Carbon nanotube dispersion solution and preparation method therefor

Abstract

A carbon nanotube dispersion solution comprising carbon nanotubes, a dispersant and a solvent is provided. The dispersant comprises a first dispersant, which comprises a first polymer compound containing an amine group, and a second dispersant, which comprises a second polymer compound containing an aromatic ring. The second dispersant comprises 65 mol% or higher of aromatic carbons on the basis of the total moles of carbon atoms. The carbon nanotube dispersion solution according to one embodiment of the present invention contains aromatic carbons at a specific level or higher as a second dispersant, and thus can remarkably reduce the initial viscosity of the carbon nanotube dispersion solution and the aging change rate of the subsequent viscosity thereof.

Description

Carbon nanotube dispersion and method for producing the same

[0001] The present invention relates to a carbon nanotube dispersion and a method for producing the same. Specifically, the present invention relates to a carbon nanotube dispersion and a method for producing the same, which comprises a first dispersant containing a first polymer compound containing an amine group and a second dispersant containing a second polymer compound containing an aromatic ring, to improve the dispersibility of carbon nanotubes.

[0002] This application claims the benefit of priority to Korean Patent Application No. 10-2023-0097140, Korean Patent Application No. 10-2023-0097142, and Korean Patent Application No. 10-2023-0097145, all of which are hereby incorporated herein by reference.

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

[0004] In general, high-density electrodes are formed by molding electrode active material particles having a size of several micrometers to several tens of micrometers using a high-pressure press. However, during the molding process, the particles may be deformed and the space between the particles may be reduced, which easily reduces the electrolyte permeability. To solve the above problems, conductive materials with excellent electrical conductivity and strength are used in the manufacture of electrodes. The conductive material is positioned between the electrode active materials, and even when going through the molding process, it maintains the micropores between the active material particles, allowing the electrolyte to easily permeate, and its excellent electrical conductivity can reduce the resistance within the electrode. Among these conductive materials, the use of carbon nanotubes, which are fibrous carbon-based conductive materials that can further reduce the electrode resistance by forming an electrically conductive path within the electrode, is increasing.

[0005] The carbon nanotubes are microscopic carbon fibers in which carbons connected by hexagonal rings form a long tube-shaped structure with a diameter of less than 1 μm. Due to the high conductivity, tensile strength, and heat resistance caused by the unique structure of the carbon nanotubes, their application and practical use in various fields are expected. In order to commercialize the carbon nanotubes as a conductive material, it is necessary to manufacture them in a dispersion state rather than a powder form. However, the carbon nanotubes have strong cohesion, making it difficult to lower their viscosity when manufactured as a dispersion. Even if the viscosity is lowered, the viscosity increases rapidly over time, making it difficult to apply them to actual processes.

[0006] To address these issues, mechanical dispersion techniques, such as sonication, have been proposed to disperse carbon nanotubes in a dispersion medium. However, mechanical dispersion techniques suffer from the problem of carbon nanotubes agglomerating immediately after the sonication process ends. This agglomeration of carbon nanotubes reduces coating properties during the process and makes it difficult to obtain a product with a uniform thickness.

[0007] Therefore, a technology for producing carbon nanotube dispersions with low viscosity and low viscosity change over time is required in this technical field. The inventors of the present invention have completed this invention after continuous research into additives to address the aforementioned problems in carbon nanotube dispersions.

[0008] [Prior Art Literature]

[0009] [Patent Document]

[0010] (Patent Document 1) Republic of Korea Patent Publication No. 10-2015-0122653

[0011] The present invention aims to provide a carbon nanotube dispersion in which carbon nanotubes are efficiently dispersed and a method for producing the same, using a first dispersant containing a first polymer compound containing an amine group and a second dispersant containing a second polymer compound containing an aromatic ring.

[0012] According to the first aspect of the present invention,

[0013] The present invention provides a carbon nanotube dispersion comprising carbon nanotubes, a dispersant, and a solvent.

[0014] In one specific example of the present invention, the dispersant includes a first dispersant containing a first polymer compound including an amine group; and a second dispersant containing a second polymer compound including an aromatic ring.

[0015] In one specific embodiment of the present invention, the second dispersant contains aromatic carbons in an amount of 65 mol% or more based on the total number of moles of carbon atoms.

[0016] In one specific embodiment of the present invention, the first polymer compound is selected from the group consisting of polyvinylpyrrolidone, polyacrylic acid hydrazide, poly-N-vinyl-5-methoxazolidone, N-alkyl polyimine, N-acetyl polyimine, polyacrylamide, poly-L-lysine hydrobromide, benzyl-dodecyl-dimethylammonium chloride, polyethyleneimine, and combinations thereof.

[0017] In one specific example of the present invention, the second polymer compound further includes a carbonyl group, and the second dispersant has a ratio of the carbonyl group to the aromatic ring (integrated average value of the carbonyl group / integrated average value of the aromatic ring) according to FT-IR of 0.2 or less.

[0018] In one specific example of the present invention, the dispersant has a Na content of 250 ppm to 500 ppm based on the total weight of the dispersant.

[0019] In one specific example of the present invention, the dispersant has a Ca content of 0.1 ppm to 50 ppm based on the total weight of the dispersant.

[0020] In one specific example of the present invention, the second polymer compound is lignosulfonate.

[0021] In one specific example of the present invention, the first dispersant is included in the carbon nanotube dispersion in an amount of 200 to 400 parts by weight based on 100 parts by weight of the second dispersant.

[0022] In one specific example of the present invention, the dispersant is included in the carbon nanotube dispersion in an amount of 100 to 300 parts by weight based on 100 parts by weight of carbon nanotubes.

[0023] In one specific example of the present invention, the carbon nanotubes are included in the carbon nanotube dispersion in an amount of 0.1 wt% to 5 wt% based on the total weight of the carbon nanotube dispersion.

[0024] In one specific example of the present invention, the carbon nanotube has a diameter of 800 m 2 / g to 5,000 m 2 It has a BET surface area of ​​ / g.

[0025] In one specific example of the present invention, the solvent is an aqueous solvent containing water.

[0026] In one specific example of the present invention, the carbon nanotube dispersion has an initial viscosity of 5,000 cP or less at 25°C.

[0027] In one specific example of the present invention, the carbon nanotube dispersion has a viscosity of 10,000 cP or less after storage at 45°C for 65 hours and cooling to 25°C.

[0028] According to the second aspect of the present invention,

[0029] The present invention provides a method for producing the carbon nanotube dispersion described above.

[0030] According to one specific example of the present invention, the manufacturing method comprises: (1) a step of preparing a mixture by mixing carbon nanotubes, a first dispersant containing a first polymer compound including an amine group, a second dispersant containing a second polymer compound including an aromatic ring, and a solvent; and (2) a step of stirring the mixture.

[0031] According to the third aspect of the present invention,

[0032] The present invention provides an electrode slurry composition for a lithium secondary battery comprising the above-described carbon nanotube dispersion and electrode active material.

[0033] A carbon nanotube dispersion according to one specific example of the present invention can effectively disperse the carbon nanotube dispersion by including a first dispersant containing a first polymer compound containing an amine group and a second dispersant containing a second polymer compound containing an aromatic ring.

