Carbon nanotube dispersion, method for producing the same, electrode slurry composition containing the same, and secondary battery

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] This 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 technology]

[0002] The rapid increase in the use of fossil fuels has led to a growing demand for alternative and clean energy sources. Currently, a typical example of an electrochemical element that utilizes this electrochemical energy is the secondary battery, and its range of applications is expanding rapidly. A secondary battery is a battery that can be used repeatedly through a discharge process in which chemical energy is converted into electrical energy, and a charging process in the reverse direction. A secondary battery may include a positive electrode, a negative electrode, an electrolyte, and a separator membrane. The positive and negative electrodes 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 coating 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] Conductive materials are used to improve the conductivity of electrode active materials, and conventionally, dot-type conductive materials such as carbon black were mainly used. However, since dot-type conductive materials do not have a high effect in improving electrical conductivity, they must be used in excess to obtain a sufficient effect, which leads to a problem of reduced electrode active material content and decreased battery capacity.

[0004] To address these issues, there are active attempts to apply highly conductive carbon nanotubes (CNTs) as conductive materials.

[0005] However, due to the properties of carbon nanotubes, their dispersibility in the slurry decreases, reducing the efficiency of the secondary battery manufacturing process. This leads to a problem where the conductivity decreases with each cycle of the secondary battery, resulting in a decline in its performance. [Overview of the project]

Problems to be Solved by the Invention

[0006] The present invention provides a carbon nanotube dispersion liquid having excellent dispersibility and long-term storage stability, which improves the 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 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 include 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 the steps 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; milling and crushing the mixture; and 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 comprises an electrode active material, a binder, and a carbon nanotube dispersion, wherein the carbon nanotube dispersion comprises carbon nanotubes, a first dispersant surrounding the surface of the carbon nanotubes, a second dispersant introducing an electric charge to the surface of the carbon nanotubes, and a storage stabilizer having electrostatic repulsion with the electric charge.

[0019] The secondary battery according to the present invention comprises an electrode, a separation membrane, and an electrolyte, wherein the electrode comprises an electrode active material, a binder, and a conductive material, the conductive material is manufactured from a carbon nanotube dispersion, and the carbon nanotube dispersion comprises carbon nanotubes, a first dispersant surrounding the surface of the carbon nanotubes, a second dispersant introducing an electric charge to the surface of the carbon nanotubes, and a storage stabilizer having electrostatic repulsion with the electric charge. [Effects of the Invention]

[0020] In the carbon nanotube dispersion according to the present invention, the carbon nanotubes are stabilized by the first and second dispersants, and an electric charge is introduced to the surface of the carbon nanotubes, thereby improving the dispersibility of the carbon nanotubes.

[0021] Furthermore, the carbon nanotube dispersion according to the present invention includes a storage stabilizer that has electrostatic repulsion with the charges introduced on the surface of the carbon nanotubes. The storage stabilizer can induce repulsive forces between the carbon nanotubes whose surfaces have been modified with charges, thereby improving the long-term storage stability of the carbon nanotube dispersion.

[0022] Furthermore, the carbon nanotube dispersion according to the present invention has an appropriate initial viscosity range due to the first dispersant, the second dispersant, and the storage stabilizer, thereby minimizing the increase in viscosity over time.

[0023] Furthermore, the carbon nanotube dispersion may contain a high content of single-walled carbon nanotubes, which have excellent dispersibility, long-term storage stability, and electrical conductivity, and the initial discharge capacity and high-efficiency characteristics of secondary batteries manufactured using the carbon nanotube dispersion may be improved. [Modes for carrying out the invention]

[0024] The structural or functional descriptions relating to the embodiments disclosed herein or in the application are merely illustrative for the purpose of illustrating embodiments of the technical concept of the present invention, and embodiments of the technical concept of the present invention can be implemented in various forms other than those disclosed herein or in the application, and the technical concept of the present invention should not be construed as being limited to the embodiments described herein or in the application.

[0025] Furthermore, when a component described herein or in the application is "included," this means, unless otherwise specified, that it does not exclude other components, but may include other components. Also, any numerical ranges indicating physical properties, dimensions, etc., of components described herein or in the application should be understood to be modified by the term "approximately" unless otherwise specified. In addition, "ppm" in this specification or application means by weight basis. In addition, the description "A and / or B" in this specification or application means "A, B, or A and B."

[0026] The following describes the carbon nanotube dispersion liquid, its manufacturing method, an electrode slurry composition containing the same, and a secondary battery according to the present invention.

[0027] Typically, conductive materials are used to improve the electrical conductivity of electrode active materials used in secondary batteries, and these conductive materials may be mixed with the electrode active materials in a dispersion state, which is a mixture of a dispersant and a solvent.

[0028] 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 other point-type conductive materials, carbon nanotubes, which are linear conductive materials, have a high specific surface area, and there is a problem in that aggregation occurs due to van der Waals forces between the carbon nanotubes.

