Carbon nanotube dispersion, method of preparing the same, and electrode slurry composition and secondary battery including the same

Abstract

To provide a carbon nanotube dispersion, a method of preparing the same, and an electrode slurry composition and a secondary battery including the same.SOLUTION: A carbon nanotube dispersion comprises carbon nanotubes, a first dispersant comprising a nonionic polymer having a weight average molecular weight of 4,000 g / mol to 30,000 g / mol, and a second dispersant comprising an anionic polymer having a sulfonic acid (salt) group, where the weight ratio of the first dispersant and the second dispersant is 5:1 to 1:5.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a carbon nanotube dispersion, a method for producing the same, an electrode slurry composition containing the same, and a secondary battery.

Background Art

[0002] Due to the rapid increase in the use of fossil fuels, the demand for the use of alternative energy and clean energy is increasing. Currently, a typical example of an electrochemical device using these electrochemical energies is a secondary battery, and its use area is gradually expanding. A secondary battery is a battery that can be repeatedly used through a discharge process in which chemical energy is converted into electrical energy and a reverse charging process. The secondary battery may include a positive electrode, a negative electrode, an electrolyte, and a separator. The positive electrode and the negative electrode may generally include an electrode current collector and an electrode active material layer formed on the electrode current collector. The electrode active material layer may be manufactured by applying an electrode slurry composition containing an electrode active material, a conductive material, a binder, etc. onto the electrode current collector, drying it, and then rolling it.

[0003] The conductive material is for improving the conductivity of the electrode active material. Conventionally, a dot-shaped conductive material such as carbon black has been mainly used. However, since the dot-shaped conductive material does not have a high effect of improving electrical conductivity, it should be used in an excessive amount to obtain a sufficient effect. As a result, there is a problem that the content of the electrode active material decreases and the battery capacity decreases.

[0004] In order to improve such problems, attempts have been actively made to apply highly conductive carbon nanotubes (CNTs) as the conductive material.

[0005] However, due to the characteristics of carbon nanotubes, the dispersibility in the slurry is poor, the manufacturability of the secondary battery manufacturing process is reduced, and the conductivity decreases as the secondary battery is cycled, resulting in a problem of reduced performance of the secondary battery.

Summary of the Invention

Problems to be Solved by the Invention

[0006] The present invention provides a carbon nanotube dispersion liquid having excellent dispersibility, a low rate of change in viscosity over time, and improved performance of a secondary battery, a method for producing the same, an electrode slurry composition containing the same, and a secondary battery.

Means for Solving the Problems

[0007] The carbon nanotube dispersion liquid according to the present invention includes carbon nanotubes, a first dispersant containing a nonionic polymer having a weight average molecular weight of 4,000 g / mol to 30,000 g / mol, and a second dispersant containing an anionic polymer having a sulfonic acid (salt) group, and the weight ratio of the first dispersant to the second dispersant is 5:1 to 1:5.

[0008] In one embodiment of the present invention, the carbon nanotubes may be single-walled carbon nanotubes.

[0009] In one embodiment of the present invention, the nonionic polymer may be in a random coil form including a main chain exhibiting hydrophobicity and a side chain exhibiting hydrophilicity.

[0010] In one embodiment of the present invention, the nonionic polymer may contain an amide group.

[0011] In one embodiment of the present invention, the content of the first dispersant may be 0.01% by weight to 10.00% by weight based on the total weight of the carbon nanotube dispersion liquid.

[0012] In one embodiment of the present invention, the anionic polymer may have at least two or more aromatic rings.

[0013] In one embodiment of the present invention, the anionic polymer may have a weight average molecular weight of 200 g / mol to 8,000 g / mol.

[0014] In one embodiment of the present invention, the content of the second dispersant may be 0.01% by weight to 10.00% by weight based on the total weight of the carbon nanotube dispersion.

[0015] In one embodiment of the present invention, the total content of the first dispersant and the second dispersant may be 100 parts by weight to 200 parts by weight based on 100 parts by weight of the carbon nanotubes.

[0016] The method for producing a carbon nanotube dispersion according to the present invention includes a step of mixing carbon nanotubes, a first dispersant containing a nonionic polymer having a weight average molecular weight of 4,000 g / mol to 30,000 g / mol, a second dispersant containing an anionic polymer having a sulfonic acid (salt) group, and an aqueous solvent to produce a mixture, a step of milling and crushing the mixture, and a step of dispersing the mixture, wherein the first dispersant and the second dispersant are mixed at a weight ratio of 5:1 to 1:5.

[0017] In one embodiment of the present invention, the mixture can be crushed so that the average particle size is less than 100 μm.

[0018] The electrode slurry composition according to the present invention includes an electrode active material, a binder, and a carbon nanotube dispersion, wherein the carbon nanotube dispersion includes carbon nanotubes, a first dispersant containing a nonionic polymer having a weight average molecular weight of 4,000 g / mol to 30,000 g / mol, and a second dispersant containing an anionic polymer having a sulfonic acid (salt) group, and the weight ratio of the first dispersant and the second dispersant is 5:1 to 1:5.

[0019] The secondary battery according to the present invention includes an electrode, a separator, and an electrolyte. The electrode includes an electrode active material, a binder, and a conductive material. The conductive material is manufactured from a carbon nanotube dispersion liquid. The carbon nanotube dispersion liquid includes carbon nanotubes, a first dispersant including a nonionic polymer having a weight average molecular weight of 4,000 g / mol to 30,000 g / mol, and a second dispersant including an anionic polymer having a sulfonic acid (salt) group. The weight ratio of the first dispersant and the second dispersant is 5:1 to 1:5.

Advantages of the Invention

[0020] The carbon nanotube dispersion liquid according to the present invention includes a first dispersant including a nonionic polymer whose weight average molecular weight satisfies a certain range. Further, the carbon nanotube dispersion liquid includes a second dispersant including an anionic polymer having a specific functional group. Further, the ratio of the first dispersant and the second dispersant satisfies 5:1 to 1:5.

[0021] Thereby, by optimizing each variable, namely, the weight average molecular weight of the nonionic polymer, the type of the anionic polymer, and the ratio of the first dispersant and the second dispersant, the dispersibility of the carbon nanotubes can be improved, the increase in the viscosity of the dispersion liquid including the same can be minimized, and the performance of the secondary battery can be improved.

Embodiments for Carrying Out the Invention

[0022] The structural or functional description regarding the embodiments disclosed in this specification or the application is merely exemplified for the purpose of explaining the embodiments according to the technical idea of the present invention. The embodiments according to the technical idea of the present invention can be implemented in various forms in addition to the embodiments disclosed in this specification or the application, and the technical idea of the present invention is not construed as being limited to the embodiments described in this specification or the application.

[0023] Also, when a component in this specification or application is described as "including", unless otherwise stated to the contrary, it does not exclude other components, but may further include other components. Also, any numerical range indicating physical property values, dimensions, etc. of the components described in this specification or application must be understood to be modified by the term "about" in all cases unless otherwise specified. Also, "ppm" in this specification or application means a weight basis. Also, the description of "A and / or B" in this specification or application means "A, B, or A and B".

[0024] Hereinafter, the carbon nanotube dispersion, its manufacturing method, the electrode slurry composition containing the same, and the secondary battery according to the present invention will be described.

[0025] Normally, in order to improve the electrical conductivity of the electrode active material used in a secondary battery, a conductive material is used, and the conductive material may be mixed with the electrode active material in a dispersed liquid state mixed with a dispersant and a solvent.

[0026] In order to further improve the electrical conductivity of the electrode active material, carbon nanotubes have attracted attention as a conductive material. However, unlike carbon black and the like which are point-like conductive materials, carbon nanotubes which are linear conductive materials have a high specific surface area, and there has been a problem that an aggregation phenomenon occurs due to the van der Waals force between the carbon nanotubes.

[0027] In particular, among carbon nanotubes, single-walled carbon nanotubes are very excellent in electrical conductivity, but due to their high specific surface area and strong attractive force, an aggregation phenomenon easily occurs, and there is a problem of very low dispersibility. Although the dispersibility of the single-walled carbon nanotubes can be improved when the proportion of the dispersant increases, there are further other problems such as impurities of a large amount of the remaining dispersant and, as a result, a decrease in the electrical conductivity of the secondary battery.

[0028] The inventors focused on the fact that in a first dispersant containing a nonionic polymer capable of stabilizing carbon nanotubes and a second dispersant containing an anionic polymer capable of further improving the dispersibility of the carbon nanotubes, variables such as the weight average molecular weight of the nonionic polymer, the type of anionic polymer, and the ratio of the first dispersant to the second dispersant have a close influence on the dispersibility of carbon nanotubes, the rate of change over time of the viscosity of the dispersion containing the same, and the performance of the secondary battery.