[0034] In particular, the second dispersant can significantly reduce not only the initial viscosity of the carbon nanotube dispersion but also the rate of change in viscosity over time by containing aromatic carbon above a certain level.

[0035] The specific embodiments provided in accordance with the present invention can all be achieved by the following description. It should be understood that the following description describes preferred embodiments of the present invention and that the present invention is not necessarily limited thereto.

[0036] For the properties described in this specification, if the measurement conditions and methods are not specifically described, the properties are measured according to the measurement conditions and methods generally used by those skilled in the art.

[0037]

[0038] Carbon nanotube dispersion

[0039] According to one aspect of the present invention, the present invention provides a carbon nanotube dispersion comprising carbon nanotubes, a dispersant, and a solvent. The carbon nanotubes have high conductivity and can be utilized as a conductive material for lithium secondary batteries, etc., but there is a problem that it is difficult to apply in an actual process because dispersion is not easy. The present invention provides a carbon nanotube dispersion with improved dispersibility of carbon nanotubes by utilizing a first dispersant containing a first polymer compound containing an amine group and a second dispersant containing a second polymer compound containing an aromatic ring as dispersants for effectively dispersing carbon nanotubes.

[0040] The carbon nanotubes above can be materials commonly used as conductive materials in the relevant technical field. The carbon nanotubes are secondary structures formed by assembling carbon nanotube units in whole or in part to form bundles, and the carbon nanotube units have a graphite sheet in the shape of a cylinder with a nano-sized diameter, and sp 2It has a bonding structure. At this time, depending on the angle and structure at which the graphite plane is rolled, it can exhibit the characteristics of a conductor or a semiconductor. The carbon nanotube unit can be classified into a single-walled carbon nanotube (SWCNT, single-walled carbon nanotube), a double-walled carbon nanotube (DWCNT, double-walled carbon nanotube), and a multi-walled carbon nanotube (MWCNT, multi-walled carbon nanotube) depending on the number of bonds forming the wall.

[0041] In this specification, unless otherwise stated, the term 'bundle type' refers to a secondary shape in the form of a bundle or rope in which a plurality of carbon nanotube units are arranged in a substantially identical orientation along the longitudinal direction of the units, or are arranged and then twisted or entangled. In addition, the term 'non-bundle type or entangled type' refers to a shape in which carbon nanotube units are entangled without a specific shape such as a bundle or rope.

[0042] While the above carbon nanotubes are highly conductive, they are prone to aggregation due to the van der Waals forces that occur between them. When the conductive material aggregates, it fails to properly form a conductive path, requiring a relatively larger amount of conductive material, reducing the amount of active material and potentially degrading electrode performance. Consequently, commercializing carbon nanotubes as a conductive material has been challenging.

[0043] The carbon nanotube dispersion according to the present invention comprises a first dispersant containing a first polymer compound containing an amine and a second dispersant containing a second polymer compound containing an aromatic ring, thereby significantly reducing the viscosity of the aqueous carbon nanotube dispersion and suppressing the occurrence of changes over time, thereby exhibiting high conductivity due to the high conductivity of the carbon nanotubes when applied to an electrode slurry of a lithium secondary battery.

[0044] Specifically, when the carbon nanotube dispersion according to the present invention is applied to the manufacture of an electrode slurry, the carbon nanotubes are uniformly positioned between the active materials, so that even during the process of manufacturing an electrode by coating and drying the electrode slurry and then rolling, the microscopic spaces between the electrode active materials can be maintained at a constant level. In addition, the carbon nanotubes are uniformly distributed without agglomeration, so that even a small amount of carbon nanotubes can sufficiently form a conductive path.

[0045] A carbon nanotube dispersion according to one specific example of the present invention may include at least one of single-walled, double-walled, and multi-walled carbon nanotube units as the carbon nanotubes, and specifically may include single-walled carbon nanotubes. Since the single-walled carbon nanotubes have a higher specific surface area than double-walled and multi-walled carbon nanotubes, they can be helpful in improving the performance of lithium secondary batteries as a conductive material.

[0046] According to one specific example of the present invention, the carbon nanotube has a diameter of 0.5 nm to 10 nm. Here, the diameter means the largest value among the distances from one outermost arbitrary point to another point based on the circular cross-section of the carbon nanotube. The diameter of the carbon nanotube can be measured by photographing with a scanning electron microscope. Specifically, the diameter of the carbon nanotube is 0.5 nm or more, 0.6 nm or more, 0.7 nm or more, 0.8 nm or more, 0.9 nm or more, 1 nm or more, 10 nm or less, 9 nm or less, 8 nm or less, 7 nm or less, 6 nm or less, 5 nm or less, and may be 0.5 nm to 10 nm, 0.7 nm to 7 nm, or 1 nm to 5 nm. Carbon nanotubes having a diameter in the above range can be effectively dispersed in an electrode of a lithium secondary battery to impart conductivity to the electrode.

[0047] According to one specific example of the present invention, the carbon nanotube has a length of 1 μm to 20 μm. Here, the length refers to the height of the cylindrical carbon nanotube. The length of the carbon nanotube can be measured by photographing with a scanning electron microscope. Specifically, the length of the carbon nanotube is 1 μm or more, 2 μm or more, 3 μm or more, 4 μm or more, 5 μm or more, 20 μm or less, 19 μm or less, 18 μm or less, 17 μm or less, 16 μm or less, 15 μm or less, and may be 1 μm to 20 μm, 3 μm to 18 μm, or 5 μm to 15 μm. Carbon nanotubes having a length in the above range can effectively connect components in an electrode of a lithium secondary battery and provide conductivity to the electrode.

[0048] According to one specific example of the present invention, the carbon nanotube has a diameter of 800 m 2 / g to 5,000 m 2 / g of BET specific surface area. The BET specific surface area is a specific surface area measured by the BET method, and specifically, it is preferably calculated by obtaining the nitrogen gas adsorption amount at liquid nitrogen temperature (77K) using BELSORP-mini II of BEL Japan. Specifically, the BET specific surface area of ​​the carbon nanotube is 800 m 2 / g or more, 850 m 2 / g or more, 900 m 2 / g or more, 950 m 2 / g or more, 1,000 m 2 / g and 5,000 m 2 / g or less, 4,500 m 2 / g or less, 4,000 m 2 / g or less, 3,500 m 2 / g or less, 3,000 m 2 / g or less, 2,500 m 2 / g or less, 2,000 m 2 / g or less, 800 m 2 / g to 5,000 m 2 / g, 900 m 2 / g to 3,500 m 2 / g, 1,000 m 2 / g to 2,000 m 2 / g. Carbon nanotubes having a BET surface area in the above range can effectively contact other components in the electrode of a lithium secondary battery and provide conductivity to the electrode.

