Carbon nanotube dispersion and method for producing same

Abstract

The present invention relates to a carbon nanotube dispersion comprising carbon nanotubes, a first dispersant which is a cellulose-based dispersant, a second dispersant which contains hexafluoropropylene (HFP) as a repeating unit, and a solvent, and a method for producing the same. The carbon nanotube dispersion of the present invention has a low initial viscosity and viscosity change rate, and is excellent in storage stability and processability.

Description

[Technical Field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2023-0044853, filed April 5, 2023, the entire contents of which are incorporated herein by reference.

[0002] The present invention relates to a carbon nanotube dispersion liquid which has a low initial viscosity, little change in viscosity over time, excellent storage stability, and excellent processability during the coating process, and a method for producing the same. [Background technology]

[0003] Carbon nanotubes are giant molecules in which a hexagonal honeycomb-shaped graphite surface, in which one carbon atom is bonded to three other carbon atoms, is rolled up with a nanometer-sized diameter. Carbon nanotubes are lightweight because they are hollow, and have electrical conductivity as good as copper, thermal conductivity as good as diamond, and tensile strength comparable to that of steel. Depending on the rolled shape, they can be divided into single-walled carbon nanotubes (SWCNT), multi-walled carbon nanotubes (MWCNT), and rope carbon nanotubes.

[0004] Carbon nanotubes have recently been widely used as conductive materials in secondary batteries due to their excellent electrical conductivity. However, carbon-based conductive materials, including carbon nanotubes, have a problem of not dispersing uniformly in electrode slurry compositions and tending to agglomerate. If the conductive material agglomerates in the electrode slurry composition, the conductive material cannot be distributed uniformly in the active material layer during the electrode formation process, which leads to reduced performance of the secondary battery. Therefore, various technologies for achieving uniform dispersion of the conductive material in the electrode slurry composition are being researched.

[0005] The most common approach is to improve dispersibility by introducing a dispersant together with the conductive material. Specifically, a method is known in which a polymer component, such as a cellulose-based dispersant or hydrogenated nitrile butadiene rubber (HNBR), is introduced as a dispersant to improve dispersibility in the dispersion state. Specifically, when a cellulose-based dispersant, which has been known as a dispersant for carbon nanotube dispersions, is used alone, it has the effect of reducing the rate of change in viscosity over time, but the initial viscosity of the dispersion itself is high. Furthermore, when the cellulose-based dispersant is used together with a conventional polymer dispersant, such as hydrogenated nitrile butadiene rubber (HNBR), not only the initial viscosity but also the rate of change in viscosity over time increases.

[0006] Therefore, there is a need for the development of a novel carbon nanotube dispersion that has low initial viscosity, minimizes viscosity change over time, and maintains excellent viscosity and viscosity stability. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] KR10-2022-0003984 A Summary of the Invention [Problem to be solved by the invention]

[0008] The present invention aims to provide a carbon nanotube dispersion liquid, which has excellent processability during the coating process due to the low initial viscosity of the dispersion liquid itself, and which has excellent storage stability due to little change in viscosity over time, and a method for producing the same. [Means for solving the problem]

[0009] In order to solve the above problems, the present invention provides a carbon nanotube dispersion and a method for producing the same.

[0010] Specifically, (1) the present invention provides a carbon nanotube dispersion liquid comprising carbon nanotubes, a first dispersant, a second dispersant, and a solvent, wherein the first dispersant is a cellulose-based dispersant, the second dispersant is a polymer dispersant containing hexafluoropropylene (HFP) as a repeating unit, and the weight ratio of the first dispersant to the second dispersant is 100:10 to 100:400.

[0011] (2) The present invention provides the carbon nanotube dispersion liquid according to (1) above, wherein the total content of the first dispersant and the second dispersant is 700 parts by weight or less per 100 parts by weight of the carbon nanotubes.

[0012] (3) The present invention provides the carbon nanotube dispersion according to (1) or (2) above, wherein the content of the first dispersant is 0.1 to 5 wt % based on the total weight of the dispersion.

[0013] (4) The present invention provides a carbon nanotube dispersion according to any one of (1) to (3) above, wherein the content of the second dispersant is 0.1 to 5 wt % based on the total weight of the dispersion.

