Carbon nanotube dispersion and method for producing the same

Abstract

A carbon nanotube dispersion is provided, comprising carbon nanotubes, a dispersant, and a solvent. The dispersant comprises a first dispersant comprising a first polymer compound containing an amine group, and a second dispersant comprising a second polymer compound containing an aromatic ring. The second dispersant contains 65 mol% or more of aromatic carbon based on the total number of moles of carbon atoms. In one specific example of the present invention, by including aromatic carbon above a certain level as the second dispersant, the carbon nanotube dispersion can significantly reduce not only the initial viscosity of the carbon nanotube dispersion but also the rate of change in viscosity over time.

Description

[Technical Field]

[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, comprising 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, in order to improve the dispersibility of carbon nanotubes.

[0002] This application claims the benefit of priority under Korean Patent Application No. 10-2023-0097140, Korean Patent Application No. 10-2023-0097142, and Korean Patent Application No. 10-2023-0097145 dated 26 July 2023, and incorporates all the contents disclosed in the relevant Korean Patent Applications as part of this Specification. [Background technology]

[0003] As technological development and demand for mobile devices increase, the demand for rechargeable batteries as an energy source is surging. Among these rechargeable batteries, lithium-ion batteries, which have high energy density and voltage, long cycle life, and low self-discharge rates, have been commercialized and are widely used. Furthermore, research is actively being conducted on methods to improve electrode density and manufacture electrodes with even higher energy density per unit volume for such high-capacity lithium-ion batteries.

[0004] Generally, high-density electrodes are formed by molding electrode active material particles with a size of several micrometers to tens of micrometers using high-pressure pressing. However, during the molding process, the particles may deform, reducing the space between them and thus lowering the permeability of the electrolyte. To solve these problems, conductive materials with excellent electrical conductivity and strength are used during electrode manufacturing. Even when the conductive material is positioned between the electrode active materials and undergoes the molding process, it maintains the fine pores between the active material particles, allowing the electrolyte to easily permeate, and its excellent electrical conductivity reduces resistance within the electrode. Among such conductive materials, the use of carbon nanotubes, which are fibrous carbon-based conductive materials that can further reduce electrode resistance by forming electrical conductive paths within the electrode, is increasing.

[0005] The carbon nanotubes described above are fine carbon fibers in which carbon atoms connected by hexagonal rings form a long, tubular structure with a diameter of 1 μm or less. Due to the high conductivity, tensile strength, and heat resistance resulting from the unique structure of the carbon nanotubes, they are expected to be applied and put into practical use in various fields. In order to commercialize the carbon nanotubes as conductive materials, it is necessary to manufacture them in a dispersion state rather than in powder form. However, due to the strong cohesiveness of the carbon nanotubes, it is difficult to reduce the viscosity when manufacturing them in a dispersion state, and even if the viscosity is reduced, it rapidly increases over time, posing a problem in terms of practical application in manufacturing processes.

[0006] To address these problems, methods have been proposed to disperse carbon nanotubes in a dispersion medium through mechanical dispersion processes such as ultrasonic treatment. However, with mechanical dispersion methods, there is a problem in that the carbon nanotubes aggregate as soon as the ultrasonic irradiation ends. If the carbon nanotubes aggregate, the coating properties will decrease during the process, and it will be difficult to obtain a product with a uniform thickness.

[0007] Therefore, in the relevant technical field, there is a need for a technology to produce carbon nanotube dispersions with low viscosity and low viscosity change rate over time. The inventors of this invention have completed the present invention through continuous research on additives as a way to solve the above-mentioned problems in carbon nanotube dispersions. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Korean Published Patent Gazette No. 10-2015-0122653 [Overview of the project] [Problems that the invention aims to solve]

[0009] The present invention aims to provide a carbon nanotube dispersion in which carbon nanotubes are efficiently dispersed 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, as well as a method for producing the same. [Means for solving the problem]

[0010] According to the first aspect of the present invention, This invention provides a carbon nanotube dispersion containing carbon nanotubes, a dispersant, and a solvent.

[0011] In one specific example of the present invention, the dispersant comprises a first dispersant comprising a first polymer compound containing an amine group; and a second dispersant comprising a second polymer compound containing an aromatic ring.

[0012] In one specific example of the present invention, the second dispersant contains 65 mol% or more of aromatic carbons based on the total number of moles of carbon atoms.

[0013] In a specific example of the present invention, the first polymer compound is selected from the group consisting of polyvinylpyrrolidone, polyacrylic hydrazide, poly-N-vinyl-5-methoxazolidone, N-alkylpolyimine, N-acetylpolyimine, polyacrylamide, poly-L-lysine hydrobromide, benzyl-dodecyldimethylammonium chloride, polyethyleneimine, and combinations thereof.

[0014] In a specific example of the present invention, the second polymer compound further contains a carbonyl group, and the ratio of the carbonyl group to the aromatic ring (average value of the integral of the carbonyl group / average value of the integral of the aromatic ring) of the second dispersant by FT-IR is 0.2 or less.

[0015] In a 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.

[0016] In a 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.

[0017] In a specific example of the present invention, the second polymer compound is lignosulfonate.

[0018] In a specific example of the present invention, 200 to 400 parts by weight of the first dispersant is contained in the carbon nanotube dispersion liquid based on 100 parts by weight of the second dispersant.

[0019] In a specific example of the present invention, 100 to 300 parts by weight of the dispersant is contained in the carbon nanotube dispersion liquid based on 100 parts by weight of the carbon nanotube.

[0020] In a specific example of the present invention, 0.1% to 5% by weight of the carbon nanotube is contained in the carbon nanotube dispersion liquid based on the total weight of the carbon nanotube dispersion liquid.

[0021] In one specific example of the present invention, the carbon nanotube is 800m 2 / g or 5,000m 2 It has a BET specific surface area of ​​ / g.

[0022] In one specific example of the present invention, the solvent is an aqueous solvent containing water.

[0023] 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.

