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 that offers superior dispersibility and long-term storage stability and enables improvement of secondary battery performance, a method of preparing the same, an electrode slurry composition and a secondary battery including the same.SOLUTION: A carbon nanotube dispersion comprises carbon nanotubes, a first dispersant that surrounds the surface of the carbon nanotubes, a second dispersant that introduces charges to the surface of the carbon nanotubes, and a storage stabilizer having electrostatic repulsion against the charges. A method for producing the carbon nanotube dispersion comprises steps of: preparing a mixture by mixing the carbon nanotubes, the first dispersant containing a nonionic polymer, the second dispersant containing an ionic polymer, the storage stabilizer containing a phenolic compound having two or more aromatic rings, and an aqueous solvent; milling the mixture to crush it; and dispersing the mixture.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 such electrochemical energy is a secondary battery, and its use area is increasingly 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. A 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 a method in which an electrode slurry composition containing an electrode active material, a conductive material, a binder, etc. is applied onto the electrode current collector, dried, and then rolled.

[0003] The conductive material is for improving the conductivity of the electrode active material, and conventionally, a dot-like conductive material such as carbon black has been mainly used. However, since the dot-like 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, which causes 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 carbon nanotubes (CNTs) with high conductivity as the conductive material.

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

Summary of the Invention

Problems to be Solved by the Invention

[0006] The present invention provides a carbon nanotube dispersion liquid that is excellent in dispersibility and long-term storage stability and improves the performance of secondary batteries, 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 surrounding the surface of the carbon nanotubes, a second dispersant introducing charges onto the surface of the carbon nanotubes, and a storage stabilizer having an electrostatic repulsive force with the charges.

[0008] In one embodiment of the present invention, the storage stabilizer may include a phenolic compound containing two or more aromatic rings.

[0009] In one embodiment of the present invention, the phenolic compound may have a weight average molecular weight of 200 g / mol to 3,000 g / mol.

[0010] In one embodiment of the present invention, the content of the storage stabilizer may be 0.01% by weight to 0.1% by weight based on the total weight of the carbon nanotube dispersion liquid.

[0011] In one embodiment of the present invention, the content of the storage stabilizer may be 1 part by weight to 10 parts by weight based on 100 parts by weight of the carbon nanotubes.

[0012] In one embodiment of the present invention, the carbon nanotubes may be single-walled carbon nanotubes.

[0013] In one embodiment of the present invention, the first dispersant may include a nonionic polymer.

[0014] In one embodiment of the present invention, the second dispersant may contain an ionic polymer.

[0015] In one embodiment of the present invention, the initial viscosity of the carbon nanotube dispersion at room temperature may be 1,000 cP to 10,000 cP.

[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 non-ionic polymer, a second dispersant containing an ionic polymer, a storage stabilizer containing a phenolic compound having two or more aromatic rings, and an aqueous solvent to produce a mixture, a step of milling and crushing the mixture, and a step of dispersing the mixture.

[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. The carbon nanotube dispersion includes carbon nanotubes, a first dispersant surrounding the surface of the carbon nanotubes, a second dispersant introducing charges onto the surface of the carbon nanotubes, and a storage stabilizer having an electrostatic repulsive force with the charges.

[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 produced from a carbon nanotube dispersion. The carbon nanotube dispersion includes carbon nanotubes, a first dispersant surrounding the surface of the carbon nanotubes, a second dispersant introducing charges onto the surface of the carbon nanotubes, and a storage stabilizer having an electrostatic repulsive force with the charges.

Advantages of the Invention

[0020] The carbon nanotube dispersion according to the present invention is such that the carbon nanotubes are stabilized by a first dispersant and a second dispersant, charges are introduced onto the surface of the carbon nanotubes, and the dispersibility of the carbon nanotubes can be improved.

[0021] Further, the carbon nanotube dispersion according to the present invention contains a storage stabilizer having an electrostatic repulsive force with the charges introduced onto the surface of the carbon nanotubes. By the storage stabilizer, a repulsive force between the carbon nanotubes whose surfaces are modified with charges can be induced, and the long-term storage stability of the carbon nanotube dispersion can be improved.

[0022] Also, the carbon nanotube dispersion according to the present invention can minimize an increase in viscosity due to time change by having an appropriate initial viscosity range by the first dispersant, the second dispersant, and the storage stabilizer.

[0023] Further, the carbon nanotube dispersion may contain a high content of single-walled carbon nanotubes excellent in dispersibility, long-term storage stability, and electrical conductivity, and the initial discharge capacity and high-rate characteristics of a secondary battery manufactured using the carbon nanotube dispersion can be improved.

Embodiments for Carrying Out the Invention

[0024] 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, and 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.

[0025] 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 on a weight basis. Also, the description of "A and / or B" in this specification or application means "A, B, or A and B".

[0026] Hereinafter, a carbon nanotube dispersion, a method for producing the same, an electrode slurry composition containing the same, and a secondary battery according to the present invention will be described.