[0014] (5) The present invention provides a carbon nanotube dispersion according to any one of (1) to (4) above, wherein the carbon nanotube content is 5% by weight or less based on the total weight of the dispersion.

[0015] (6) The present invention provides a carbon nanotube dispersion liquid according to any one of (1) to (5), wherein the first dispersant is one or more selected from the group consisting of carboxymethyl cellulose (CMC), carboxyethyl cellulose (CEC), hydroxyethyl methyl cellulose (HEMC), hydroxypropyl methyl cellulose (HPMC), hydroxymethyl cellulose (HMC), hydroxyethyl cellulose (HEC), and hydroxypropyl cellulose (HPC).

[0016] (7) The present invention provides the carbon nanotube dispersion liquid according to any one of (1) to (6) above, wherein the first dispersant has an average molecular weight of 9,000 g / mol or less.

[0017] (8) The present invention provides a carbon nanotube dispersion liquid according to any one of (1) to (7), wherein the second dispersant is one or more selected from the group consisting of PVdF-co-HFP, TFE-co-HFP, PTFE-co-HFP, and PVdF-co-HFP-TFE.

[0018] (9) The present invention provides the carbon nanotube dispersion liquid according to any one of (1) to (8) above, wherein the second dispersant has an average molecular weight of 700,000 g / mol or less.

[0019] (10) The present invention provides a method for producing a carbon nanotube dispersion liquid according to any one of (1) to (9), comprising a step (S10) of mixing carbon nanotubes, a first dispersant, a second dispersant and a solvent, and a step (S20) of dispersing the mixture.

[0020] (11) The present invention provides the method for producing a carbon nanotube dispersion according to (10), wherein the step S20 involves dispersion using a high-pressure disperser. [Effects of the Invention]

[0021] The carbon nanotube dispersion of the present invention has excellent processability during the coating process due to the low initial viscosity of the dispersion itself, and also has excellent storage stability due to little change in viscosity over time. DETAILED DESCRIPTION OF THE INVENTION

[0022] The present invention will now be described in more detail.

[0023] The terms and words used in this specification and claims should not be interpreted as being limited to their ordinary or dictionary meanings, but should be interpreted as having meanings and concepts that are consistent with the technical idea of ​​the present invention, based on the principle that inventors can appropriately define the concepts of terms in order to best explain their inventions.

[0024] The terms used in this specification are merely used to describe exemplary embodiments and are not intended to limit the present invention. The singular expressions include the plural expressions unless the context clearly indicates otherwise.

[0025] In this specification, the terms "comprises," "includes," "has," and the like are intended to specify the presence of embodied features, numbers, steps, components, or combinations thereof, but are not intended to preclude the possible presence or addition of one or more different features, numbers, steps, components, or combinations thereof.

[0026] In this specification, the "specific surface area" is measured by the BET method, and specifically, can be calculated from the amount of nitrogen gas adsorbed at liquid nitrogen temperature (77 K) using a BELSORP-mino II manufactured by BEL Japan.

[0027] In this specification, the "length of a carbon nanotube" can be measured using an atomic force microscope or a scanning electron microscope.

[0028] Carbon nanotube dispersion The present invention provides a carbon nanotube dispersion liquid comprising carbon nanotubes, a first dispersant, a second dispersant, and a solvent, wherein the first dispersant is a dispersant that is a cellulose-based component, and the second dispersant is a polymer dispersant that contains hexafluoropropylene (HFP) as a repeating unit, and the weight ratio of the first dispersant to the second dispersant is 100:10 to 100:400.

[0029] As mentioned above, when a cellulose-based dispersant, which is known as a dispersant for conventional carbon nanotube dispersions, is used as the sole dispersant, it has the effect of reducing the rate of viscosity change over time, but suffers from the problem of high initial viscosity of the dispersion itself. To address this drawback, conventional polymer-based dispersants, such as hydrogenated nitrile butadiene rubber (HNBR), have been used in addition to the cellulose-based dispersant. However, this approach results in an increase in not only the initial viscosity but also the rate of viscosity change over time. Therefore, the inventors of the present invention conducted extensive research into a dispersant that can maintain the technical advantages of conventional cellulose-based dispersants while improving their disadvantage of high initial viscosity. As a result, they discovered that when a polymer dispersant containing hexafluoropropylene (HFP) as a repeating unit is used together with a cellulose-based dispersant, both the initial viscosity and the rate of viscosity change over time can be reduced, leading to the completion of the present invention.