[0029] The nonionic polymer binds to each carbon nanotube so that the carbon nanotubes can be dispersed. Here, the nonionic polymer can be selected so that the weight average molecular weight is different, and according to the weight average molecular weight, the ratio of the nonionic polymer that can bind to the carbon nanotubes can be determined. Further, based on the total surface area of the carbon nanotubes, the ratio of the surface area of the carbon nanotubes surrounded by the nonionic polymer can be determined. That is, it was confirmed that the dispersibility, the content of the residue, and the electrical conductivity of the carbon nanotubes can change according to the weight average molecular weight of the nonionic polymer.

[0030] The anionic polymer may bind to the surface of the carbon nanotubes that is not bound to the nonionic polymer, and a negative charge may be introduced onto the surface of the carbon nanotubes. As a result, an electrostatic repulsive force may be generated between the carbon nanotubes with a negative charge introduced on the surface, and the dispersibility of the carbon nanotubes may be further improved. Here, the three-dimensional structure of the anionic polymer and the type of functional group exhibiting an anion can be selected, and according to the three-dimensional structure and the type of functional group, the ratio of the anionic polymer that can bind to the carbon nanotubes, the distribution of the negative charges introduced on the surface of the carbon nanotubes, and the polarity of the negative charges can be determined. That is, it was confirmed that the dispersibility of the carbon nanotubes, the rate of change over time of the viscosity of the dispersion containing the same, and the electrical conductivity can change according to the three-dimensional structure of the anionic polymer and the type of functional group.

[0031] The ratio of the first dispersant to the second dispersant can be selected to be different. As described above, the first dispersant and the second dispersant can function differently in terms of the form of binding to the carbon nanotube, the function imparted to the carbon nanotube, etc. That is, depending on the ratio of the first dispersant to the second dispersant, the ratio of the nonionic polymer and the anionic polymer that can bind to each carbon nanotube, the ratio of the first dispersant to the second dispersant remaining in the dispersion, and the change in electrical conductivity thereby, the initial discharge capacity of the secondary battery, and the high-rate characteristics were confirmed to be changeable points.

[0032] The carbon nanotube dispersion according to the present invention contains carbon nanotubes.

[0033] The carbon nanotube is in the shape of a cylinder having a nanosize diameter of a graphite sheet, and may have a secondary structure in which a plurality of carbon nanotubes are arranged or aggregated. When the carbon nanotube is used as a conductive material, the electrical conductivity of the electrode can be improved.

[0034] The content of the carbon nanotube may be 0.01% by weight to 15.00% by weight, 0.01% by weight to 10.00% by weight, 0.01% by weight to 8.00% by weight, 0.05% by weight to 8.00% by weight, 0.1% by weight to 8.00% by weight, or 0.1% by weight to 5.00% by weight with respect to the total weight of the carbon nanotube dispersion. When the above range is satisfied, an increase in the viscosity of the carbon nanotube dispersion can be suppressed, and when used as a conductive material for a secondary battery, it can have an appropriate adhesive force with a binder during electrode manufacturing and can have an appropriate loading amount, so the process efficiency can be improved.

[0035] The carbon nanotube may be a multi-walled carbon nanotube (MWCNT) having a large number of binding numbers forming the wall, a thin-walled carbon nanotube (TWCNT), or a single-walled carbon nanotube (SWCNT) having a single wall.

[0036] Preferably, the carbon nanotube may be a single-walled carbon nanotube. The single-walled carbon nanotube is superior in electrical conductivity compared to the multi-walled carbon nanotube, and the initial efficiency, life characteristics, and high-rate discharge characteristics of the secondary battery can be improved.

[0037] Due to high cohesive force, the dispersion liquid containing the single-walled carbon nanotube is inferior in long-term storage stability, and it has been difficult to commercialize the single-walled carbon nanotube as a conductive material. However, the present inventors have found that when a first dispersant containing a nonionic polymer having a weight average molecular weight within a certain range and a second dispersant containing an anionic polymer having a specific functional group are included in a weight ratio of 5:1 to 1:5 together with the single-walled carbon nanotube, excellent dispersibility and minimization of the increase in viscosity due to changes over time can be achieved, and it has been shown that it can be commercialized as a conductive material.

[0038] The BET specific surface area of the single-walled carbon nanotube is 800 m 2 / g to 1,800 m 2 / g, 1,000 m 2 / g to 1,800 m 2 / g, 1,200 m 2 / g to 1,800 m 2 / g, 1,200 m 2 / g to 1,700 m 2 / g, 1,300 m 2 / g to 1,700 m 2 / g, 1,400 m 2 / g to 1,700 m2 / g, or 1,500 m 2 / g to 1,700 m 2 / g may be acceptable. The BET specific surface area can be measured from the nitrogen gas adsorption amount at liquid nitrogen temperature (77K) using BEL Japan's BELSORP-miniII.

[0039] The single-walled carbon nanotube may have a rolling density of 1 g / cc or more and a powder resistance of 0.001 ohm·cm or less, 0.0009 ohm·cm or less, 0.0008 ohm·cm or less, or 0.0007 ohm·cm or less. The lower the powder resistance value, the more the electrical conductivity of the single-walled carbon nanotube can be improved. When the above range is satisfied, the performance of a secondary battery using the single-walled carbon nanotube as a conductive material can be improved.

[0040] The powder resistance can be measured using a powder resistance measuring machine (MCP-PD51) equipped with a 4-pin probe at the powder resistance value when the rolling density is 1 g / cc.

[0041] The length of the single-walled carbon nanotube may be 10 nm to 20,000 nm, 100 nm to 20,000 nm, 300 nm to 20,000 nm, 500 nm to 20,000 nm, or 800 nm to 15,000 nm.

[0042] The average diameter (D 50 ) of the single-walled carbon nanotube may be 0.5 nm to 25 nm, 0.5 nm to 20 nm, 0.5 nm to 15 nm, 0.5 nm to 10 nm, 0.8 nm to 10 nm, 1 nm to 10 nm, or 1 nm to 5 nm.

[0043] The length and diameter can be measured using an Atomic Force Microscope (AFM). The length corresponds to the average value of the top 100 single-walled carbon nanotubes with a large average length and the bottom 100 single-walled carbon nanotubes, and the diameter may correspond to the average value of the top 100 single-walled carbon nanotubes with a large average diameter and the bottom 100 single-walled carbon nanotubes.

[0044] The single-walled carbon nanotubes can measure the weight change due to temperature change using a Thermogravimetric analysis. The temperature change can be measured while increasing the temperature at intervals of 10°C / min in the temperature range of 40°C to 1,000°C under a nitrogen atmosphere.

[0045] The single-walled carbon nanotubes can measure the temperature at which thermal decomposition starts using the Thermogravimetric analysis. By measuring the weight change of the single-walled carbon nanotubes due to temperature change, the purity of the single-walled carbon nanotubes can be evaluated.

[0046] The weight change of the single-walled carbon nanotubes measured by the Thermogravimetric analysis at 40°C to 300°C may be 2% or less, 1.9% or less, 1.8% or less, 1.7% or less, or 1.5% or less.

[0047] The weight change of the single-walled carbon nanotubes measured by the Thermogravimetric analysis at 300°C to 550°C may be 2% or less, 1.5% or less, 1.3% or less, 1.2% or less, or 1% or less.

[0048] The weight change of the single-walled carbon nanotubes measured by the Thermogravimetric analysis at 40°C to 550°C may be 2% or less, 1.98% or less, 1.97% or less, 1.96% or less, or 1.95% or less.

[0049] The single-walled carbon nanotube may have a thermal decomposition start temperature measured by the thermogravimetric analyzer of 500°C to 700°C, 520°C to 700°C, 530°C to 650°C, or 550°C to 600°C. The thermal decomposition start temperature can be derived from the peak point obtained by differentiating the temperature-weight graph measured by the thermogravimetric analyzer.

[0050] The single-walled carbon nanotube may have a residue content of 1% or less, 0.5% or less, 0.1% or less, 0.05% or less, 0.03% or less, 0.02% or less, or 0.01% or less after the thermal decomposition measured by the thermogravimetric analyzer is completed.

[0051] When the single-walled carbon nanotube satisfies the weight change, thermal decomposition start temperature, and residue content within the above ranges, impurities are minimized and the purity is improved. When used as a conductive material, the electrical conductivity is improved, the performance of the secondary battery can be improved, the dispersibility is improved, and the coating property and processability can be improved.

