High density carbon nanotube composition, preparation method therefor, and carbon nanotube dispersion liquid and positive electrode

Abstract

The present invention relates to a carbon nanotube composition having a bulk density of 500 / mm3 to 2500 / mm3 as defined by Equation 1, in which carbon nanotubes in the carbon nanotube composition have a high bulk density while maintaining a bundle shape, and thus have excellent dispersibility and productivity.

Description

[0001] Cross - reference to related applications

[0002] This application claims the benefit of Korean Patent Application Nos. 10 - 2023 - 0028574 filed on March 3, 2023 and 10 - 2023 - 0028575 filed on March 3, 2023 with the Korean Intellectual Property Office, the disclosures of which are incorporated herein by reference in their entirety. Technical field

[0003] The present invention relates to a carbon nanotube composition having a high density and packing density, a method for preparing the same, and a dispersion and a positive electrode paste composition containing the carbon nanotube composition. Background art

[0004] According to the shape of the material, carbon nanomaterials can be classified into fullerenes, carbon nanotubes (CNTs), graphene, graphite nanoplates, etc. Among them, carbon nanotubes are macromolecules in which the surface of hexagonal honeycomb graphite in which one carbon atom is bonded to three other carbon atoms is curled into a nanoscale diameter.

[0005] Carbon nanotubes are hollow, so they are light in weight, and have electrical conductivity as good as copper, excellent thermal conductivity as good as diamond, and tensile strength as good as steel. According to their winding shape, carbon nanotubes can be classified into single - wall carbon nanotubes (SWCNT), multi - wall carbon nanotubes (MWCNT), and rope - like carbon nanotubes.

[0006] Recently, the most active research area regarding the use of carbon nanotubes is the field of lithium secondary batteries. The ultimate goal of lithium secondary batteries is to store more electrical energy in a smaller size, and as one of the methods to improve the electrode density of lithium secondary batteries to manufacture electrodes with a higher energy density per unit volume, the application method of using carbon nanotubes as a conductive material is being studied. Generally, electrode active material particles with a size of several μm to several tens of μm are formed into a high - density electrode by a high - pressure press. Therefore, during the forming process, the particles are easily deformed, the gaps between the particles become smaller, and the electrolyte permeability becomes poor. To solve the above problems, a material with excellent conductivity and strength is used as a conductive material in the manufacture of electrodes. Carbon nanotubes are also widely used as a conductive material due to their excellent strength and conductivity. When a conductive material is used in the manufacture of an electrode, the conductive material is dispersed between the compressed electrode active materials, thereby maintaining micropores between the particles of the active material to promote the penetration of the electrolyte solution, and also reducing the resistance in the electrode due to its excellent conductivity.

[0007] However, when using carbon nanotubes as a conductive material, the most problematic issue is the low dispersibility of the carbon nanotubes themselves. Due to the strong van der Waals attractive force between them, carbon nanotubes have the problem of aggregating together rather than being stably dispersed in an aqueous solution. When carbon nanotubes agglomerate in a dispersion, the processability of the dispersion decreases, making it difficult to uniformly coat the dispersion. Therefore, it is preferable to coat the dispersion in a state where its viscosity is minimized.

[0008] Carbon nanotubes are classified into a bundled type and a tangled type according to their shape. The bundled type refers to a secondary shape in which multiple carbon nanotube units are arranged side by side in the longitudinal direction of the unit with an orientation substantially the same as the axis, or a bundle or rope shape that is twisted or tangled after arrangement. On the other hand, the tangled type refers to a shape in which carbon nanotube units are wound together without a defined shape such as a bundle or rope. Between the bundled carbon nanotubes and the tangled carbon nanotubes, the bundled carbon nanotubes are excellent in terms of dispersibility, but the limitation of the bundled carbon nanotubes is that they have a low packing density in the powder state, resulting in a low productivity during the synthesis process. Therefore, in order to improve the dispersibility of carbon nanotubes, it is necessary to study how to increase the packing density of carbon nanotubes in the powder state while maintaining their shape as a bundle, thereby also improving the productivity.

[0009] Prior art documents

[0010] (Patent Document 1) KR 10-2018-0106929A Summary of the invention

[0011] Technical problem

[0012] An object of the present invention is to provide carbon nanotubes and a method for preparing the same, in which the carbon nanotubes have a high packing density while maintaining a bundled shape, and thus both dispersibility and productivity are excellent.

[0013] In addition, the present invention provides a carbon nanotube dispersion and a positive electrode paste composition containing the carbon nanotube dispersion. The carbon nanotube dispersion has a low viscosity by containing bundled carbon nanotubes, so it has excellent processability, and also exhibits the same or higher conductivity as a carbon nanotube dispersion containing typical tangled carbon nanotubes.

[0014] Technical solution

[0015] To achieve the above object, the present invention provides a carbon nanotube composition, a method for preparing the carbon nanotube composition, a carbon nanotube dispersion, and a positive electrode paste composition.

[0016] More specifically, (1) the present invention provides a carbon nanotube composition having a volume density of 500 / mm 3 to 2500 / mm 3 as defined by the following Equation 1:

[0017] [Equation 1]

[0018] Bulk density = Yield of carbon nanotubes / Volume of carbon nanotube composition

[0019] Wherein, the yield of the carbon nanotubes is calculated by (Mass of the carbon nanotube composition - Mass of the catalyst in the carbon nanotube composition) / (Mass of the catalyst in the carbon nanotube composition).

[0020] (2) In the above (1), the present invention provides a carbon nanotube composition, wherein the carbon nanotube composition has a particle density of 50 / mm to 120 / mm defined by the following Equation 2:

[0021] [Equation 2]

[0022] Particle density = Yield of carbon nanotubes / Volume average particle size of carbon nanotubes

[0023] Wherein, the yield of the carbon nanotubes is calculated in the same manner as in Equation 1.

[0024] (3) In the above (1) or (2), the present invention provides a carbon nanotube composition having a bulk density of 40 kg / m 3 to 85 kg / m 3 .

[0025] (4) In any one of the above (1) to (3), the present invention provides a carbon nanotube composition, wherein the yield of carbon nanotubes is 30 or more.