[0024] In one specific example of the present invention, the carbon nanotube dispersion has a viscosity of 10,000 cP or less after being stored at 45°C for 65 hours and then cooled to 25°C.

[0025] According to a second aspect of the present invention, The present invention provides a method for producing the carbon nanotube dispersion described above.

[0026] According to one specific example of the present invention, the production method comprises (1) the step of mixing carbon nanotubes, 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 mixture; and (2) the step of stirring the mixture.

[0027] According to the third aspect of the present invention, The present invention provides an electrode slurry composition for lithium secondary batteries, comprising the above-mentioned carbon nanotube dispersion and electrode active material. [Effects of the Invention]

[0028] A carbon nanotube dispersion according to one specific example of the present invention can effectively disperse carbon nanotube dispersions by comprising 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.

[0029] In particular, by containing aromatic carbon above a certain level, 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. [Modes for carrying out the invention]

[0030] All specific examples provided by the present invention can be achieved by the following description. The following description should be understood as describing preferred examples of the present invention, and it should be understood that the invention is not necessarily limited thereto.

[0031] If the measurement conditions and methods for the physical properties described herein are not specifically described, such physical properties shall be measured using measurement conditions and methods commonly used by ordinary technicians in the relevant art.

[0032] <Carbon nanotube dispersion> According to one aspect of the present invention, the present invention provides a carbon nanotube dispersion containing carbon nanotubes, a dispersant, and a solvent. Although carbon nanotubes have high conductivity and can be used as conductive materials in lithium secondary batteries and the like, they are difficult to disperse, which makes them difficult to apply in actual processes. In the present invention, a carbon nanotube dispersion is provided in which the dispersibility of carbon nanotubes is improved 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.

[0033] The carbon nanotubes can be made of materials commonly used as conductive materials in the relevant art. The carbon nanotubes are secondary structures formed by assembling carbon nanotube units so as a whole or partially bundle, and the carbon nanotube units have a graphite sheet that is cylindrical in shape with a nanoscale diameter, sp 2It has a bonding structure. In this case, depending on the angle and structure in which the graphite surface is wound, it can exhibit conductive or semiconductor properties. The carbon nanotube units can be classified into single-walled carbon nanotubes (SWCNTs), double-walled carbon nanotubes (DWCNTs), and multi-walled carbon nanotubes (MWCNTs) depending on the number of bonds forming the wall.

[0034] In this specification, "bundle type" refers to a secondary form of carbon nanotube units in which multiple units are arranged in a bundle or rope shape, with their longitudinal axes substantially identical in orientation, or which units become twisted or entangled after being arranged. "Non-bundle type" or "entangled type" refers to a form in which carbon nanotube units do not have a fixed shape such as a bundle or rope shape, but are entangled.

[0035] While the aforementioned carbon nanotubes have high conductivity, they also exhibit high cohesiveness due to van der Waals forces generated between them. If the conductive material aggregates, it becomes difficult to properly form conductive pathways, leading to the need for relatively more conductive material and thus a reduction in the amount of active material, potentially degrading the electrode performance. Therefore, commercializing carbon nanotubes as conductive materials has been challenging.

[0036] The carbon nanotube dispersion according to the present invention contains a first dispersant containing a first polymer compound containing an amine and a second dispersant containing a second polymer compound containing an aromatic ring. This significantly reduces the viscosity of the aqueous carbon nanotube dispersion and suppresses changes over time. When applied to an electrode slurry for a lithium secondary battery, it exhibits high conductivity due to the high conductivity of the carbon nanotubes.

[0037] Specifically, when the carbon nanotube dispersion according to the present invention is applied to the production of an electrode slurry, the carbon nanotubes are uniformly positioned between the active materials, and even during the process of manufacturing the electrode by rolling after coating and drying the electrode slurry, the fine spaces between the electrode active materials can be consistently maintained. Furthermore, the carbon nanotubes do not aggregate and are uniformly distributed, allowing for the sufficient formation of conductive pathways even with a small amount of carbon nanotubes.

[0038] A carbon nanotube dispersion according to one specific example of the present invention may contain one or more single-walled, double-walled, and multi-walled carbon nanotube units as the carbon nanotube, and more specifically, it may contain single-walled carbon nanotubes. Since the single-walled carbon nanotube has a higher specific surface area than double-walled and multi-walled carbon nanotubes, it can be useful as a conductive material for lithium secondary batteries to improve battery performance.

[0039] 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 refers to the maximum value among the distances from any one point on the outermost edge of the circular cross-section of the carbon nanotube to other points. The diameter of the carbon nanotube can be measured by imaging with a scanning electron microscope. Specifically, the diameter of the carbon nanotube may be 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, 0.5 nm to 10 nm, 0.7 nm to 7 nm, or 1 nm to 5 nm. Carbon nanotubes having a diameter within the above range can be effectively dispersed in the electrodes of a lithium secondary battery and can impart conductivity to the electrodes.

[0040] 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 carbon nanotube in a cylindrical form. The length of the carbon nanotube can be measured by imaging with a scanning electron microscope. Specifically, the length of the carbon nanotube may be 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, 1 μm to 20 μm, 3 μm to 18 μm, or 5 μm to 15 μm. Carbon nanotubes having a length within the above range can effectively link their constituent components within the electrodes of a lithium secondary battery, thereby providing conductivity to the electrodes.

[0041] According to one specific example of the present invention, the carbon nanotube is 800m 2 / g or 5,000m 2 It has a BET specific surface area of ​​1 / g. The BET specific surface area is the specific surface area measured according to the BET method, and more preferably, it is calculated by determining the amount of nitrogen gas adsorbed at liquid nitrogen temperature (77K) using BELSORP-mini II from BEL Japan. Specifically, the BET specific surface area of ​​the carbon nanotube is 800m². 2above / g, 850 m 2 above / g, 900 m 2 above / g, 950 m 2 above / g, 1,000 m 2 / g, 5,000 m 2 below / g, 4,500 m 2 below / g, 4,000 m 2 below / g, 3,500 m 2 below / g, 3,000 m 2 below / g, 2,500 m 2 below / g, 2,000 m 2 below / g, 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 It may be / g. The carbon nanotubes having a BET specific surface area within the above range can effectively contact other components in the electrode of the lithium secondary battery and impart conductivity to the electrode.

