented below. However, these embodiments are merely illustrative or explanatory of the invention and are not intended to limit the invention. Furthermore, matters not described herein are technically sufficient to be inferred by those skilled in the art, and therefore, their description has been omitted.

[0138] Example

[0139] Example 1

[0140] (1) Add 5 parts by weight of a material with a specific surface area of ​​250 m² to the homogenizer. 2 / g of multi-walled carbon nanotubes (MWCNT, BT1001M, manufactured by LG Chemical), 1 part by weight of hydrogenated nitrile butadiene rubber (HNBR) (Mw 19,000, PDI 2.8) as the first dispersant, 0.5 parts by weight of an alkanol ammonium salt compound containing an acidic functional group polymer (BYK Corporation, product name: BYK-ET 3001, amine value of 37 mg KOH / g, acid value of 29 mg KOH / g) as the second dispersant, and 93.5 parts by weight of N-methyl-2-pyrrolidone (NMP) as the solvent, such that the solid content is 5 parts by weight relative to the total weight of the primary dispersion of carbon nanotubes, and then the mixture is stirred and mixed at 5,000 rpm for 1 hour to prepare the primary dispersion of carbon nanotubes. In this case, the first dispersant used is a dispersant obtained by a decomposition reaction (ozone decomposition) caused by adding ozone to hydrogenated nitrile rubber (Mw270,000, hydrogenation degree 84.5%) for 3 hours.

[0141] The weight-average molecular weight of hydrogenated nitrile butadiene rubber (NBR) as the first dispersant was measured using gel permeation chromatography (GPC) under the following conditions. DMF was used as the solvent when measuring molecular weight. In the dispersed state, the molecular weight of the supernatant could be measured by centrifugation, and in the electrode and cell states, the molecular weight could be measured by scraping the electrode and extracting the partially hydrogenated NBR with THF.

[0142] - Equipment: Alliance e2695 from Waters

[0143] – Detector: Waters 2414 RID

[0144] - Column: Using 1 PKgel MiniMIX-B

[0145] - Solvent: THF (stabilized)

[0146] - Column temperature: 40℃

[0147] - Flow rate: 0.3 ml / min

[0148] - Sample concentration: 1 mg / ml, 20 μl injection

[0149] - Standard samples: Polystyrene (Mp: 4230000, 1270000, 327000, 113300, 31420, 9600, 3790, 580)

[0150] The analytical procedure used OmmiSEC from Malvern, and obtained the weight-average molecular weight (Mw) and number-average molecular weight (Mn) via GPC, and calculated the molecular weight distribution (PDI) from the weight-average molecular weight / number-average molecular weight (Mw / Mn).

[0151] (2) The primary dispersion of carbon nanotubes was uniformly dispersed five times at a pressure of 20,000 psi using a high-pressure disperser (PICOMAX, manufactured by Micronox) to prepare the secondary dispersion of carbon nanotubes.

[0152] Example 2

[0153] Carbon nanotube dispersions were prepared in the same manner as in Example 1, except that hydrogenated nitrile butadiene rubber (HNBR) (Mw 12,000, PDI 2.7) was used as the first dispersant.

[0154] Example 3

[0155] The carbon nanotube dispersion was prepared in the same manner as in Example 1, except that 3.3 parts by weight of carbon nanotubes, 0.66 parts by weight of hydrogenated nitrile butadiene rubber (HNBR) (Mw 19,000, PDI 2.8) as the first dispersant and 0.33 parts by weight of the second dispersant were used, so that the solid content was 3.3 parts by weight relative to the total weight of the primary dispersion of carbon nanotubes.

[0156] Example 4

[0157] The carbon nanotube dispersion was prepared in the same manner as in Example 1, except that 3.3 parts by weight of carbon nanotubes, 0.66 parts by weight of hydrogenated nitrile butadiene rubber (HNBR) (Mw 12,000, PDI 2.7) as the first dispersant and 0.33 parts by weight of the second dispersant were used, such that the solid content was 3.3 parts by weight relative to the total weight of the primary dispersion of carbon nanotubes.