[0026] (5) In any one of the above (1) to (4), the present invention provides a carbon nanotube composition, wherein the specific surface area of the carbon nanotubes is 160 m2 / g or more.

[0027] (6) In any one of the above (1) to (5), the present invention provides a carbon nanotube composition, and the carbon nanotube composition contains bundled carbon nanotubes.

[0028] (7) The present invention provides a method for preparing a carbon nanotube composition, which is the carbon nanotube composition according to any one of the above (1) to (6), wherein the method includes: S1 filling a fluidized bed reactor with a supported catalyst in which Co and V are supported on boehmite and carbon nanotube powder for a fluidized bed; and S2 synthesizing carbon nanotubes by reacting while supplying a carbon source gas to the fluidized bed reactor.

[0029] (8) In the above (7), the present invention provides a method for preparing a carbon nanotube composition, wherein the Co content of the supported catalyst is 22% by weight; and the molar ratio of Co to V in the supported catalyst is 2:1 to 4:1.

[0030] (9) In the above (7) or (8), the present invention provides a method for preparing a carbon nanotube composition, wherein the internal temperature of the fluidized bed reactor is heated to 650 °C to 750 °C in step S2.

[0031] (10) In any one of the above (7) to (9), the present invention provides a method for preparing a carbon nanotube composition, wherein the carbon source gas and the flowing gas are supplied together in step S2; and the supply flow rate ratio between the carbon source gas and the flowing gas is 1:1 to 1:10.

[0032] (11) The present invention provides a carbon nanotube dispersion liquid, which contains the carbon nanotube composition according to any one of the above (1) to (6) and a dispersion medium.

[0033] (12) In the above (11), the present invention provides a carbon nanotube dispersion liquid, wherein the content of the carbon nanotube composition in the dispersion liquid is 0.5% by weight to 5% by weight.

[0034] (13) In the above (11) or (12), the present invention provides a carbon nanotube dispersion liquid, wherein the dispersion liquid contains one or more dispersants selected from styrene-butadiene rubber (SBR), carboxymethyl cellulose (CMC), hydrogenated acrylonitrile-butadiene rubber (H-NBR), polyvinylpyrrolidone (PVP), and polyvinyl butyral (PVB).

[0035] (14) In any one of the above (11) to (13), the present invention provides a carbon nanotube dispersion liquid, wherein the initial viscosity of the carbon nanotube dispersion liquid is 15,000 cP or less.

[0036] (15) The present invention provides a positive electrode paste composition, which contains the carbon nanotube dispersion liquid according to any one of the above (11) to (14), a positive electrode active material, a binder, and a solvent.

[0037] Advantageous Effects

[0038] The carbon nanotube composition of the present invention has a high bulk density while maintaining a bundle shape, and thus has excellent dispersibility and productivity.

[0039] In addition, the carbon nanotube dispersion liquid of the present invention has excellent processability due to its low viscosity and can contain a relatively high content of carbon nanotubes. Therefore, it is easy to process in the preparation of the positive electrode paste and can maintain excellent electrical properties. Brief Description of the Drawings

[0040] Figure 1Shows the morphology of the carbon nanotubes of Example 1 observed using an SEM image with a magnification of x3000.

[0041] Figure 2 Shows the morphology of the carbon nanotubes of Comparative Example 3 observed using an SEM image with a magnification of x3000.

[0042] Figure 3 Shows the morphology of the carbon nanotubes of Comparative Example 4 observed using an SEM image with a magnification of x3000.

[0043] Figure 4 Shows the morphology of the carbon nanotubes of Example 8 observed using an SEM image with a magnification of x400.

[0044] Figure 5 Shows the morphology of the carbon nanotubes of Example 9 observed using an SEM image with a magnification of x400.

[0045] Figure 6 Shows the morphology of the carbon nanotubes of Example 10 observed using an SEM image with a magnification of x400.

[0046] Figure 7 Shows the morphology of the carbon nanotubes of Example 11 observed using an SEM image with a magnification of x400. Detailed Description of the Invention

[0047] Hereinafter, the present invention will be described in more detail.

[0048] It should be understood that the terms or words used in this specification and claims should not be construed as limited to the meanings defined in a common dictionary, but should be construed as having meanings and concepts consistent with the technical idea of the present invention based on the concept that the inventor can appropriately define the terms to best explain the principles of the present invention.

[0049] The term "carbon nanotube" used in the present invention refers to a secondary structure in which carbon nanotube units are assembled in whole or in part into bundles. The carbon nanotube units have a cylindrical graphite surface with a nanoscale diameter and have an sp2 bonding structure. At this time, depending on the winding angle and structure of the graphite sheets, conductor characteristics or semiconductor characteristics can be exhibited. According to the number of bonds forming the wall, the carbon nanotube units can be classified into single-walled carbon nanotubes (SWCNT), double-walled carbon nanotubes (DWCNT), and multi-walled carbon nanotubes (MWCNT), and the thinner the wall, the lower the resistance.

[0050] The carbon nanotubes of the present invention may include one or more of single-walled carbon nanotube units, double-walled carbon nanotube units, and multi-walled carbon nanotube units.

[0051] In the present invention, the bundled carbon nanotubes refer to carbon nanotubes having a secondary shape in a bundled or rope-like form, in which a plurality of carbon nanotube units are arranged in an orientation substantially the same as the axis in the longitudinal direction of the unit, or are twisted or wound after being arranged.

[0052] In the present invention, the entangled carbon nanotubes refer to carbon nanotubes having a shape in which the carbon nanotube units are entangled without a predetermined shape such as a bundle or a rope.

[0053] In the present invention, the carbon nanotube composition refers to a product obtained by a method for preparing carbon nanotubes using a fluidized bed reactor, and refers to a mixture containing synthesized carbon nanotubes and a supported catalyst used in the synthesis. More specifically, the carbon nanotube composition includes a supported catalyst and carbon nanotubes grown from the supported catalyst.

[0054] Carbon nanotube composition

[0055] As is known, the bundled carbon nanotubes have excellent dispersibility and thus have the advantage of excellent electrical properties. However, the content of carbon nanotubes contained per unit volume is relatively small, and thus there is a disadvantage that the content of carbon nanotubes obtained in each batch manufacturing process is small. Therefore, if carbon nanotubes having carbon nanotube strands existing in a denser form can be obtained while maintaining the secondary shape of the bundle, carbon nanotubes excellent in both performance and productivity can be provided.