[0027] Generally, in order to improve the electrical conductivity of an 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.

[0028] In order to further improve the electrical conductivity of the electrode active material, carbon nanotubes have been attracting 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 problem that due to their high specific surface area, an aggregation phenomenon occurs due to the van der Waals force between the carbon nanotubes.

[0029] 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 the dispersibility is very low.

[0030] The inventors of the present invention focused on the fact that by combining a first dispersant capable of stabilizing carbon nanotubes and a second dispersant capable of introducing charges onto the surface of the carbon nanotubes, if the carbon nanotubes with the introduced charges have a repulsive force so as not to aggregate with each other, the dispersibility and long-term storage stability can be improved.

[0031] Therefore, by including a substance having an electrostatic repulsive force between the carbon nanotubes into which the charge is introduced in the dispersion liquid, the dispersibility and long-term storage stability can be improved. As a result, the dispersion liquid can contain a high content of carbon nanotubes, and attention is paid to the point that the performance of a secondary battery containing the carbon nanotubes as a conductive material can be improved.

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

[0033] The carbon nanotubes are in a cylindrical shape in which a graphite sheet has a nano-sized diameter, and may have a secondary structure in which a plurality of carbon nanotubes are arranged or aggregated. When the carbon nanotubes are used as a conductive material, the electrical conductivity of the electrode can be improved.

[0034] The content of the carbon nanotubes may be 0.01 wt% to 15.00 wt%, 0.01 wt% to 10.00 wt%, 0.01 wt% to 8.00 wt%, 0.05 wt% to 8.00 wt%, 0.1 wt% to 8.00 wt%, or 0.1 wt% to 5.00 wt% with respect to the total weight of the carbon nanotube dispersion liquid. When the above range is satisfied, an increase in the viscosity of the carbon nanotube dispersion liquid can be suppressed. 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 nanotubes may be multi-walled carbon nanotubes (MWCNT) having a large number of binding numbers forming the walls, thin-walled carbon nanotubes (TWCNT), or single-walled carbon nanotubes (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 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 inventors of the present invention have found that when using a first dispersant capable of stabilizing the single-walled carbon nanotube, a second dispersant capable of introducing charges to the surface of the single-walled carbon nanotube, and a storage stabilizer having an electrostatic repulsive force with the charges formed on the surface of the single-walled carbon nanotube together with the single-walled carbon nanotube, excellent dispersibility and long-term storage stability can be shown despite using single-walled carbon nanotubes having high cohesive force, 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, 1,00 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 m 2 / g, or 1,500 m 2 / g to 1,700 m 2 / g may be sufficient. The BET specific surface area can be measured from the nitrogen gas adsorption amount at liquid nitrogen temperature (77K) using BELSORP-miniII of BEL Japan.

[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 instrument (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 a scanning probe microscope (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 nanotube can measure the weight change due to temperature change by a thermogravimetric analyzer. 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 nanotube can measure the temperature at which thermal decomposition starts by the thermogravimetric analyzer. By measuring the weight change of the single-walled carbon nanotube due to temperature change, the purity of the single-walled carbon nanotube can be evaluated.

[0046] The single-walled carbon nanotube may have a weight change of 2% or less, 1.9% or less, 1.8% or less, 1.7% or less, or 1.5% or less at 40 °C to 300 °C measured by the thermogravimetric analyzer.

[0047] The single-walled carbon nanotube may have a weight change of 2% or less, 1.5% or less, 1.3% or less, 1.2% or less, or 1% or less at 300 °C to 550 °C measured by the thermogravimetric analyzer.

[0048] The single-walled carbon nanotube may have a weight change of 2% or less, 1.98% or less, 1.97% or less, 1.96% or less, or 1.95% or less at 40 °C to 550 °C measured by the thermogravimetric analyzer.

[0049] The single-walled carbon nanotube may have a thermal decomposition start temperature of 500 °C to 700 °C, 520 °C to 700 °C, 530 °C to 650 °C, or 550 °C to 600 °C measured by the thermogravimetric analyzer. 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 content of the residue after the pyrolysis measured by the thermogravimetric analyzer for the single-walled carbon nanotube may be 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.

[0051] When the single-walled carbon nanotube satisfies the weight change, pyrolysis start temperature, and residue content within the above ranges, impurities are minimized, purity is improved, and when used as a conductive material, electrical conductivity is improved, the performance of the secondary battery can be improved, dispersibility is improved, and coating properties 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 are entangled into a ball or potato shape without a certain directionality.

[0053] The single-walled carbon nanotube may be manufactured by a step of synthesizing a 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 step 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 this step. 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 / cm2 ~290 mJ / cm 2 、 or 120 mJ / cm 2 ~280 mJ / cm 2 may also be acceptable.