[0049] According to one specific example of the present invention, the carbon nanotubes are included in the carbon nanotube dispersion in an amount of 0.1 wt% to 5 wt% based on the total weight of the carbon nanotube dispersion. Specifically, the content of the carbon nanotubes is 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, 5 wt% or less, 4.5 wt% or less, 4 wt% or less, 3.5 wt% or less, 3 wt% or less, 2.5 wt% or less, 2 wt% or less, 1.5 wt% or less, and may be 0.1 wt% to 5 wt%, 0.3 wt% to 3 wt%, or 0.5 wt% to 1.5 wt%. When the carbon nanotubes in the carbon nanotube dispersion are controlled within the above-described range, the carbon nanotubes can be effectively dispersed, making it easy to apply the carbon nanotubes to a lithium secondary battery.

[0050] A carbon nanotube dispersion according to one embodiment of the present invention comprises a first dispersant and a second dispersant in addition to a solvent to effectively disperse the carbon nanotubes described above. Since the carbon nanotube dispersion has a relatively high content of carbon nanotubes, it may be important to appropriately combine components other than carbon nanotubes to effectively disperse the carbon nanotubes without agglomeration and to increase their utility value. On the other hand, if the content of carbon nanotubes is low, the solid content of the electrode slurry produced during the production of the electrode slurry may decrease, which may unnecessarily thicken the electrode slurry before drying, which may lead to a deterioration in the quality of the electrode after drying.

[0051] The solvent primarily serves to disperse carbon nanotubes, the first dispersant, and the second dispersant. Carbon nanotubes are used as conductive materials in practical products such as lithium secondary batteries. However, if the carbon nanotubes are added to the electrode slurry in their powder form, they will aggregate and fail to function properly within the electrode. To address this issue, the carbon nanotubes are pre-dispersed and supplied as a carbon nanotube dispersion.

[0052] The solvent is not particularly limited as long as it can effectively disperse the carbon nanotubes, the first dispersant, and the second dispersant. According to one specific example of the present invention, the solvent is an aqueous solvent containing water. The aqueous solvent may be included in an amount such that the electrode slurry composition prepared using the carbon nanotube dispersion can have an appropriate viscosity, taking into account the coating properties of the electrode slurry composition, etc. Even if the content of the solvent is not specifically mentioned herein, the content of the solvent may be the content of the carbon nanotube dispersion, excluding the respective contents of the carbon nanotubes, the first dispersant, and the second dispersant.

[0053] A carbon nanotube dispersion according to one embodiment of the present invention further comprises a dispersant, since a solvent alone cannot effectively disperse carbon nanotubes. The dispersant may be a single substance, or a combination of two or more substances. According to one embodiment of the present invention, the dispersant comprises a first dispersant and a second dispersant. The first dispersant and the second dispersant may be distinguished based on the amount used, and the dispersant used in a larger amount among the two dispersants may be the first dispersant.

[0054] According to one specific embodiment of the present invention, the first dispersant comprises a first polymer compound comprising an amine group. In this specification, the amine group may be broadly interpreted as a nitrogen-containing functional group. When the first polymer compound comprising an amine group is used as the first dispersant, viscosity improvement effects and changes in viscosity over time can be achieved in a carbon nanotube dispersion. The first polymer compound may preferably be dissolved in a solvent, particularly an aqueous solvent, and may be selected from the group consisting of, for example, polyvinylpyrrolidone, polyacrylic acid hydrazide, poly-N-vinyl-5-methoxazolidon, N-alkyl polyimine, N-acetyl polyimine, polyacrylamide, poly-L-lysine hydrobromide, benzyl-dodecyl-dimethylammonium chloride, polyethylenimine, and combinations thereof.

[0055] The second dispersant may be a material that can be used together with the first dispersant described above to produce a synergistic effect in dispersing carbon nanotubes. According to one specific example of the present invention, the second dispersant contains a second polymer compound containing an aromatic ring. Although the second dispersant described above contains an aromatic ring, the content of carbon constituting the aromatic ring may play an important role in dispersing carbon nanotubes in relation to the first dispersant. In addition, since the aromatic ring contained in the second dispersant has a molecular structure similar to that of carbon nanotubes, it can form a strong bond with individual carbon nanotubes through π-π interaction or hydrophobic interaction, and thus, it can have the functionality of dispersing carbon nanotubes without causing the carbon nanotubes to aggregate with each other.

[0056] According to one specific example of the present invention, the second dispersant includes aromatic carbon at 65 mol% or more based on the total number of moles of carbon atoms. The aromatic carbon refers to a carbon atom constituting an aromatic ring. The content of aromatic carbon in the second dispersant can be confirmed, for example, using an NMR device. Specifically, the content of aromatic carbon was measured by 1D normal NMR (Bruker Prodigy 500MHz NMR, 13C, Probe (PABBO), D-solvent: D2O or DMSO-d6, temperature: 298K). Specifically, the content of aromatic carbon may be 65 mol% or more, 65.5 mol% or more, 66 mol% or more, 66.5 mol% or more, or 67 mol% or more. The upper limit of the content of the aromatic carbon can be naturally adjusted depending on the presence of other components in the compound, but for example, it can be 90 mol% or less, 89 mol% or less, 88 mol% or less, 87 mol% or less, 86 mol% or less, 85 mol% or less, 84 mol% or less, and can be 65 mol% to 90 mol%, 66 mol% to 87 mol%, or 67 mol% to 84 mol%. When the content of the aromatic carbon in the second dispersant is within the above-described range, the synergistic effect with the first dispersant can be maximized.

[0057] According to one specific example of the present invention, when the second polymer compound analyzes an aromatic ring using an FT-IR device, the second polymer compound has an integrated average value of 20 to 150. A specific analysis method and device for deriving the integrated average value may follow the description of the following examples. Specifically, the integrated average value of the aromatic ring is 20 or more, 25 or more, 30 or more, 35 or more, or 40 or more, and 150 or less, 140 or less, 130 or less, 120 or less, or 110 or less, and may be 20 to 150, 30 to 130, or 40 to 110. The second polymer compound may be further specified within the above-described range.

[0058] According to one specific example of the present invention, the second polymer compound further includes a carbonyl group. In the second dispersant described above, the ratio of the carbonyl group to the aromatic ring may play an important role in dispersing carbon nanotubes in relation to the first dispersant. According to one specific example of the present invention, when the second dispersant analyzes the carbonyl group (C=O) and the aromatic ring with an FT-IR device, the ratio of the carbonyl group to the aromatic ring (integrated average value of the carbonyl group / integrated average value of the aromatic ring) is 0.2 or less. A specific analysis method and device for deriving the integrated average value may follow the description of the following examples. The integrated value is performed in a range generally known in the relevant technical field. For example, 1,800 cm - -1 , 900cm -1 With 1,738 cm as the baseline, the carbonyl group - -1 ~1,675cm - -1 Integrate the region of the aromatic ring at 1,523 cm - -1 ~1,478cm - -1 The area of ​​the carbonyl group is integrated. Specifically, the ratio of the carbonyl group to the aromatic ring (integrated average value of the carbonyl group / integrated average value of the aromatic ring) may be 0.2 or less, 0.05 to 0.2, 0.06 to 0.2, 0.07 to 0.2, or 0.08 to 0.2. When the ratio of the carbonyl group to the aromatic ring in the second dispersant is within the above-described range, the synergistic effect with the first dispersant can be maximized.