[0030] In particular, in the present invention, it has been confirmed that the initial viscosity and the rate of change in viscosity over time can be further reduced by controlling the weight ratio of the first dispersant, which is a cellulose-based dispersant, to the second dispersant, which is a polymer dispersant containing hexafluoropropylene (HFP) as a repeating unit, to 100:10 to 100:400.

[0031] (1) Carbon nanotubes The carbon nanotubes function as the conductive material in the dispersions of the present invention and can be single-walled or multi-walled carbon nanotubes.

[0032] The carbon nanotubes used in the present invention are not particularly limited, but preferably have a specific surface area of ​​800 to 2,000 m 2 / g, and the length is preferably 0.1 to 10 μm. When the carbon nanotubes satisfy the above conditions, they can have particularly excellent electrical conductivity. The specific surface area is measured by the BET method, and specifically, can be calculated from the amount of nitrogen gas adsorbed at liquid nitrogen temperature (77 K) using a specific surface area measuring device (BELSORP-mino II manufactured by BEL Japan). The length can be measured using an atomic force microscope or a scanning electron microscope.

[0033] In the carbon nanotube dispersion of the present invention, the carbon nanotube content can be 5.0 wt% or less, specifically 0.1 wt% or more, 0.2 wt% or more, 0.3 wt% or more, 0.4 wt% or more, 0.5 wt% or more, or 5.0 wt% or less, 4.5 wt% or less, 4.0 wt% or less, 3.5 wt% or less, 3.0 wt% or less, 2.5 wt% or less. On the other hand, if the carbon nanotube content is too low, sufficient conductivity cannot be achieved when used for applications such as conductive materials, and if the carbon nanotube content is too high, the viscosity of the dispersion may become too high, reducing processability.

[0034] (2) Dispersant In the carbon nanotube dispersion according to the present invention, a cellulose-based dispersant is used as the first dispersant, and a polymer dispersant containing hexafluoropropylene as a repeating unit is used as the second dispersant in order to improve the dispersibility of the carbon nanotubes.

[0035] (2-1) First dispersant The first dispersant used in the present invention is characterized by being a cellulose-based dispersant.

[0036] Specifically, the first dispersant may be one or more selected from the group consisting of carboxymethyl cellulose (CMC), carboxyethyl cellulose (CEC), hydroxyethyl methyl cellulose (HEMC), hydroxypropyl methyl cellulose (HPMC), hydroxymethyl cellulose (HMC), hydroxyethyl cellulose (HEC), and hydroxypropyl cellulose (HPC). The cellulose-based component significantly contributes to suppressing an increase in the viscosity of the dispersion over time, thereby improving the dispersibility of the carbon nanotube dispersion.

[0037] In the carbon nanotube dispersion of the present invention, the content of the first dispersant can be 0.1 to 5 wt % relative to the total weight of the dispersion, specifically 0.1 wt % or more, 0.2 wt % or more, 0.3 wt % or more, 0.4 wt % or more, 0.5 wt % or more, 0.6 wt % or more, 0.7 wt % or more, 0.8 wt % or more, 0.9 wt % or more, 1 wt % or more, and can be 5 wt % or less, 4.8 wt % or less, 4.6 wt % or less, 4.4 wt % or less, 4.2 wt % or less, 4.0 wt % or less, 3.8 wt % or less, 3.6 wt % or less, 3.4 wt % or less, 3.2 wt % or less, or 3.0 wt % or less.

[0038] If the content of the first dispersant component is less than the above range, the effect of the cellulose-based dispersant may be insufficient, resulting in a decrease in the dispersibility of the dispersion or a significant change in the viscosity of the dispersion over time. Also, if the content of the first dispersant component is more than the above range, when the carbon nanotube dispersion is applied to an electrode, an excessive amount of dispersant may inhibit the conductivity of the electrode, and the dispersant may act as an impurity in the electrode.