[0052] The single-walled carbon nanotube can be a bundle in which a plurality of single-walled carbon nanotubes are arranged side by side in a certain direction, a rope-like bundle type, or an entangled type in which a plurality of single-walled carbon nanotubes have no specific directionality and are entangled like balls or potatoes.

[0053] The single-walled carbon nanotube may be manufactured by a step of synthesizing the single-walled carbon nanotube and a step of purifying the synthesized single-walled carbon nanotube.

[0054] The single-walled carbon nanotube may be synthesized by laser ablation. The laser ablation means a process of irradiating a laser beam onto a mixture of a carbon-containing raw material and a catalyst in an inert gas atmosphere, and single-walled carbon nanotubes may be synthesized by the above process. The inert gas may be argon or nitrogen. The carbon-containing raw material may be graphite. The catalyst may be a metal catalyst. The intensity of the laser beam is 100 mJ / cm 2 ~300 mJ / cm 2 、110 mJ / cm 2 ~300 mJ / cm 2 、110 mJ / cm 2 ~290 mJ / cm 2 、or 120 mJ / cm 2 ~280 mJ / cm 2 and may be.

[0055] The single-walled carbon nanotube may be synthesized by arc discharge. The arc discharge means a process of causing an arc discharge between a pair of electrodes and depositing the evaporated material generated at the anode, and single-walled carbon nanotubes may be synthesized by the above process. The anode may contain a carbon-containing raw material. The carbon-containing raw material may be graphite. The anode may contain a transition metal. The transition metal may contain at least one or more of iron element, cobalt element, yttrium element, and nickel element. The graphite may be rod-shaped with voids. The transition metal may be mixed in the voids of the graphite. The arc discharge can be carried out in an inert gas, or an inert gas and hydrogen gas atmosphere. The arc discharge can be carried out in a small amount of hydrocarbon gas atmosphere. The hydrocarbon gas may contain at least one or more of methane, ethylene, and acetylene. The pair of electrodes may be separated by a certain distance.

[0056] The pair of electrodes may be separated by 5 mm or less, 4 mm or less, 3 mm or less, 2 mm or less, or 1 mm or less. The arc discharge method may be a direct current arc discharge method. The direct current power source in the direct current arc discharge method may have a voltage range of 20 V to 70 V, 22 V to 70 V, 22 V to 65 V, or 25 V to 65 V. The direct current power source in the direct current arc discharge method may have a current range of 40 A to 120 A, 40 V to 115 V, 40 V to 100 V, or 45 V to 100 V.

[0057] Preferably, the single-walled carbon nanotube may be synthesized by chemical vapor deposition. The chemical vapor discharge method means a process of thermally decomposing hydrocarbons such as methane, ethylene, and acetylene, and benzene, toluene, or xylene in the gas phase in the presence of a catalyst, and the single-walled carbon nanotube may be synthesized by the above process. As the catalyst, nanoparticles supported with an iron element, a cobalt element, a nickel element, a molybdenum element, etc., or alumina or silica supporting the nanoparticles can be used. The chemical vapor deposition method has an advantage that it is easy to control the diameter, length, density, structure, crystallinity, etc. of the single-walled carbon nanotube, and high-purity single-walled carbon nanotubes can be mass-produced.

[0058] The synthesized single-walled carbon nanotube may contain impurities. The impurities may contain at least one of metal oxides, metals, and non-metals. The metal oxide may contain a ceramic metal. The ceramic metal may be derived from a catalyst support in the single-walled carbon nanotube synthesis process. The metal may contain at least one or more of an iron element, a cobalt element, a nickel element, a chromium element, a copper element, a manganese element, a nickel element, and a zinc element. The non-metal may contain a sulfur element. The metal and the non-metal may be derived from a catalyst in the single-walled carbon nanotube synthesis process.

[0059] Among the impurities, the nickel element may cut the single-walled carbon nanotubes, shortening their length or oxidizing their surface, and may deteriorate their electrical and mechanical properties. The nickel element may damage the inherent characteristics of the single-walled carbon nanotubes. Therefore, it is more preferable to perform a step of purifying the synthesized single-walled carbon nanotubes to remove the nickel element. The BET specific surface area of the single-walled carbon nanotubes and the content of the nickel element can be adjusted not only by the synthesis process of the single-walled carbon nanotubes but also by the process conditions for removing the impurities.

[0060] The synthesized single-walled carbon nanotubes may be purified by a physical method or a chemical method.

[0061] The physical methods include centrifugation, solubilization of carbon nanotubes, high temperature annealing, etc.

[0062] The centrifugation applies centrifugal force to a mixture with different masses and separates substances by the difference in sedimentation rates. By this centrifugation, amorphous carbon, carbon nanoparticles, and single-walled carbon nanotubes contained in the synthesized single-walled carbon nanotubes can be separated.

[0063] The solubilization of the carbon nanotubes introduces functional groups to the surface of the single-walled carbon nanotubes, dissolves them in a solvent, and then high-purity carbon nanotubes can be separated from the impurities using filtration or chromatography.

[0064] In high temperature annealing, carbon does not undergo a phase change even at a high temperature of about 1,500 °C or higher under an inert gas or vacuum condition. The single-walled carbon nanotubes are treated under an inert gas or vacuum condition at a high temperature not lower than the evaporation temperature of the impurities, so that the impurities formed on the carbon nanotubes can be removed.

[0065] The chemical methods include electrochemical oxidation, gas-phase oxidation, liquid-phase oxidation, etc.

[0066] The electrochemical oxidation can remove the amorphous carbon and impurities contained in the single-walled carbon nanotubes by electrochemically oxidizing the synthesized single-walled carbon nanotubes with a potassium hydroxide solution or a sulfuric acid solution.

[0067] The liquid-phase oxidation can react the synthesized single-walled carbon nanotubes with an oxidizing liquid to remove the amorphous carbon and impurities contained in the single-walled carbon nanotubes. As the oxidizing liquid, hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, etc. can be used. The liquid-phase oxidation can remove metal oxides and metals among the impurities contained in the single-walled carbon nanotubes. The liquid-phase oxidation can be carried out under the conditions of about 20°C to 25°C. Conventionally, the liquid-phase oxidation has been carried out in a high-temperature range of about 50°C to 70°C, but there are problems that the structure such as the cutting and end opening of the single-walled carbon nanotubes may be destroyed during the purification process, and the oxidizing liquid reactant exists as secondary impurities on the single-walled carbon nanotubes. Therefore, when the liquid-phase oxidation satisfies the above temperature range, the problem of generation of secondary impurities on the purified single-walled carbon nanotubes can be suppressed, and the structural stability of the single-walled carbon nanotubes after purification can be improved.

[0068] The gas-phase oxidation can remove the amorphous carbon and impurities contained in the single-walled carbon nanotubes by heat-treating the synthesized single-walled carbon nanotubes in an oxidizing gas atmosphere within a temperature range of about 700°C to 1,000°C. As the oxidizing gas, air, chlorine, a mixture of water vapor and hydrogen chloride, hydrogen sulfide, argon, etc. can be used.

[0069] The purification treatment step can be carried out for 30 minutes to 200 minutes, 30 minutes to 150 minutes, 40 minutes to 120 minutes, 40 minutes to 110 minutes, or 40 minutes to 100 minutes.

[0070] The purification step can be carried out at a temperature of 900 °C or higher, 920 °C or higher, 950 °C or higher, or 1,000 °C or higher.

[0071] After the purification treatment, a step of cooling to room temperature in a vacuum state can be carried out.

[0072] By the purification step, the metal, which is an impurity contained in the single-walled carbon nanotube, can be removed more efficiently.

[0073] The carbon nanotube dispersion according to the present invention contains a first dispersant containing a nonionic polymer having a weight average molecular weight of 4,000 g / mol to 30,000 g / mol.

[0074] Preferably, the nonionic polymer may have a weight average molecular weight of 4,000 g / mol to 30,000 g / mol, 4,000 g / mol to 20,000 g / mol, 5,000 g / mol to 20,000 g / mol, 6,000 g / mol to 20,000 g / mol, 10,000 g / mol to 20,000 g / mol, or 15,000 g / mol to 20,000 g / mol.

[0075] When the above range is satisfied, during the manufacture of the electrode, the phenomenon of elution of the first dispersant can be suppressed, the dispersibility of the carbon nanotubes can be improved, the content of the residue of the first dispersant can be reduced, and the electrical conductivity can be improved.

[0076] The nonionic polymer may contain one or more selected from the group consisting of polyethylene glycol, polypropylene glycol, polybutylene glycol, polyvinyl alcohol, polyvinylpyrrolidone, polyacrylic acid hydrazide, poly-N-vinyl-5-methoxazolidone, N-alkyl polyimine, N-acetyl polyimine, polyacrylamide, poly-L-lysine, polyethyleneimine, and polyethylene glycol-polypropylene glycol copolymer.