[0056] To achieve the above object, the present invention provides a carbon nanotube composition having a bulk density defined by the following formula 1 of 500 / mm 3 ~2500 / mm 3 .

[0057] [Formula 1]

[0058] Bulk density = Yield of carbon nanotubes / Volume of carbon nanotube composition

[0059] The yield of carbon nanotubes is calculated by (Mass of carbon nanotube composition - Mass of catalyst in carbon nanotube composition) / (Mass of catalyst in carbon nanotube composition).

[0060] The bulk density is an index indicating how many carbon nanotubes are contained per unit volume based on the carbon nanotube composition obtained after the synthesis reaction. In particular, since the bulk density is also affected by the yield of carbon nanotubes, if the yield of carbon nanotubes is higher than a certain level and the volume of the carbon nanotube composition is within a specific range, a bulk density within the above range can be obtained.

[0061] The bulk density can be 500 / mm 3 to 2500 / mm 3 , preferably 500 / mm3 Above, 510 / mm 3 Above, 520 / mm 3 Above, 530 / mm 3 Above, or 540 / mm 3 , but 2500 / mm 3 Below, 2400 / mm 3 Below, 2300 / mm 3 Below, 2200 / mm 3 Below, 2100 / mm 3 Below, 2000 / mm 3 Below, 1900 / mm 3 Below, 1850 / mm 3 Below, 1800 / mm 3 Below, 1800 / mm 3 Below, or 1780 / mm 3 Below. If the bulk density exceeds the above range, the secondary shape of the carbon nanotubes will change from a bundle shape to a tangled shape, which may reduce the electrochemical performance of the carbon nanotubes themselves.

[0062] In the carbon nanotube composition provided by the present invention, the carbon nanotube composition may have a particle density of 50 / mm to 120 / mm defined by the following formula 2.

[0063] [Formula 2]

[0064] Particle density = Yield of carbon nanotubes / Volume average particle diameter of carbon nanotubes

[0065] The yield of carbon nanotubes is calculated in the same way as in Equation 1.

[0066] Similar to the bulk density, the particle density is an index indicating how much carbon nanotubes are contained in the composition based on the volume average particle diameter of the carbon nanotubes, and similar to the bulk density, it is also an index related to the density of the carbon nanotubes.

[0067] The particle density can be 50 / mm to 120 / mm, preferably above 50 / mm, above 53 / mm, above 55 / mm, above 57 / mm, above 60 / mm, above 62 / mm, above 64 / mm, or above 66 / mm, and below 120 / mm, below 118 / mm, below 115 / mm, below 113 / mm, below 110 / mm, below 107 / mm, below 105 / mm, or below 102 / mm. Similarly, if the particle density exceeds the above range, the secondary shape of the carbon nanotubes will change from a bundle shape to a tangled shape, which may reduce the electrochemical performance of the carbon nanotubes themselves.

[0068] In the carbon nanotube composition provided by the present invention, the bulk density can be 40 kg / m 3 ~85 kg / m 3 and preferably 40 kg / m 3 or more, 45 kg / m 3 or more, 50 kg / m 3 or more, 55 kg / m 3 or more, 57 kg / m 3 or more, but 80 kg / m 3 or less, 77 kg / m 3 or less, 75 kg / m 3 or less. The bulk density value of the carbon nanotube composition of the present invention is higher than that of typical bundled carbon nanotubes, which means that the carbon nanotube content per unit volume of the carbon nanotube composition of the present invention is high. Therefore, the productivity per batch is high. At the same time, the bulk density can be calculated as follows: fill the carbon nanotube composition into a 50 mL container by free fall, measure the weight of the carbon nanotubes in the container, and then divide the corresponding weight by the volume of the container, 50 mL.

[0069] In the carbon nanotube composition provided by the present invention, the yield of the carbon nanotubes can be 23 or more, preferably 23 or more, 23.5 or more, or 24 or more, but 45 or less, 43 or less, or 40 or less. The yield is an index indicating how much carbon nanotubes are obtained relative to the mass of the catalyst. If the yield is within the above range, it means that the carbon nanotube composition of the present invention is obtained from the supported catalyst with a high yield. That is, the carbon nanotube composition of the present invention has the same excellent productivity as typical entangled carbon nanotubes. At the same time, the yield of the carbon nanotubes can be calculated by (the mass of the carbon nanotube composition - the mass of the catalyst in the carbon nanotube composition) / (the mass of the catalyst in the carbon nanotube composition). More specifically, the mass of the catalyst in the carbon nanotube composition can be the value obtained in the following manner: burn all the carbon nanotubes by oxidizing the carbon nanotube composition in an alumina crucible at 750 °C and under atmospheric conditions for 4 hours, so that only the supported catalyst remains in the composition, and then measure the weight of the remaining supported catalyst.

[0070] In the carbon nanotube composition provided by the present invention, the specific surface area of the carbon nanotubes can be 160 m 2 / g or more, preferably 163 m 2 / g or more, 165 m 2 / g or more, or 168 m 2 / g or more, but 220 m 2 / g or less, 210 m 2 / g or less, or 205 m 2Less than / g. The above specific surface area range is similar to that of typical bundled carbon nanotubes. As described above, while the carbon nanotube composition of the present invention is similar to typical bundled carbon nanotubes in terms of specific surface area, it has a packing density similar to that of entangled carbon nanotubes, thus showing high productivity. Therefore, it can be confirmed that it is more excellent in terms of dispersibility and conductivity.

[0071] The carbon nanotube composition provided by the present invention may include bundled carbon nanotubes. More specifically, all the carbon nanotubes in the composition may be bundled carbon nanotubes. As described above, the carbon nanotubes in the carbon nanotube composition of the present invention are bundled, having the technical advantages of entangled carbon nanotubes, and the content of the bundled carbon nanotubes in the composition may be as high as the above range.

[0072] Preparation method of carbon nanotube composition

[0073] The present invention provides a method for preparing the above carbon nanotube composition. Specifically, the present invention provides a method for preparing a carbon nanotube composition, the method comprising S1 filling a supported catalyst in which Co and V are supported on boehmite and carbon nanotube powder for a fluidized bed in a fluidized bed reactor, and S2 synthesizing carbon nanotubes by reacting while supplying a carbon source gas to the fluidized bed reactor.