[0039] Meanwhile, the first dispersant used in the present invention may have a weight average molecular weight (Mw) of 9,000 g / mol or less.

[0040] (2-2) Second dispersant The second dispersant used in the present invention is characterized by containing a polymer dispersant containing hexafluoropropylene (HFP) as a repeating unit.

[0041] The second dispersant may be one or more selected from the group consisting of PVdF-co-HFP, TFE-co-HFP, PTFE-co-HFP, and PVdF-co-HFP-TFE. When the polymer dispersant containing hexafluoropropylene as a repeating unit is applied to a carbon nanotube dispersion, it can induce an interaction between the carbon nanotubes and the numerous F atoms present in the dispersant, and in particular, can play a role in reducing the initial viscosity of the dispersion.

[0042] In the carbon nanotube dispersion of the present invention, the content of the second dispersant can be 0.1 to 5 wt % relative to the total weight of the dispersion, specifically 0.1 wt % or more, 0.2 wt % or more, 0.3 wt % or more, 0.4 wt % or more, 0.5 wt % or more, 0.6 wt % or more, 0.7 wt % or more, 0.8 wt % or more, 0.9 wt % or more, 1 wt % or more, and can be 5 wt % or less, 4.8 wt % or less, 4.6 wt % or less, 4.4 wt % or less, 4.2 wt % or less, 4.0 wt % or less, 3.8 wt % or less, 3.6 wt % or less, 3.4 wt % or less, 3.2 wt % or less, or 3.0 wt % or less.

[0043] If the content of the second dispersant component is less than the above range, the effect achieved by the hexafluoropropylene component will be insufficient, and the initial viscosity of the dispersion itself may become excessively high. If the content of the second dispersant component is more than the above range, the content of the cellulose-based component will decrease relatively, and the viscosity of the dispersion may change significantly over time.

[0044] Meanwhile, the second dispersant used in the present invention may have a weight average molecular weight (Mw) of 700,000 g / mol or less.

[0045] The weight ratio of the first dispersant to the second dispersant may be 100:10 to 100:400. Specifically, with respect to 100 parts by weight of the first dispersant, the second dispersant may be 10 parts by weight or more, 20 parts by weight or more, 30 parts by weight or more, 40 parts by weight or more, 50 parts by weight or more, 60 parts by weight or more, 70 parts by weight or more, 80 parts by weight or more, 90 parts by weight or more, 100 parts by weight or more, or 400 parts by weight or less, 390 parts by weight or less, 380 parts by weight or less, 370 parts by weight or less, 360 parts by weight or less. The amount may be 50 parts by weight or less, 340 parts by weight or less, 330 parts by weight or less, 320 parts by weight or less, 310 parts by weight or less, 300 parts by weight or less, 290 parts by weight or less, 280 parts by weight or less, 270 parts by weight or less, 260 parts by weight or less, or 250 parts by weight or less. Within this range, the synergistic effect of the first dispersant and the second dispersant is maximized, carbon nanotubes are uniformly dispersed in the carbon nanotube dispersion, and the viscosity can be maintained at a predetermined level over time along with low viscosity.

[0046] On the other hand, the total content of the first dispersant and the second dispersant may be 700 parts by weight or less per 100 parts by weight of carbon nanotubes. Specifically, the total content of the first dispersant and the second dispersant may be 50 parts by weight or more, 100 parts by weight or more, 150 parts by weight or more, or 200 parts by weight or more per 100 parts by weight of carbon nanotubes, or may be 700 parts by weight or less, 650 parts by weight or less, 600 parts by weight or less, or 550 parts by weight or less.

[0047] If the total content of the first dispersant and the second dispersant is greater than the above range, the excessive amount of dispersant may inhibit the conductivity of the electrode when the carbon nanotube dispersion is applied to the electrode, and the dispersant may act as an impurity in the electrode, increasing the viscosity of the dispersion and reducing viscosity stability. On the other hand, if the amount is less than the above range, the effects of improving dispersibility, reducing viscosity, and suppressing changes in viscosity over time may be insufficient.