[0029] In particular, single-walled carbon nanotubes, while possessing excellent electrical conductivity, suffer from a problem of very low dispersibility due to their high specific surface area and strong attractive forces, which easily lead to aggregation.

[0030] The inventors focused on the fact that if a first dispersant capable of stabilizing carbon nanotubes and a second dispersant capable of introducing an electric charge to the surface of the carbon nanotubes are combined, and the resulting mixture has a repulsive force that prevents the carbon nanotubes with the introduced electric charge from aggregating with each other, then dispersibility and long-term storage stability can be improved.

[0031] Therefore, we focused on the fact that by including a substance having electrostatic repulsion between the carbon nanotubes into which the charge has been introduced in the dispersion, dispersibility and long-term storage stability can be improved, and as a result, the dispersion can contain a high content of carbon nanotubes, and the performance of secondary batteries containing the carbon nanotubes as a conductive material can be improved.

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

[0033] The carbon nanotubes may be in the form of a secondary structure where a graphite sheet is cylindrical with a nano-sized diameter, and multiple carbon nanotubes are arranged or aggregated. When the carbon nanotubes are used as a conductive material, the electrical conductivity of the electrode may be improved.

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

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

[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, together with the single-walled carbon nanotube, 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, 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 used. 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 nanotubes 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 better the electrical conductivity of the single-walled carbon nanotubes can be, and if the above range is met, the performance of a secondary battery using the single-walled carbon nanotubes as a conductive material can be improved.

[0040] The aforementioned powder resistance can be measured using a powder resistance measuring instrument (MCP-PD51) equipped with a 4-pin probe, at a rolling density of 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) of the single-walled carbon nanotube 50 The wavelength may be 0.5nm to 25nm, 0.5nm to 20nm, 0.5nm to 15nm, 0.5nm to 10nm, 0.8nm to 10nm, 1nm to 10nm, or 1nm to 5nm.

[0043] The length and diameter can be measured using an atomic force microscope (AFM). The length may correspond to the average value of the top 100 single-walled carbon nanotubes with the largest 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 the largest average diameter and the bottom 100 single-walled carbon nanotubes.

[0044] The weight change of the single-walled carbon nanotube can be measured by thermogravimetric analysis. This temperature change can be measured in a nitrogen atmosphere, within a temperature range of 40°C to 1,000°C, while increasing the temperature at intervals of 10°C / min.

[0045] The temperature at which the single-walled carbon nanotube begins to decompose can be measured using the thermogravimetric analyzer. The purity of the single-walled carbon nanotube can be evaluated by measuring the weight change due to temperature changes.

[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, as measured by the thermogravimetric analyzer, at temperatures between 40°C and 300°C.

[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, as measured by the thermogravimetric analyzer, at 300°C to 550°C.

[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, as measured by the thermogravimetric analyzer, at temperatures between 40°C and 550°C.

[0049] The single-walled carbon nanotube may have a thermal decomposition onset 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 onset 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 nanotubes 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, as measured by the thermogravimetric analyzer.

[0051] When the single-walled carbon nanotubes satisfy the above-mentioned weight change, thermal decomposition initiation temperature, and residue content, impurities are minimized and purity is improved. When used as a conductive material, this improves electrical conductivity, thereby improving the performance of secondary batteries, and improves dispersibility, thereby improving coating properties and processability.

[0052] The single-walled carbon nanotubes can exhibit a bundle type in which multiple single-walled carbon nanotubes are arranged in a specific direction, a rope-like bundle type, or an entangled type in which multiple single-walled carbon nanotubes are entangled in a spherical or potato-like shape without a specific direction.

[0053] The single-walled carbon nanotube may be produced 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 nanotubes may be synthesized by laser ablation. Laser ablation refers to a process of irradiating a mixture of a carbon-containing raw material and a catalyst with a laser beam under an inert gas atmosphere, and single-walled carbon nanotubes may be synthesized by this 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 / cm². 2 ~300 mJ / cm 2 , 110 mJ / cm 2 ~300 mJ / cm 2 , 110 mJ / cm2 ~290 mJ / cm² 2 , or 120 mJ / cm² 2 ~280 mJ / cm² 2 That's fine.

[0055] The single-walled carbon nanotubes may be synthesized by arc discharge. The arc discharge method means a process of generating an arc discharge between a pair of electrodes and depositing the evaporated material generated at the anode, and the single-walled carbon nanotubes 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 of iron, cobalt, yttrium, and nickel. The graphite may be in the form of a rod with voids. The transition metal may be mixed in the voids of the graphite. The arc discharge method can be carried out in an atmosphere of inert gas, or an atmosphere of inert gas and hydrogen gas. The arc discharge method can be carried out in an atmosphere of a small amount of hydrocarbon gas. The hydrocarbon gas may contain at least one of methane, ethylene, and acetylene. The pair of electrodes may be separated by a certain distance. The pair of electrodes may be separated by a distance of 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 DC arc discharge method. The DC power supply in the DC arc discharge method may have a voltage range of 20V to 70V, 22V to 70V, 22V to 65V, or 25V to 65V. The DC power supply in the DC 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 nanotubes may be synthesized by chemical vapor deposition. The chemical vapor deposition method refers to 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 single-walled carbon nanotubes may be synthesized by this process. The catalyst can be nanoparticles supported with iron, cobalt, nickel, or molybdenum, or alumina or silica supported with such nanoparticles. The chemical vapor deposition method has the advantage that it is easy to control the diameter, length, density, structure, and crystallinity of the single-walled carbon nanotubes, and that high-purity single-walled carbon nanotubes can be mass-produced.