[0077] Preferably, the nonionic polymer may contain an amide group.

[0078] The nitrogen and oxygen contained in the amide group can improve the kneadability of the carbon nanotube dispersion with the solvent, and the intermolecular interaction with the anionic polymer having a sulfonic acid (salt) group contained in the second dispersant can further suppress the increase in viscosity over time.

[0079] Preferably, the nonionic polymer may be polypyrrolidone having a weight average molecular weight of 4,000 g / mol to 30,000 g / mol, 4,000 g / mol to 20,000 g / mol, 5,000 g / mol to 20,000 g / mol, 6,000 g / mol to 20,000 g / mol, 10,000 g / mol to 20,000 g / mol, or 15,000 g / mol to 20,000 g / mol.

[0080] The nonionic polymer may be in a random coil state.

[0081] The nonionic polymer may be in a random coil state including a hydrophobic main chain and a hydrophilic side chain.

[0082] By including the random coil-shaped nonionic polymer containing the hydrophobicity and hydrophilicity, the first dispersant may stably bind to the carbon nanotube and surround the surface of the carbon nanotube. By the first dispersant, the cohesive force between the carbon nanotubes can be reduced, and the carbon nanotubes can be smoothly dispersed.

[0083] The content of the first dispersant may be 0.01 wt% to 10.00 wt%, 0.01 wt% to 5.00 wt%, 0.01 wt% to 3.00 wt%, 0.01 wt% to 2.00 wt%, 0.05 wt% to 2.00 wt%, or 0.05 wt% to 1.50 wt% based on the total weight of the carbon nanotube dispersion liquid. When the above range is satisfied, the dispersion effect of the carbon nanotubes is improved, and the carbon nanotube dispersion liquid can have an appropriate initial viscosity.

[0084] The carbon nanotube dispersion liquid according to the present invention contains a second dispersant containing an anionic polymer having a sulfonic acid (salt) group.

[0085] The anionic polymer may have an aromatic ring. The second dispersant may contain an anionic polymer having an aromatic ring and a sulfonic acid (salt) group. The anionic polymer having a sulfonic acid (salt) group may contain benzene.

[0086] The anionic polymer may have at least two or more aromatic rings.

[0087] The second dispersant may contain an anionic polymer having at least two or more aromatic rings and a sulfonic acid (salt) group.

[0088] The anionic polymer having a sulfonic acid (salt) group may contain one or more selected from the group consisting of naphthalene, pyrene, anthracene, and phenanthrene.

[0089] The anionic polymer can bind to the carbon nanotube and change the electrical properties of the surface of the carbon nanotube. By means of the anionic polymer, a charge can be introduced onto the surface of the carbon nanotube. By means of the anionic polymer, a negative charge can be introduced onto the surface of the carbon nanotube. By introducing a charge onto the surface of the carbon nanotube by means of the anionic polymer, the dispersion effect between the carbon nanotubes can be improved, and the rate of change over time of the viscosity and the electrical conductivity of the dispersion liquid containing the same can be improved.

[0090] Moreover, by means of the anionic polymer containing the sulfonic acid (salt) group, the proportion of the anionic polymer capable of binding to the carbon nanotube can be increased, and the negative charge introduced onto the surface of the carbon nanotube can be uniformly distributed.

[0091] In addition, due to the steric effect generated by the aromatic ring, the anionic polymer can reduce the cohesive force between the carbon nanotubes bound to the second dispersant.

[0092] If necessary, the second dispersant may include one or more selected from the group consisting of polyacrylic acid, polymethacrylic acid, polyacrylic maleic acid, phosphoric acid, phosphate ester, acrylic-styrene copolymer, polyacrylic acid-styrene copolymer, polyacrylamide-acrylic acid copolymer, and polyacrylic acid-maleic acid copolymer.

[0093] The weight average molecular weight of the anionic polymer may be 200 g / mol to 8,000 g / mol, 200 g / mol to 7,000 g / mol, 200 g / mol to 6,000 g / mol, 200 g / mol to 5,000 g / mol, 200 g / mol to 4,000 g / mol, 200 g / mol to 3,500 g / mol, 200 g / mol to 3,000 g / mol, 200 g / mol to 2,500 g / mol, or 200 g / mol to 2,000 g / mol. The weight average molecular weight of the anionic polymer is preferably less than the weight average molecular weight of the nonionic polymer contained in the first dispersant.

[0094] When the above range is satisfied, a strong interaction with the carbon nanotube is possible, charges can be smoothly introduced onto the surface of the carbon nanotube, the dispersibility is further improved, and changes in viscosity due to changes over time can be minimized.

[0095] The content of the second dispersant may be 0.01 wt% to 10.00 wt%, 0.01 wt% to 5.00 wt%, 0.01 wt% to 3.00 wt%, 0.01 wt% to 2.00 wt%, 0.05 wt% to 2.00 wt%, or 0.05 wt% to 1.50 wt% based on the total weight of the carbon nanotube dispersion. When the above range is satisfied, the dispersion effect of the carbon nanotube can be further improved.

[0096] The weight ratio of the first dispersant to the second dispersant may be 5:1 to 1:5, 4:1 to 1:5, 3:1 to 1:5, 2:1 to 1:5, 1:1 to 1:5, 1:1 to 1:4, 1:1 to 1:3, 1:1 to 1:2.8, 1:1 to 1:2.5, 1:1 to 1:2, or 1:1 to 1:1.5.

[0097] The total content of the first dispersant and the second dispersant may be 100 parts by weight to 200 parts by weight, 100 parts by weight to 180 parts by weight, 100 parts by weight to 170 parts by weight, or 120 parts by weight to 170 parts by weight based on 100 parts by weight of the carbon nanotube.

[0098] When the above range is satisfied, the charge by the second dispersant can be introduced onto the surface of the carbon nanotubes stabilized by the first dispersant in a well-balanced manner, the dispersibility of the carbon nanotubes can be improved, and the initial discharge capacity and high-rate characteristics of the secondary battery including the carbon nanotubes can be improved.

[0099] The carbon nanotube dispersion may contain a solvent. When the solvent is used to mix the carbon nanotubes with an electrode active material or the like to form an electrode slurry composition, by previously dispersing the carbon nanotubes, the aggregation between the carbon nanotubes or the phenomenon of aggregating with the electrode active material can be suppressed.

[0100] The solvent may be an aqueous solvent. The aqueous solvent may be water.

[0101] The solvent may be an aqueous solvent, an organic solvent, or a mixture thereof.

[0102] The organic solvent may be an amide-based polar organic solvent such as dimethylformamide (DMF), diethylformamide, dimethylacetamide (DMAc), N-methylpyrrolidone (NMP); alcohols such as methanol, ethanol, 1-propanol, 2-propanol (isopropyl alcohol), 1-butanol (n-butanol), 2-methyl-1-propanol (isobutanol), 2-butanol (sec-butanol), 1-methyl-2-propanol (tert-butanol), pentanol, hexanol, heptanol, or octanol; glycols such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, 1,3-propanediol, 1,3-butanediol, 1,5-pentanediol, or hexylene glycol; polyhydric alcohols such as glycerin, trimethylolpropane, pentaerythritol, or sorbitol; glycol ethers such as ethylene glycol monomethyl ether, diethylene glycol monomethyl ether, triethylene glycol monomethyl ether, tetraethylene glycol monomethyl ether, ethylene glycol monoethyl ether, diethylene glycol monoethyl ether, triethylene glycol monoethyl ether, tetraethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, or tetraethylene glycol monobutyl ether; ketones such as acetone, methyl ethyl ketone, methyl propyl ketone, or cyclopentanone; esters such as ethyl acetate, γ-butyrolactone, and ε-propiolactone, etc. Any one or a mixture of two or more of these can be used.

[0103] The carbon nanotube dispersion may contain an additive having an electrostatic repulsive force with the charge formed on the surface of the carbon nanotube.

[0104] The additive can suppress the phenomenon that the first dispersant and the second dispersant not bound to the carbon nanotubes aggregate with each other, and can suppress the phenomenon that the carbon nanotubes bound to the first dispersant and the second dispersant aggregate with each other.

[0105] The additive can induce a repulsive force between the carbon nanotubes whose surfaces are modified with charges. The additive can induce an electrostatic repulsive force between the carbon nanotubes dispersed by the first dispersant and the second dispersant and whose surfaces are modified with negative charges.