[0074] 1) Step S1

[0075] Catalyst

[0076] The catalyst used in the method for preparing the carbon nanotube composition of the present invention uses a boehmite carrier, characterized in that Co and V are simultaneously supported on the carrier. Boehmite is an aluminum-based carrier represented by γ-AlO(OH), and the main catalyst component Co and the promoter component V are uniformly supported on the surface through hydroxyl groups.

[0077] Meanwhile, the number average particle size of boehmite may be 20 μm to 100 μm, preferably 40 μm to 60 μm. If the number average particle diameter of boehmite is within the above range, Co and V can be efficiently supported, and the specific surface area of the carbon nanotubes prepared by the catalyst can be shown to be particularly high.

[0078] In addition, boehmite may have a specific surface area of 150 m 2 / g to 250 m 2 / g, preferably 170 m 2 / g to 220 m 2 / g. The packing density of boehmite may be 500 kg / m 3 to 1200 kg / m 3 , preferably 700 kg / m 3 to 1000 kg / m 3If the physical properties of boehmite are within the above ranges, the technical advantage is that the durability of the carrier is excellent, and a large amount of metal components can be loaded without any difficulty.

[0079] The shape of boehmite is not particularly limited and can be spherical or potato-shaped. In addition, boehmite can have a porous structure, a molecular sieve structure, a honeycomb structure, etc., to have a relatively high surface area per unit mass or unit volume.

[0080] In the catalyst used in the method for preparing the carbon nanotube composition of the present invention, Co is the main catalyst component and promotes the carbon nanotube synthesis reaction by directly reducing the activation energy of the reaction for synthesizing carbon nanotubes from a carbon source gas. In particular, when Co is used instead of Ni or Fe as the main catalyst component, it is easy to generate the activity of the particle region of the main catalyst component on the carrier. Therefore, compared with using Ni or Fe as the main catalyst component, it has the technical advantage of being easier to form a bundled structure of carbon nanotubes. In addition, when using a catalyst with Co loaded on boehmite, carbon nanotubes can be prepared with a higher yield compared to using a catalyst with Ni or Fe loaded on boehmite. At the same time, V is a promoter component used to further improve the catalytic activity of Co, and the synergistic effect between V and Co is particularly excellent, so Co aggregation during the preparation process can be inhibited.

[0081] At the same time, in the supported catalyst, the content of Co in the supported catalyst can be 16 wt% to 22 wt%, preferably 18 wt% to 20 wt%. In addition, the molar ratio between Co and V in the supported catalyst can be 2:1 to 4:1, preferably 2.5:1 to 3.5:1. If the content conditions of the Co and V components contained in the supported catalyst are within the above ranges, the carbon nanotube composition of the present invention with a desired bulk density can be prepared.

[0082] The catalyst can be prepared by adding the above-mentioned boehmite carrier to a solution containing a Co precursor and a V precursor, and then drying and calcining. The calcination temperature during the catalyst preparation process can be 660 °C or higher and 740 °C or lower, preferably 660 °C or higher or 670 °C or higher, but 740 °C or lower, 730 °C or lower, or 720 °C or lower. If the calcination temperature during the catalyst preparation process is not appropriate, the particle density and bulk density of the carbon nanotubes obtained from the obtained catalyst may exceed the range required by the present invention.

[0083] Carbon nanotube powder for fluidized bed

[0084] In the method for preparing the carbon nanotube composition of the present invention, the carbon nanotube powder for fluidized bed is introduced into the fluidized bed reactor together with the above catalyst. The carbon nanotube powder for fluidized bed is a pre-synthesized carbon nanotube powder introduced together with the catalyst and is introduced to ensure the reaction temperature in the fluidized bed reactor. Specifically, if only the supported catalyst is introduced without introducing the above carbon nanotube powder, 1) when a sufficient amount of the supported catalyst is introduced, carbon nanotubes overgrow from each catalyst, resulting in the preparation of carbon nanotubes with a volume larger than the internal volume of the fluidized bed reactor, making it impossible to prepare carbon nanotubes with uniform physical properties, and to prevent this phenomenon, 2) when a small amount of the supported catalyst is introduced, the volume occupied by the supported catalyst in the internal space of the fluidized bed reactor is small, such that the supported catalyst may not be heated to a sufficiently high temperature during the reaction. On the other hand, if the supported catalyst and the carbon nanotube powder for fluidized bed are introduced together into the fluidized bed reactor to form a fluidized bed, the two components occupy more than a certain percentage of the internal space of the fluidized bed reactor, thereby ensuring a sufficient reaction temperature, and after the reaction is completed, the final product can be easily obtained without separately separating the carbon nanotube powder for fluidized bed introduced to form the fluidized bed.

[0085] There is no particular limitation on the carbon nanotubes used as the carbon nanotube powder for fluidized bed. However, from the viewpoint of obtaining a more uniform carbon nanotube composition, as the carbon nanotube powder for fluidized bed, it is preferable to use carbon nanotubes having properties such as bulk density, specific surface area, particle size, etc. similar to those of the carbon nanotubes to be prepared.

[0086] 2) Step S2

[0087] After filling the fluidized bed reactor with the supported catalyst and the carbon nanotube powder for fluidized bed in the previous step, a carbon source gas can be injected into the fluidized bed reactor to synthesize carbon nanotubes.

[0088] The carbon source gas is a carbon-containing gas that can be decomposed at high temperature to form carbon nanotubes, and specific examples thereof may include various carbon-containing compounds such as aliphatic alkanes, aliphatic alkenes, aliphatic alkynes, aromatic compounds, etc. More specifically, compounds such as methane, ethane, ethylene, acetylene, ethanol, methanol, acetone, carbon monoxide, propane, butane, benzene, cyclohexane, propylene, butene, isobutene, toluene, xylene, cumene, ethylbenzene, naphthalene, phenanthrene, anthracene, acetylene, formaldehyde, acetaldehyde, etc. can be used. Particularly preferably, the carbon source gas can be ethylene.