[0057] The synthesized single-walled carbon nanotubes may contain impurities. The impurities may include at least one of metal oxides, metals, and nonmetals. The metal oxides may include ceramic metals. The ceramic metals may be derived from the catalyst support in the synthesis process of the single-walled carbon nanotubes. The metals may include at least one of iron, cobalt, nickel, chromium, copper, manganese, nickel, and zinc. The nonmetals may include sulfur. The metals and nonmetals may be derived from the catalyst in the synthesis process of the single-walled carbon nanotubes.

[0058] Among the impurities, nickel can cause the single-walled carbon nanotubes to be cut, shortened in length, or oxidize on the surface, reducing their electrical and mechanical properties. The nickel can also damage the unique characteristics of the single-walled carbon nanotubes. Therefore, it is more preferable to purify the synthesized single-walled carbon nanotubes to remove the nickel. The BET specific surface area and nickel content of the single-walled carbon nanotubes can be adjusted not only by the synthesis process of the single-walled carbon nanotubes but also by the conditions of the impurity removal process.

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

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

[0061] The aforementioned centrifugation method involves applying centrifugal force to a mixture of substances with different masses to separate them based on the difference in precipitation rates. By this centrifugation method, it is possible to separate the amorphous carbon, carbon nanoparticles, and single-walled carbon nanotubes contained in the synthesized single-walled carbon nanotubes.

[0062] The solubilization of the carbon nanotubes involves introducing an active group onto the surface of the single-walled carbon nanotubes, dissolving them in a solvent, and then separating the high-purity carbon nanotubes from impurities using filtration or chromatography.

[0063] In the aforementioned high-temperature aniling, while carbon does not undergo a phase change even at high temperatures of approximately 1,500°C or higher under inactive gas or vacuum conditions, the single-walled carbon nanotubes can be treated at a temperature above the evaporation temperature of the impurities under inactive gas or vacuum conditions to remove the impurities formed on the carbon nanotubes.

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

[0065] The electrochemical oxidation process involves electrically oxidizing the synthesized single-walled carbon nanotubes with a potassium hydroxide solution or a sulfuric acid solution, thereby removing amorphous carbon and impurities contained within the single-walled carbon nanotubes.

[0066] The liquid-phase oxidation process involves reacting the synthesized single-walled carbon nanotubes with an oxidizing liquid to remove amorphous carbon and impurities contained within the single-walled carbon nanotubes. The oxidizing liquid can be hydrochloric acid, nitrous acid, sulfuric acid, phosphoric acid, etc. This liquid-phase oxidation process can remove metal oxides and metals from the impurities contained within the single-walled carbon nanotubes. The liquid-phase oxidation process can be carried out at a temperature of approximately 20°C to 25°C. Conventionally, this liquid-phase oxidation was carried out at a high temperature range of approximately 50°C to 70°C, but this process could destroy the structure of the single-walled carbon nanotubes, such as causing cleavage and end-opening, and resulting in the presence of oxidizing liquid reaction products as secondary impurities on the single-walled carbon nanotubes. Therefore, when the liquid-phase oxidation process satisfies the above temperature range, the problem of secondary impurities forming on the purified single-walled carbon nanotubes can be suppressed, and the structural stability of the purified single-walled carbon nanotubes can be improved.

[0067] The aforementioned gas-phase oxidation process involves heat-treating the synthesized single-walled carbon nanotubes in an oxidizing gas atmosphere at a temperature range of approximately 700°C to 1,000°C, thereby removing amorphous carbon and impurities contained in the single-walled carbon nanotubes. The oxidizing gas can be air, chlorine, a mixture of water vapor and hydrogen chloride, hydrogen sulfide, argon, or the like.

[0068] The purification process can be carried out for 30 to 200 minutes, 30 to 150 minutes, 40 to 120 minutes, 40 to 110 minutes, or 40 to 100 minutes.

[0069] The purification process can be carried out at temperatures of 900°C or higher, 920°C or higher, 950°C or higher, or 1,000°C or higher.

[0070] After the purification process, a step of cooling at room temperature under vacuum can be performed.

[0071] The aforementioned purification process allows for more efficient removal of metal impurities contained in the single-walled carbon nanotubes.