[0106] The additive may contain a phenolic compound containing two or more aromatic rings. The additive may contain a phenolic single-molecule compound containing two or more aromatic rings and carrying a negative charge.

[0107] The negative charge of the phenolic compound can induce an electrostatic repulsive force between the carbon nanotubes by showing the same polarity as the carbon nanotubes whose surfaces are modified with negative charges. Thereby, the carbon nanotube dispersion may have an appropriate initial viscosity range, the increase in viscosity due to time change can be minimized, and the long-term storage stability can be improved.

[0108] The phenolic compound may contain one or more selected from the group consisting of tannic acid, luteolin, baicalin, taxifolin, myricetin, quercetin, rutin, catechin, epigallocatechin gallate, butein, and piceatannol.

[0109] The phenolic compound may have a weight average molecular weight of 200 g / mol to 3,000 g / mol, 200 g / mol to 2,500 g / mol, 500 g / mol to 2,500 g / mol, or 500 g / mol to 2,000 g / mol. When the above range is satisfied, the phenomenon of elution of the additive during electrode manufacturing can be suppressed, and the coating property and processability can be improved.

[0110] The content of the additive may be 0.01 wt% to 0.1 wt%, 0.01 wt% to 0.08 wt%, 0.01 wt% to 0.07 wt%, or 0.02 wt% to 0.07 wt% based on the total weight of the carbon nanotube dispersion.

[0111] The content of the additive may be 1 part by weight to 10 parts by weight, 2 parts by weight to 10 parts by weight, 2 parts by weight to 9 parts by weight, or 2 parts by weight to 6 parts by weight based on 100 parts by weight of the carbon nanotubes.

[0112] When the above range is satisfied, the electrostatic repulsive force between the carbon nanotubes can be induced more efficiently, and the increase in viscosity due to time change can be minimized.

[0113] The additive may contain a silicate. The additive may contain a layered silicate. When the storage stabilizer contains the layered silicate, the dispersibility of the carbon nanotubes can be further improved.

[0114] The total content of the first dispersant, the second dispersant, and the additive may be 1 wt% to 2.5 wt%, 1 wt% to 2.2 wt%, 1 wt% to 2 wt%, or 1.5 wt% to 2 wt% based on the total weight of the carbon nanotube dispersion.

[0115] When the above range is satisfied, smooth dispersion can be achieved between the high-content carbon nanotubes in the carbon nanotube dispersion, and the performance of the secondary battery containing the high-content carbon nanotubes can be further improved.

[0116] The initial viscosity of the carbon nanotube dispersion at room temperature may be 1,000 cP to 10,000 cP, 4,000 cP to 10,000 cP, 4,000 cP to 9,000 cP, 4,000 cP to 8,000 cP, or 5,000 cP to 8,000 cP. When the above range is satisfied, the aggregation phenomenon of the carbon nanotubes can be suppressed, and the process of repeatedly reintroducing and dispersing the carbon nanotubes can be minimized, and the process efficiency can be improved.

[0117] The viscosity can be measured using a B-type viscometer, a rotary cylinder viscometer, etc. Specifically, it can be measured using a DV2T LV viscometer (Brookfield).

[0118] The viscosity change rate of the carbon nanotube dispersion according to the following formula 1 may be 20% or less, 18% or less, 16% or less, 14% or less, 12% or less, or 5% or less. When the above range is satisfied, the increase in viscosity of the dispersion containing carbon nanotubes due to time change can be minimized, and the long-term storage stability can be improved.

[0119] [Formula 1] Viscosity change rate (%) = (viscosity after 7 days - initial viscosity) / initial viscosity × 100

[0120] The pH of the carbon nanotube dispersion at room temperature may be 3 to 10, 4 to 10, 4 to 9, 5 to 9, 5 to 8, or 6 to 8. When the above range is satisfied, the occurrence of the aggregation phenomenon due to hydrogen bonding can be suppressed.

[0121] The carbon nanotube dispersion may be one in which the absorbance is measured. The absorbance may be an index indicating the degree of light absorption. Since the absorbance is proportional to the concentration of the substance, a high absorbance of the carbon nanotube dispersion means that the carbon nanotubes capable of absorbing light are uniformly dispersed at a high concentration. That is, the absorbance may be a dispersibility index of the carbon nanotubes contained in the carbon nanotube dispersion.

[0122] The absorbance of the carbon nanotube dispersion may be 0.1 or more and 10 or less, 0.15 or more and 10 or less, 0.15 or more and 5 or less, or 0.2 or more and 5 or less. When the above range is satisfied, the aggregates contained in the carbon nanotube dispersion are minimized, and the carbon nanotubes contained in the carbon nanotube dispersion may be contained with high purity and have excellent dispersibility. The absorbance can be measured in a wavelength range of 550 nm using a spectrophotometer.

[0123] The method for producing a carbon nanotube dispersion according to the present invention includes a step of mixing carbon nanotubes, a first dispersant containing a nonionic polymer having a weight average molecular weight of 4,000 g / mol to 30,000 g / mol, a second dispersant containing an anionic polymer having a sulfonic acid (salt) group, and an aqueous solvent to produce a mixture, a step of milling and disintegrating the mixture, and a step of dispersing the mixture, and the first dispersant and the second dispersant are mixed at a weight ratio of 1:1 to 1:3.

[0124] The production method includes a step of mixing the carbon nanotubes, the first dispersant, the second dispersant, and the aqueous solvent described above to produce a mixture.

[0125] The step of producing the mixture can be carried out under temperature conditions where the physical properties of the carbon nanotubes, the first dispersant, and the second dispersant do not change.

[0126] The step of producing the mixture can be carried out under temperature conditions of 3°C to 50°C, 5°C to 50°C, 5°C to 45°C, 5°C to 40°C, or 20°C to 30°C.

[0127] The production method includes a step of milling and disintegrating the mixture. By this step, the particle size distribution of the carbon nanotubes contained in the mixture can be adjusted.

[0128] The above step can use a high-shear mixer, and the mixer can be used to carry out the operation under the conditions of 1,000 rpm to 10,000 rpm, 2,000 rpm to 10,000 rpm, 5,000 rpm to 10,000 rpm, or 7,000 rpm to 10,000 rpm for 5 minutes to 60 minutes, 5 minutes to 50 minutes, 10 minutes to 50 minutes, or 10 minutes to 30 minutes.

[0129] By the above step, the mixture can be crushed so that the average particle size is less than 100 μm, less than 95 μm, less than 90 μm, or less than 80 μm. When the above range is satisfied, the dispersibility of the carbon nanotubes can be further improved.

[0130] The manufacturing method includes a step of dispersing the mixture.

[0131] The above step may be a step of redispersing the linearly dispersed mixture under high-pressure conditions by a crushing process.

[0132] The above step can be repeatedly carried out by using a ball mill, a bead mill, a disc mill, a basket mill, or a high-pressure homogenizer to mill the mixture. Preferably, it can be carried out by using a high-pressure homogenizer.

[0133] The milling by the high-pressure homogenizer can be carried out under pressure conditions of 200 bar to 3,000 bar, 500 bar to 3,000 bar, 1,000 bar to 3,000 bar, or 1,000 bar to 2,000 bar.

[0134] The step of dispersing the mixture can be carried out 1 to 30 times, 2 to 30 times, 5 to 30 times, 5 to 20 times, or 5 to 10 times.

[0135] The electrode slurry composition according to the present invention includes an electrode active material, a binder, and a carbon nanotube dispersion. The carbon nanotube dispersion includes carbon nanotubes, a first dispersant containing a nonionic polymer having a weight average molecular weight of 4,000 g / mol to 30,000 g / mol, and a second dispersant containing an anionic polymer having a sulfonic acid (salt) group. The weight ratio of the first dispersant to the second dispersant is 5:1 to 1:5.

[0136] The carbon nanotube dispersion may be the same as the carbon nanotube dispersion described above.

[0137] The electrode active material may be a positive electrode active material.

[0138] The positive electrode active material is a compound capable of reversible intercalation and deintercalation of lithium, and specifically may include a lithium composite metal oxide containing one or more metals such as cobalt, manganese, nickel, or aluminum and lithium.