[0158] Example 5

[0159] The carbon nanotube dispersion was prepared in the same manner as in Example 1, except that 3.3 parts by weight of carbon nanotubes, 0.66 parts by weight of hydrogenated 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, such that the solid content was 3.3 parts by weight relative to the total weight of the primary dispersion of carbon nanotubes.

[0160] Example 6

[0161] The carbon nanotube dispersion was prepared in the same manner as in Example 1, except that 3.3 parts by weight of carbon nanotubes, 0.66 parts by weight of hydrogenated 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, such that the solid content was 3.3 parts by weight relative to the total weight of the primary dispersion of carbon nanotubes.

[0162] Example 7

[0163] The carbon nanotube dispersion was prepared in the same manner as in Example 1, except that 3.3 parts by weight of carbon nanotubes, 0.66 parts by weight of hydrogenated nitrile butadiene rubber (HNBR) (Mw 13,000, PDI 2.8) as the first dispersant and 0.33 parts by weight of the second dispersant were used, so that the solid content was 3.3 parts by weight relative to the total weight of the primary dispersion of carbon nanotubes.

[0164] Comparative Example 1

[0165] Carbon nanotube dispersions were prepared in the same manner as in Example 1, except that hydrogenated nitrile butadiene rubber (HNBR) (Mw 19,000, PDI 4.3) was used as the first dispersant.

[0166] Comparative Example 2

[0167] Carbon nanotube dispersions were prepared in the same manner as in Example 1, except that hydrogenated nitrile butadiene rubber (HNBR) (Mw 19,000, PDI 4.6) was used as the first dispersant.

[0168] Comparative Example 3

[0169] Carbon nanotube dispersions were prepared in the same manner as in Example 1, except that hydrogenated nitrile butadiene rubber (HNBR) (Mw 8,200, PDI 1.9) was used as the first dispersant.

[0170] Comparative Example 4

[0171] The carbon nanotube dispersion was prepared in the same manner as in Example 1, except that 3.3 parts by weight of carbon nanotubes, 0.66 parts by weight of hydrogenated 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, such that the solid content was 3.3 parts by weight relative to the total weight of the primary dispersion of carbon nanotubes.

[0172] Comparative Example 5

[0173] The carbon nanotube dispersion was prepared in the same manner as in Example 1, except that 3.3 parts by weight of carbon nanotubes, 0.66 parts by weight of hydrogenated nitrile butadiene rubber (HNBR) (Mw 26,000, PDI 4.8) as the first dispersant and 0.33 parts by weight of the second dispersant were used, so that the solid content was 3.3 parts by weight relative to the total weight of the primary dispersion of carbon nanotubes.

[0174] Comparative Example 6

[0175] The carbon nanotube dispersion was prepared in the same manner as in Example 1, except that 3.3 parts by weight of carbon nanotubes, 0.66 parts by weight of hydrogenated nitrile butadiene rubber (HNBR) (Mw 39,000, PDI 5.5) as the first dispersant and 0.33 parts by weight of the second dispersant were used, so that the solid content was 3.3 parts by weight relative to the total weight of the primary dispersion of carbon nanotubes.

[0176] Comparative Example 7

[0177] The carbon nanotube dispersion was prepared in the same manner as in Example 1, except that 3.3 parts by weight of carbon nanotubes, 0.66 parts by weight of hydrogenated nitrile butadiene rubber (HNBR) (Mw 170,000, PDI 3.7) as the first dispersant and 0.33 parts by weight of the second dispersant were used, such that the solid content was 3.3 parts by weight relative to the total weight of the primary dispersion of carbon nanotubes.

[0178] Experimental Example

[0179] Experimental Example 1: Measurement of viscosity and particle size of carbon nanotube dispersions

[0180] 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.

