Carbon nanotube dispersion and preparation method thereof, electrode slurry composition and secondary battery

Abstract

The present invention provides a carbon nanotube dispersion, a method for preparing the same, an electrode slurry composition comprising the carbon nanotube dispersion, and a secondary battery, the carbon nanotube dispersion comprising: carbon nanotubes; a first dispersant surrounding the surface of the carbon nanotubes; a second dispersant for introducing charges to the surfaces of the carbon nanotubes; and a storage stabilizer having an electrostatic repulsive force to the charge.

Description

Technical Field

[0001] The present invention relates to a carbon nanotube dispersion, a method for preparing the same, an electrode paste composition including the carbon nanotube dispersion, and a secondary battery. Background Art

[0002] Due to the rapid growth in the use of fossil fuels, the demand for alternative or clean energy is increasing day by day. Currently, a representative example of an electrochemical device using electrochemical energy is a secondary battery, and its application fields are gradually expanding. A secondary battery is a battery that can be repeatedly used through a discharging process (in which chemical energy is converted into electrical energy) and a charging process (in the reverse direction). A secondary battery may include a cathode, an anode, an electrolyte, and a separator. The cathode and the anode generally may include an electrode current collector and an electrode active material layer formed on the electrode current collector. The electrode active material layer may be manufactured by applying an electrode paste composition including an electrode active material, a conductive agent, a binder, etc. on the electrode current collector, drying the electrode paste composition, and then calendering the electrode paste composition.

[0003] The conductive agent is intended to improve the conductivity of the electrode active material, and currently mainly uses a dot-like conductive agent such as carbon black. However, the dot-like conductive agent does not have a good effect in improving the conductivity, so the dot-like conductive agent should be used in excess to obtain a sufficient effect, which will reduce the content of the electrode active material and thus reduce the battery capacity.

[0004] To solve this problem, people are actively trying to apply highly conductive carbon nanotubes (CNTs) as the conductive agent.

[0005] However, due to the characteristics of carbon nanotubes, the dispersibility of carbon nanotubes in the paste is poor, which deteriorates the manufacturing processability of the secondary battery, and as the cycle of the secondary battery progresses, the conductivity decreases, resulting in the deterioration of the performance of the secondary battery. Summary of the Invention

[0006] Technical Problem

[0007] Therefore, the present invention is proposed in view of the above problems, and an object of the present invention is to provide a carbon nanotube dispersion having excellent dispersibility and excellent long-term storage stability and capable of improving the performance of a secondary battery, a method for preparing the carbon nanotube dispersion, an electrode paste composition including the carbon nanotube dispersion, and a secondary battery.

[0008] Technical Solution

[0009] According to one aspect of the present invention, the above and other objects can be achieved by providing a carbon nanotube dispersion, which includes: 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 that has an electrostatic repulsive force against the charges.

[0010] In an embodiment of the present invention, the storage stabilizer may include a phenolic compound having two or more aromatic rings.

[0011] In an embodiment of the present invention, the phenolic compound may have a weight average molecular weight of 200 g / mol to 3,000 g / mol.

[0012] In an embodiment of the present invention, the content of the storage stabilizer may account for 0.01 wt% to 0.1 wt% of the total weight of the carbon nanotube dispersion.

[0013] In an embodiment of the present invention, the content of the storage stabilizer may account for 1 part by weight to 10 parts by weight of 100 parts by weight of the carbon nanotubes.

[0014] In an embodiment of the present invention, the carbon nanotubes may be single-walled carbon nanotubes.

[0015] In an embodiment of the present invention, the first dispersant may include a nonionic polymer.

[0016] In an embodiment of the present invention, the second dispersant may include an ionic polymer.

[0017] In an 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.

[0018] According to another aspect of the present invention, a method for preparing a carbon nanotube dispersion is provided, which includes: mixing carbon nanotubes, a first dispersant, a second dispersant, a storage stabilizer, and an aqueous solvent to prepare a mixture, where the first dispersant includes a nonionic polymer, the second dispersant includes an ionic polymer, and the storage stabilizer includes a phenolic compound having two or more aromatic rings; grinding and pulverizing the mixture; and dispersing the mixture.

[0019] According to an embodiment of the present invention, the mixture may be crushed so that the average particle diameter of the mixture is less than 100 μm.