[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 the single-walled carbon nanotube may be synthesized by this 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 atmosphere of an inert gas and hydrogen gas. The arc discharge can be carried out in an atmosphere of a small amount of hydrocarbon gas. The hydrocarbon gas may contain at least one or more of methane, ethylene, and acetylene. The pair of electrodes may be separated by a fixed distance. 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 may be a direct current arc discharge method. The direct current power supply in the direct current arc discharge method may have a voltage range of 20V to 70V, 22V to 70V, 22V to 65V, or 25V to 65V. The direct current power supply in the direct current arc discharge method may have a current range of 40A to 120A, 40V to 115V, 40V to 100V, or 45V to 100V.

[0056] Preferably, the single-walled carbon nanotube may be synthesized by chemical vapor deposition. The chemical vapor deposition means a process of thermally decomposing hydrocarbons such as methane, ethylene, and acetylene, benzene, toluene, or xylene in the gas phase in the presence of a catalyst, and the single-walled carbon nanotube may be synthesized by this process. As the catalyst, nanoparticles supporting 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 has the advantage that high-purity single-walled carbon nanotubes can be mass-produced, and it is easy to control the diameter, length, density, structure, crystallinity, etc. of the single-walled carbon nanotubes.

[0057] The synthesized single-walled carbon nanotubes 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 the 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 the catalyst in the single-walled carbon nanotube synthesis process.

[0058] Among the impurities, the nickel element may cause the single-walled carbon nanotubes to be cut and their length to be shortened, or the surface to be oxidized, resulting in a decrease in 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.

[0059] The synthesized single-walled carbon nanotubes may be purified by a physical method or a chemical method.

[0060] The physical methods include centrifugation, solubilization of carbon nanotubes, high temperature annealing, etc.

[0061] Centrifugation applies centrifugal force to a mixture with different masses and separates substances based on the difference in sedimentation rates. By centrifugation, amorphous carbon, carbon nanoparticles, and single-walled carbon nanotubes contained in the synthesized single-walled carbon nanotubes can be separated.

[0062] The solubilization of 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.

[0063] High temperature annealing is a process where 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 temperature above the evaporation temperature of the impurities to remove the impurities formed on the carbon nanotubes.

[0064] The chemical methods include electrochemical oxidation, gas-phase oxidation, liquid-phase oxidation, etc.

[0065] In the electrochemical oxidation, the synthesized single-walled carbon nanotubes can be electrochemically oxidized with a potassium hydroxide solution or a sulfuric acid solution to remove the amorphous carbon and impurities contained in the single-walled carbon nanotubes.

[0066] In the liquid-phase oxidation, the synthesized single-walled carbon nanotubes can be reacted 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 has been a problem that the structure such as cutting and end opening of single-walled carbon nanotubes may be destroyed during the purification process, and the oxidizing liquid reactant may exist 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.

[0067] In the gas-phase oxidation, the synthesized single-walled carbon nanotubes can be heat-treated in an oxidizing gas atmosphere within a temperature range of about 700°C to 1,000°C to remove the amorphous carbon and impurities contained in the single-walled carbon nanotubes. As the oxidizing gas, air, chlorine, a mixture of water vapor and hydrogen chloride, hydrogen sulfide, argon, etc. can be used.

[0068] 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.

[0069] 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.

[0070] After the purification treatment, a step of cooling at room temperature in a vacuum state can be carried out.

[0071] By the purification step, the metal, which is an impurity contained in the single-walled carbon nanotube, can be removed more efficiently.

[0072] The carbon nanotube dispersion according to the present invention contains a first dispersant surrounding the surface of the carbon nanotube.

[0073] The first dispersant may contain a nonionic polymer.

[0074] The first dispersant is a nonionic polymer and may contain one or more selected from the group consisting of polyethylene glycol, polypropylene glycol, polybutylene glycol, polyvinyl alcohol, polyvinyl pyrrolidone, 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.

[0075] Preferably, the first dispersant is a nonionic polymer and may contain polyvinyl pyrrolidone having a weight average molecular weight of 4,000 g / mol to 80,000 g / mol, 5,000 g / mol to 80,000 g / mol, 5,000 g / mol to 60,000 g / mol, 10,000 g / mol to 50,000 g / mol, or 17,000 g / mol to 50,000 g / mol.

[0076] When the above range is satisfied, during the production of the electrode, the phenomenon of elution of the first dispersant can be suppressed, the kneadability with other materials in the carbon nanotube dispersion liquid is improved, the dispersibility is improved, and the change in viscosity due to the change over time can be minimized.

[0077] The nonionic polymer may be in the form of a random coil.

[0078] The nonionic polymer may be in the form of a random coil including a hydrophobic main chain and a hydrophilic side chain.

[0079] By including the random coil-shaped nonionic polymer including the hydrophobicity and hydrophilicity, the first dispersant may stably bind to the carbon nanotube and surround the surface of the carbon nanotube. The cohesive force between the carbon nanotubes can be reduced by the first dispersant, and the carbon nanotubes can be smoothly dispersed.