[0048] By controlling the weight ratio of the first dispersant and the second dispersant, the carbon nanotube dispersion of the present invention can reduce both the initial viscosity and the change in viscosity over time, as described above, thereby achieving excellent coating processability and storage stability.

[0049] (3) Solvent The solvent used in the present invention is a solvent for dispersing the carbon nanotubes and the dispersant, and can be used to prevent aggregation when powdered carbon nanotubes are directly applied to the preparation of an electrode slurry composition.

[0050] The solvent may be one that can dissolve or disperse the carbon nanotubes and dispersant to a predetermined level or more, and may be included in an amount that allows the electrode slurry composition to have an appropriate viscosity, taking into consideration the processability of the electrode slurry composition to be prepared using the carbon nanotube dispersion liquid.

[0051] The solvent is not particularly limited as long as it is one that is commonly used in the art for dispersing the carbon nanotubes and dispersants, and can be, for example, one or more selected from the group consisting of amide-based polar organic solvents, alcohol-based solvents, glycol-based solvents, glycol ether-based solvents, ketone-based solvents, ester-based solvents, and aqueous solvents.

[0052] The amide-based polar organic solvent may be one or more selected from the group consisting of N-methylpyrrolidone (NMP), dimethylformamide (DMF), diethylformamide, and dimethylacetamide (DMAc).

[0053] The alcohol solvent may be one or more selected from the group consisting of methanol, ethanol, 1-propanol, 2-propanol (or isopropyl alcohol), 1-butanol, 2-methyl-1-propanol, 2-butanol, 1-methyl-2-propanol, pentanol, hexanol, heptanol, octanol, glycerin, trimethylolpropane, pentaerythritol, and sorbitol.

[0054] The glycol-based solvent may be one or more selected from the group consisting of ethylene glycol, diethyl glycol, triethylene glycol, propylene glycol, 1,3-propanediol, 1,3-butanediol, 1,5-pentanediol, and hexylene glycol.

[0055] The glycol ether solvent may be one or more selected from the group consisting of 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, and tetraethylene glycol monobutyl ether.

[0056] The ketone solvent may be one or more selected from the group consisting of acetone, methyl ethyl ketone, methyl propyl ketone, and cyclopentanone.

[0057] The ester solvent can be one or more selected from the group consisting of ethyl acetate, gamma-butyrolactone, and epsilon-propiolactone.

[0058] The aqueous solvent may be water.

[0059] The carbon nanotube dispersion of the present invention can have an initial viscosity of 10,500 cP or less, preferably 10,000 cP or less, when measured at 25°C with a No. 1 rotor at 1 rpm using a viscometer (Viscometer TV-25, manufactured by TOKI SANGYO Co., Ltd.). Furthermore, the viscosity of the dispersion that satisfies the initial viscosity requirement can change by 25% or less, preferably 20% or less, over one week.

[0060] The one-week viscosity change rate is calculated by determining how much the viscosity increases over one week when the dispersion is stored at 25°C for one week, and can be calculated using the following formula 1.

[0061] [Formula 1] Viscosity change rate (%) = (viscosity after 1 week - initial viscosity) / (initial viscosity) * 100% On the other hand, the viscosity can be measured using a viscometer (viscometer TV-25, manufactured by TOKI SANGYO Co., Ltd.) by starting measurement at 1 rpm with a No. 1 rotor and recording the value after 10 minutes.

[0062] Method for producing carbon nanotube dispersion The present invention provides a method for producing the above-mentioned carbon nanotube dispersion liquid, specifically, a method for producing a carbon nanotube dispersion liquid including a step (S10) of mixing carbon nanotubes, a first dispersant, a second dispersant and a solvent, and a step (S20) of dispersing the mixture.

[0063] In the method for producing a carbon nanotube dispersion of the present invention, the carbon nanotubes, the first dispersant, the second dispersant, and the solvent are as described above.

[0064] Meanwhile, step S10, in which all of the above components are mixed, can be carried out using a method generally applied to mixing processes. For example, an impeller and a container can be attached to a dissolution tank (Dispermat-CA, manufactured by VMA-Getzmann) and mixed at 400 rpm for 10 minutes, and then carbon nanotubes can be added and treated at 8,000 rpm for 60 minutes.