[0089] While injecting a carbon source gas into a fluidized bed reactor, the internal temperature of the fluidized bed reactor can be increased to decompose the carbon source gas and synthesize carbon nanotubes. The internal temperature of the fluidized bed reactor in this step can preferably be 650 °C to 750 °C, and particularly preferably 670 °C to 730 °C. The carbon nanotube composition of the present invention can be prepared only in the case of using the above-mentioned supported catalyst while controlling the reaction temperature within the above range. If the reaction temperature is lower than the above range, the yield of the carbon nanotube composition may be too low, and if it is higher than this range, there may be a problem that the synthesized carbon nanotubes decompose again.

[0090] Meanwhile, in this step, a flowing gas can be supplied to the fluidized bed reactor together with the carbon source gas. The flowing gas is for further increasing the fluidity of the catalyst particles and the carbon nanotube powder for the fluidized bed introduced in advance, and a gas having high thermal stability and not reacting with the carbon source gas or the carbon nanotubes can be used. As the flowing gas, for example, nitrogen or an inert gas can be used.

[0091] The supply flow rate ratio of the carbon source gas to the flowing gas can be 1:1 to 1:10 by volume, and preferably 1:2 to 1:8. When the supply flow rate ratio between the two gases is within the above range, the carbon nanotube composition can be obtained in a high yield.

[0092] Carbon nanotube dispersion

[0093] The present invention provides a carbon nanotube dispersion containing the above carbon nanotube composition. More specifically, the present invention provides a carbon nanotube dispersion containing the above carbon nanotube composition and a dispersion medium.

[0094] Dispersion medium

[0095] In the carbon nanotube dispersion of the present invention, as the dispersion medium, both aqueous solvents and organic solvents can be used. For example, water can be used; amide-based polar organic solvents such as dimethylformamide (DMF), diethylformamide, dimethylacetamide (DMAc), 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, and octanol; diols such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, 1,3-propanediol, 1,3-butanediol, 1,5-pentanediol, hexanediol; polyols such as glycerol, trimethylolpropane, pentaerythritol, sorbitol; diol 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, tetraethylene glycol monobutyl ether; ketones such as acetone, methyl ethyl ketone, methyl propyl ketone, and cyclopentanone; esters such as ethyl acetate, γ-butyrolactone, ε-propiolactone, and any one or a mixture of two or more thereof. More specifically, when considering the effect of improving the dispersibility of carbon nanotubes and the dispersant, the dispersion medium can be an amide-based polar organic solvent, particularly N-methylpyrrolidone.

[0096] The carbon nanotube dispersion of the present invention can further contain a dispersant to further improve the dispersibility. As the dispersant, an aqueous dispersant or an organic dispersant can be used. The aqueous dispersant can be selected from, for example, styrene-butadiene rubber (SBR) or carboxymethyl cellulose (CMC), and the organic dispersant can be, for example, hydrogenated acrylonitrile-butadiene rubber (H-NBR), polyvinylpyrrolidone (PVP), or polyvinyl butyral (PVB).

[0097] In the carbon nanotube dispersion of the present invention, the initial viscosity of the dispersion can be 15,000 cP or less, preferably 12,000 cP or less, 10,000 cP or less, 8,000 cP or less, 7,000 cP or less, 6,000 cP or less, 5,000 cP or less, 4,500 cP or less, 4,000 cP or less, or 3,500 cP or less, but 200 cP or more, 500 cP or more, 700 cP or more, 1,000 cP or more, 1,200 cP or more, or 1,400 cP or more. By including the above carbon nanotube composition, the dispersion of the present invention can maintain a relatively low viscosity as described above. In addition, the viscosity can be measured using a viscometer. Specifically, it can be measured under the conditions of a shaft rotation speed of 12 rpm and a measurement temperature of 20 °C to 25 °C.

[0098] In the carbon nanotube dispersion of the present invention, the content of the carbon nanotube composition in the dispersion can be 0.5 wt% to 5 wt%, preferably 1 wt% to 5 wt%. In the carbon nanotube dispersion, as the content of the carbon nanotubes increases, the viscosity of the dispersion increases. Therefore, an appropriate amount of carbon nanotubes needs to be included to enable the dispersion to be processed smoothly. If the content of the carbon nanotubes in the dispersion is less than the above range, the conductivity may decrease when coating the slurry later. If the content of the carbon nanotubes is greater than the above range, the viscosity of the dispersion may increase excessively, resulting in unsmooth processing.

[0099] In the carbon nanotube dispersion of the present invention, the volume average particle diameter (Mv) of the carbon nanotube particles dispersed in the dispersion can be 3 μm or more, 4 μm or more, 5 μm or more, 6 μm or more, 6.5 μm or more, 7 μm or more, but 30 μm or less, 25 μm or less, 20 μm or less, 18 μm or less, 15 μm or less, 13 μm or less. Additionally, the D10 value of the carbon nanotube particles can be 1.8 μm or more, 2.0 μm or more, 2.2 μm or more, 2.4 μm or more, 2.5 μm or more, 2.6 μm or more, 2.7 μm or more, but 10 μm or less, 9 μm or less, 8 μm or less, 7 μm or less, 6 μm or less, 5 μm or less, 4.5 μm or less. Additionally, the D50 value of the carbon nanotube particles can be 2.5 μm or more, 3 μm or more, 4 μm or more, 4.5 μm or more, or 5 μm or more, but 15 μm or less, 14 μm or less, 13 μm or less, 12 μm or less, 11 μm or less, 10 μm or less, or 9 μm or less. Additionally, the D90 value of the carbon nanotube particles can be 8 μm or more, 9 μm or more, 10 μm or more, 11 μm or more, 12 μm or more, 13 μm or more, but 30 μm or less, 29 μm or less, 28 μm or less, 27 μm or less, 26 μm or less, 25 μm or less. Additionally, the span ((D90 - D10) / D50) value obtained from the particle size distribution of the carbon nanotube particles can be 1.6 or more, 1.65 or more, 1.7 or more, 1.75 or more, or 1.78 or more, but 3.0 or less, 2.7 or less, 2.5 or less, 2.4 or less, or 2.3 or less. If the span value in the particle size distribution obtained for the carbon nanotube particles dispersed in the dispersion is within the above range, there is an advantage that the viscosity of the dispersion is low and the conductivity is excellent.