[0181] Specifically, Table 1 below shows the results of measuring the viscosity and particle size of the primary dispersions of carbon nanotube dispersions according to Examples 1 and 2 and Comparative Examples 1 to 3; Table 2 shows the results of the secondary dispersions of carbon nanotube dispersions according to Examples 1, 2 and Comparative Examples 1 to 3 (wherein, the solid content of the carbon nanotube dispersions in each example and comparative example is 5% (5 parts by weight of solid content relative to the total weight of the dispersion); and Table 3 shows the results of the secondary dispersions of carbon nanotube dispersions according to Examples 3 to 7 and Comparative Examples 4 to 7 (wherein, the solid content of the carbon nanotube dispersions in each example and comparative example is 3.3% (3.3 parts by weight of solid content relative to the total weight of the dispersion)).

[0182] Viscosity was measured at 25°C and 1 rpm using a viscometer (TV-25, rotor code 01, manufactured by TOKI SANGYO).

[0183] Particle size was measured at 2,000 rpm using a Mastersizer (manufactured by Malvern Panalytical) for measuring particle size distribution using laser diffraction scattering. The particle size at 50% volume was defined as D. 50 And define the particle size at 90% volume as D 90 .

[0184] [Table 1]

[0185]

[0186] [Table 2]

[0187]

[0188] [Table 3]

[0189]

[0190] Referring to Table 1 above, it can be determined that in Examples 1 and 2, as a result of using hydrogenated nitrile butadiene rubber with a weight-average molecular weight of 10,000 g / mol to 20,000 g / mol and a polydispersity index (PDI) of 2.0 to 4.0 as the first dispersant, the viscosity and particle size of the primary dispersion of carbon nanotubes remain low. On the other hand, it can be seen that in Comparative Examples 1 and 2, as a result of using hydrogenated nitrile butadiene rubber with a polydispersity index exceeding 4.0 as the first dispersant, the particle size of the primary dispersion of carbon nanotubes increases. Furthermore, it can be seen that in Comparative Example 3, as a result of using hydrogenated nitrile butadiene rubber with a weight-average molecular weight of less than 10,000 g / mol and a polydispersity index of less than 2.0 as the first dispersant, the particle size of the primary dispersion of carbon nanotubes actually increases.

[0191] Refer to Table 2 above and Figure 1 It can be determined that in Examples 1 and 2, as a result of using hydrogenated nitrile butadiene rubber with a weight-average molecular weight of 10,000 g / mol to 20,000 g / mol and a polydispersity index (PDI) of 2.0 to 4.0 as the first dispersant, the viscosity and particle size of the carbon nanotube secondary dispersion also remain low. On the other hand, it can be seen that in Comparative Examples 1 and 2, as a result of using hydrogenated nitrile butadiene rubber with a polydispersity index exceeding 4.0 as the second dispersant, both the viscosity and particle size of the carbon nanotube secondary dispersion increase. Furthermore, it can be seen that in Comparative Example 3, as a result of using hydrogenated nitrile butadiene rubber with a weight-average molecular weight of less than 10,000 g / mol and a polydispersity index of less than 2.0 as the first dispersant, the viscosity and particle size of the carbon nanotube secondary dispersion actually increase.

[0192] Referring to Table 3 above, it can be determined that even in the case of carbon nanotube dispersions according to Examples 3 to 7, where the solid content remains low compared to Examples 1 and 2 in Table 2 above, the viscosity and particle size of the secondary dispersion of carbon nanotubes remain low as a result of using hydrogenated nitrile butadiene rubber with a weight-average molecular weight of 10,000 g / mol to 20,000 g / mol and a polydispersity index (PDI) of 2.0 to 4.0 as the first dispersant. In contrast, it can be determined that in the case of carbon nanotube dispersions according to Comparative Examples 4 to 6, the particle size of the secondary dispersion of carbon nanotubes is significantly increased because the polydispersity index of the hydrogenated nitrile butadiene rubber as the first dispersant 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). Furthermore, it can be determined that in the case of the carbon nanotube dispersion according to Comparative Example 7, since the polydispersity index of the hydrogenated nitrile rubber as the first dispersant is 2.0 to 4.0 but the weight-average molecular weight exceeds 20,000 g / mol, the viscosity of the secondary dispersion of carbon nanotubes and the particle size of the dispersed particles are significantly increased.