[0042] According to a specific example of the present invention, 0.1% by weight to 5% by weight of the carbon nanotubes is contained in the carbon nanotube dispersion based on the total weight of the carbon nanotube dispersion. Specifically, the content of the carbon nanotubes is 0.1% by weight or more, 0.2% by weight or more, 0.3% by weight or more, 0.4% by weight or more, 0.5% by weight or more, and 5% by weight or less, 4.5% by weight or less, 4% by weight or less, 3.5% by weight or less, 3% by weight or less, 2.5% by weight or less, 2% by weight or less, 1.5% by weight or less, and may be 0.1% by weight to 5% by weight, 0.3% by weight to 3% by weight, 0.5% by weight to 1.5% by weight. When adjusting the carbon nanotubes within the above range in the carbon nanotube dispersion, it may be easy to effectively disperse the carbon nanotubes and apply them to the lithium secondary battery.

[0043] A carbon nanotube dispersion according to one specific example of the present invention contains not only a solvent but also a first dispersant and a second dispersant in order to effectively disperse the carbon nanotubes mentioned above. Since the carbon nanotube dispersion has a relatively high carbon nanotube content, it is important to appropriately combine components other than carbon nanotubes in order to prevent aggregation of carbon nanotubes and to effectively disperse them to enhance their usability. On the other hand, if the carbon nanotube content is low, the solid content of the manufactured electrode slurry decreases during electrode slurry production, and the electrode slurry may become unnecessarily thick before drying, which can lead to a decrease in the quality of the electrode after drying.

[0044] The aforementioned solvent essentially serves to disperse the carbon nanotubes, the first dispersant, and the second dispersant. In actual products such as lithium secondary batteries, carbon nanotubes are used as conductive materials. However, if the carbon nanotubes are added to the electrode slurry in powder form, they will aggregate and will not be able to exhibit proper functionality within the electrode. To solve this problem, the carbon nanotubes are linearly dispersed and supplied to the carbon nanotube dispersion liquid.

[0045] 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 a content that allows the electrode slurry composition to have an appropriate viscosity, in view of the coating properties of the electrode slurry composition produced using the carbon nanotube dispersion. Even without specifically mentioning the content of the solvent in this specification, the content of the solvent can be obtained by subtracting the content of the carbon nanotubes, the first dispersant, and the second dispersant from the carbon nanotube dispersion.

[0046] A carbon nanotube dispersion according to one specific example of the present invention further contains a dispersant because the solvent alone cannot effectively disperse the carbon nanotubes. The dispersant may be a single substance, or it may be a combination of two or more substances. According to one specific example of the present invention, the dispersant includes a first dispersant and a second dispersant. The first and second dispersants can be distinguished by the content used, and the dispersant used in a larger quantity among the two dispersants can become the first dispersant.

[0047] According to one specific example of the present invention, the first dispersant comprises a first polymer compound containing an amine group. In this specification, the amine group can be most broadly interpreted as a nitrogen-containing working group. When a first polymer compound containing an amine group is used as the first dispersant, viscosity improvement and viscosity change over time effects can be obtained in a carbon nanotube dispersion. The first polymer compound is preferably one that is soluble in a solvent, particularly an aqueous solvent, and can 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, polyethyleneimine, and combinations thereof.

[0048] The second dispersant is used together with the first dispersant described above, and a substance that can create synergy in the dispersion of carbon nanotubes may be used. According to one specific example of the present invention, the second dispersant contains a second polymer compound containing an aromatic ring. The second dispersant contains an aromatic ring, and the carbon content constituting the aromatic ring can play an important role in dispersing carbon nanotubes in relation to the first dispersant. Furthermore, the aromatic ring contained in the second dispersant has a molecular structure similar to that of carbon nanotubes and can form strong bonds with individual carbon nanotubes through π-π interactions or hydrophobic interactions, etc., so that the carbon nanotubes do not aggregate with each other and the dispersant has the functionality to disperse carbon nanotubes.

[0049] According to one specific example of the present invention, the second dispersant contains 65 mol% or more of aromatic carbon based on the total number of moles of carbon atoms. The aromatic carbon refers to carbon atoms constituting an aromatic ring. The aromatic carbon content in the second dispersant can be confirmed, for example, by an NMR spectrometer. Specifically, the aromatic carbon content was measured by 1D normal NMR (Bruker Prodigy 500 MHz NMR, 13C, Probe (PABBO), D-solvent: D2O or DMSO-d6, temperature: 298 K). Specifically, the aromatic carbon content 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 aromatic carbon content can be naturally adjusted by the presence of other components in the compound, for example, 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 may be 65 mol% to 90 mol%, 66 mol% to 87 mol%, or 67 mol% to 84 mol%. When the aromatic carbon content of the second dispersant is within the above range, the synergistic effect with the first dispersant can be maximized.

[0050] According to one specific example of the present invention, the second polymer compound has an average integral value of 20 to 150 when the aromatic ring is analyzed with an FT-IR instrument. A specific analytical method and apparatus for deriving the average integral value can be described in the following examples. Specifically, the average integral value of the aromatic ring may be 20 or more, 25 or more, 30 or more, 35 or more, 40 or more, 150 or less, 140 or less, 130 or less, 120 or less, 110 or less, 20 to 150, 30 to 130, or 40 to 110. The second polymer compound can be further specified within the above range.