[0080] With respect to the total weight of the carbon nanotube dispersion liquid, 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%. When the above range is satisfied, the dispersion effect of the carbon nanotubes is improved, and the carbon nanotube dispersion liquid may have an appropriate initial viscosity.

[0081] The carbon nanotube dispersion liquid according to the present invention includes a second dispersant that introduces charges to the surface of the carbon nanotube.

[0082] The second dispersant may include an ionic polymer.

[0083] The second dispersant may include a cationic polymer and / or an anionic polymer.

[0084] Preferably, the second dispersant may contain an anionic polymer.

[0085] The second dispersant is an anionic polymer and may contain one or more selected from the group consisting of polyacrylic acid (salt), polymethacrylic acid (salt), polyacrylic maleic acid (salt), sulfonic acid (salt), sulfonic acid ester, phosphoric acid (salt), phosphoric acid ester, acrylic-styrene copolymer, polyacrylic acid-styrene copolymer, polyacrylamide-acrylic acid copolymer, polyacrylic acid-sulfonic acid copolymer, and polyacrylic acid-maleic acid copolymer.

[0086] 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. It is preferable that the weight average molecular weight of the anionic polymer is less than the weight average molecular weight of the nonionic polymer contained in the first dispersant.

[0087] 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 the change in viscosity due to the change over time can be minimized.

[0088] The second dispersant may contain an anionic polymer having an aromatic ring.

[0089] 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.

[0090] The anionic polymer may have at least two or more aromatic rings.

[0091] The second dispersant may contain an anionic polymer having at least two or more aromatic rings and having a sulfonic acid (salt) group.

[0092] 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.

[0093] The second dispersant can be combined with the carbon nanotube to change the electrical physical properties of the surface of the carbon nanotube. By the second dispersant, a charge can be introduced onto the surface of the carbon nanotube. By the second dispersant, 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 the second dispersant, the charge formed on the surface of the carbon nanotube may have an electrostatic repulsive force with a storage stabilizer described later.

[0094] In addition, due to the steric effect generated by the aromatic ring, the cohesive force between the carbon nanotubes combined with the second dispersant can be reduced.

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

[0096] The content ratio of the first dispersant to the second dispersant may be 10:1 to 1:10, 5:1 to 1:5, 3:1 to 1:3, 2.5:1 to 1:3, 2:1 to 1:3, 1.5:1 to 1:3, or 1:1 to 1:3.

[0097] The total content ratio of the carbon nanotubes to the first dispersant and the second dispersant may be 1:1 to 1:2, 1:1 to 1:1.8, 1:1 to 1:1.7, or 1:1 to 1.2:1.7.

[0098] When the above ranges are satisfied, the charges of 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 performance of the secondary battery including the carbon nanotubes can be improved.

[0099] The carbon nanotube dispersion liquid according to the present invention includes a storage stabilizer having an electrostatic repulsive force with the charges formed on the surface of the carbon nanotubes.

[0100] By the storage stabilizer, the phenomenon that the first dispersant and the second dispersant not bound to the carbon nanotubes aggregate with each other can be suppressed, and the phenomenon that the carbon nanotubes bound to the first dispersant and the second dispersant aggregate with each other can be suppressed.

[0101] By the storage stabilizer, a repulsive force between the carbon nanotubes whose surfaces are modified with charges can be induced. By the storage stabilizer, 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 can be induced.

[0102] The storage stabilizer may include a phenolic compound containing two or more aromatic rings. The storage stabilizer may include a phenolic monomolecular compound containing two or more aromatic rings and having a negative charge.

[0103] The negative charge of the phenolic compound can induce an electrostatic repulsive force between the carbon nanotubes by exhibiting the same polarity as the carbon nanotubes whose surface is modified with a negative charge.

[0104] As a result, the carbon nanotube dispersion may have an appropriate initial viscosity range, minimize the increase in viscosity due to time change, and improve long-term storage stability.

[0105] 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, epicatechin gallate, butein, and piceatannol.

[0106] 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.

[0107] When the above range is satisfied, the phenomenon of elution of the storage stabilizer during electrode manufacturing can be suppressed, and the coating property and processability can be improved.

[0108] The content of the storage stabilizer may be 0.01% by weight to 0.1% by weight, 0.01% by weight to 0.08% by weight, 0.01% by weight to 0.07% by weight, or 0.02% by weight to 0.07% by weight based on the total weight of the carbon nanotube dispersion. The content of the storage stabilizer 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.

[0109] 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.

[0110] The total content of the first dispersant, the second dispersant, and the storage stabilizer 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 liquid.

[0111] When the above range is satisfied, smooth dispersion between the high-content carbon nanotubes in the carbon nanotube dispersion liquid can be achieved, and the performance of the secondary battery containing the high-content carbon nanotubes can be further improved.

[0112] The storage stabilizer may contain silicate. The storage stabilizer may contain layered silicate. When the storage stabilizer contains the layered silicate, the dispersibility of the carbon nanotubes can be further improved.