[0100] The above carbon nanotube dispersion can be prepared by mixing a carbon nanotube composition with a dispersion medium. In the method for preparing the carbon nanotube dispersion, a pretreatment step S0 of grinding the carbon nanotube composition can be carried out before mixing. By pre-grinding the carbon nanotube composition and then mixing it with the dispersion medium, the viscosity in the dispersed state can be further reduced. The grinding can be carried out by a typical method called a grinding method, which can be, for example, ball milling. The time for carrying out the grinding is not particularly limited either, but since the structure of the carbon nanotubes themselves may break if the grinding is carried out excessively, it is preferably ground for 10 hours or less.

[0101] In addition, the mixing process can be carried out in a high-pressure homogenizer. By mixing in a high-pressure homogenizer, a uniform dispersion can be prepared in a short time. The mixing in the high-pressure homogenizer can be carried out once, or can be repeated 2 times or 5 times. As the number of repetitions increases, the viscosity in the dispersed state can be lower. Since it is important that the viscosity of the dispersion is within an appropriate range during slurry coating, before carrying out the mixing, the number of times of repeated mixing in the high-pressure homogenizer can be determined according to the required viscosity value of the dispersion.

[0102] Positive electrode slurry

[0103] The present invention provides a positive electrode slurry containing the above carbon nanotube dispersion. Since the carbon nanotube dispersion has an appropriate viscosity and excellent conductivity, it is particularly suitable as a conductive material. Therefore, the dispersion, a positive electrode active material, a binder, and a solvent can be mixed to be used as a positive electrode slurry.

[0104] The positive electrode active material, binder, and solvent used in the positive electrode slurry of the present invention can be used in the present invention without particular limitation as long as they are commonly used.

[0105] Hereinafter, the present invention will be described in more detail by way of examples and experimental examples, but the present invention is not limited by these examples and experimental examples. The examples according to the present invention can be modified into various other forms, and the scope of the present invention should not be construed as being limited to the examples described below. The examples of the present invention are provided to more comprehensively describe the present invention to those skilled in the art.

[0106] Catalyst preparation example 1-1

[0107] 109.4 g of Co(NO 3 ) 2 ·6H 2 O and 14.6 g of NH 4 VO 3Dissolve in 146 g of water, and dissolve 10.5 g of anhydrous citric acid as a polycarboxylic acid together to prepare a catalyst composition. Stir the catalyst composition well, and then introduce it into boehmite as a carrier. Then, dry it in an oven at 170 °C for 6 hours, and then calcine it at 690 °C for 1 hour to obtain a catalyst. The content of Co in the catalyst obtained in Catalyst Preparation Example 1-1 is 19 wt%, and the molar ratio of Co to V is 3:1.

[0108] Catalyst Preparation Examples 1-2 to 1-9

[0109] Based on the weight of the cobalt and vanadium precursors used in Catalyst Preparation Example 1-1 set as 100% loading, change the loading amount and the catalyst calcination temperature as shown in Table 1 below to obtain a catalyst.

[0110] [Table 1]

[0111] Loading amount (%) Calcination temperature (°C) Catalyst Preparation Example 1-1 100％ 690 Catalyst Preparation Example 1-2 65％ 690 Catalyst Preparation Example 1-3 80％ 690 Catalyst Preparation Example 1-4 120％ 690 Catalyst Preparation Example 1-5 135％ 690 Catalyst Preparation Example 1-6 100％ 650 Catalyst Preparation Example 1-7 100％ 670 Catalyst Preparation Example 1-8 100％ 720 Catalyst Preparation Example 1-9 100％ 750

[0112] Catalyst Preparation Example 2

[0113] Dissolve 58.9 g of Co(NO 3 ) 2 ·6H 2 O and 2.4 g of NH 4 VO 3 in 78.8 g of water, and dissolve 2.4 g of anhydrous citric acid as a polycarboxylic acid together to prepare a catalyst composition. Stir the catalyst composition well, and then introduce it into boehmite as a carrier. Then, dry it in an oven at 190 °C for 6 hours, and then calcine it at 690 °C for 1 hour to obtain a catalyst. The content of Co in the catalyst obtained in Example 1 is 13 wt%, and the molar ratio of Co to V is 10:1.

[0114] Examples and Comparative Examples

[0115] Introduce 800 g of the catalyst prepared in each catalyst preparation example and the pre-synthesized carbon nanotube composition into a fluidized bed reactor, and while injecting ethylene gas and nitrogen into the fluidized bed reactor, heat it so that the internal temperature of the fluidized bed reactor becomes a predetermined temperature. Continue the reaction for 100 minutes to obtain a carbon nanotube composition containing carbon nanotubes synthesized with the catalyst.

[0116] Summarize the types of catalysts used in each example and comparative example, the weight of the pre-synthesized carbon nanotube composition (bed) pre-introduced into the fluidized bed reactor, the flow rate ratio of ethylene gas to nitrogen (based on volume), and the reaction temperature in Table 2 below.

[0117] [Table 2]

[0118] Catalyst Bed weight (kg) Nitrogen:ethylene ratio Reaction temperature (°C) Example 1 Catalyst Preparation Example 1-1 11.6 2:1 710 Example 2 Catalyst Preparation Example 1-2 11.6 2:1 710 Example 3 Catalyst Preparation Example 1-3 11.6 2:1 710 Example 4 Catalyst Preparation Example 1-4 11.6 2:1 710 Example 5 Catalyst Preparation Example 1-5 11.6 2:1 710 Comparative Example 1 Catalyst Preparation Example 1-6 11.6 2:1 710 Example 6 Catalyst Preparation Example 1-7 11.6 2:1 710 Example 7 Catalyst Preparation Example 1-8 11.6 2:1 710 Comparative Example 2 Catalyst Preparation Example 1-9 11.6 2:1 710 Comparative Example 3 Catalyst Preparation Example 2 11.6 2:1 710 Example 8 Catalyst Preparation Example 1-1 11.6 2:1 670 Example 9 Catalyst Preparation Example 1-1 11.6 2:1 690 Example 10 Catalyst Preparation Example 1-1 11.6 2:1 710 Example 11 Catalyst Preparation Example 1-1 11.6 2:1 730 Example 12 Catalyst Preparation Example 1-1 11.6 1:1 710 Example 13 Catalyst Preparation Example 1-1 11.6 1.5:1 710 Example 14 Catalyst Preparation Example 1-1 11.6 2:1 710 Example 15 Catalyst Preparation Example 1-1 11.6 2.5:1 710 Example 16 Catalyst Preparation Example 1-1 18 2:1 710 Example 17 Catalyst Preparation Example 1-1 15 2:1 710

[0119] Comparative Example 4

[0120] The product FT9100 of CNano Co. was used, which is a tangled carbon nanotube.