[0051] According to one specific example of the present invention, the second polymer compound further comprises carbonyl groups. In the above-described second dispersant, the ratio of carbonyl groups to aromatic rings can 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 carbonyl groups (C=O) and aromatic rings of the second dispersant are analyzed using an FT-IR instrument, the ratio of carbonyl groups to aromatic rings (average integral of carbonyl groups / average integral of aromatic rings) is 0.2 or less. Specific analytical methods and apparatus for deriving the average integral can be described in the following examples. The integral values ​​are calculated in a range generally known in the relevant art. For example, 1,800 cm- ‐1 , 900cm ‐1 Using this as the baseline, the carbonyl group is 1,738 cm- ‐1 ~1,675cm- ‐1 Integrating the region, the aromatic ring is 1,523 cm- ‐1 ~1,478cm- ‐1 The region is integrated. Specifically, the ratio of the carbonyl group to the aromatic ring (average value of the integral of the carbonyl group / average value of the integral 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 range, the synergistic effect with the first dispersant can be maximized.

[0052] According to one specific example of the present invention, the second polymer compound has an average integral value of 1 to 50 when the C=O active group is analyzed using an FT-IR instrument. Specifically, the average integral value of the C=O active group may be 1 or more, 2 or more, 3 or more, 50 or less, 45 or less, 40 or less, 35 or less, 30 or less, 1 to 50, 2 to 40, or 3 to 30. The second polymer compound can be further specified within the above range.

[0053] According to one specific example of the present invention, the second polymer compound further comprises a sulfone group and a hydroxyl group in addition to the aromatic ring and carbonyl group. In the second polymer compound according to one specific example of the present invention, although the sulfone group and hydroxyl group are not present in high amounts compared to the aromatic ring, they can form the structure of the second polymer compound and play an auxiliary role in the interaction with the carbon nanotube and the first dispersant.

[0054] According to one specific example of the present invention, the second polymer compound has an average integral value of 50 to 250 when the S=O active group is analyzed using an FT-IR instrument. Specifically, the average integral value of the S=O active group may be 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, 50 to 250, 80 to 230, or 110 to 210. The second polymer compound can be further specified within the above range.

[0055] According to one specific example of the present invention, the second polymer compound has an average integral value of 500 to 1,000 when the O-H active group is analyzed using an FT-IR instrument. Specifically, the average integral value of the O-H active group may be 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, 500 to 1,000, 550 to 970, or 600 to 950. The second polymer compound can be further specified within the above range.

[0056] According to one specific example of the present invention, the second polymer compound further comprises an alkoxy group in addition to the above-described active group. According to one specific example of the present invention, when the CH3O-active group of the second polymer compound is analyzed with an FT-IR instrument, the average integral value of the second polymer compound is between 1 and 30. Specifically, the average integral value of the CH3O-active group may be 1 or more, 2 or more, 3 or more, 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, 20 or less, 1 to 30, 2 to 25, or 3 to 20. The second polymer compound can be further specified within the above range.

[0057] Furthermore, according to one specific example of the present invention, the second polymer compound has an average integral value of 1 to 50 when analyzed with an FT-IR instrument with respect to C-H, which is the basic component of the organic compound. Specifically, the average integral value of C-H may be 1 or more, 5 or more, 10 or more, 50 or less, 45 or less, 40 or less, 35 or less, 30 or less, 1 to 50, 5 to 40, or 10 to 30. The second polymer compound can be further specified within the above range.

[0058] According to one specific example of the present invention, the second polymer compound is a lignosulfonate. The lignosulfonate is a derivative of lignin, and is a salt of lignosulfonic acid obtained by converting lignin with sulfite or a sulfite salt. The salt of lignosulfonic acid may contain sodium, ammonium, calcium, magnesium, etc., depending on the base used to neutralize the lignosulfonic acid during the manufacturing process. The lignosulfonate is suitable for use as a dispersant in carbon nanotube dispersions because it is soluble in aqueous solvents.

[0059] Lignin, the starting material for the aforementioned lignosulfonates, is a naturally occurring, abundant, and renewable polymer. While rich in cellulose, it is characterized by its superior chemical stability compared to cellulose due to its aromatic structure. The structure of lignin is very diverse and cannot be clearly identified, and since lignosulfonates are derivatives of lignin, the structure of lignosulfonates cannot be clearly identified either. However, the lignosulfonates according to the present invention contain aromatic rings, sulfonate groups, hydroxyl groups, and carbonyl groups, and the content of aromatic carbons is above a certain level, allowing for the selection of lignosulfates suitable for the present invention from among various lignosulfonates.

[0060] The dispersant comprising the first and second dispersants may contain Na (sodium). When Na is present in a specific range of concentrations, it can play an important role in dispersing carbon nanotubes. According to 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. The Na content can be determined using methods commonly used in the art, and for example, specific analytical methods and apparatus for deriving the Na content can be described in the following examples. Specifically, the Na content may be 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, 250 ppm to 500 ppm, 270 ppm to 470 ppm, or 300 ppm to 450 ppm. When the Na content of the dispersant is within the above range, the functionality of the dispersant for dispersing carbon nanotubes can be further improved.

[0061] The dispersant comprising the first and second dispersants may contain calcium (Ca). When present in a specific range of concentrations, the Ca can play an important role in dispersing carbon nanotubes. According to 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. This can be measured in the same manner as the Na. Specifically, the Ca content may be 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, 0.1 ppm to 50 ppm, 0.5 ppm to 30 ppm, or 1 ppm to 10 ppm. When the Ca content of the dispersant is within the above range, the functionality of the dispersant for dispersing carbon nanotubes can be further improved.

[0062] When used in an appropriate ratio, the above-described dispersant can effectively disperse carbon nanotubes in a carbon nanotube dispersion while maintaining a high carbon nanotube content. In one specific example of the present invention, the dispersant is contained in the carbon nanotube dispersion in an amount of 100 to 300 parts by weight, based on 100 parts by weight of carbon nanotubes. Here, the content of the dispersant refers to the sum of the content of the first dispersant and the content of the second dispersant. Specifically, the content of the dispersant may be 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, 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 ratios, carbon nanotubes can be effectively dispersed without excessively increasing the content of the dispersant.