[0113] The carbon nanotube dispersion liquid according to the present invention may contain a solvent. When the solvent is mixed with the carbon nanotubes and an electrode active material or the like to be used as an electrode slurry composition, by previously dispersing the carbon nanotubes, the phenomenon of aggregation between the carbon nanotubes or aggregation with the electrode active material can be suppressed.

[0114] The solvent may be an aqueous solvent. The aqueous solvent may be water.

[0115] The solvent may be an aqueous solvent, an organic solvent, or a mixture thereof.

[0116] The organic solvent includes amide-based polar organic solvents such as dimethylformamide (DMF), diethylformamide, dimethylacetamide (DMAc), and 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.

[0117] 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, thereby improving the process efficiency.

[0118] The viscosity can be measured using a B-type viscometer, a rotating cylinder viscometer, etc. Specifically, it can be measured using a DV2T LV viscometer (Brookfield).

[0119] The carbon nanotube dispersion may have a viscosity change rate according to the following formula 1 of 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.

[0120] [Formula 1] Viscosity change rate (%) = (viscosity after 7 days - initial viscosity) / initial viscosity × 100

[0121] 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.

[0122] The carbon nanotube dispersion may be one in which the absorbance is measured. The absorbance may be an index meaning the degree of light absorption. The absorbance is proportional to the concentration of the substance. When the absorbance of the carbon nanotube dispersion is high, it means that the carbon nanotubes capable of absorbing light are uniformly dispersed at a high concentration. That is, the absorbance may be an index of the dispersibility of the carbon nanotubes contained in the carbon nanotube dispersion.

[0123] 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 may have excellent dispersibility. The absorbance may be measured in a wavelength range of 550 nm using a spectrophotometer.

[0124] 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, a second dispersant containing an ionic polymer, a storage stabilizer containing a phenolic compound containing two or more aromatic rings, and an aqueous solvent to produce a mixture, a step of milling and crushing the mixture, and a step of dispersing the mixture.

[0125] The production method includes a step of mixing the above-described carbon nanotubes, the first dispersant, the second dispersant, the storage stabilizer, and the aqueous solvent to produce a mixture.

[0126] The step of producing the mixture can be carried out under temperature conditions under which the physical properties of the carbon nanotubes, the first dispersant, the second dispersant, and the storage stabilizer do not change.

[0127] 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.

[0128] 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.

[0129] The above step can use a high-shear mixer, and the mixture can be processed for 5 to 60 minutes, 5 to 50 minutes, 10 to 50 minutes, or 10 to 30 minutes 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 using the mixer.

[0130] 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.

[0131] The manufacturing method includes a step of dispersing the mixture.

[0132] The above step may be a step of redispersing the pre-dispersed mixture under high-pressure conditions by a crushing process.

[0133] The above step can be repeatedly performed by milling the mixture using a ball mill, bead mill, disc mill, basket mill, or high-pressure homogenizer. Preferably, it can be performed using a high-pressure homogenizer.

[0134] The milling by the high-pressure homogenizer can be performed 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.

[0135] The step of dispersing the mixture can be performed 1 to 30 times, 2 to 30 times, 5 to 30 times, 5 to 20 times, or 5 to 10 times.

[0136] The electrode slurry composition according to the present invention contains an electrode active material, a binder, and a carbon nanotube dispersion. The carbon nanotube dispersion contains carbon nanotubes, a first dispersant surrounding the surface of the carbon nanotubes, a second dispersant introducing charges to the surface of the carbon nanotubes, and a storage stabilizer having an electrostatic repulsive force with the charges.

[0137] The carbon nanotube dispersion may be the same as the carbon nanotube dispersion described above.

[0138] The electrode active material may be a positive electrode active material.

[0139] The positive electrode active material is a compound capable of reversible intercalation and di-intercalation 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.

[0140] 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(Ni p Co q Mnr1 )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 may also be used. 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 Co 0.15 )O2, or Li(Ni 0.8Mn 0.1 Co 0.1 It may also be, for example, O2, and any one or a mixture of two or more of these can be used.

[0141] The electrode active material may be a negative electrode active material.

[0142] 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.

[0143] The negative electrode active material may contain a carbon-based material. The carbon-based material may contain natural graphite particles and artificial graphite particles. The negative electrode active material may contain a silicon-based material.

[0144] The negative electrode active material may contain a silicon-graphite composite. The proportion of the silicon weight 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.

[0145] 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). The element Y 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.

[0146] 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 according to the present invention as a conductive material, 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.

[0147] 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 a polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), fluororubber, poly acrylic acid, and various binder polymers such as polymers in which hydrogen thereof is substituted with Li, Na, Ca, etc., or various copolymers, etc.

[0148] 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, the effect as a binder is excellent without a decrease in the capacity per volume due to a decrease in the relative content of the electrode active material.

[0149] The electrode slurry composition may contain a solvent.

[0150] 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 used to dissolve and disperse the electrode active material, the binder, and the carbon nanotube dispersion liquid in consideration of the coating thickness and manufacturing yield of the electrode slurry composition.