[0121] Comparative Example 5

[0122] Using a bulk density of 123.7 kg / m 3 , a specific surface area of 194 m 2 / g, a purity of 97.5%, and a yield of 39.2 times the tangled carbon nanotube composition.

[0123] Experimental Example 1. Confirmation of the characteristics of the carbon nanotube compositions of the examples and comparative examples

[0124] For the carbon nanotube compositions obtained in each of the examples and comparative examples, the following characteristics were confirmed.

[0125] 1) Bulk density: The obtained carbon nanotube composition was filled into a 50 mL container by free fall, and then the weight of the carbon nanotube composition in the container was measured. The measured weight was divided by the volume of the container, 50 mL, to calculate the bulk density.

[0126] 2) Specific surface area: The specific surface area was measured using Trista 2000 of Microtrac Co. by a standard measurement method.

[0127] 3) Purity: The weight of the obtained carbon nanotube composition was measured. The obtained carbon nanotube composition was introduced into an alumina crucible and oxidized in an atmosphere at 750 °C for 4 hours, and then the weight of the remaining ash (catalyst) was measured. From the weight of the oxidized carbon nanotubes and the weight of the remaining catalyst obtained above, the purity was calculated using the following formula.

[0128] Purity (wt%) = (mass of carbon nanotube composition - mass of catalyst in carbon nanotube composition) / (mass of carbon nanotube composition) * 100%

[0129] 4) Yield: The weight of the obtained carbon nanotube composition was measured. The obtained carbon nanotube composition was introduced into an alumina crucible and oxidized in an atmosphere at 750 °C for 4 hours, and then the weight of the remaining ash (catalyst) was measured. In addition, the yield was calculated using the following formula.

[0130] Yield = (mass of carbon nanotube composition - mass of catalyst in carbon nanotube composition) / (mass of catalyst in carbon nanotube composition)

[0131] 5) Mv (volume average particle size, μm): 0.1 g of the carbon nanotube composition was dispersed in 50 g of water, and then the particle size distribution and volume average particle size were measured using a spectrometer.

[0132] 6) Bulk density: The bulk density is calculated by the following Equation 1.

[0133] [Equation 1]

[0134] Bulk density = Yield of carbon nanotubes / Volume of carbon nanotube composition

[0135] 7) Granularity density: The granularity density is calculated by the following Equation 2.

[0136] [Equation 2]

[0137] Granularity density = Yield of carbon nanotubes / Volume average particle diameter of carbon nanotubes

[0138] The measurement and calculation results are summarized in Table 3 below.

[0139] [Table 3]

[0140]

[0141]

[0142] As shown in Table 3 above, compared with the carbon nanotube compositions of Comparative Examples 2 and 3, the carbon nanotube compositions of the present invention in each Example have higher yields and bulk densities. Comparative Example 2 is a bundled carbon nanotube composition prepared using a catalyst calcined at a higher temperature, and Comparative Example 3 is also a typical bundled carbon nanotube composition, which means that the carbon nanotube compositions of the present invention contain more carbon nanotubes per unit volume than typical bundled carbon nanotube compositions, and thus can be obtained with high productivity.

[0143] Meanwhile, Examples and Comparative Example 3 exhibit similar levels of specific surface area and volume average particle size. Based on the above, it is confirmed that the carbon nanotube compositions of the present invention can be obtained with a higher productivity than Comparative Example 3, while having carbon nanotubes with physical properties similar to those of typical bundled carbon nanotubes, and based on the results, it can be predicted that the carbon nanotube compositions of the present invention can exhibit a conductivity level similar to that of typical bundled carbon nanotube compositions.

[0144] Meanwhile, in the results of Table 2 above, Examples 1 and 10 used catalysts prepared under the same conditions, and some of the differences in the values of Examples 1 and 10 were caused by errors in the catalyst synthesis and carbon nanotube synthesis processes.

[0145] Experimental Example 2. Confirmation of characteristics of carbon nanotube compositions of Examples and Comparative Examples in a dispersed state

[0146] Carbon nanotube dispersions were prepared using the carbon nanotube compositions of Examples 8 to 11 and Comparative Examples 3 to 5, which used the same catalyst but different synthesis temperatures. Specifically, zirconium balls with a diameter of 10 mm were used to grind each carbon nanotube composition under the condition of a rotation speed of 175 rpm. 18 g of the ground carbon nanotube composition was mixed with 578.5 g of N-methylpyrrolidone, and 3.5 g of HNBR was added as a dispersant at the same time to prepare a carbon nanotube dispersion with a carbon nanotube content of 3 wt%.

[0147] For the prepared dispersions, the viscosity, slurry powder resistance, and particle size distribution in the dispersion state were measured. Each property was determined as follows.

[0148] 1) Viscosity: The viscosity was measured using a viscometer under the conditions that the shaft rotated at 12 rpm and the measurement temperature was 20 ± 1°C.

[0149] 2) Slurry powder resistance: 19 g of the prepared dispersion was mixed with 74 g of an NCM cathode material (chemical formula: LiNi 0.5 Co 0.2 Mn 0.3 ), 1 g of PVDF as a binder, and 32 g of 1-methyl-2-pyrrolidone as a solvent, and the mixture was stirred to prepare a slurry. Then, the prepared slurry was coated on an aluminum plate and dried in a convection oven at 130°C to form an electrode layer. The electrode layer was peeled off and then collected in the form of particles, and a certain amount of it was introduced into a powder resistance measurement module (Nittoseiko Analytech Co., MCP-PD51). The powder resistance was measured while increasing the pressure in the module to 4 kN to 20 kN, and the powder resistance value under the condition of a density of 2.7 g / cc was derived.