[0059] According to one specific example of the present invention, the second polymer compound has an integrated average value of 1 to 50 when analyzing the C=O functional group with an FT-IR device. Specifically, the integrated average value of the C=O functional group is 1 or more, 2 or more, or 3 or more, and 50 or less, 45 or less, 40 or less, 35 or less, or 30 or less, and may be 1 to 50, 2 to 40, or 3 to 30. The second polymer compound may be further specified within the above-described range.

[0060] According to one specific embodiment of the present invention, the second polymer compound further comprises a sulfone group and a hydroxyl group in addition to an aromatic ring and a carbonyl group. In the second polymer compound according to one specific embodiment of the present invention, the sulfone group and the hydroxyl group are not present in a high content compared to the aromatic ring, but they form the structure of the second polymer compound and can play a supporting role in the interaction with the carbon nanotubes and the first dispersant.

[0061] According to one specific example of the present invention, the second polymer compound has an integrated average value of 50 to 250 when analyzing the S=O functional group with an FT-IR device. Specifically, the integrated average value of the S=O functional group is 50 or more, 60 or more, 70 or more, 80 or more, 90 or more, 100 or more, 110 or more, 250 or less, 240 or less, 230 or less, 220 or less, 210 or less, and may be 50 to 250, 80 to 230, or 110 to 210. The second polymer compound may be more specific within the above-described range.

[0062] According to one specific example of the present invention, when the second polymer compound analyzes the OH functional group with an FT-IR device, the integrated average value is 500 to 1,000. Specifically, the integrated average value of the OH functional group is 500 or more, 525 or more, 550 or more, 575 or more, 600 or more, 1,000 or less, 990 or less, 980 or less, 970 or less, 960 or less, 950 or less, and may be 500 to 1,000, 550 to 970, or 600 to 950. The second polymer compound may be more specific within the above-described range.

[0063] According to one specific example of the present invention, the second polymer compound further includes an alkoxy group in addition to the functional group described above. According to one specific example of the present invention, when the CH3O- functional group of the second polymer compound is analyzed with an FT-IR device, the integrated average value is 1 to 30. Specifically, the integrated average value of the CH3O- functional group is 1 or more, 2 or more, or 3 or more, and 30 or less, 29 or less, 28 or less, 27 or less, 26 or less, 25 or less, 24 or less, 23 or less, 22 or less, 21 or less, or 20 or less, and may be 1 to 30, 2 to 25, or 3 to 20. The second polymer compound may be further specified within the above-described range.

[0064] In addition, according to one specific example of the present invention, the second polymer compound has an integrated average value of 1 to 50 when analyzed with an FT-IR device for CH, which is the basis of the organic compound. Specifically, the integrated average value of CH is 1 or more, 5 or more, or 10 or more, and 50 or less, 45 or less, 40 or less, 35 or less, or 30 or less, and may be 1 to 50, 5 to 40, or 10 to 30. The second polymer compound may be more specific within the above-described range.

[0065] According to one specific example of the present invention, the second polymer compound is lignosulfonate. Lignosulfonate is a lignin derivative and is a salt of lignosulfonic acid obtained by converting lignin using sulfurous acid or a sulfite. The salt of lignosulfonic acid may include sodium, ammonium, calcium, magnesium, etc., depending on the base used to neutralize the lignosulfonic acid during the manufacturing process. Since lignosulfonate is a soluble substance in aqueous solvents, it may be suitable for use as a dispersing agent in a carbon nanotube dispersion.

[0066] Lignin, the starting material of the above lignosulfonate, is an abundant renewable polymer found in nature, and is a material characterized by being rich in cellulose but having superior chemical stability, etc., due to its aromatic structure. The structure of lignin is very diverse and cannot be clearly specified, and since lignosulfonate is a derivative of lignin, its structure also cannot be clearly specified. However, since the lignosulfonate according to the present invention contains an aromatic ring, a sulfonic group, a hydroxyl group, and a carbonyl group, and the content of aromatic carbon is above a certain level, lignosulfate suitable for the present invention can be selected from among various lignosulfonates.

[0067] The dispersant comprising the first dispersant and the second dispersant may contain sodium (Na). Na can play an important role in dispersing carbon nanotubes when present in a specific range of contents. According to one embodiment of the present invention, the dispersant has a Na content of 250 ppm to 500 ppm based on the total weight of the dispersant. The Na content can be determined using a method commonly used in the art, and for example, specific analytical methods and devices for deriving the Na content can be as described in the following examples. Specifically, the Na content is 250 ppm or more, 260 ppm or more, 270 ppm or more, 280 ppm or more, 290 ppm or more, 300 ppm or more, 500 ppm or less, 490 ppm or less, 480 ppm or less, 470 ppm or less, 460 ppm or less, 450 ppm or less, and may be 250 ppm to 500 ppm, 270 ppm to 470 ppm, or 300 ppm to 450 ppm. When the Na content in the dispersant is within the above-described range, the functionality of the dispersant for dispersing carbon nanotubes can be further improved.

[0068] The dispersant including the first dispersant and the second dispersant may include Ca (calcium). The Ca may play an important role in dispersing carbon nanotubes when present in a specific range of contents. According to one embodiment of the present invention, the dispersant has a Ca content of 0.1 ppm to 50 ppm based on the total weight of the dispersant. It can be measured in the same manner as the Na. Specifically, the Ca content is 0.1 ppm or more, 0.5 ppm or more, 1 ppm or more, 50 ppm or less, 40 ppm or less, 30 ppm or less, 20 ppm or less, 10 ppm or less, and may be 0.1 ppm to 50 ppm, 0.5 ppm to 30 ppm, or 1 ppm to 10 ppm. When the Ca content in the dispersant is within the above-described range, the functionality of the dispersant for dispersing carbon nanotubes can be further improved.

[0069] The above-described dispersant, when used in an appropriate ratio, can effectively disperse carbon nanotubes within a carbon nanotube dispersion while increasing the content of carbon nanotubes. According to one specific example of the present invention, the carbon nanotube dispersion contains 100 to 300 parts by weight of the dispersant based on 100 parts by weight of carbon nanotubes. Here, the content of the dispersant means the sum of the content of the first dispersant and the content of the second dispersant. Specifically, the content of the dispersant is 100 parts by weight or more, 110 parts by weight or more, 120 parts by weight or more, 130 parts by weight or more, 140 parts by weight or more, 150 parts by weight or more, 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, 250 parts by weight or less, 240 parts by weight or less, 230 parts by weight or less, 220 parts by weight or less, 210 parts by weight or less, 200 parts by weight or less, and may be 100 to 300 parts by weight, 130 to 250 parts by weight, or 150 to 200 parts by weight. By adjusting the content of the dispersant in the above-described ratio, carbon nanotubes can be effectively dispersed without excessively increasing the content of the dispersant.