[0020] According to another aspect of the present invention, there is provided an electrode paste composition, which includes: an electrode active material; a binder; and a carbon nanotube dispersion, wherein the carbon nanotube dispersion includes: 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 that has an electrostatic repulsive force against the charges.

[0021] According to another aspect of the present invention, there is provided a secondary battery, which includes: an electrode; a separator; and an electrolyte, wherein the electrode includes: an electrode active material, a binder, and a conductive agent, wherein the conductive agent is made from a carbon nanotube dispersion, and the carbon nanotube dispersion includes: 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 that has an electrostatic repulsive force against the charges.

[0022] Advantageous Effects

[0023] The carbon nanotubes in the carbon nanotube dispersion according to the present invention are stabilized by the first dispersant and the second dispersant, and charges are introduced to the surface of the carbon nanotubes, so that the dispersibility of the carbon nanotubes can be improved.

[0024] In addition, the carbon nanotube dispersion according to the present invention includes a storage stabilizer that has an electrostatic repulsive force against the charges introduced to the surface of the carbon nanotubes. By this storage stabilizer, the repulsive force between the carbon nanotubes with surface-modified charges can be induced, so that the long-term storage stability of the carbon nanotube dispersion can be improved.

[0025] In addition, since the carbon nanotube dispersion according to the present invention includes: a first dispersant, a second dispersant, and a storage stabilizer, and thus, the carbon nanotube dispersion has an appropriate initial viscosity range, the increase in viscosity over time can be minimized.

[0026] In addition, the carbon nanotube dispersion has excellent dispersibility and long-term storage stability, and thus, the carbon nanotube dispersion can include a high content of single-walled carbon nanotubes with electrical conductivity, so that the initial discharge capacity and high-rate characteristics of the secondary battery manufactured using the carbon nanotube dispersion can be improved.

[0027] Best Mode

[0028] The structural or functional descriptions of the embodiments disclosed in this specification or the application are merely shown to explain the embodiments according to the technical idea of the present invention. The embodiments according to the technical idea of the present invention can be implemented in various forms other than the embodiments disclosed in this specification or the application, and it should not be understood that the technical idea of the present invention is limited to the embodiments disclosed in this specification or the application.

[0029] In this specification or this application, when "comprising" a certain component, unless there is a different disclosure, this means including only this component or this component may further include other components. In addition, it should be understood that unless otherwise specified, all numerical ranges representing physical property values, dimensions, etc. of the components described in this specification or this application are all modified by the term "about" in all cases. In addition, in this specification or this application, "ppm" is based on weight. In addition, in this specification or this application, "A and / or B" means "A, B, or A and B".

[0030] Hereinafter, a carbon nanotube dispersion according to the present invention, a method for preparing the same, an electrode paste composition containing the carbon nanotube dispersion, and a secondary battery will be described.

[0031] Generally, a conductive material is used to improve the conductivity of the electrode active material used in a secondary battery, and the conductive material can be mixed with the electrode active material in a dispersed state in which a dispersant and a solvent are mixed.

[0032] In order to further improve the conductivity of the electrode active material, carbon nanotubes have attracted attention as a conductive material. However, different from dot-like conductive materials such as carbon black, carbon nanotubes as linear conductive materials have a high specific surface area, and carbon nanotubes have a problem of aggregation due to van der Waals attraction between carbon nanotubes.

[0033] In particular, single-walled carbon nanotubes among carbon nanotubes have excellent conductivity, but due to their high specific surface area and strong attraction, they have problems of easy aggregation and very low dispersibility.

[0034] The inventors combined a first dispersant capable of stabilizing carbon nanotubes with a second dispersant capable of introducing charges to the surface of carbon nanotubes, and the inventors noticed that when there is a repulsive force preventing the mutual aggregation between the carbon nanotubes with charges introduced, the dispersibility and long-term storage stability can be improved.

[0035] Therefore, it is conceivable that in the case where the dispersion contains a substance having an electrostatic repulsive force between the carbon nanotubes introducing charges, the dispersibility and long-term storage stability can be improved, and thus, a high content of carbon nanotubes can be included in the dispersion, thereby improving the performance of a secondary battery including carbon nanotubes as a conductive agent.

[0036] The carbon nanotube dispersion according to the present invention includes carbon nanotubes.