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

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

[0074] The first dispersant is a nonionic polymer that may contain one or more selected from the group consisting of polyethylene glycol, polypropylene glycol, polybutylene glycol, polyvinyl alcohol, polyvinylpyrrolidone, polyacrylate hydrazide, poly-N-vinyl-5-methoxazolidone, N-alkyl polyimine, N-acetylpolyimine, polyacrylamide, poly-L-lysine, polyethyleneimine, and polyethylene glycol-polypropylene glycol copolymer.

[0075] Preferably, the first dispersant may contain polyvinylpyrrolidone, a nonionic polymer 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 met, the phenomenon of the first dispersant dissolving during electrode manufacturing can be suppressed, the kneadability with other materials in the carbon nanotube dispersion is improved, the dispersibility is improved, and the change in viscosity 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, containing a hydrophobic main chain and hydrophilic side chains.

[0079] The first dispersant may contain a random coil-shaped nonionic polymer that includes hydrophobic and hydrophilic properties, thereby stably binding to the carbon nanotubes and surrounding their surfaces. The first dispersant may reduce the cohesive force between the carbon nanotubes, allowing for smooth dispersion of the carbon nanotubes.

[0080] The content of the first dispersant relative to the total weight of the carbon nanotube dispersion may be 0.01% to 10.00% by weight, 0.01% to 5.00% by weight, 0.01% to 3.00% by weight, 0.01% to 2.00% by weight, 0.05% to 2.00% by weight, or 0.05% to 1.50% by weight. When the above ranges are met, the dispersion effect of the carbon nanotubes is improved, and the carbon nanotube dispersion may have an appropriate initial viscosity.

[0081] The carbon nanotube dispersion according to the present invention includes a second dispersant that introduces an electric charge to the surface of the carbon nanotubes.

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

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

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

[0085] The second dispersant is an anionic polymer that may contain one or more selected from the group consisting of polyacrylic acid (salt), polymethacrylic acid (salt), polyacrylmaleic 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 anionic polymer may have a weight-average molecular weight of 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. Preferably, 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 met, strong interaction with the carbon nanotube is possible, allowing for smooth introduction of charge to the surface of the carbon nanotube, further improving dispersibility and minimizing changes in viscosity over time.

[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 aromatic rings.

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

[0092] The anionic polymer having a sulfonic acid (salt) group may include one or more selected from the group consisting of naphthalene, pyrene, anthracene, and phenanthrene.

[0093] The second dispersant can bind to the carbon nanotubes and alter the electrical properties of the carbon nanotubes' surface. The second dispersant can introduce an electric charge to the surface of the carbon nanotubes. The second dispersant can introduce a negative charge to the surface of the carbon nanotubes. By introducing an electric charge to the surface of the carbon nanotubes with the second dispersant, the charge formed on the surface of the carbon nanotubes may have electrostatic repulsion with the storage stabilizer described later.

[0094] Furthermore, the second dispersant may reduce the cohesive force between the carbon nanotubes bound to the second dispersant due to the steric effect generated by the aromatic ring.

[0095] The content of the second dispersant relative to the total weight of the carbon nanotube dispersion may be 0.01% to 10.00% by weight, 0.01% to 5.00% by weight, 0.01% to 3.00% by weight, 0.01% to 2.00% by weight, 0.05% to 2.00% by weight, or 0.05% to 1.50% by weight. When the above ranges are met, the dispersion effect of the carbon nanotubes may be further improved.

[0096] The 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 of the carbon nanotubes, 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 range is met, the charge from the second dispersant can be introduced in a balanced manner onto the surface of the carbon nanotube stabilized by the first dispersant, which can improve the dispersibility of the carbon nanotube and improve the performance of the secondary battery containing the carbon nanotube.

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

[0100] The storage stabilizer can suppress the aggregation of the first and second dispersants that are not bound to the carbon nanotubes, and can also suppress the aggregation of the carbon nanotubes that are bound to the first and second dispersants.

[0101] The storage stabilizer can induce repulsive forces between the carbon nanotubes whose surfaces have been modified to have an electric charge. The storage stabilizer can induce electrostatic repulsive forces between the carbon nanotubes which have been dispersed by the first and second dispersants and whose surfaces have been modified to have a negative charge.

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

[0103] The negative charge of the phenolic compound exhibits the same polarity as the carbon nanotubes whose surfaces have been modified to have a negative charge, thereby inducing an electrostatic repulsion force between the carbon nanotubes.

[0104] As a result, the carbon nanotube dispersion may have an appropriate initial viscosity range, minimizing the increase in viscosity over time and potentially improving 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 met, the phenomenon of the storage stabilizer leaching out during electrode manufacturing can be suppressed, and coating properties and processability can be improved.