[0070] According to one specific example of the present invention, the first dispersant is included in the carbon nanotube dispersion in an amount of 200 to 400 parts by weight based on 100 parts by weight of the second dispersant. As described above, since the names of the first dispersant and the second dispersant are based on the content of the dispersant, the content of the first dispersant may be basically equal to or greater than the content of the second dispersant. Specifically, the content of the first dispersant is 200 parts by weight or more, 210 parts by weight or more, 220 parts by weight or more, 230 parts by weight or more, 240 parts by weight or more, 250 parts by weight or more, 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, 350 parts by weight or less, and may be 200 to 400 parts by weight, 230 to 370 parts by weight, or 250 to 350 parts by weight. When the first dispersant and the second dispersant are used in combination, when used in the corresponding ratio, carbon nanotubes can be effectively dispersed compared to the same total amount of dispersant.

[0071] The carbon nanotube dispersion according to the present invention has excellent dispersibility for carbon nanotubes. This dispersibility can be confirmed through the viscosity of the carbon nanotube dispersion. According to one specific example of the present invention, the carbon nanotube dispersion has an initial viscosity of 5,000 cP or less at 25°C. Here, the initial viscosity refers to a value obtained by measuring the viscosity of the carbon nanotube dispersion immediately after stirring the mixture. A specific viscosity measurement method can follow the method described in the experimental examples below. The initial viscosity can be 5,000 cP or less, 4,900 cP or less, 4,800 cP or less, 4,700 cP or less, 4,600 cP or less, 4,500 cP or less, 4,400 cP or less, or 4,300 cP or less. Since there is a limit to how much the viscosity can be reduced while including a certain amount of carbon nanotubes in the above carbon nanotube dispersion, the lower limit may not be particularly important. The lower limit of the initial viscosity may be, for example, 3,000 cP or more, 3,100 cP or more, 3,200 cP or more, 3,300 cP or more, 3,400 cP or more, 3,500 cP or more, or 3,600 cP or more.

[0072] According to one specific example of the present invention, the carbon nanotube dispersion has a viscosity of 10,000 cP or less after storage at 45°C for 65 hours and cooling to 25°C. A specific method for measuring the viscosity may follow the method described in the experimental examples below. The viscosity may be 10,000 cP or less, 9,000 cP or less, 8,000 cP or less, 7,000 cP or less, 6,000 cP or less, or 5,000 cP or less. Since there is a limit to how much the viscosity can be reduced after storage at 45°C for 65 hours and cooling to 25°C while containing a certain amount of carbon nanotubes in the carbon nanotube dispersion, the lower limit may not be particularly important. The lower limit of the initial viscosity may be, for example, 3,000 cP or more, 3,100 cP or more, 3,200 cP or more, 3,300 cP or more, 3,400 cP or more, or 3,500 cP or more.

[0073] According to one specific example of the present invention, the carbon nanotube dispersion has a viscosity change rate of 1.5 or less. The viscosity change rate is a value obtained by dividing the viscosity after storage at 45°C for 65 hours and cooling to 25°C by the initial viscosity at 25°C. Specifically, the viscosity change rate may be 1.5 or less, 1.4 or less, 1.3 or less, 1.2 or less, 1.1 or less, and may be 0.8 or more, 0.85 or more, or 0.9 or more.

[0074] As described above, the carbon nanotube dispersion according to one specific example of the present invention not only has a low initial viscosity, but also has a low rate of change in viscosity even after storage for a certain period of time under specific conditions, thereby having stable dispersibility.

[0075]

[0076] <Method for producing carbon nanotube dispersion>

[0077] According to one aspect of the present invention, the present invention provides a method for preparing the carbon nanotube dispersion described above. The method for preparing the carbon nanotube dispersion according to one specific example of the present invention comprises: (1) mixing carbon nanotubes, a first dispersant containing a first polymer compound including an amine group, a second dispersant containing a second polymer compound including an aromatic ring, and a solvent to prepare a mixture; and (2) stirring the mixture.

[0078] In the above step (1), the mixing can be performed under temperature conditions in which the physical properties of the mixture, including viscosity, do not change due to evaporation of the solvent. For example, the mixing can be performed at a temperature of 50°C or lower, specifically, 5°C to 50°C.

[0079] In the above step (2), stirring can be performed by an impeller, milling, or a high pressure homogenizer. The milling can be performed by a method such as a ball mill, a bead mill, a disc mill, or a basket mill, and specifically, can be performed by a disc mill.

[0080] When milling using the above disk mill, the size of the beads can be appropriately determined depending on the type and amount of carbon nanotubes and the type of dispersant, and specifically, the diameter of the beads can be 0.1 mm to 5 mm, more specifically, 0.5 mm to 4 mm. In addition, the bead milling process can be performed at a speed of 2,000 rpm to 10,000 rpm, and more specifically, can be performed at a speed of 5,000 rpm to 9,000 rpm.

[0081] The stirring by the high-pressure homogenizer is performed by pressurizing the mixture with, for example, a plunger pump of the high-pressure homogenizer and pushing it through the gap of the homogenization valve, thereby generating forces such as cavitation, shear, impact, and explosion when passing through the gap.

[0082] The above stirring process can be performed depending on the degree of dispersion of the carbon nanotube dispersion, and can be performed specifically for 30 to 120 minutes, more specifically for 60 to 90 minutes.

[0083] A method for producing a carbon nanotube dispersion according to one specific example of the present invention comprises the steps of: (1) mixing a first dispersant containing a first polymer compound containing an amine group, a second dispersant containing a second polymer compound containing an aromatic ring, and a solvent to produce a first mixture; (2) mixing carbon nanotubes into the first mixture to produce a second mixture; and (3) stirring the second mixture. Separate stirring may be performed in step (1) to produce the second mixture. However, since the first mixture is not used to produce a final product, it may be performed under simpler conditions compared to the stirring in step (3).

[0084]

[0085] <Electrode slurry composition>

[0086] According to one aspect of the present invention, the present invention provides an electrode slurry composition for a lithium secondary battery, which comprises the carbon nanotube dispersion and an electrode active material. The electrode slurry composition for a lithium secondary battery may be a positive electrode slurry composition or an negative electrode slurry composition, and specifically, may be a negative electrode slurry composition. The electrode slurry composition for a lithium secondary battery may comprise a carbon nanotube dispersion, a positive electrode active material or a negative electrode active material as an electrode active material, a binder, a solvent, and / or other additives as needed.

[0087] As the positive electrode active material, positive electrode active materials well known in the art can be used without limitation, and for example, lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium iron phosphate, lithium nickel manganese cobalt oxide, or a combination thereof can be used. Specifically, the positive electrode active material includes LiCoO2, LiNiO2, LiMn2O4, LiCoPO4, LiFePO4, and LiNi a Mn b Co c O 2　 (Here, 0 <a,b,c<1) 등이 사용될 수 있으나, 이에 한정되는 것은 아니다.

[0088] The negative electrode active material may include one or more negative electrode active materials selected from the group consisting of natural graphite, artificial graphite, carbonaceous materials; lithium-containing titanium composite oxide (LTO); metals (Me) of Si, Sn, Li, Zn, Mg, Cd, Ce, Ni or Fe; alloys composed of the metals (Me); oxides (MeOx) of the metals (Me); and complexes of the metals (Me) and carbon. The negative electrode active material may be included in an amount of 60 to 98 wt%, more preferably 70 to 98 wt%, based on the total weight of solids excluding the solvent in the negative electrode slurry.