[0151] 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.

[0152] 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; conductive materials such as polyphenylene derivatives.

[0153] 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 surrounding the surface of the carbon nanotubes, a second dispersant introducing charges to the surface of the carbon nanotubes, and a storage stabilizer having an electrostatic repulsive force with the charges.

[0154] 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 the initial efficiency, life characteristics, and high-rate discharge characteristics of the secondary battery can be improved.

[0155] 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 the 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 may be carried out under appropriate conditions considering the physical properties of the electrode to be finally manufactured.

[0156] 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, plastic carbon, or those with a surface treatment of carbon, nickel, titanium, silver, etc. on the surface of aluminum or stainless steel can be used. Also, 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 films, sheets, foils, nets, porous bodies, foams, non-woven fabrics, etc., and may have a thickness of 3 μm to 500 μm.

[0157] The electrode may be a negative electrode (anode). The negative electrode may include 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.

[0158] 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, plastic 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 fabric bodies, etc.

[0159] 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 include 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 include high melting point glass fibers and polyethylene terephthalate fibers. However, it is not limited thereto, and according to the embodiment, the separator may be a high heat resistance separator (CCS; Ceramic Coated Separator) containing ceramics.

[0160] The electrolytic solution may be a non-aqueous electrolytic solution. The electrolytic solution 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.

[0161] 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 electrolytic solution 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.

[0162] The secondary battery can be used for a high-output and large-capacity secondary battery that requires a long life and excellent durability, or for a module or pack including a plurality of the secondary batteries as unit cells.

[0163] The plurality of secondary batteries may be manufactured into a module. The plurality of modules may be manufactured into a pack.

[0164] 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.

[0165] Hereinafter, the present invention will be described more specifically based on examples and comparative examples. However, the following examples and comparative examples are only illustrative for explaining the present invention in more detail, and the present invention is not limited by the following examples and comparative examples.

[0166] Manufacturing Example Production Example 1 200 mg of single-walled carbon nanotubes were produced by chemical vapor deposition (CVD) using a catalyst. Then, the reaction furnace was filled with the single-walled carbon nanotubes.

[0167] 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.

[0168] Using water as a solvent, a mixture was prepared containing the single-walled carbon nanotubes: the first dispersant (polyvinylpyrrolidone, Mw 17,000 g / mol): the second dispersant (polynaphthalenesulfonate, Mw 5,000 g / mol): the storage stabilizer (tannic acid, Mw 1,700 g / mol) in a weight ratio of 26:19.5:19.5:1.

[0169] Subsequently, using a mixer, the mixture was treated 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.

[0170] Subsequently, using a high pressure homogenizer, the mixture was treated 10 times under a pressure condition of 1,200 bar to produce a carbon nanotube dispersion.

[0171] Production Example 2 A carbon nanotube dispersion was produced by the same process as in Production Example 1, except that tannic acid with a weight ratio of 0.6 was used instead of tannic acid with a weight ratio of 1 as the storage stabilizer in Production Example 1.

[0172] Production Example 3 A carbon nanotube dispersion was produced by the same process as in Production Example 1, except that tannic acid with a weight ratio of 0.4 was used instead of tannic acid with a weight ratio of 1 as the storage stabilizer in Production Example 1.

[0173] Production Example 4 A carbon nanotube dispersion was produced by the same process as in Production Example 1, except that tannic acid with a weight ratio of 1.2 was used instead of tannic acid with a weight ratio of 1 as the storage stabilizer in Production Example 1.

[0174] Production Example 5 A carbon nanotube dispersion was produced by the same process as in Production Example 1, except that tannic acid with a weight ratio of 1.4 was used instead of tannic acid with a weight ratio of 1 as the storage stabilizer in Production Example 1.

[0175] Production Example 6 A carbon nanotube dispersion was produced by the same process as in Production Example 1, except that epigallocatechin gallate was used instead of tannic acid as the storage stabilizer in Production Example 1.

[0176] Production Example 7 A carbon nanotube dispersion was produced by the same process as in Production Example 1, except that epicatechin gallate was used instead of tannic acid as the storage stabilizer in Production Example 1.

[0177] Production Example 8 A carbon nanotube dispersion was produced by the same process as in Production Example 1, except that 19.5 parts by weight of polyacrylic acid having a weight average molecular weight of about 1,500 g / mol was used instead of 19.5 parts by weight of polynaphthalene sulfonate having a weight average molecular weight of about 5,000 g / mol as the second dispersant in Production Example 1.

[0178] Production Example 9 A carbon nanotube dispersion was produced by the same process as in Production Example 1, except that polyvinylpyrrolidone having a weight average molecular weight of about 30,000 g / mol was used instead of polyvinylpyrrolidone having a weight average molecular weight of about 17,000 g / mol as the first dispersant in Production Example 1.