[0065] In addition, the step S20 can disperse the mixture to produce a final dispersion. This dispersion step can make the physical properties of the carbon nanotubes in the dispersion uniform. The dispersion method can be selected from the group consisting of bead milling, ball milling, and high-pressure homogenization, and is preferably a dispersion method using a high-pressure disperser. When a dispersion method using a high-pressure disperser is used, more uniform dispersion is possible, and the viscosity of the resulting carbon nanotube dispersion can be maintained lower.

[0066] For example, in step S20, the mixture produced in step S10 can be treated 10 times at a pressure of 20,000 psi using a high-pressure disperser (PICOMAX, manufactured by Micronox) to produce a carbon nanotube dispersion.

[0067] The carbon nanotube dispersion produced by the carbon nanotube dispersion production method of the present invention may have an initial viscosity of 10,500 cP or less, preferably 10,000 cP or less. Furthermore, while satisfying the initial viscosity requirement, the viscosity change rate of the dispersion over one week may be 25% or less, preferably 20% or less.

[0068] Hereinafter, the present invention will be described in detail with reference to examples and experimental examples in order to specifically explain the present invention. However, the present invention is not limited to 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 interpreted as being limited to the examples detailed below. The examples of the present invention are provided to more completely explain the present invention to those skilled in the art.

[0069] material Specific surface area is 1,160m 2 Carbon nanotubes (TUBALL, manufactured by OCSiAl) with a molecular weight of 1 / g and a length of 5 μm or more were prepared. N-methyl-2-pyrrolidone (NMP) was prepared as a solvent.

[0070] In the examples, carboxymethyl cellulose (weight average molecular weight: 5,200 g / mol) or carboxyethyl cellulose (weight average molecular weight: 7,000 g / mol) was used as the first dispersant, and PVdF-co-HFP (weight average molecular weight: 148,000 g / mol) was used as the second dispersant.

[0071] In the comparative examples, carboxymethyl cellulose (weight average molecular weight: 5,200 g / mol) or polyvinylpyrrolidone (PVP) (weight average molecular weight: 10,000 g / mol) was used as the first dispersant, and polyvinylidene fluoride (PVdF) (weight average molecular weight: 1,000,000 g / mol), hydrogenated nitrile butadiene rubber (HNBR) (weight average molecular weight: 200,000 g / mol) or PVdF-co-HFP (weight average molecular weight: 148,000 g / mol) was used as the second dispersant.

[0072] Examples and Comparative Examples A mixture was prepared by mixing the first dispersant, second dispersant, and NMP as a solvent, as described above. After fitting an impeller and container into a dissolution tank (Dispermat-CA, VMA-Getzmann), the mixture was stirred at 400 rpm for 10 minutes to mix the dispersant and solvent. Carbon nanotubes (TUBALL, OCSiAl) were added so that their content in the dispersion was 0.6 wt %, and the mixture was processed at 8,000 rpm for 60 minutes.

[0073] The resultant was treated 10 times at a pressure of 20,000 psi using a high-pressure disperser (PICOMAX, manufactured by Micronox) to prepare a carbon nanotube dispersion.

[0074] The concentration of carbon nanotubes used in each example and comparative example, the type and content (based on the total weight of the dispersion) of the first dispersant and the second dispersant used, and the weight ratio between the dispersants are summarized in Table 1 below.

[0075] [Table 1A]

[0076] [Table 1B]

[0077] Experimental example: Confirming the initial viscosity and viscosity change rate of the dispersion liquid The viscosity of the carbon nanotube dispersions of Examples 1 to 5 and Comparative Examples 1 to 9 was measured, and the viscosity was measured again after leaving them at 25° C. for one week. The results are shown in Table 2 below.

[0078] The viscosity was measured using a viscometer (viscometer TV-25, manufactured by TOKI SANGYO) at 25°C and 1 rpm using a No. 1 rotor.