[0089] The above binder is a component that assists in the bonding of the active material and the conductive material and the bonding to the current collector, and is typically added in an amount of 1 to 30 wt% based on the total weight of the mixture including the electrode active material. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluororubber, and various copolymers.

[0090] The solvents mentioned above include organic solvents such as N-methyl pyrrolidone (NMP), dimethyl formamide (DMF), acetone, dimethyl acetamide, etc., or water, and these solvents may be used alone or in combination of two or more. The amount of solvent used is sufficient to dissolve and disperse the electrode active material, binder, and conductive agent, taking into account the coating thickness of the slurry and the manufacturing yield.

[0091] The above viscosity modifier may be carboxymethylcellulose, polyacrylic acid, or the like, and by adding it, the viscosity of the electrode slurry can be adjusted to facilitate the manufacturing of the electrode slurry and the application process on the electrode current collector.

[0092] The above filler is optionally used as a component that suppresses the expansion of the electrode, and is not particularly limited as long as it is a fibrous material that does not cause a chemical change in the battery. For example, olefin polymers such as polyethylene and polypropylene; fibrous materials such as glass fiber and carbon fiber are used.

[0093] When the above electrode slurry composition is a composition of a positive electrode slurry for forming a positive electrode, the positive electrode can be manufactured by applying the composition of the positive electrode slurry onto a positive electrode current collector, followed by drying and rolling. Alternatively, the positive electrode slurry can be manufactured by casting the positive electrode slurry onto a separate support, and then laminating the film obtained by peeling it off from the support onto the positive electrode current collector.

[0094] The thickness of the positive electrode active material layer formed by the positive electrode slurry may vary depending on the loading amount, loading speed, etc. for applying the positive electrode slurry.

[0095] The above-described positive electrode current collector generally has a thickness of 3 μm to 500 μm. The positive electrode current collector is not particularly limited as long as it has high conductivity and does not cause chemical changes in the battery. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. can be used. In addition, the surface of the positive electrode current collector may be formed with fine irregularities to strengthen the bonding strength of the positive electrode active material, and the positive electrode current collector can be used in various forms such as a film, sheet, foil, net, porous body, foam, or non-woven fabric.

[0096] When the above electrode slurry composition is a composition of a negative electrode slurry for forming a negative electrode, the negative electrode can be manufactured by applying the composition of the negative electrode slurry onto a negative electrode current collector, followed by drying and rolling. Alternatively, the negative electrode slurry can be manufactured by casting the negative electrode slurry onto a separate support, and then laminating the resulting film onto the negative electrode current collector by peeling it off from the support.

[0097] The thickness of the negative electrode active material layer formed by the above negative electrode slurry may vary depending on the loading amount, loading speed, etc. for applying the negative electrode slurry.

[0098] The above negative electrode current collector generally has a thickness of 3 ㎛ to 500 ㎛. The negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloy, etc. can be used. In addition, like the negative electrode current collector, the bonding strength of the negative electrode active material can be strengthened by forming fine unevenness on the surface, and can be used in various forms such as a film, sheet, foil, net, porous body, foam, non-woven fabric, etc.

[0099]

[0100] Lithium secondary battery

[0101] According to one aspect of the present invention, a lithium secondary battery is provided, comprising a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and an electrolyte, utilizing the carbon nanotube dispersion described above. The positive electrode and the negative electrode are the same as those described above, and thus a detailed description thereof will be omitted.

[0102] The above separator separates the negative electrode and the positive electrode and provides a passage for lithium ions to move. Any separator commonly used in lithium secondary batteries can be used without any particular restrictions, and in particular, one having low resistance to ion movement of the electrolyte and excellent electrolyte moisture retention capacity is preferable. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof, may be used. In addition, a conventional porous nonwoven fabric, for example, a nonwoven fabric made of high-melting-point glass fiber, polyethylene terephthalate fiber, etc. may be used. In addition, a coated separator containing a ceramic component or a polymer material to secure heat resistance or mechanical strength may be used, and may optionally be used in a single-layer or multi-layer structure.

[0103] The electrolyte may be, but is not limited to, an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel-type polymer electrolyte, a solid inorganic electrolyte, a molten inorganic electrolyte, etc. that can be used in the manufacture of a lithium secondary battery. Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0104] The organic solvent may be used without any particular limitation as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the organic solvent may include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; Carbonate solvents such as dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (wherein R is a C2 to C20 linear, branched, or cyclic hydrocarbon group, and may include a double-bonded aromatic ring or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes can be used. Among these, a carbonate solvent is preferable, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate, etc.) having high ionic conductivity and high dielectric constant that can improve the charge / discharge performance of the battery and a linear carbonate compound having low viscosity (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate, etc.) is more preferable.In this case, the performance of the electrolyte may be excellent when the cyclic carbonate and the chain carbonate are mixed and used in a volume ratio of about 1:1 to about 1:9.

[0105] The lithium salt may be used without any particular limitation as long as it is a compound capable of providing lithium ions used in a lithium secondary battery. Specifically, the lithium salt may include LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAl04, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2. LiCl, LiI, or LiB(C2O4)2. It is preferable that the concentration of the lithium salt be used within the range of 0.1M to 2.0M. When the concentration of the lithium salt is within the above range, the electrolyte can exhibit excellent electrolyte performance because it has appropriate conductivity and viscosity, and lithium ions can move effectively.

[0106] In addition to the electrolyte components, the electrolyte may further include one or more additives, such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, cyclic ethers, ethylene diamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, for the purpose of improving the life characteristics of the battery, suppressing battery capacity decrease, and improving the discharge capacity of the battery. At this time, the additives may be included in an amount of 0.1 wt% to 5 wt% based on the total weight of the electrolyte.

[0107] A lithium secondary battery comprising an electrode manufactured using a carbon nanotube dispersion according to the present invention, specifically a lithium secondary battery comprising an anode manufactured using a carbon nanotube dispersion, has carbon nanotubes uniformly dispersed within the anode, and can reduce the content thereof compared to a case where a conductive material such as conventional carbon black is included, thereby stably exhibiting excellent discharge capacity and output characteristics. As a result, the lithium secondary battery can be usefully used in portable devices such as mobile phones, laptop computers, and digital cameras, and electric vehicles such as hybrid electric vehicles (HEVs).

[0108] Accordingly, according to another specific example of the present invention, a lithium secondary battery, a battery module including the lithium secondary battery as a unit cell, and a battery pack including the same can be provided.

[0109] The above battery module or battery pack can be used as a power source for one or more medium- to large-sized devices, such as a power tool; an electric vehicle (EV), a hybrid electric vehicle, and a plug-in hybrid electric vehicle (PHEV); or a power storage system.

[0110] Hereinafter, preferred examples are presented to help understand the present invention, but the following examples are provided only to make it easier to understand the present invention and the present invention is not limited thereto.

[0111]

[0112] Example (Preparation of carbon nanotube dispersion)

[0113]

[0114] The lignosulfonates used in the examples and comparative examples have integrated average values ​​as shown in Table 1 below when the functional groups are analyzed using an FT-IR device (manufacturer: Agilent, product name: Cary 620-FTIR) (analysis accessory: Specac Golden Gate ATR accessory (diamond crystal), analysis conditions: 8 resolution, 32 scans).