[0193] Experimental Example 2: Measurement of the presence or absence of hydroxyl functional groups in hydrogenated nitrile butadiene rubber

[0194] For the hydrogenated nitrile butadiene rubber (HNBR) (Mw 19,000, PDI 2.8) used as the first dispersant in Example 1, the presence or absence of hydroxyl groups (-OH) was measured using infrared spectroscopy, and the results are shown below. Figure 2 middle.

[0195] Reference Figure 2 It can be observed at 3,200 cm -1 Up to 3,600 cm -1 The broad spectrum in the region determines that the hydrogenated nitrile butadiene rubber (HNBR) used as the first dispersant in Example 1 contains hydroxyl groups in its molecule as a result of the decomposition reaction by adding ozone, which allows it to have a low weight-average molecular weight and polydispersity index.

[0196] While preferred embodiments of the invention have been described in detail above, the scope of the invention is not limited thereto, and various modifications and improvements made by those skilled in the art using the basic concept of the invention as defined in the appended claims also fall within the scope of the invention.

Claims

1. A carbon nanotube dispersion comprising: Carbon nanotubes; A first dispersant containing hydrogenated nitrile butadiene rubber; A second dispersant comprising an alkanoic ammonium salt compound of a polymer containing acidic functional groups; and Solvent, The hydrogenated nitrile butadiene rubber has a weight-average molecular weight of 10,000 g / mol to 20,000 g / mol.

2. The carbon nanotube dispersion according to claim 1, wherein the polydispersity index (PDI) of the hydrogenated nitrile rubber is 2.0 to 4.

0.

3. The carbon nanotube dispersion according to claim 1, wherein the hydrogenated nitrile rubber further comprises hydroxyl groups in its molecule.

4. The carbon nanotube dispersion according to claim 1, wherein the second dispersant has an amine value of 30 mg KOH / g to 40 mg KOH / g and an acid value of 20 mg KOH / g to 30 mg KOH / g.

5. The carbon nanotube dispersion of claim 1, wherein the carbon nanotube dispersion contains the first dispersant in an amount of 10 to 50 parts by weight, based on 100 parts by weight of the carbon nanotubes.

6. The carbon nanotube dispersion of claim 1, wherein the carbon nanotube dispersion contains the second dispersant in an amount of 5 to 40 parts by weight, based on 100 parts by weight of the carbon nanotubes.

7. The carbon nanotube dispersion according to claim 1, wherein the solid content of the dispersion is from 0.1 parts by weight to 10 parts by weight relative to the total weight of the carbon nanotube dispersion.

8. The carbon nanotube dispersion according to claim 1, wherein the particle size distribution D of the dispersed particles contained in the dispersion is... 90 The range is from 1 μm to 5 μm.

9. The carbon nanotube dispersion according to claim 1, wherein the initial viscosity of the carbon nanotube dispersion, measured at 25°C and 1 rpm, is from 0.5 Pa·s to 10 Pa·s.

10. A method for preparing the carbon nanotube dispersion according to claim 1, comprising the following steps: A primary dispersion of carbon nanotubes is prepared by mixing a first dispersant containing hydrogenated nitrile butadiene rubber, a second dispersant containing an alkanol ammonium salt compound of a polymer containing acidic functional groups, and a solvent. as well as The primary dispersion of the carbon nanotubes is dispersed to prepare a secondary dispersion of carbon nanotubes.

11. The method for preparing the carbon nanotube dispersion according to claim 10, wherein the hydrogenated nitrile rubber has a weight-average molecular weight of 10,000 g / mol to 20,000 g / mol and a polydispersity index (PDI) of 2.0 to 4.0.

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