[0063] 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, the naming of the first and second dispersants is based on the content of the dispersants, so the content of the first dispersant can be basically the same as or greater than the content of the second dispersant. Specifically, the content of the first dispersant may be 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, 200 to 400 parts by weight, 230 to 370 parts by weight, or 250 to 350 parts by weight. When the first and second dispersants are used in combination, using them in the specified ratio allows for effective dispersion of carbon nanotubes compared to the same total amount of dispersant.

[0064] The carbon nanotube dispersion according to the present invention exhibits excellent dispersibility with respect to carbon nanotubes. This dispersibility is confirmed by 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 the value measured immediately after stirring of the mixture and before the viscosity of the prepared carbon nanotube dispersion is measured. The specific method for measuring viscosity can be followed according to the method described in the experimental example below. The initial viscosity may 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. The lower limit is not particularly important because there is a limit to how low the viscosity can be while containing a certain amount of carbon nanotubes in the carbon nanotube dispersion. The lower limit of the initial viscosity may be, for example, 3,000 cP or higher, 3,100 cP or higher, 3,200 cP or higher, 3,300 cP or higher, 3,400 cP or higher, 3,500 cP or higher, or 3,600 cP or higher.

[0065] According to one specific example of the present invention, the carbon nanotube dispersion has a viscosity of 10,000 cP or less after being stored at 45°C for 65 hours and then cooled to 25°C. The specific method for measuring the viscosity can be followed according to the method described in the experimental example 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. The lower limit is not particularly important because there is a limit to how much the viscosity can be reduced after storing the carbon nanotube dispersion at 45°C for 65 hours and then cooling to 25°C while containing a certain amount of carbon nanotubes. 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.

[0066] 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 the 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, 0.8 or more, 0.85 or more, or 0.9 or more.

[0067] 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 exhibits stable dispersibility because the rate of change in viscosity is small even after storage for a certain period of time under specific conditions.

[0068] <Method for producing a carbon nanotube dispersion> According to one aspect of the present invention, the present invention provides a method for producing the carbon nanotube dispersion described above. A specific example of a method for producing a carbon nanotube dispersion according to the present invention includes the steps of (1) mixing carbon nanotubes, 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 mixture; and (2) stirring the mixture.

[0069] In step (1) above, the mixing can be carried out under temperature conditions in which the physical properties of the mixture, such as viscosity, do not change due to the evaporation of the solvent. For example, it can be carried out at a temperature of 50°C or lower, specifically between 5°C and 50°C.

[0070] In step (2) above, stirring can be carried out by an impeller, milling, or high-pressure homogenizer. The milling can be carried out by methods such as a ball mill, bead mill, disc mill, or basket mill, and more specifically by a disc mill.

[0071] During milling with the aforementioned disc mill, the size of the beads can be appropriately determined by the type and amount of carbon nanotubes and the type of dispersant. Specifically, the diameter of the beads may be 0.1 mm to 5 mm, or more specifically, 0.5 mm to 4 mm. Furthermore, the bead milling process can be carried out at a speed of 2,000 rpm to 10,000 rpm, or more specifically, at a speed of 5,000 rpm to 9,000 rpm.

[0072] The stirring by the high-pressure homogenizer is performed, for example, by pressurizing the mixture with the 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 as it passes through the gap.

[0073] The stirring step can be performed depending on the degree of dispersion of the carbon nanotube dispersion, and more specifically, it can be performed for 30 to 120 minutes, or more specifically, 60 to 90 minutes.

[0074] According to a specific example of the present invention, a method for producing a carbon nanotube dispersion liquid includes: (1) a step of 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) a step of mixing carbon nanotubes into the first mixture to produce a second mixture; (3) a step of stirring the second mixture. In the step (1), separate stirring can be performed to produce the second mixture. However, since the first mixture is not used to produce the final product, it can be performed under simpler conditions compared to the stirring in the step (3).

[0075] <Electrode slurry composition> According to one aspect of the present invention, the present invention provides an electrode slurry composition for a lithium secondary battery containing the carbon nanotube dispersion liquid and an electrode active material. The electrode slurry composition for the lithium secondary battery may be a positive electrode slurry composition or a negative electrode slurry composition, specifically, it may be a negative electrode slurry composition. The electrode slurry composition for the lithium secondary battery may contain a carbon nanotube dispersion liquid, a positive electrode active material or a negative electrode active material as an electrode active material, a binder, and optionally a solvent and / or other additives.

[0076] As the positive electrode active material, well-known positive electrode active materials in the technical field can be used without limitation. For example, lithium cobalt-based oxides, lithium nickel-based oxides, lithium manganese-based oxides, lithium iron phosphate, lithium nickel manganese cobalt-based oxides or combinations thereof can be used. Specifically, as the positive electrode active material, LiCoO2, LiNiO2, LiMn2O4, LiCoPO4, LiFePO4 and LiNi a Mn b Co c O2 (where 0 < a, b, c < 1) etc. can be used, but it is not limited thereto.

[0077] Examples of the negative electrode active material 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) which are Si, Sn, Li, Zn, Mg, Cd, Ce, Ni, or Fe; alloys composed of the metals (Me); oxides of the metals (Me) (MeOx); and composites of the metals (Me) and carbon. The negative electrode active material may be present in the negative electrode slurry at a concentration of 60 to 98% by weight, more preferably 70 to 98% by weight, based on the total weight of solid matter excluding the solvent.

[0078] The aforementioned binder is a component that assists in the bonding of the active material to conductive materials and to the current collector, and is usually added in an amount of 1 to 30% by weight based on the total weight of the mixture containing the electrode active material. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluororubber, and various copolymerizers.

[0079] The solvent may be an organic solvent such as N-methylpyrrolidone (NMP), dimethylformamide (DMF), acetone, or dimethylacetamide, or water. These solvents can be used individually or in mixtures of two or more. The amount of solvent used should be sufficient to dissolve and disperse the electrode active material, binder, and conductive material, taking into consideration the thickness of the slurry coating and the production yield.