[0179] Production Example 10 A carbon nanotube dispersion was produced by the same process as in Production Example 1, except that single-walled carbon nanotubes (TUBALL, OCSiAl) having a specific surface area of 1,160 m 2 / g were used instead of the single-walled carbon nanotubes produced in Production Example 1.

[0180] Production Example 11 A carbon nanotube dispersion was produced by the same process as in Production Example 1, except that 0.16 part by weight of tannic acid was used instead of 1 part by weight of tannic acid as the storage stabilizer in Production Example 1.

[0181] Production Example 12 A carbon nanotube dispersion was produced by the same process as in Production Example 1, except that tannic acid at a ratio of 3 parts by weight was used instead of tannic acid at a ratio of 1 part by weight as the storage stabilizer in Production Example 1.

[0182] Production Example 13 A carbon nanotube dispersion was produced by the same process as in Production Example 1, except that polyvinylpyrrolidone with a weight average molecular weight of about 30,000 g / mol at a ratio of 29.26 parts by weight was used instead of polyvinylpyrrolidone with a weight average molecular weight of about 17,000 g / mol at a ratio of 19.5 parts by weight as the first dispersant in Production Example 1, and polyvinylnaphthalene sulfonate at a ratio of 9.74 parts by weight was used instead of polyvinylnaphthalene sulfonate at a ratio of 19.5 parts by weight as the second dispersant.

[0183] Comparative Production Example 1 A carbon nanotube dispersion was produced by the same process as in Production Example 1, except that tannic acid, which is the storage stabilizer in Production Example 1, was not used.

[0184] Comparative Production Example 2 A carbon nanotube dispersion was produced by the same process as in Production Example 1, except that polyvinylpyrrolidone, which is the first dispersant in Production Example 1, and tannic acid, which is the storage stabilizer, were not used, and polyacrylic acid with a weight average molecular weight of about 1,500 g / mol at a ratio of 19.5 parts by weight was used instead of polyvinylnaphthalene sulfonate with a weight average molecular weight of about 5,000 g / mol at a ratio of 19.5 parts by weight as the second dispersant.

[0185] Comparative Production Example 3 A carbon nanotube dispersion was produced by the same process as in Production Example 1, except that polyvinylpyrrolidone, which is the first dispersant in Production Example 1, and tannic acid, which is the storage stabilizer, were not used, and polyvinylnaphthalene sulfonate at a ratio of 60 parts by weight was used instead of polyvinylnaphthalene sulfonate at a ratio of 19.5 parts by weight as the second dispersant.

[0186] Comparative Production Example 4 A carbon nanotube dispersion was produced by the same process as in Production Example 1, except that the polynaphthalene sulfonate, which was the second dispersant in Production Example 1, was not used.

[0187] Comparative Production Example 5 A carbon nanotube dispersion was produced by the same process as in Production Example 1, except that 40 parts by weight of polyvinylpyrrolidone was used instead of 19.5 parts by weight of polyvinylpyrrolidone as the first dispersant in Production Example 1 and the polynaphthalene sulfonate, which was the second dispersant, was not used.

[0188] Comparative Production Example 6 A carbon nanotube dispersion was produced by the same process as in Production Example 1, except that the polyvinylpyrrolidone, which was the first dispersant in Production Example 1, was not used.

[0189]

Table 1

[0190] Example Example 1 <Manufacture of negative electrode> A negative electrode active material slurry containing a silicon graphite composite: the carbon nanotube dispersion of Production Example 1: a carboxymethyl cellulose (CMC) thickener: a styrene butadiene rubber (SBR) binder in a weight ratio of 96.5:0.1:1.2:2.2 was coated on a Cu foil current collector with a thickness of about 10 μm to a thickness of about 30 μm, and then dried at 100 °C for about 12 hours to produce a negative electrode.

[0191] <Manufacture of secondary battery (coin half cell)> An approximately 0.3 mm metal lithium foil was used as the positive electrode. After a polyethylene separator was interposed between the positive electrode and the negative electrode, a non-aqueous electrolyte in which EC:EMC was mixed at 3:7 and LiPF6 1M was injected to produce a coin half cell.

[0192] Examples 2 to 13 and Comparative Examples 1 to 6 A coin half-cell was manufactured by the same process as in Example 1, except that the carbon nanotube dispersion liquid described in Table 2 below was used instead of the carbon nanotube dispersion liquid of Production Example 1 in Example 1.

[0193] Experimental Example Experimental Example 1 - Initial Viscosity Regarding the carbon nanotube dispersion liquids of each of Production Examples 1 to 13 and Comparative Production Examples 1 to 6, the initial viscosity at room temperature was measured using a DV2T LV viscometer (Brookfield), and the results are shown in Table 2 below.

[0194] Experimental Example 2 - Viscosity Change Rate Under the same conditions as in Experimental Example 1, regarding the carbon nanotube dispersion liquids of each of Production Examples 1 to 13 and Comparative Production Examples 1 to 6, the viscosity after 7 days was measured, and the viscosity change rate was calculated by the following formula 1. The results are shown in Table 2 below.