[0139] The lithium composite metal oxide includes lithium-manganese-based oxides (e.g., LiMnO2, LiMn2O4, etc.), lithium-cobalt-based oxides (e.g., LiCoO2, etc.), lithium-nickel-based oxides (e.g., LiNiO2, etc.), lithium-nickel-manganese-based oxides (e.g., LiNi 1-Y Mn Y O2 (where 0 < Y < 1), LiMn 2-z Ni z O4 (where 0 < Z < 2), etc.), lithium-nickel-cobalt-based oxides (e.g., LiNi 1-Y1 Co Y1 O2 (where 0 < Y1 < 1), etc.), lithium-manganese-cobalt-based oxides (e.g., LiCo 1-Y2 Mn Y2 O2 (where 0 < Y2 < 1), LiMn 2-z1 Co z1 O4 (where 0 < Z1 < 2), etc.), lithium-nickel-manganese-cobalt-based oxides (e.g., Li(Nip Co q Mn r1 )O2 (where 0 < p < 1, 0 < q < 1, 0 < r1 < 1, and p + q + r1 = 1), or Li(Ni p1 Co q1 Mn r2 )O4 (where 0 < p1 < 2, 0 < q1 < 2, 0 < r2 < 2, and p1 + q1 + r2 = 2), etc.), or lithium-nickel-cobalt-transition metal (M) oxide (e.g., Li(Ni p2 Co q2 Mn r3 M S2 )O2 (where M is selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg, and Mo, and p2, q2, r3, and s2 are the atomic fractions of independent elements, 0 < p2 < 1, 0 < q2 < 1, 0 < r3 < 1, 0 < s2 < 1, and p2 + q2 + r3 + s2 = 1), etc.), and the like, and any one or two or more of these compounds may be included. Among these, in terms of being able to enhance the capacity characteristics and stability of the battery, the lithium composite metal oxide is LiCoO2, LiMnO2, LiNiO2, lithium nickel manganese cobalt oxide (e.g., Li(Ni 0.6 Mn 0.2 Co 0.2 )O2, Li(Ni 0.5 Mn 0.3 Co 0.2 )O2, or Li(Ni 0.8 Mn 0.1 Co 0.1 )O2, etc.), or lithium nickel cobalt aluminum oxide (e.g., Li(Ni 0.8 Co 0.15 Al 0.05 )O2, etc.), and the like. Considering that the improvement effect by controlling the types and content ratios of the constituent elements forming the lithium composite metal oxide is remarkable, the lithium composite metal oxide is Li(Ni 0.6 Mn 0.2 Co 0.2 )O2, Li(Ni 0.5 Mn 0.3 Co 0.2 )O2, Li(Ni 0.7 Mn 0.15 Co0.15 ) O2, or Li(Ni 0.8 Mn 0.1 Co 0.1 )O2 or the like may be used, and any one or a mixture of two or more of these can be used.

[0140] The electrode active material may be a negative electrode active material.

[0141] The negative electrode active material may be contained in an amount of 90% to 99% by weight, 91% to 99% by weight, 92% to 99% by weight, 94% to 99% by weight, or 95% to 99% by weight based on the total weight of the electrode slurry composition. When the above range is satisfied, the charge and discharge capacity of the secondary battery can increase.

[0142] The negative electrode active material may contain a carbon-based material. The carbon-based material may contain natural graphite particles or artificial graphite particles. The negative electrode active material may contain a silicon-based material. The negative electrode active material may contain a silicon-graphite composite. The weight ratio of silicon in the silicon-graphite composite may be 1% to 70% by weight, 5% to 70% by weight, 5% to 50% by weight, 5% to 40% by weight, or 10% to 40% by weight. When the above range is satisfied, the decrease in the life characteristics of the secondary battery can be minimized and the charge and discharge capacity can increase significantly.

[0143] The silicon-based material may contain one or more selected from the group consisting of metallic silicon (Si), silicon oxide (SiOx, 0 < x < 2), silicon carbide (SiC), and Si-Y alloy (wherein Y is an element selected from the group consisting of alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, transition metals, rare earth elements, and combinations thereof, and is not Si). In the element Y, it may be selected from the group consisting of Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Ti, Ge, P, As, Sb, Bi, S, Se, Te, Po, and combinations thereof.

[0144] The silicon-based material can exhibit high capacity characteristics compared to the carbon-based material. When the silicon-based material is included in the negative electrode active material, the capacity characteristics can be improved. However, the silicon-based material has a problem that the volume change is large during charge and discharge compared to the carbon-based material, and the cycle characteristics deteriorate. Therefore, when using carbon nanotubes as a conductive material according to the present invention, the high electron transfer path can be improved compared to the conventional conductive material, the electrical conductivity can be improved, the dispersibility can be improved, the structural stability can be increased, and when the negative electrode active material contains the silicon-based material, not only the capacity characteristics can be improved, but also the cycle characteristics can be improved.

[0145] The binder can improve the adhesion between the electrode active materials or between the electrode active material and the current collector. The binder can be polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethylmethacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, polyacrylic acid, and polymers in which the hydrogen thereof is substituted with Li, Na, Ca, etc., or various binder polymers such as various copolymers can be used.

[0146] The binder may be contained in an amount of 0.1 wt% to 10 wt%, 0.1 wt% to 8 wt%, 0.1 wt% to 7 wt%, 0.1 wt% to 6 wt%, or 0.1 wt% to 5 wt% based on the total weight of the electrode slurry composition. When the above range is satisfied, it can be excellent in the effect as a binder without a decrease in the capacity per unit volume due to a decrease in the relative content of the electrode active material.

[0147] The electrode slurry composition may contain a solvent.

[0148] The solvent can mix each component in the electrode slurry composition to adjust the viscosity. The solvent includes organic solvents such as NMP (N-methylpyrrolidone), DMF (dimethylformamide), acetone, dimethylacetamide, or water, etc. These solvents can be used alone or in combination of two or more. The usage amount of the solvent can be such that it can dissolve and disperse the electrode active material, the binder, and the carbon nanotube dispersion liquid in consideration of the coating thickness of the electrode slurry composition and the manufacturing yield.

[0149] The carbon nanotube dispersion liquid can be used as a conductive material. By using the carbon nanotube dispersion liquid as a conductive material, the initial discharge capacity and high-rate characteristics of the secondary battery can be improved.

[0150] The conductive material can improve electrical conductivity. The conductive material may further include graphite such as natural graphite and artificial graphite; carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black; metal powders such as fluorocarbon, aluminum, nickel powder; conductive whiskers such as zinc oxide, potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives.

[0151] The secondary battery according to the present invention includes an electrode, a separator, and an electrolyte. The electrode includes an electrode active material, a binder, and a conductive material. The conductive material is manufactured from a carbon nanotube dispersion liquid. The carbon nanotube dispersion liquid includes carbon nanotubes, a first dispersant containing a nonionic polymer with a weight average molecular weight of 4,000 g / mol to 30,000 g / mol, and a second dispersant containing an anionic polymer having a sulfonic acid (salt) group. The weight ratio of the first dispersant to the second dispersant is 5:1 to 1:5.

[0152] The carbon nanotube dispersion may be the same as the carbon nanotube dispersion described above. By including the carbon nanotubes contained in the carbon nanotube dispersion as a conductive material, the secondary battery can improve its electrical conductivity, and thus the initial efficiency, life characteristics, and high-rate discharge characteristics of the secondary battery can be improved.

[0153] The electrode may be a cathode. The cathode may include the cathode active material, binder, and conductive material described above. The cathode may be manufactured by applying a cathode slurry composition containing a cathode active material onto a cathode current collector and then drying it to form a cathode active material layer. The cathode active material layer may be formed by a method of applying a cathode slurry composition onto the cathode current collector and then drying it, or by a method of applying a cathode slurry composition onto a separate support, peeling the film obtained from the support, and laminating it onto the cathode current collector. After forming the cathode active material layer, a rolling process can be carried out. The drying and rolling can be carried out under appropriate conditions in consideration of the physical properties of the electrode to be finally manufactured.

[0154] The cathode current collector is a metal with high conductivity, a metal to which the slurry of the cathode active material easily adheres, and is not particularly limited as long as it does not cause a chemical change in the secondary battery and has high conductivity. For example, stainless steel, aluminum, nickel, titanium, fired carbon, or a material obtained by surface-treating the surface of aluminum or stainless steel with carbon, nickel, titanium, silver, etc. can be used. In addition, fine irregularities can be formed on the surface of the cathode current collector to enhance the adhesive force of the cathode active material. The cathode current collector can be used in various forms such as a film, sheet, foil, net, porous body, foam, non-woven fabric body, etc., and may have a thickness of 3 μm to 500 μm.

[0155] The electrode may be a negative electrode (anode). The negative electrode may contain the negative electrode active material, binder, and conductive material described above. The negative electrode may be manufactured by applying a negative electrode slurry composition containing a negative electrode active material onto a negative electrode current collector and then drying it to form a negative electrode active material layer.