[0108] The content of the storage stabilizer may be 0.01% to 0.1% by weight, 0.01% to 0.08% by weight, 0.01% to 0.07% by weight, or 0.02% to 0.07% by weight with respect to the total weight of the carbon nanotube dispersion. The content of the storage stabilizer may be 1 to 10 parts by weight, 2 to 10 parts by weight, 2 to 9 parts by weight, or 2 to 6 parts by weight per 100 parts by weight of the carbon nanotube.

[0109] When the above range is met, electrostatic repulsion between carbon nanotubes can be induced more efficiently, and the increase in viscosity due to changes over time can be minimized.

[0110] The total content of the first dispersant, the second dispersant, and the storage stabilizer may be 1% to 2.5% by weight, 1% to 2.2% by weight, 1% to 2% by weight, or 1.5% to 2% by weight, relative to the total weight of the carbon nanotube dispersion.

[0111] If the above range is met, smooth dispersion occurs among the high-content carbon nanotubes in the carbon nanotube dispersion, which can further improve the performance of the secondary battery containing the high-content carbon nanotubes.

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

[0113] The carbon nanotube dispersion according to the present invention may contain a solvent. The solvent can suppress the aggregation of carbon nanotubes between the carbon nanotubes or with the electrode active material by pre-dispersing the carbon nanotubes when the carbon nanotubes are mixed with an electrode active material or the like to be used as an electrode slurry composition.

[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 aforementioned organic solvents include amide-type 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; and glycerin, trimethylolpropane, pentaerythritol, or sorbitol. Examples include polyhydric alcohols such as; 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; and esters such as ethyl acetate, γ-butyl lactone, and ε-propiolactone. 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 met, the aggregation phenomenon of the carbon nanotubes can be suppressed, the process of repeatedly adding and dispersing the carbon nanotubes can be minimized, and process efficiency can be improved.

[0118] The viscosity can be measured using a B-type viscometer, a rotary cylindrical viscometer, or, more specifically, a DV2T LV viscometer (Brookfield).

[0119] The carbon nanotube dispersion may have a viscosity change rate of 20% or less, 18% or less, 16% or less, 14% or less, 12% or less, or 5% or less according to the following formula 1. When the above range is satisfied, the dispersion containing carbon nanotubes may have an increased viscosity over time, thereby improving long-term storage stability.

[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 3-10, 4-10, 4-9, 5-9, 5-8, or 6-8. When the above range is met, the occurrence of aggregation due to hydrogen bonding can be suppressed.

[0122] The carbon nanotube dispersion may be one whose absorbance can be measured. The absorbance may be an index that represents the degree to which light is absorbed. Since the absorbance is proportional to the concentration of the substance, a high absorbance of the carbon nanotube dispersion means that carbon nanotubes capable of absorbing light are uniformly dispersed at a high concentration. In other words, 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 between 0.1 and 10, between 0.15 and 10, between 0.15 and 5, or between 0.2 and 5. When the above ranges are met, aggregates contained in the carbon nanotube dispersion are minimized, the carbon nanotubes contained in the dispersion are of high purity, and the dispersion may have excellent dispersibility. The absorbance may be measured using a spectrophotometer in the wavelength range of 550 nm.

[0124] The method for producing a carbon nanotube dispersion according to the present invention includes the steps 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; milling and crushing the mixture; and dispersing the mixture.

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

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

[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 manufacturing method includes a step of milling the mixture to disintegrate it. This step can adjust the particle size distribution of the carbon nanotubes contained in the mixture.

[0129] The aforementioned step can be performed using a high-shear force mixer, which can be used to perform the step at speeds 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 to 60 minutes, 5 to 50 minutes, 10 to 50 minutes, or 10 to 30 minutes.

[0130] The mixture can be broken down by the above step so that its average particle size is less than 100 μm, less than 95 μm, less than 90 μm, or less than 80 μm. If the above range is met, the dispersibility of the carbon nanotubes may be further improved.

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

[0132] The aforementioned step may also be a step in which the previously dispersed mixture is redispersed under high-pressure conditions by a crushing step.

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

[0134] Milling using the aforementioned 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 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 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 (such as LiMnO2, LiMn2O4, etc.), lithium-cobalt-based oxides (such as LiCoO2, etc.), lithium-nickel-based oxides (such as LiNiO2, etc.), lithium-nickel-manganese-based oxides (such as 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 (such as LiNi 1-Y1 Co Y1 O2 (where 0 < Y1 < 1), etc.), lithium-manganese-cobalt-based oxides (such as 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 (such as 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 atomic fractions of independent elements, 0 < p2 < 1, 0 < q2 < 1, 0 < r3 < 1, 0 < s2 < 1, and p2 + q2 + r3 + s2 = 1), etc.), etc. may be mentioned, 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[[ID=3৪]] 0.8 Co 0.15 Al 0.05 )O2, etc.), etc. may be, considering the remarkable improvement effect by controlling the types and content ratios of the constituent elements forming the lithium composite metal oxide, 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 )This could also be O2, and any one or a mixture of two or more of these may be used.