[0115]

[0116] Lignosulfonate Integral Average Value Aromatic Ring S=OO-HCH3O-C=OC-H176.20186.65835.5013.986.7329.74265.74183.05821.038.3513.6417.16344.84194.95905.4110.5022.0522.95450.95197.26751.448.598.6619.36597.59119.52755.447.5219. 0819.85645.45204.35890.3210.5226.9422.61766.47164.60713.059.6510.5519.718103.33118.74736.128.5718.6321.14948.09195.78911.2210.1719.3321.7410100.11121.97638.786.7114.8417.68

[0117]

[0118] Example 1

[0119] A carbon nanotube dispersion having a total weight of 500 g was prepared by the following method. 3.375 g (0.675 wt%) of polyvinylpyrrolidone (PVP K15 product of Zhangzhou Huafu Chemical Co.) as a first dispersant, 1.125 g (0.225 wt%) of a first lignosulfonate (aromatic carbon content: 75 mol%, integral average value of carbonyl group / integral average value of aromatic ring: 0.0882) as a second dispersant, and 492.5 g of water as a solvent were mixed to prepare a first mixture weighing 497 g. Here, the total content of Na in the first and second dispersants was 329 ppm, and the total content of Ca was 3 ppm. The above Na content and Ca content were measured using an ICP-OES device (Manufacturer: Perkin-eimer, Product Name: Optima 8300DV) (Operating Conditions: RF power (W): 1,300, Torch Height (mm): 15.0, Plasma Gas Flow (L / min): 15.00, Sample Gas Flow (L / min): 0.8, Aux. Gas Flow (L / min): 0.20, Pump Speed ​​(mL / min): 1.5). Specifically, the measurement was performed by dispersing and diluting in tertiary ultrapure water, and the experimental detection limit (Method detection limit) was <5 mg / kg. The first mixture was prepared by installing an impeller and a container in a dissolution tank (Dispermat-CA product of VMA-Getzmann), adding a dispersant and a solvent, and stirring at 400 rpm for 10 minutes. 3.0 g (0.6 wt%) of single-walled carbon nanotubes (BET surface area: 1,160 m2 / g, length: 5 μm or more, OCSoAl TUBALL product) were added to the prepared first mixture, and stirred at 8,000 rpm for 60 minutes to prepare a second mixture. The prepared second mixture was homogeneously dispersed 7 times at a pressure of 20,000 psi using a high-pressure disperser (Micronox PICOMAX product) to prepare a carbon nanotube dispersion.

[0120]

[0121] Example 2

[0122] A carbon nanotube dispersion was prepared in the same manner as in Example 1, except that the fourth lignosulfonate (aromatic carbon content: 74 mol%, integrated average value of carbonyl groups / integrated average value of aromatic rings: 0.1700) was used as the second dispersant, and the total content of Na in the first and second dispersants was 396 ppm and the total content of Ca was 3 ppm.

[0123]

[0124] Example 3

[0125] A carbon nanotube dispersion was prepared in the same manner as in Example 1, except that the fifth lignosulfonate (aromatic carbon content: 81 mol%, integrated average value of carbonyl group / integrated average value of aromatic ring: 0.1956) was used as the second dispersant, and the total content of Na in the first and second dispersants was 302 ppm and the total content of Ca was 3 ppm.

[0126]

[0127] Example 4

[0128] A carbon nanotube dispersion was prepared in the same manner as in Example 1, except that the seventh lignosulfonate (aromatic carbon content: 67 mol%, integrated average value of carbonyl groups / integrated average value of aromatic rings: 0.1586) was used as the second dispersant, and the total content of Na in the first and second dispersants was 412 ppm and the total content of Ca was 4 ppm.

[0129]

[0130] Example 5

[0131] A carbon nanotube dispersion was prepared in the same manner as in Example 1, except that the eighth lignosulfonate (aromatic carbon content: 84 mol%, integral average value of carbonyl group / integral average value of aromatic ring: 0.1804) was used as the second dispersant, and the total content of Na in the first and second dispersants was 311 ppm and the total content of Ca was 3 ppm.

[0132]

[0133] Example 6

[0134] A carbon nanotube dispersion was prepared in the same manner as in Example 1, except that the 10th lignosulfonate (aromatic carbon content: 82 mol%, integrated average value of carbonyl group / integrated average value of aromatic ring: 0.1483) was used as the second dispersant, and the total content of Na in the first and second dispersants was 315 ppm and the total content of Ca was 3 ppm.

[0135]

[0136] Comparative Example 1

[0137] A carbon nanotube dispersion was prepared in the same manner as in Example 1, except that only 4.5 g (0.9 wt%) of the first dispersant was used without using the second dispersant, and the total content of Na in the first dispersant was 129 ppm and the total content of Ca was 3 ppm.

[0138]

[0139] Comparative Example 2

[0140] A carbon nanotube dispersion was prepared in the same manner as in Example 1, except that a second lignosulfonate (aromatic carbon content: 51 mol%, integrated average value of carbonyl groups / integrated average value of aromatic rings: 0.2075) was used as the second dispersant, and the total content of Na in the first dispersant and the second dispersant was 129 ppm and the total content of Ca was 177 ppm.

[0141]

[0142] Comparative Example 3

[0143] A carbon nanotube dispersion was prepared in the same manner as in Example 1, except that a third lignosulfonate (aromatic carbon content: 63 mol%, integrated average value of carbonyl groups / integrated average value of aromatic rings: 0.4917) was used as the second dispersant, and the total content of Na in the first and second dispersants was 147 ppm and the total content of Ca was 159 ppm.

[0144]

[0145] Comparative Example 4

[0146] A carbon nanotube dispersion was prepared in the same manner as in Example 1, except that the sixth lignosulfonate (aromatic carbon content: 58 mol%, integrated average value of carbonyl groups / integrated average value of aromatic rings: 0.5928) was used as the second dispersant, and the total content of Na in the first and second dispersants was 167 ppm and the total content of Ca was 102 ppm.

[0147]

[0148] Comparative Example 5

[0149] A carbon nanotube dispersion was prepared in the same manner as in Example 1, except that the ninth lignosulfonate (aromatic carbon content: 62 mol%, integrated average value of carbonyl group / integrated average value of aromatic ring: 0.4098) was used as the second dispersant, and the total content of Na in the first and second dispersants was 153 ppm and the total content of Ca was 105 ppm.

[0150]

[0151] Experimental example

[0152]

[0153] The viscosity (initial, 25°C) of the carbon nanotubes manufactured according to Examples 1 to 6 and Comparative Examples 1 to 5 was measured, and then the viscosity after being stored at 45°C for 65 hours and then cooled to 25°C was measured, and the results are shown in Table 2 below. The viscosity was measured using a viscometer (TOKISANGYO viscometer TV-25 product) at a temperature of 25°C, 1 rpm, and Rotor Code 01.