[0080] The viscosity modifier may be carboxymethylcellulose or polyacrylic acid, and by adding it, the viscosity of the electrode slurry can be adjusted to facilitate the manufacturing of the electrode slurry and the coating process on the electrode current collector.

[0081] The aforementioned filler is used selectively as a component to suppress electrode swelling and does not cause chemical changes in the battery. It is not particularly limited as long as it is a fibrous material, for example, polyethylene, polypropylene or other orefin polymers; or fibrous materials such as glass fibers and carbon fibers.

[0082] If the electrode slurry composition is a composition for a positive electrode slurry to form a positive electrode, the positive electrode can be manufactured by applying the positive electrode slurry composition onto a positive electrode current collector, followed by drying and rolling. Alternatively, the positive electrode slurry can be cast separately onto a support, and the film obtained by peeling it off the support can be laminated onto the positive electrode current collector.

[0083] The thickness of the positive electrode active material layer formed by the positive electrode slurry may vary depending on the loading amount and loading speed for applying the positive electrode slurry.

[0084] The positive electrode current collector generally has a thickness of 3 μm to 500 μm. Such a positive electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes to the battery. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel with surface treatment of carbon, nickel, titanium, silver, etc. can be used. Furthermore, fine irregularities can be formed on the surface of the positive electrode current collector to strengthen the bonding force of the positive electrode active material, and it can be used in various forms such as film, sheet, foil, net, porous material, foam, nonwoven fabric.

[0085] If the electrode slurry composition is a negative electrode slurry composition for forming a negative electrode, the negative electrode can be manufactured by applying the negative electrode slurry composition onto a negative electrode current collector, followed by drying and rolling. Alternatively, the negative electrode slurry can be cast separately onto a support, and the resulting film, obtained by peeling it off the support, can be laminated onto the negative electrode current collector.

[0086] The thickness of the negative electrode active material layer formed by the negative electrode slurry may vary depending on the loading amount and loading speed for applying the negative electrode slurry.

[0087] The negative electrode current collector generally has a thickness of 3 μm to 500 μm. Such a negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes to the battery, and can be made of materials such as copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., or aluminum-cadmium alloy. In addition, similar to the negative electrode current collector, fine irregularities can be formed on the surface to strengthen the bonding force of the negative electrode active material, and it can be used in various forms such as film, sheet, foil, net, porous material, foam, nonwoven fabric.

[0088] <Lithium-ion secondary battery> According to one aspect of the present invention, the present invention provides a lithium secondary battery comprising a positive electrode, a negative electrode, a separation membrane disposed between the positive and negative electrodes, and an electrolyte, utilizing the carbon nanotube dispersion described above. The positive electrode and negative electrode are the same as described above, so a detailed explanation is omitted.

[0089] The separation membrane separates the negative electrode and the positive electrode, providing a pathway for lithium ions to move. Generally, any membrane used as a separation membrane in lithium secondary batteries can be used without particular limitations, but those with low resistance to ion movement of the electrolyte while having excellent moisture-absorbing capacity for the electrolyte are particularly preferred. Specifically, porous polymer films, such as those made from polyolefin polymers like ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or laminated structures of two or more layers thereof, can be used. Ordinary porous nonwoven fabrics, such as those made from high-melting-point glass fibers or polyethylene terephthalate fibers, can also be used. Furthermore, coated separation membranes containing ceramic components or polymeric substances can be used to ensure heat resistance or mechanical strength, and they can be selectively used in single-layer or multi-layer structures.

[0090] The electrolyte may be, but is not limited to, an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel-like polymer electrolyte, a solid inorganic electrolyte, or a molten inorganic electrolyte that can be used in the manufacture of lithium secondary batteries. Specifically, the electrolyte may contain an organic solvent and a lithium salt.

[0091] The organic solvent can be any solvent that can act as a medium through which ions involved in the electrochemical reaction of the battery can move, without any particular limitations. Specifically, the organic solvents 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; dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (propylene Carbonate solvents such as carbonate (PC); alcohol solvents such as ethanol and isopropyl alcohol; nitriles such as R-CN (where R is a linear, branched, or cyclic hydrocarbon group of C2 to C20, and can include a double-bonded aromatic ring or ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes can be used. Among these, carbonate solvents are preferred, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate) having high ionic conductivity and high dielectric constant that can improve the charge and discharge performance of the battery, and a low-viscosity linear carbonate compound (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) is more preferred. In this case, mixing the cyclic carbonate and the linear carbonate in a volume ratio of about 1:1 to about 1:9 can demonstrate excellent electrolyte performance.

[0092] The lithium salt can be used without particular limitations as long as it is a compound that can provide lithium ions for use in lithium secondary batteries. Specifically, the lithium salts include LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, and LiN(CF3SO2). 2. LiCl, LiI, or LiB(C2O4)2 can be used. The concentration of the lithium salt is preferably within the range of 0.1 M to 2.0 M. When the concentration of the lithium salt falls within this range, the electrolyte has appropriate conductivity and viscosity, so it can exhibit excellent electrolyte performance and lithium ions can move effectively.

[0093] In addition to the components of the electrolyte, the electrolyte may also contain one or more additives for the purpose of improving battery life characteristics, suppressing the decrease in battery capacity, and improving battery discharge capacity, such as haloalkylene carbonate compounds like difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexaphosphate triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride. In this case, the additive may be included in an amount of 0.1% to 5% by weight relative to the total weight of the electrolyte.

[0094] A lithium secondary battery containing an electrode manufactured using the carbon nanotube dispersion according to the present invention, specifically a lithium secondary battery containing a negative electrode manufactured using the carbon nanotube dispersion, has carbon nanotubes uniformly dispersed within the negative electrode. Compared to conventional batteries containing conductive materials such as carbon black, the content of such materials can be reduced, allowing for stable and superior discharge capacity and output characteristics. As a result, it can be usefully utilized in portable devices such as mobile phones, laptop computers, and digital cameras, as well as in electric vehicles such as hybrid electric vehicles (HEVs).