[0150] 3) Particle size distribution in the dispersion state (Mv, D10, D50, D90, span ((D90 - D10) / D50)): A diluted solution of the carbon nanotube dispersion was introduced into a laser diffraction particle size analyzer (Malvern Paanalytic, Mastersizer 3000), and then the particle size and distribution were analyzed. The volume average particle size (Mv) and D10, D50, D90 values were derived from the analysis values, and the span value was calculated using the derived D10, D50, D90 values.

[0151] The results are summarized in Table 4 below.

[0152] [Table 4]

[0153]

[0154] From the results in Table 4 above, it can be confirmed that the carbon nanotube composition dispersion of the present invention contains bundled carbon nanotubes, and thus exhibits a conductivity level similar to that of Comparative Example 3 which also contains bundled carbon nanotubes. However, it has a significantly lower viscosity in the dispersed state than the dispersion of Comparative Example 3, and thus has better processability. On the other hand, the dispersions of Comparative Examples 4 and 5 containing entangled carbon nanotubes each have excellent effects in terms of viscosity because the entangled carbon nanotubes are easily dispersed in the process of preparing the dispersion. However, it can be confirmed that they have significantly higher slurry powder resistance compared to the examples of the present invention in terms of conductivity.

[0155] Based on the above, it can be confirmed that the carbon nanotube composition of the present invention combines the advantages of bundled carbon nanotubes, namely excellent conductivity, and the advantages of entangled carbon nanotubes, namely excellent dispersibility and processability.

[0156] Experimental Example 3. Morphological Observation of Carbon Nanotubes in Examples and Comparative Examples

[0157] The morphology of the carbon nanotube composition obtained in each of the examples and comparative examples was observed using SEM images. First, the morphology of the carbon nanotubes obtained in Example 1 and Comparative Examples 3 and 4 was observed using SEM images at a magnification of ×3000, and the results are shown respectively in Figures 1 to 3 .

[0158] From Figures 1 to 3 it can be seen that the carbon nanotubes in Comparative Example 3 are in a bundled shape, and the carbon nanotubes in Comparative Example 4 are in an entangled shape. It was confirmed that the carbon nanotubes of the examples of the present invention are in a shape very similar to that of the carbon nanotubes in Comparative Example 3, and are bundled carbon nanotubes. From the above, it can be confirmed that the carbon nanotube composition of the present invention is similar to entangled carbon nanotubes in terms of bulk density and yield, but has the actual shape of bundled carbon nanotubes.

[0159] In addition, in order to compare the morphology of carbon nanotubes according to volume and particle size density, the morphology of the carbon nanotubes obtained in Examples 8 to 11 was observed using SEM images at a magnification of ×400, and the results are shown in sequence in Figures 4 to 7 . According to Figures 4 to 7 it can be confirmed that as the density of the carbon nanotube composition increases, the morphology partially changes from a bundled shape to an entangled shape where fine carbon nanotube strands are intertwined with each other. It is expected that this is because as the synthesis temperature of the carbon nanotubes increases, the yield of the carbon nanotubes also increases, and as the particle size of the catalyst on the carrier increases, the density of the carbon nanotube particles also increases.

Claims

1. A bulk density of 500 / mm2 defined by the following equation 1 3 Up to 2500 / mm 3 Composition of carbon nanotubes: [Equation 1] Volume density = yield of carbon nanotubes / volume of carbon nanotube composition in, The yield of the carbon nanotubes is calculated by (the mass of the carbon nanotube composition-the mass of the catalyst in the carbon nanotube composition) / (the mass of the catalyst in the carbon nanotube composition).

2. The carbon nanotube composition according to claim 1, wherein the particle size density of the carbon nanotube composition defined by the following equation 2 is 50 / mm to 120 / mm: [Formula 2] Particle density = yield of carbon nanotubes / volume average particle size of carbon nanotubes in, The yield of the carbon nanotubes was calculated in the same manner as in Equation 1.

3. The carbon nanotube composition according to claim 1, wherein the carbon nanotube composition has a carbon content of 40 kg / m 3 Up to 85kg / m 3 The bulk density. The carbon nanotube composition according to claim 1 , wherein the yield of the carbon nanotubes is 30% or more.

5. The carbon nanotube composition according to claim 1, wherein the specific surface area of ​​the carbon nanotubes is 160 m 2 / g or above. The carbon nanotube composition according to claim 1 , wherein the carbon nanotube composition comprises bundled carbon nanotubes.

7. A method for preparing the carbon nanotube composition according to claim 1, the method comprising: (S1) filling a fluidized bed reactor with a supported catalyst in which Co and V are supported on boehmite and carbon nanotube powder for a fluidized bed; and (S2) Synthesizing carbon nanotubes by reacting while supplying a carbon source gas to the fluidized bed reactor.

8. The method according to claim 7, wherein: The Co content of the supported catalyst is 22 wt %; and The molar ratio of Co to V in the supported catalyst is 2:1 to 4:

1.

9. The method according to claim 7, wherein step S2 is performed by heating so that the internal temperature of the fluidized bed reactor is 650°C to 750°C.

10. The method according to claim 7, wherein: Step S2: supplying the carbon source gas and the flowing gas together; and A supply flow ratio between the carbon source gas and the flowing gas is 1:1 to 1:

10.

11. A carbon nanotube dispersion comprising: The carbon nanotube composition according to any one of claims 1 to 6; and Dispersion medium. 12 . The carbon nanotube dispersion according to claim 11 , wherein the content of the carbon nanotube composition in the dispersion is 0.5 wt % to 5 wt %.

13. The carbon nanotube dispersion of claim 11, wherein the dispersion comprises one or more dispersants selected from the group consisting of styrene butadiene rubber (SBR), carboxymethyl cellulose (CMC), hydrogenated acrylonitrile butadiene rubber (H-NBR), polyvinyl pyrrolidone (PVP) and polyvinyl butyral (PVB). 14 . The carbon nanotube dispersion according to claim 11 , wherein the initial viscosity of the carbon nanotube dispersion is 15000 cP or less.

15. A positive electrode slurry composition comprising: The carbon nanotube dispersion according to any one of claims 11 to 14; Positive electrode active material; Adhesives; and Solvent.

Images