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

[0142] The negative electrode active material may be present in amounts 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, relative to the total weight of the electrode slurry composition. When the above ranges are met, the charge and discharge capacity of the secondary battery may increase.

[0143] The negative electrode active material may include a carbon-based material. The carbon-based material may include natural graphite particles or artificial graphite particles. The negative electrode active material may also include a silicon-based material.

[0144] The negative electrode active material may include a silicon graphite composite. The proportion of silicon by 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 ranges are met, the deterioration of the secondary battery's life characteristics can be minimized and the charge / discharge capacity can be significantly increased.

[0145] The silicon-based substance 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 (where 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). For 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).

[0146] The silicon-based substance can exhibit high capacity characteristics compared to the carbon-based substance. When the silicon-based substance is included in the negative electrode active material, the capacity characteristics can be improved. However, the silicon-based substance has a problem that the volume change is large during charge and discharge compared to the carbon-based substance, 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 substance, not only the capacity characteristics can be improved, but the cycle characteristics can also be improved.

[0147] The binder can improve the adhesion between the electrode active materials or between the electrode active materials and the current collector. The binder can be a variety of binder polymers such as polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, polyacrylic acid, and polymers of these in which hydrogen is substituted with Li, Na, or Ca, or various copolymers.

[0148] The binder may be present in amounts of 0.1% to 10% by weight, 0.1% to 8% by weight, 0.1% to 7% by weight, 0.1% to 6% by weight, or 0.1% to 5% by weight relative to the total weight of the electrode slurry composition. When the above ranges are met, the binder exhibits excellent effects without a decrease in volume per unit volume due to a relative decrease in the content of the electrode active material.

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

[0150] The solvent can be used to mix the components in the electrode slurry composition and adjust the viscosity. The solvent may be an organic solvent such as NMP (N-methylpyrrolidone), DMF (dimethylformamide), acetone, or dimethylacetamide, or water. These solvents can be used individually or in combination of two or more. The amount of solvent used should be sufficient to dissolve and disperse the electrode active material, the binder, and the carbon nanotube dispersion, taking into consideration the coating thickness of the electrode slurry composition and the production yield.

[0151] The carbon nanotube dispersion can be used as a conductive material. The use of the carbon nanotube dispersion as a conductive material can improve the initial discharge capacity and high-efficiency characteristics of secondary batteries.

[0152] The conductive material can improve electrical conductivity. The conductive material may further include graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, ketchene black, channel black, furnace black, lamp black, and thermal black; metal powders such as fluorocarbon, aluminum, and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives.

[0153] The secondary battery according to the present invention comprises an electrode, a separation membrane, and an electrolyte, wherein the electrode comprises an electrode active material, a binder, and a conductive material, the conductive material is manufactured from a carbon nanotube dispersion, and the carbon nanotube dispersion comprises carbon nanotubes, a first dispersant surrounding the surface of the carbon nanotubes, a second dispersant introducing an electric charge to the surface of the carbon nanotubes, and a storage stabilizer having electrostatic repulsion with the electric charge.

[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 electrical conductivity of the secondary battery can be improved, and the initial efficiency, lifespan characteristics, and high-rate discharge characteristics of the secondary battery can be improved.

[0155] The electrode may be a cathode. The cathode may contain the positive electrode active material, binder, and conductive material described above. The cathode may be manufactured by applying a cathode slurry composition containing the positive electrode 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 applying the cathode slurry composition onto the cathode current collector and then drying it, or by applying the cathode slurry composition separately onto a support, peeling it off the support, and then laminating the resulting film 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 performed under appropriate conditions, taking into account the physical properties of the electrode to be ultimately manufactured.

[0156] The positive electrode current collector is not particularly limited as long as it is a highly conductive metal that the slurry of the positive electrode active material adheres to easily, does not cause chemical changes in the secondary battery, and has high conductivity. For example, stainless steel, aluminum, nickel, titanium, plastic carbon, or aluminum or stainless steel with a surface treatment of carbon, nickel, titanium, silver, etc. can be used. Furthermore, fine irregularities can be formed on the surface of the positive electrode current collector to increase the adhesion strength of the positive electrode active material. The positive electrode current collector can be used in various forms such as film, sheet, foil, net, porous material, foam, nonwoven fabric, 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 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 the 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 chemical changes in the secondary battery and is conductive. For example, copper, stainless steel, aluminum, nickel, titanium, plastic carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloy can be used. Furthermore, fine irregularities can be formed on the surface to strengthen the bonding force of the negative electrode active material, and it can be used in various forms such as films, sheets, foils, nets, porous materials, foams, and nonwoven fabrics.

[0159] The separation membrane may be interposed between the negative electrode and the positive electrode. The separation membrane may be configured to prevent electrical short circuits between the negative electrode and the positive electrode, thereby generating an ion flow. The separation membrane may include a porous polymer film or a porous nonwoven fabric. The porous polymer film may consist of a single layer or multiple layers containing polyolefin polymers such as ethylene polymer, propylene polymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer. The porous nonwoven fabric may contain high-melting-point glass fibers or polyethylene terephthalate fibers. However, it is not limited thereto, and according to the embodiment, the separation membrane may be a ceramic-coated separation membrane (CCS) containing ceramics.