[0095] Accordingly, according to another specific example of the present invention, a lithium secondary battery, a battery module containing the lithium secondary battery as a unit cell, and a battery pack containing the same can be provided.

[0096] The aforementioned battery module or battery pack can be used as a power source for one or more medium-to-large devices in a power tool; an electric vehicle (EV), a hybrid electric vehicle, or a plug-in hybrid electric vehicle (PHEV); or a power storage system.

[0097] The following examples are provided to aid in understanding the present invention, but these examples are provided to make the present invention easier to understand and the invention is not limited thereto.

[0098] Examples (Production of carbon nanotube dispersion) The lignosulfonates used in the examples and comparative examples had the average integral values ​​shown in Table 1 below when their active groups were analyzed using an FT-IR instrument (manufacturer: Agilent, product name: Cary 620-FTIR) (analytical accessory: Specac Golden Gate ATR accessory (diamond crystal), analytical conditions: 8 resolution, 32 scans).

[0099] [Table 1]

[0100] Example 1 A carbon nanotube dispersion weighing 500 g was prepared by the following method. 3.375 g (0.675 wt%) of polyvinylpyrrolidone (Zhangzhou Huafu Chemical PVP K15 product) was used as the first dispersant, 1.125 g (0.225 wt%) of primary lignosulfonate (aromatic carbon content: 75 mol%, mean integral of carbonyl group / mean integral of aromatic ring: 0.0882) was used as the second dispersant, and 492.5 g of water was mixed with the solvent to prepare 497 g of the first mixture. In this mixture, the total Na content of the first and second dispersants was 329 ppm, and the total Ca content was 3 ppm. The Na and Ca content were measured using an ICP-OES instrument (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, measurements were taken after dispersion and dilution in tertiary ultrapure water, and the experimental detection limit (Method detection limit) was <5 mg / kg. The first mixture was prepared by attaching an impeller and container to a dissolution vessel (VMA-Getzmann Dispermat-CA product), adding a dispersant and solvent, and stirring at 400 rpm for 10 minutes. Single-walled carbon nanotubes (BET specific surface area: 1,160 m²) were added to the prepared first mixture. 2 A second mixture was prepared by adding 3.0 g (0.6 wt%) of OCSoAl TUBALL product (length: 5 μm or more, / g) and stirring at 8,000 rpm for 60 minutes. The prepared second mixture was homogeneously dispersed seven times at a pressure of 20,000 psi using a high-pressure disperser (Micronox PICOMAX product) to produce a carbon nanotube dispersion.

[0101] Example 2 A carbon nanotube dispersion was prepared in the same manner as in Example 1, except that a quaternary lignosulfonate (aromatic carbon content: 74 mol%, mean value of integral of carbonyl group / mean value of integral of aromatic ring: 0.1700) was used as the second dispersant, and the total Na content in the first and second dispersants was 396 ppm and the total Ca content was 3 ppm.

[0102] Example 3 A carbon nanotube dispersion was prepared in the same manner as in Example 1, except that a fifth lignosulfonate (aromatic carbon content: 81 mol%, mean value of integral of carbonyl group / mean value of integral of aromatic ring: 0.1956) was used as the second dispersant, and the total Na content in the first and second dispersants was 302 ppm and the total Ca content was 3 ppm.

[0103] Example 4 A carbon nanotube dispersion was prepared in the same manner as in Example 1, except that a third lignosulfonate (aromatic carbon content: 67 mol%, mean value of integral of carbonyl group / mean value of integral of aromatic ring: 0.1586) was used as the second dispersant, and the total Na content in the first and second dispersants was 412 ppm and the total Ca content was 4 ppm.

[0104] Example 5 A carbon nanotube dispersion was prepared in the same manner as in Example 1, except that a 2nd lignosulfonate (aromatic carbon content: 84 mol%, mean value of integral of carbonyl group / mean value of integral of aromatic ring: 0.1804) was used as the second dispersant, and the total Na content in the first and second dispersants was 311 ppm and the total Ca content was 3 ppm.

[0105] Example 6 A carbon nanotube dispersion was prepared in the same manner as in Example 1, except that a 10-lignosulfonate (aromatic carbon content: 82 mol%, mean value of integral of carbonyl group / mean value of integral of aromatic ring: 0.1483) was used as the second dispersant, and the total Na content in the first and second dispersants was 315 ppm and the total Ca content was 3 ppm.

[0106] Comparative Example 1 A carbon nanotube dispersion was prepared in the same manner as in Example 1, except that 4.5 g (0.9% by weight) of the first dispersant was used without the second dispersant, and the total Na content of the first dispersant was 129 ppm and the total Ca content was 3 ppm.

[0107] Comparative Example 2 A carbon nanotube dispersion was prepared in the same manner as in Example 1, except that a secondary lignosulfonate (aromatic carbon content: 51 mol%, mean value of integral of carbonyl group / mean value of integral of aromatic ring: 0.2075) was used as the second dispersant, and the total Na content in the first and second dispersants was 129 ppm and the total Ca content was 177 ppm.

[0108] Comparative Example 3 A carbon nanotube dispersion was prepared in the same manner as in Example 1, except that a third lignosulfonate (aromatic carbon content: 63 mol%, mean value of integral of carbonyl group / mean value of integral of aromatic ring: 0.4917) was used as the second dispersant, and the total Na content in the first and second dispersants was 147 ppm and the total Ca content was 159 ppm.

[0109] Comparative Example 4 A carbon nanotube dispersion was prepared in the same manner as in Example 1, except that a sixth lignosulfonate (aromatic carbon content: 58 mol%, mean value of integral of carbonyl group / mean value of integral of aromatic ring: 0.5928) was used as the second dispersant, and the total Na content in the first and second dispersants was 167 ppm and the total Ca content was 102 ppm.

[0110] Comparative Example 5 A carbon nanotube dispersion was prepared in the same manner as in Example 1, except that a 9th lignosulfonate (aromatic carbon content: 62 mol%, mean value of integral of carbonyl group / mean value of integral of aromatic ring: 0.4098) was used as the second dispersant, and the total Na content in the first and second dispersants was 153 ppm and the total Ca content was 105 ppm.