[0156] The negative electrode current collector is not particularly limited as long as it does not cause a chemical change in the secondary battery and has conductivity. For example, copper, stainless steel, aluminum, nickel, titanium, fired carbon, those surface-treated with carbon, nickel, titanium, silver, etc. on the surface of copper or stainless steel, aluminum-cadmium alloy, etc. can be used. Also, fine irregularities can be formed on the surface to strengthen the binding force of the negative electrode active material, and it can be used in various forms such as films, sheets, foils, nets, porous bodies, foams, non-woven fabrics.

[0157] The separator may be interposed between the negative electrode and the positive electrode. The separator may be configured to prevent an electrical short circuit between the negative electrode and the positive electrode and allow the flow of ions. The separator may contain a porous polymer film or a porous non-woven fabric. The porous polymer film may be composed of a single layer or multiple layers containing polyolefin-based polymers such as ethylene polymers, propylene polymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers. The porous non-woven fabric may contain high melting point glass fibers and polyethylene terephthalate fibers. However, it is not limited thereto, and depending on the embodiment, the separator may be a high heat-resistant separator (CCS; Ceramic Coated Separator) containing ceramics.

[0158] The electrolyte may be a non-aqueous electrolyte. The electrolyte may contain a lithium salt and an organic solvent. The organic solvent may contain at least one of propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), methyl propyl carbonate (MPC), dipropyl carbonate (DPC), vinylene carbonate (VC), dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, sulfolane, gamma-butyrolactone, propylene sulfide, or tetrahydrofuran.

[0159] The positive electrode, negative electrode, and the separator may be manufactured into an electrode assembly by a winding, lamination, folding, or Zigzag stacking process. The electrode assembly may be provided together with the electrolyte and manufactured into a secondary battery. The secondary battery may be any of a cylindrical type, square type, pouch type, and coin type using a can, but is not limited thereto.

[0160] The secondary battery can be used for a high-output and large-capacity secondary battery that requires a long lifespan and excellent durability, or for a module or pack that includes a plurality of the secondary batteries as unit cells.

[0161] The plurality of secondary batteries may be manufactured into a module. The plurality of modules may be manufactured into a pack.

[0162] The pack can be used as a power source for medium and large-sized devices that require high-temperature stability, long cycle characteristics, and high rate characteristics. Among the types of medium and large-sized devices, there are power tools powered by battery motors; electric vehicles including electric vehicles (EV), hybrid electric vehicles (HEV), and plug-in hybrid electric vehicles (PHEV); electric two-wheel vehicles including electric bicycles (E-bike) and electric scooters (E-scooter); electric golf carts; electric trucks; electric commercial vehicles, or power storage systems.

[0163] Hereinafter, the present invention will be described more specifically based on examples and comparative examples. However, the following examples and comparative examples are only illustrations for explaining the present invention in more detail, and the present invention is not limited by the following examples and comparative examples.

[0164] Production Example - Dispersant #1: Polyvinylpyrrolidone (Mw 17,000 g / mol) - Dispersant #2: Polyvinylpyrrolidone (Mw 4,000 g / mol) - Dispersant #3: Polyvinylpyrrolidone (Mw 30,000 g / mol) - Dispersant #4: Polyvinylpyrrolidone (Mw 40,000 g / mol) - Dispersant #5: Polyvinylpyrrolidone (Mw 90,000 g / mol) - Dispersant #6: Poly(2-naphthalenesulfonate) (Mw 2,000 g / mol) - Dispersant #7: Poly(2,7-naphthalenedisulfonate) (Mw 3,000 g / mol) - Dispersant #8: Polystyrenesulfonate (Mw 5,000 g / mol) - Dispersant #9: Polystyrenesulfonate (Mw 7,000 g / mol) - Dispersant #10: Polyacrylic acid (Mw 2,000 g / mol)

[0165] Production Example 1 Using a catalyst, 200 mg of single-walled carbon nanotubes were produced by chemical vapor deposition (CVD). Then, the reaction furnace was filled with the single-walled carbon nanotubes.

[0166] Thereafter, the reaction furnace was purified at about 1,000 °C for 60 minutes under an argon atmosphere and vacuum conditions, and then cooled to room temperature range to produce single-walled carbon nanotubes with a specific surface area of about 1,557 m 2 / g.

[0167] Using water as a solvent, a mixture containing single-walled carbon nanotubes: dispersant #1: dispersant #6 in a weight ratio of 8:3:9 was produced.

[0168] Thereafter, using a mixer, the mixture was processed at 8,000 rpm for 20 minutes to crush the particles contained in the mixture so that the average particle size was less than about 100 μm.

[0169] Thereafter, using a high pressure homogenizer, the mixture was processed 10 times under a pressure condition of 1,200 bar to produce a carbon nanotube dispersion.

[0170] Production Example 2 In Production Example 1, except that the weight ratio of single-walled carbon nanotubes: dispersant #1: dispersant #6 was changed from 8:3:9 to 8:6:6, a carbon nanotube dispersion was produced by the same process as in Production Example 1.

[0171] Production Example 3 In Production Example 1, a carbon nanotube dispersion was produced by the same process as in Production Example 1, except that the single-walled carbon nanotube: Dispersant #1: Dispersant #6 was used at a weight ratio of 8:4:8 instead of 8:3:9.

[0172] Production Example 4 In Production Example 1, a carbon nanotube dispersion was produced by the same process as in Production Example 1, except that Dispersant #7 was used instead of Dispersant #6.

[0173] Production Example 5 In Production Example 1, a carbon nanotube dispersion was produced by the same process as in Production Example 1, except that the single-walled carbon nanotube: Dispersant #1: Dispersant #7 was used at a weight ratio of 8:6:6 instead of the weight ratio of 8:3:9 of the single-walled carbon nanotube: Dispersant #1: Dispersant #6.

[0174] Production Example 6 In Production Example 1, a carbon nanotube dispersion was produced by the same process as in Production Example 1, except that the single-walled carbon nanotube: Dispersant #1: Dispersant #7 was used at a weight ratio of 8:4:8 instead of the weight ratio of 8:3:9 of the single-walled carbon nanotube: Dispersant #1: Dispersant #6.

[0175] Production Example 7 In Production Example 1, a carbon nanotube dispersion was produced by the same process as in Production Example 1, except that single-walled carbon nanotubes (TUBALL, OCSiAl) with a specific surface area of 1,160 m 2 / g were used instead of the single-walled carbon nanotubes produced.

[0176] Production Example 8 In Production Example 1, a carbon nanotube dispersion was produced by the same process as in Production Example 1, except that the weight ratio of the single-walled carbon nanotube: Dispersant #1: Dispersant #6 was changed from 8:3:9 to 8:8:4.

[0177] Production Example 9 In Production Example 1, a carbon nanotube dispersion was produced by the same process as in Production Example 1, except that the weight ratio of the single-walled carbon nanotube: Dispersant #1: Dispersant #6 was changed from 8:3:9 to 8:9:3.

[0178] Production Example 10 In Production Example 1, a carbon nanotube dispersion was produced by the same process as in Production Example 1, except that the weight ratio of the single-walled carbon nanotube: Dispersant #1: Dispersant #6 was changed from 8:3:9 to 8:9:3, and Dispersant #2 was replaced with Dispersant #7.

[0179] Production Example 11 In Production Example 1, a carbon nanotube dispersion was produced by the same process as in Production Example 1, except that the weight ratio of the single-walled carbon nanotube: Dispersant #1: Dispersant #6 was changed from 8:3:9 to 8:9.6:2.4.

[0180] Production Example 12 In Production Example 1, a carbon nanotube dispersion was produced by the same process as in Production Example 1, except that the weight ratio of the single-walled carbon nanotube: Dispersant #1: Dispersant #6 was changed from 8:3:9 to 8:9.6:2.4, and Dispersant #1 was replaced with Dispersant #3.

[0181] Comparative Production Example 1 In Production Example 1, a carbon nanotube dispersion was produced by the same process as in Production Example 1, except that the weight ratio of the single-walled carbon nanotube: Dispersant #1: Dispersant #6 was changed to 8:6:1 instead of 8:3:9.

[0182] Comparative Production Example 2 In Production Example 1, a carbon nanotube dispersion was produced by the same process as in Production Example 1, except that the weight ratio of the single-walled carbon nanotube: Dispersant #1: Dispersant #6 was changed to 8:6:1 and Dispersant #4 was used instead of Dispersant #1.

[0183] Comparative Production Example 3 In Production Example 1, a carbon nanotube dispersion was produced by the same process as in Production Example 1, except that the weight ratio of the single-walled carbon nanotube: Dispersant #1: Dispersant #6 was changed to 8:6:1 and Dispersant #10 was used instead of Dispersant #6.