[0195] [Formula 1] Viscosity change rate (%) = (viscosity after 7 days - initial viscosity) / initial viscosity × 100

[0196] Experimental Example 3 - Dispersibility Regarding the carbon nanotube dispersion liquids of each of Production Examples 1 to 13 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.

[0197] - ○: Absolute value exceeds 30 mV - △: Absolute value is 10 mV to 30 mV or less - ×: Absolute value is less than 10 mV

[0198] Experimental Example 4 - Dispersion Stability After putting each of the carbon nanotube dispersion liquids of Production Examples 1 to 13 and Comparative Production Examples 1 to 6 into a glass bottle, the presence or absence of aggregation was measured for 120 days. Evaluation was carried out according to the following criteria, and the results are shown in Table 2 below.

[0199] - ○: Aggregation occurred after 2 weeks - △: Aggregation occurred within 1 to 2 weeks - ×: Aggregation occurred within 1 week

[0200] Experimental Example 5 - Evaluation of the initial discharge capacity of a coin half-cell For each of the coin half-cells of Examples 1 to 13 and Comparative Examples 1 to 6, under normal temperature conditions, during charging, it was started in CC (constant current) mode at a current of 0.1C up to 0.01V, and then converted to CV (constant voltage) and set to be cut off at 0.01C. During discharging, it was carried out in CC (constant current) mode at a current of 0.1C up to 1.5V.

[0201] After performing charge and discharge up to the second cycle under the above charge and discharge conditions, the discharge capacity in the second cycle was measured, and the results are shown in Table 2 below.

[0202] Experimental Example 6 - Evaluation of high-rate characteristics For each of the coin half-cells of Examples 1 to 13 and Comparative Examples 1 to 6, after charging under normal temperature conditions at a constant current (0.2C) and constant voltage (0.01V, 0.01C cut-off), it was rested for 10 minutes (rest), and then discharged under the condition of a constant current (3.0C) until it reached 1.5V.

[0203] After performing the above charge and discharge, the discharge capacity and capacity retention rate were measured, and the results are shown in Table 2 below.

[0204]

Table 2

[0205] As can be confirmed from Tables 1 and 2 above, it was confirmed that the carbon nanotube dispersions according to Production Examples 1 to 13 containing the first and second dispersants and the storage stabilizer were superior in dispersibility and long-term storage stability compared to Comparative Production Examples 1 to 6.

[0206] In addition, it was confirmed that the secondary batteries of Examples 1 to 13 containing the carbon nanotube dispersions according to Production Examples 1 to 13 were superior in initial discharge capacity and high-rate characteristics compared to the secondary batteries of Comparative Examples 1 to 6 containing the carbon nanotube dispersions according to Comparative Production Examples 1 to 6.

Claims

1. Carbon nanotubes, a first dispersant surrounding the surface of the carbon nanotubes; A second dispersant that introduces charges onto the surface of the carbon nanotubes; a storage stabilizer having electrostatic repulsion with the charge; Including, Carbon nanotube dispersion.

2. The storage stabilizer contains a phenolic compound containing two or more aromatic rings. The carbon nanotube dispersion liquid according to claim 1 .

3. The phenolic compound has a weight average molecular weight of 200 g / mol to 3,000 g / mol. The carbon nanotube dispersion liquid according to claim 2 .

4. The content of the storage stabilizer is 0.01% by weight to 0.1% by weight based on the total weight of the carbon nanotube dispersion. The carbon nanotube dispersion liquid according to claim 1 .

5. The content of the storage stabilizer is 1 to 10 parts by weight based on 100 parts by weight of the carbon nanotubes. The carbon nanotube dispersion liquid according to claim 1 .

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

7. The first dispersant contains a nonionic polymer. The carbon nanotube dispersion liquid according to claim 1 .

8. The second dispersant contains an ionic polymer. The carbon nanotube dispersion liquid according to claim 1 .

9. The initial viscosity of the carbon nanotube dispersion at room temperature is 1,000 cP to 10,000 cP. The carbon nanotube dispersion liquid according to claim 1 .

10. preparing a mixture by mixing carbon nanotubes, a first dispersant including a nonionic polymer, a second dispersant including an ionic polymer, a storage stabilizer including a phenolic compound having two or more aromatic rings, and an aqueous solvent; milling and disintegrating the mixture; dispersing the mixture; Including, 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 surrounding the surfaces of the carbon nanotubes, a second dispersant introducing charges onto the surfaces of the carbon nanotubes, and a storage stabilizer having an electrostatic repulsive force with the charges. 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 produced from a carbon nanotube dispersion liquid, The carbon nanotube dispersion liquid includes carbon nanotubes, a first dispersant surrounding the surfaces of the carbon nanotubes, a second dispersant introducing charges onto the surfaces of the carbon nanotubes, and a storage stabilizer having an electrostatic repulsive force with the charges. Secondary battery.

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