[0111] Experimental example The viscosity (initial, at 25°C) of the carbon nanotubes produced by Examples 1 to 6 and Comparative Examples 1 to 5 was measured. After storage at 45°C for 65 hours, the viscosity was measured again after cooling to 25°C, 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 and 1 rpm, with a rotor code of 01.

[0112] [Table 2]

[0113] As shown in Table 2 above, it can be confirmed that the aromatic carbon content of the second dispersant affects the viscosity of the carbon nanotube dispersion. Specifically, when the aromatic carbon content of the second dispersant was less than 65 mol%, the initial viscosity of the carbon nanotube dispersion exceeded 5,000 cP, and the viscosity after storage at 45°C for 65 hours and then cooling to 25°C also exceeded 10,000 cP, with a viscosity change ratio exceeding 2.0, indicating a slight improvement in dispersibility obtained by adding the second dispersant. On the other hand, when the aromatic carbon content of the second dispersant was 65 mol% or more, not only did the initial viscosity of the carbon nanotube dispersion not exceed 5,000 cP, but the viscosity after storage at 45°C for 65 hours and then cooling to 25°C also did not exceed 5,000 cP, indicating a significant improvement in dispersibility.

[0114] The second dispersant allows us to confirm that the ratio of carbonyl groups to aromatic rings affects the rate of change in viscosity of the carbon nanotube dispersion. Specifically, when the ratio of the average integral of carbonyl groups to the average integral of aromatic rings exceeds 0.2 with the second dispersant, the initial viscosity exceeds 5,000 cP, and the viscosity after storage at 45°C for 65 hours and then cooling to 25°C also exceeds 10,000 cP, with a viscosity change ratio exceeding 2.0, indicating a slight improvement in dispersibility obtained by adding the second dispersant. On the other hand, when the ratio of the average integral of carbonyl groups to the average integral of aromatic rings with the second dispersant is 0.2 or less, not only does the initial viscosity of the carbon nanotube dispersion not exceed 5,000 cP, but the viscosity after storage at 45°C for 65 hours and then cooling to 25°C also does not exceed 5,000 cP, indicating a significant improvement in dispersibility. In the second dispersant, the carbon content of most other active groups did not have any particular correlation with the dispersibility of the carbon nanotube dispersion.

[0115] It can be confirmed that the Na content or Ca content of the dispersant affects the rate of change in viscosity of the carbon nanotube dispersion. Specifically, when the Na content of the dispersant (including the second dispersant) was less than 250 ppm or the Ca content exceeded 50 ppm, the initial viscosity exceeded 5,000 cP, and the viscosity after storage at 45°C for 65 hours and then cooling to 25°C also exceeded 10,000 cP, with a viscosity change ratio exceeding 2.0, indicating a slight improvement in dispersibility obtained by adding the second dispersant. On the other hand, when the Na content of the dispersant (including the second dispersant) was between 250 ppm and 500 ppm, or the Ca content was between 0.1 ppm and 50 ppm, not only did the initial viscosity of the carbon nanotube dispersion not exceed 5,000 cP, but the viscosity after storage at 45°C for 65 hours and then cooling to 25°C also did not exceed 5,000 cP, indicating a significant improvement in dispersibility. In dispersants, the metal content of most metals did not show any particular correlation with the dispersibility of carbon nanotube dispersions.

[0116] Any simple modifications or changes to the present invention fall within the scope of the present invention, and the specific scope of protection of the present invention is clarified by the appended claims.

Claims

1. The mixture comprises carbon nanotubes, a dispersant, and a solvent. The aforementioned dispersant is A first dispersant comprising a first polymer compound containing an amine group; and It contains a second dispersant containing a second polymer compound containing an aromatic ring, The second dispersant is a carbon nanotube dispersion containing 65 mol% or more aromatic carbon based on the total number of moles of carbon atoms.

2. The carbon nanotube dispersion according to claim 1, characterized in that the first polymer compound is selected from the group consisting of polyvinylpyrrolidone, polyacrylate hydrazide, poly-N-vinyl-5-methoxazolidone, N-alkylpolyimine, N-acetylpolyimine, polyacrylamide, poly-L-lysine hydrobromide, benzyl-dodecyl-dimethylammonium chloride, polyethyleneimine, and combinations thereof.

3. The second polymer compound further contains a carbonyl group, The carbon nanotube dispersion according to claim 1, characterized in that the second dispersant has a ratio of carbonyl groups to aromatic rings (average value of integrals of carbonyl groups / average value of integrals of aromatic rings) of 0.2 or less as determined by FT-IR.

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

5. The carbon nanotube dispersion according to claim 4, 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. The carbon nanotube dispersion according to claim 1, characterized in that the second polymer compound is a lignosulfonate.

7. The carbon nanotube dispersion according to claim 1, characterized in that the first dispersant is contained 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. The carbon nanotube dispersion according to claim 1, characterized in that the dispersant is contained 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. The carbon nanotube dispersion according to claim 1, characterized in that the carbon nanotubes are contained in the carbon nanotube dispersion at an amount of 0.1% to 5% by weight, based on the total weight of the carbon nanotube dispersion.

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

11. The carbon nanotube dispersion according to claim 1, characterized in that the solvent is an aqueous solvent containing water.

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

13. The carbon nanotube dispersion according to claim 1, characterized in that the carbon nanotube dispersion has a viscosity of 10,000 cP or less after being stored at 45°C for 65 hours and then cooled to 25°C.

14. A method for producing a carbon nanotube dispersion according to claim 1, The aforementioned manufacturing method is (1) A step of mixing carbon nanotubes, 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 mixture; and (2) A method for producing a carbon nanotube dispersion, comprising the step of stirring the mixture.

15. An electrode slurry composition for lithium secondary batteries comprising the carbon nanotube dispersion and electrode active material described in claim 1.

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