[0160] 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 the following: 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 separator membrane may be manufactured into an electrode assembly by winding, lamination, folding, or zigzag stacking processes. The electrode assembly may be provided together with the electrolyte to manufacture a secondary battery. The secondary battery may be, but is not limited to, a cylindrical, prismatic, pouch, or coin-type battery using a can.

[0162] The aforementioned secondary battery can be used as a high-output, high-capacity secondary battery requiring a long lifespan and excellent durability, or in a module or pack containing multiple such secondary batteries as unit batteries.

[0163] The aforementioned multiple secondary batteries may be manufactured as modules. The aforementioned multiple modules may be manufactured as packs.

[0164] The pack can be used as a power source for medium to large devices that require high temperature stability, long cycle characteristics, and high rate characteristics. The types of medium to large devices may include power tools powered by battery motors; electric vehicles including electric vehicles (EVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs); electric motorcycles including electric bicycles (E-bikes) and electric scooters; electric golf carts; electric trucks; electric commercial vehicles; or power storage systems.

[0165] The present invention will be described in more detail below based on examples and comparative examples. However, the following examples and comparative examples are merely illustrative to further illustrate the present invention, and the present invention is not limited to the following examples and comparative examples.

[0166] Manufacturing example Manufacturing Example 1 200 mg of single-walled carbon nanotubes were produced by chemical vapor deposition (CVD) using a catalyst. Subsequently, the single-walled carbon nanotubes were packed into a reactor.

[0167] Subsequently, the reactor was purified in an argon atmosphere and under vacuum conditions at approximately 1,000°C for 60 minutes, and then cooled to room temperature, resulting in a specific surface area of ​​approximately 1,557 m². 2 We fabricated single-walled carbon nanotubes with a density of / g.

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

[0169] Subsequently, the mixture was processed using a mixer at 8,000 rpm for 20 minutes to break it down so that the average particle size of the particles contained in the mixture was less than approximately 100 μm.

[0170] Subsequently, a carbon nanotube dispersion was produced by processing the mixture 10 times at a pressure of 1,200 bar using a high-pressure homogenizer.

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

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

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

[0174] Manufacturing Example 5 A carbon nanotube dispersion was prepared using the same process as in Production Example 1, except that 1.4 times the weight of tannic acid was used as the storage stabilizer instead of 1 time by weight of tannic acid in Production Example 1.

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

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

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

[0178] Manufacturing Example 9 A carbon nanotube dispersion was prepared using the same process as in Production Example 1, except that polyvinylpyrrolidone with a weight-average molecular weight of approximately 30,000 g / mol was used as the first dispersant, instead of polyvinylpyrrolidone with a weight-average molecular weight of approximately 17,000 g / mol as in Production Example 1.

[0179] Manufacturing Example 10 Instead of the single-walled carbon nanotubes produced in the above production example 1, a specific surface area of ​​1,160 m² was used. 2 A carbon nanotube dispersion was prepared using the same process as in Production Example 1, except that single-walled carbon nanotubes (TUBALL, OCSiAl) with a density of / g were used.

[0180] Manufacturing Example 11 A carbon nanotube dispersion was prepared using the same process as in Production Example 1, except that tannic acid at a ratio of 0.16 by weight was used as the storage stabilizer instead of tannic acid at a ratio of 1 by weight as in Production Example 1.

[0181] Manufacturing Example 12 A carbon nanotube dispersion was prepared using the same process as in Production Example 1, except that tannic acid was used in a 3:1:1 ratio as the storage stabilizer in Production Example 1.

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

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

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

[0185] Comparative Manufacturing 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, and tannic acid, which is the storage stabilizer, were not used, and polynaphthalene sulfonate at a ratio of 60 by weight was used as the second dispersant instead of 19.5 by weight.

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

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

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

[0189] [Table 1]

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

[0191] <Manufacturing of rechargeable batteries (coin half-cells)> A metallic lithium foil of approximately 0.3 mm thickness was used as the positive electrode. After interposing a polyethylene separation membrane between the positive and negative electrodes, EC:EMC was mixed in a 3:7 ratio, and a non-aqueous electrolyte of LiPF61M was injected to produce a coin half-cell.

[0192] Examples 2-13 and Comparative Examples 1-6 Coin half-cells were manufactured using the same process as in Example 1, except that the carbon nanotube dispersions listed in Table 2 below were used instead of the carbon nanotube dispersion used in Manufacturing Example 1 in Example 1.