[0079] [Table 2]

[0080] As can be seen from Table 2, comparing Examples 1-5 and Comparative Examples 1-9, which used the same carbon nanotubes and solvents at the same content, it can be seen that Examples 1-5, which used the first dispersant and second dispersant of the present invention in a specific weight ratio range, not only had low initial viscosities but also low viscosity change rates after one week. On the other hand, Comparative Example 1, which did not use a second dispersant, had a low viscosity change rate but a high initial viscosity of 13,000 cP. Comparative Example 2, which used PVdF as the second dispersant, also had a low viscosity change rate but a high initial viscosity of 11,000 cP. Furthermore, gel shrinkage (syneresis) was observed, confirming poor storage stability. In particular, Comparative Example 3, which used hydrogenated nitrile butadiene rubber (HNBR) as the second dispersant, showed both high initial viscosity and viscosity change rates, significantly reducing storage stability. In Comparative Example 8, in which a polymer dispersant containing HFP was used as the second dispersant but PVP was used instead of a cellulose-based dispersant as the first dispersant, the initial viscosity was high at nearly 11,000 cP. In Comparative Example 9, in which a polymer dispersant containing HFP was used alone, not only was the initial viscosity high, but the rate of change in viscosity was so high that storage stability was significantly reduced and gel shrinkage was also observed.

[0081] In addition, as in the examples, a cellulose-based dispersant and a polymer dispersant containing HFP were used as the first and second dispersants, but in Comparative Examples 4 to 7, where the weight ratio between the dispersants was outside the range of 100:10 to 100:400, the initial viscosity was 12,500 cP or higher in all cases. In particular, in Comparative Example 5, where an excessive amount of polymer dispersant containing HFP was used, the rate of change in viscosity was also high.

[0082] Therefore, it was confirmed that the dispersion of the present invention has excellent processability due to its low initial viscosity and low rate of change in viscosity, and thus has improved storage stability.

Claims

1. carbon nanotubes, a first dispersant, a second dispersant, and a solvent; the first dispersant is a cellulose-based dispersant; the second dispersant is a polymer dispersant containing hexafluoropropylene (HFP) as a repeating unit, The carbon nanotube dispersion liquid, wherein the weight ratio of the first dispersant to the second dispersant is 100:10 to 100:

400.

2. 2 . The carbon nanotube dispersion liquid according to claim 1 , wherein the total content of the first dispersant and the second dispersant is 700 parts by weight or less with respect to 100 parts by weight of the carbon nanotubes.

3. 2 . The carbon nanotube dispersion liquid according to claim 1 , wherein the content of the first dispersant is 0.1% by weight or more and 5% by weight or less with respect to the total weight of the dispersion liquid.

4. 2. The carbon nanotube dispersion liquid according to claim 1, wherein the content of the second dispersant is 0.1 wt % or more and 5 wt % or less with respect to the total weight of the dispersion liquid.

5. 2. The carbon nanotube dispersion according to claim 1, wherein the carbon nanotube content is 5% by weight or less based on the total weight of the dispersion.

6. 2. The carbon nanotube dispersion according to claim 1, wherein the first dispersant is one or more selected from the group consisting of carboxymethyl cellulose (CMC), carboxyethyl cellulose (CEC), hydroxyethyl methyl cellulose (HEMC), hydroxypropyl methyl cellulose (HPMC), hydroxymethyl cellulose (HMC), hydroxyethyl cellulose (HEC), and hydroxypropyl cellulose (HPC).

7. The carbon nanotube dispersion liquid according to claim 1 , wherein the first dispersant has an average molecular weight of 9,000 g / mol or less.

8. 2. The carbon nanotube dispersion according to claim 1, wherein the second dispersant is one or more selected from the group consisting of PVdF-co-HFP, TFE-co-HFP, PTFE-co-HFP, and PVdF-co-HFP-TFE.

9. The carbon nanotube dispersion liquid according to claim 1 , wherein the second dispersant has an average molecular weight of 700,000 g / mol or less.

10. A step (S10) of mixing carbon nanotubes, a first dispersant, a second dispersant, and a solvent; The method for producing a carbon nanotube dispersion liquid according to any one of claims 1 to 9, further comprising the step (S20) of dispersing the mixture.

11. The method for producing a carbon nanotube dispersion liquid according to claim 10 , wherein the step S20 involves dispersion using a high-pressure disperser.

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