[0154]

[0155] Second dispersant viscosity (25℃) 25℃ Initial (cP) 45℃ 65h post-cooling (cP) ratio ** Example 1 1st lignosulfonate 4,2003,7900.90 Example 2 4th lignosulfonate 4,2504,1600.98 Example 3 5th lignosulfonate 3,8003,7100.98 Example 4 7th lignosulfonate 4,0603,8200.94 Example 5 8th lignosulfonate 3,8403,5900.93 Example 6 10th lignosulfonate 3,6603,8301.05 Comparative Example 1- * 9,79015,2001.55 Comparative Example 2 Second lignosulfonate 7,20016,4102.28 Comparative Example 3 Third lignosulfonate 5,91017,7603.01 Comparative Example 4 Sixth lignosulfonate 5,46022,9904.21 Comparative Example 5 Ninth lignosulfonate 6,02012,4002.06* In Comparative Example 1, instead of using the second dispersant, the first dispersant was additionally used in the same amount as the second dispersant** (Cooling viscosity after 65h at 45℃) / (Initial viscosity at 25℃)

[0156]

[0157] According to Table 2 above, it can be confirmed that the content of aromatic carbon in the second dispersant affects the viscosity of the carbon nanotube dispersion. Specifically, when the content of aromatic carbon in the second dispersant is less than 65 mol%, the initial viscosity of the carbon nanotube dispersion exceeds 5,000 cP, and the viscosity after cooling to 25°C after storage at 45°C for 65 hours also exceeds 10,000 cP, and the viscosity change ratio also exceeds 2.0, indicating that the effect of improving dispersibility obtained by adding the second dispersant was minimal. On the other hand, when the content of aromatic carbon in the second dispersant is 65 mol% or more, not only did the initial viscosity of the carbon nanotube dispersion not exceed 5,000 cP, but the viscosity after cooling to 25°C after storage at 45°C for 65 hours also did not exceed 5,000 cP, indicating that the dispersibility was significantly improved.

[0158] It can be confirmed that the ratio of carbonyl groups to aromatic rings in the second dispersant affects the viscosity change rate of the carbon nanotube dispersion. Specifically, when the integrated average value of carbonyl groups / integrated average value of aromatic rings in the second dispersant exceeds 0.2, the initial viscosity exceeds 5,000 cP, and the viscosity after cooling to 25°C after 65 hours of storage at 45°C also exceeds 10,000 cP, and the viscosity change rate also exceeds 2.0, indicating that the effect of improving dispersibility by adding the second dispersant was minimal. On the other hand, when the integrated average value of carbonyl groups / integrated average value of aromatic rings in the second dispersant is 0.2 or less, not only did the initial viscosity of the carbon nanotube dispersion not exceed 5,000 cP, but the viscosity after cooling to 25°C after 65 hours of storage at 45°C also did not exceed 5,000 cP, indicating a significant improvement in dispersibility. In the second dispersant, the carbon content of most other functional groups had no particular correlation with the dispersibility of the carbon nanotube dispersion.

[0159] It can be confirmed that the Na content or Ca content in the dispersant affects the viscosity change rate of the carbon nanotube dispersion. Specifically, when the Na content in the dispersant (including the second dispersant) is less than 250 ppm or the Ca content exceeds 50 ppm, the initial viscosity exceeds 5,000 cP, the viscosity after cooling to 25°C after 65 hours of storage at 45°C also exceeds 10,000 cP, and the viscosity change rate also exceeds 2.0, indicating that the effect of improving dispersibility obtained by adding the second dispersant was minimal. On the other hand, when the Na content in the dispersant (including the second dispersant) was 250 ppm to 500 ppm or the Ca content was 0.1 ppm to 50 ppm, not only did the initial viscosity of the carbon nanotube dispersion not exceed 5,000 cP, but the viscosity after cooling to 25°C after storage at 45°C for 65 hours also not exceed 5,000 cP, indicating a significant improvement in dispersibility. In the dispersant, most metal contents had no particular correlation with the dispersibility of the carbon nanotube dispersion.

[0160]

[0161] All simple modifications or changes of the present invention fall within the scope of the present invention, and the specific scope of protection of the present invention will be made clear by the appended claims.

Claims

1. Containing carbon nanotubes, a dispersant and a solvent, The above dispersant is, A first dispersant containing a first polymer compound including an amine group; and A second dispersant comprising a second polymer compound including an aromatic ring, The second dispersant is a carbon nanotube dispersion containing aromatic carbon in an amount of 65 mol% or more based on the total number of carbon atoms.

2. In claim 1, A carbon nanotube dispersion, characterized in that the first polymer compound is selected from the group consisting of polyvinylpyrrolidone, polyacrylic acid hydrazide, poly-N-vinyl-5-methoxazolidone, N-alkyl polyimine, N-acetyl polyimine, polyacrylamide, poly-L-lysine hydrobromide, benzyl-dodecyl-dimethylammonium chloride, polyethyleneimine, and combinations thereof.

3. In claim 1, The second polymer compound further comprises a carbonyl group, The second dispersant is a carbon nanotube dispersion characterized in that the ratio of carbonyl groups to aromatic rings (integrated average value of carbonyl groups / integrated average value of aromatic rings) according to FT-IR is 0.2 or less.

4. In claim 1, A carbon nanotube dispersion, characterized in that the dispersant has a Na content of 250 ppm to 500 ppm based on the total weight of the dispersant.

5. In claim 4, A carbon nanotube dispersion characterized in that the dispersant has a Ca content of 0.1 ppm to 50 ppm based on the total weight of the dispersant.

6. In claim 1, A carbon nanotube dispersion characterized in that the second polymer compound is lignosulfonate.

7. In claim 1, A carbon nanotube dispersion, characterized in that the first dispersant is included in the carbon nanotube dispersion in an amount of 200 to 400 parts by weight based on 100 parts by weight of the second dispersant.

8. In claim 1, A carbon nanotube dispersion, characterized in that the dispersant is included in the carbon nanotube dispersion in an amount of 100 to 300 parts by weight based on 100 parts by weight of carbon nanotubes.

9. In claim 1, A carbon nanotube dispersion, characterized in that the carbon nanotubes are included in the carbon nanotube dispersion in an amount of 0.1 wt% to 5 wt% based on the total weight of the carbon nanotube dispersion.

10. In claim 1, The above carbon nanotubes are 800 m 2 / g to 5,000 m 2 A carbon nanotube dispersion characterized by having a BET surface area of ​​ / g.

11. In claim 1, A carbon nanotube dispersion, characterized in that the solvent is an aqueous solvent containing water.

12. In claim 1, A carbon nanotube dispersion characterized in that the above carbon nanotube dispersion has an initial viscosity of 5,000 cP or less at 25°C.

13. In claim 1, A carbon nanotube dispersion characterized in that the above carbon nanotube dispersion has a viscosity of 10,000 cP or less after storage at 45°C for 65 hours and cooling to 25°C.

14. A method for producing a carbon nanotube dispersion according to claim 1, The above manufacturing method is, (1) a step of preparing a mixture by mixing carbon nanotubes, a first dispersant containing a first polymer compound including an amine group, a second dispersant containing a second polymer compound including an aromatic ring, and a solvent; and (2) A method for producing a carbon nanotube dispersion, comprising the step of stirring the above mixture.

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