[0193] Experimental example Experimental Example 1 - Initial Viscosity The initial viscosity at room temperature was measured for each of the carbon nanotube dispersions from Production Examples 1-13 and Comparative Production Examples 1-6 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, the viscosity of each carbon nanotube dispersion from Production Examples 1-13 and Comparative Production Examples 1-6 was measured after 7 days, and the viscosity change rate was calculated using Equation 1 below. 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 - Dispersion The zeta potential was measured for each of the carbon nanotube dispersions from Production Examples 1-13 and Comparative Production Examples 1-6. The evaluation was performed according to the following criteria, and the results are shown in Table 2 below.

[0197] -○: Absolute value is greater than 30mV -△: Absolute value is between 10mV and 30mV or less. -×: Absolute value is less than 10mV

[0198] Experimental Example 4 - Dispersion Stability The carbon nanotube dispersions of Production Examples 1-13 and Comparative Production Examples 1-6 were placed in glass bottles, and the presence or absence of aggregation was measured for 120 days. The results were evaluated according to the following criteria and are shown in Table 2 below.

[0199] -○: Aggregation occurs after 2 weeks -△: Aggregation occurs within 1-2 weeks. -×: Aggregation occurs 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 in Examples 1 to 13 and Comparative Examples 1 to 6, under room temperature conditions, charging was started in CC (constant current) mode with a current of 0.1C down to 0.01V, then converted to CV (constant voltage), and cut off at 0.01C. Discharging was performed in CC (constant current) mode with a current of 0.1C down to 1.5V.

[0201] Under the aforementioned charge-discharge conditions, the charge-discharge cycle was performed up to the second cycle, and the discharge capacity in the second cycle was measured. The results are shown in Table 2 below.

[0202] Experimental Example 6 - Evaluation of High-Frequency Characteristics Each of the coin half-cells in Examples 1 to 13 and Comparative Examples 1 to 6 was charged at room temperature under constant current (0.2C) and constant voltage (0.01V, 0.01C cut-off) conditions, then rested for 10 minutes, and discharged under constant current (3.0C) conditions until the voltage reached 1.5V.

[0203] The discharge capacity and capacity retention rate after the aforementioned charge and discharge were measured, and the results are shown in Table 2 below.

[0204] [Table 2]

[0205] As can be seen from Tables 1 and 2 above, the carbon nanotube dispersions produced by Production Examples 1 to 13, which include the first and second dispersants and storage stabilizers, were found to have superior dispersibility and long-term storage stability compared to Comparative Production Examples 1 to 6.

[0206] Furthermore, it was confirmed that the secondary batteries of Examples 1 to 13, which contain the carbon nanotube dispersions produced by Manufacturing Examples 1 to 13, exhibit superior initial discharge capacity and high-rate characteristics compared to the secondary batteries of Comparative Examples 1 to 6, which contain the carbon nanotube dispersions produced by Comparative Manufacturing Examples 1 to 6.

Claims

1. Carbon nanotubes and A first dispersant surrounding the surface of the carbon nanotube, A second dispersant that introduces a negative charge to the surface of the carbon nanotube, A storage stabilizer having electrostatic repulsion with the aforementioned negative charge, Includes, The second dispersant contains an anionic polymer. Carbon nanotube dispersion.

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

3. The phenolic compounds have a weight-average molecular weight of 200 g / mol to 3,000 g / mol. The carbon nanotube dispersion according to claim 2.

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

5. The storage stabilizer is present in an amount of 1 to 10 parts by weight per 100 parts by weight of carbon nanotubes. The carbon nanotube dispersion according to claim 1.

6. The carbon nanotube is a single-walled carbon nanotube. The carbon nanotube dispersion according to claim 1.

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

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

9. A step of producing a mixture by mixing a first dispersant containing carbon nanotubes and a nonionic polymer, a second dispersant containing an anionic polymer, a storage stabilizer containing a phenolic compound containing two or more aromatic rings, and an aqueous solvent, The steps include milling and crushing the aforementioned mixture, The step of dispersing the mixture, including, A method for producing a carbon nanotube dispersion.

10. The mixture is crushed so that the average particle size is less than 100 μm. A method for producing a carbon nanotube dispersion according to claim 9.

11. Electrode active material and, Binder and, Carbon nanotube dispersion, Includes, The carbon nanotube dispersion comprises carbon nanotubes, a first dispersant surrounding the surface of the carbon nanotubes, a second dispersant introducing a negative charge to the surface of the carbon nanotubes, and a storage stabilizer having electrostatic repulsion with the negative charge. The second dispersant contains an anionic polymer. Electrode slurry composition.

12. Electrodes and, Separation membrane and Electrolyte and Includes, The electrode comprises an electrode active material, a binder, and a conductive material. The conductive material is manufactured from a carbon nanotube dispersion. The carbon nanotube dispersion comprises carbon nanotubes, a first dispersant surrounding the surface of the carbon nanotubes, a second dispersant introducing a negative charge to the surface of the carbon nanotubes, and a storage stabilizer having electrostatic repulsion with the negative charge. The second dispersant contains an anionic polymer. Secondary battery.

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