[0184] Comparative Production Example 4 In Production Example 1, a carbon nanotube dispersion was produced by the same process as in Production Example 1, except that Dispersant #4 was used instead of Dispersant #1.

[0185] Comparative Production Example 5 In Production Example 1, a carbon nanotube dispersion was produced by the same process as in Production Example 1, except that Dispersant #5 was used instead of Dispersant #1.

[0186] Comparative Production Example 6 In Production Example 1, instead of the produced single-walled carbon nanotubes, those with a specific surface area of 1,160 m 2Using single-walled carbon nanotubes (TUBALL, OCSiAl) at 1 / g, except that the single-walled carbon nanotubes: dispersant #1: dispersant #6 were used in a weight ratio of 8:3:9 and instead, the single-walled carbon nanotubes: dispersant #4: dispersant #6 were used in a weight ratio of 8:1:6, a carbon nanotube dispersion was produced by the same process as in Production Example 1.

[0187]

Table 1

[0188] Example Example 1 <Manufacture of negative electrode> A negative electrode active material slurry containing silicon graphite composite: the carbon nanotube dispersion of Production Example 1: carboxymethyl cellulose (CMC) thickener: styrene butadiene rubber (SBR) binder in a weight ratio of 96.54:0.06:1.2:2.2 was coated on a Cu foil current collector about 10 μm thick to a thickness of about 30 μm, and then dried at 100 °C for about 12 hours to produce a negative electrode.

[0189] <Manufacture of secondary battery (coin half cell)> Using about 0.3 mm of metallic lithium foil as the positive electrode, after interposing a polyethylene separator between the positive electrode and the negative electrode, EC:EMC was mixed at 3:7, and a non-aqueous electrolyte of LiPF6 1M was injected to manufacture a coin half cell.

[0190] Examples 2 to 13 and Comparative Examples 1 to 6 Except for using the carbon nanotube dispersions described in Table 2 below instead of the carbon nanotube dispersion of Production Example 1 in Example 1, coin half cells were manufactured by the same process as in Example 1.

[0191] Experimental Example Experimental Example 1 - Initial viscosity For each of the carbon nanotube dispersions of Production Examples 1 to 13 and Comparative Production Examples 1 to 6, the initial viscosity at room temperature and the viscosity after 7 days were measured using a DV2T LV viscometer (Brookfield), and the viscosity change rate was calculated by the following formula 1. The results are shown in Table 2 below.

[0192] [Formula 1] Viscosity change rate (%) = (viscosity after 7 days - initial viscosity) / initial viscosity × 100

[0193] Experimental Example 2 - Dispersibility For each of the carbon nanotube dispersions of Production Examples 1 to 12 and Comparative Production Examples 1 to 6, the zeta potential was measured. Evaluation was carried out according to the following criteria, and the results are shown in Table 2 below.

[0194] - ○: Absolute value exceeds 30 mV - △: Absolute value is 10 mV to 30 mV or less - ×: Absolute value is less than 10 mV

[0195] Experimental Example 3 - Dispersion Stability After putting each of the carbon nanotube dispersions of Production Examples 1 to 12 and Comparative Production Examples 1 to 6 into a glass bottle, it was measured whether aggregation occurred within 120 days. Evaluation was carried out according to the following criteria, and the results are shown in Table 2 below.

[0196] - ○: Aggregation occurs after 2 weeks - △: Aggregation occurs within 1 to 2 weeks - ×: Aggregation occurs within 1 week

[0197] Experimental Example 4 - Evaluation of Initial Discharge Capacity of Coin Half-Cell For each of the coin half-cells of Examples 1 to 12 and Comparative Examples 1 to 6, under normal temperature conditions, during charging, it was set to start in CC (constant current) mode with a current of 0.1C up to 0.01V, and then converted to CV (constant voltage), and cut off at 0.01C. During discharging, it was carried out in CC (constant current) mode with a current of 0.1C up to 1.5V.

[0198] Under the above charge-discharge conditions, after performing charge-discharge up to the second cycle, the discharge capacity in the second cycle was measured, and the results are shown in Table 2 below.

[0199] Experimental Example 5 - Evaluation of High Rate Characteristics For each of the coin half-cells of Examples 1 to 12 and Comparative Examples 1 to 6, under normal temperature conditions, during charging, it was set to start in CC (constant current) mode with a current of 0.2C up to 0.01V, and then converted to CV (constant voltage), and cut off at 0.01C. During discharging, it was carried out in CC (constant current) mode with a current of 3C up to 1.5V.

[0200] After performing the above charge-discharge, the discharge capacity and capacity retention rate were measured, and the results are shown in Table 2 below.

[0201]

Table 2

[0202] As can be confirmed from Table 1 and Table 2 above, the dispersions of Production Examples 1 to 12 containing a first dispersant containing a nonionic polymer with a weight average molecular weight of 4,000 g / mol to 30,000 g / mol and a second dispersant containing an anionic polymer having a sulfonic acid (salt) group in a weight ratio of 5:1 to 1:5 had improved dispersibility compared to Comparative Production Examples 1 to 6, and it was confirmed that the increase in the viscosity of the dispersion was minimized.

[0203] In addition, it was confirmed that the secondary batteries of Examples 1 to 12 containing the carbon nanotube dispersion liquids according to the above Production Examples 1 to 12 were superior in initial discharge capacity and high rate characteristics as compared with the secondary batteries of Comparative Examples 1 to 6 containing the carbon nanotube dispersion liquids according to the above Comparative Production Examples 1 to 6.

Claims

1. Carbon nanotubes, A first dispersant including a nonionic polymer having a weight average molecular weight of 4,000 g / mol to 30,000 g / mol; a second dispersant including an anionic polymer having a sulfonic acid (salt) group; Including, The weight ratio of the first dispersant to the second dispersant is from 5:1 to 1:5; Carbon nanotube dispersion.

2. The carbon nanotubes are single-walled carbon nanotubes. The carbon nanotube dispersion liquid according to claim 1 .

3. The nonionic polymer is a random coil polymer having a hydrophobic main chain and a hydrophilic side chain. The carbon nanotube dispersion liquid according to claim 1 .

4. The nonionic polymer contains an amide group. The carbon nanotube dispersion liquid according to claim 1 .

5. The content of the first dispersant is 0.01 wt % to 10.00 wt % based on the total weight of the carbon nanotube dispersion liquid. The carbon nanotube dispersion liquid according to claim 1 .

6. The anionic polymer has at least two aromatic rings. The carbon nanotube dispersion liquid according to claim 1 .

7. The anionic polymer has a weight average molecular weight of 200 g / mol to 8,000 g / mol. The carbon nanotube dispersion liquid according to claim 1 .

8. The content of the second dispersant is 0.01 wt % to 10.00 wt % based on the total weight of the carbon nanotube dispersion liquid. The carbon nanotube dispersion liquid according to claim 1 .

9. The total content of the first dispersant and the second dispersant is 100 to 200 parts by weight based on 100 parts by weight of the carbon nanotubes. The carbon nanotube dispersion liquid according to claim 1 .

10. preparing a mixture by mixing carbon nanotubes, a first dispersant including a nonionic polymer having a weight average molecular weight of 4,000 g / mol to 30,000 g / mol, a second dispersant including an anionic polymer having a sulfonic acid (salt) group, and an aqueous solvent; milling and disintegrating the mixture; dispersing the mixture; Including, The first dispersant and the second dispersant are mixed in a weight ratio of 5:1 to 1:

5. A method for producing a carbon nanotube dispersion.

11. The mixture is crushed to an average particle size of less than 100 μm. The method for producing a carbon nanotube dispersion liquid according to claim 10 .

12. An electrode active material; Binder and A carbon nanotube dispersion liquid; Including, The carbon nanotube dispersion liquid includes carbon nanotubes, a first dispersant including a nonionic polymer having a weight average molecular weight of 4,000 g / mol to 30,000 g / mol, and a second dispersant including an anionic polymer having a sulfonic acid (salt) group, and the weight ratio of the first dispersant to the second dispersant is 5:1 to 1:

5. Electrode Slurry Composition.

13. An electrode; A separation membrane; An electrolyte; Including, The electrode includes an electrode active material, a binder, and a conductive material, The conductive material is manufactured from a carbon nanotube dispersion liquid, The carbon nanotube dispersion liquid includes carbon nanotubes, a first dispersant including a nonionic polymer having a weight average molecular weight of 4,000 g / mol to 30,000 g / mol, and a second dispersant including an anionic polymer having a sulfonic acid (salt) group, and the weight ratio of the first dispersant to the second dispersant is 5:1 to 1:

5. Secondary battery.

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