[0037] The carbon nanotubes may have a cylindrical shape in which the graphite sheets have a nanoscale diameter; and the carbon nanotubes may also have a secondary structure in which a plurality of carbon nanotubes are arranged or aggregated. When the carbon nanotubes are used as a conductive agent, the conductivity of the electrode can be improved.

[0038] 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% of the total weight of the carbon nanotube dispersion. When this range is satisfied, an increase in the viscosity of the carbon nanotube dispersion can be suppressed, and when the carbon nanotubes are used as a conductive agent for a secondary battery, it can have an appropriate adhesive force like a binder during electrode manufacturing, and it has an appropriate loading amount, so that the processing efficiency can be improved.

[0039] The carbon nanotubes may be multi-walled carbon nanotubes (MWCNT) (the multi-walled carbon nanotubes having a large number of bonds forming the walls), thin-walled carbon nanotubes (TWCNT), or single-walled carbon nanotubes (SWCNT).

[0040] Preferably, the carbon nanotubes may be single-walled carbon nanotubes. Compared with multi-walled carbon nanotubes, single-walled carbon nanotubes have excellent conductivity, thereby enabling the improvement of the initial efficiency, life characteristics, and high-rate discharge characteristics of the secondary battery.

[0041] Single-walled carbon nanotubes have high cohesive force, so the dispersion containing single-walled carbon nanotubes exhibits poor long-term storage stability, and it is difficult to commercialize single-walled carbon nanotubes as a conductive agent. However, the present inventors have confirmed that when a first dispersant (the first dispersant can stabilize single-walled carbon nanotubes), a second dispersant (the second dispersant can introduce charges to the surface of single-walled carbon nanotubes), and a storage stabilizer (the storage stabilizer has an electrostatic repulsive force against the charges formed on the surface of single-walled carbon nanotubes) are used together with single-walled carbon nanotubes, even when using single-walled carbon nanotubes with high cohesive force, excellent dispersibility and long-term storage stability are exhibited, so it is possible to commercialize them as a conductive agent.

[0042] Single-walled carbon nanotubes may have the following BET specific surface area: 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. The BET specific surface area can be measured by nitrogen adsorption at liquid nitrogen temperature (77K) using BELSORP-mini II of BEL Japan Inc.

[0043] Single-walled carbon nanotubes may have the following powder resistance at a rolling density of 1 g / cc or greater: 0.001 Ω·cm or less, 0.0009 Ω·cm or less, 0.0008 Ω·cm or less, or 0.0007 Ω·cm or less. When the powder resistance value is low, the conductivity of single-walled carbon nanotubes can be improved. Therefore, when this range is satisfied, the performance of secondary batteries using single-walled carbon nanotubes as a conductive agent can be improved.

[0044] The powder resistance can be measured as the powder resistance value at a rolling density of 1 g / cc using a powder resistance meter (MCP-PD51) equipped with a 4-pin probe.

[0045] The length of single-walled carbon nanotubes can 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.

[0046] The average diameter (D 50 ) of single-walled carbon nanotubes can 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.

[0047] An atomic force microscope (AFM) can be used to measure the length and diameter. The length can correspond to the average of the top 100 single-walled carbon nanotubes with larger average lengths and the bottom 100 single-walled carbon nanotubes, and the diameter can correspond to the average of the top 100 single-walled carbon nanotubes with larger average diameters and the bottom 100 single-walled carbon nanotubes.

[0048] In single-walled carbon nanotubes, a thermogravimetric analyzer can be used to measure the weight change depending on the temperature change. The temperature can be increased at intervals of 10 °C in the temperature range of 40 °C to 1,000 °C under a nitrogen atmosphere while measuring the temperature change.

[0049] The temperature of thermal decomposition of single-walled carbon nanotubes can be measured using a thermogravimetric analyzer. The purity of single-walled carbon nanotubes can be evaluated by measuring the weight change of single-walled carbon nanotubes depending on the temperature change.

[0050] The weight change of single-walled carbon nanotubes measured by a thermogravimetric analyzer at 40 °C to 300 °C can be 2% or less, 1.9% or less, 1.8% or less, 1.7% or less, or 1.5% or less.

[0051] The weight change of single-walled carbon nanotubes measured by a thermogravimetric analyzer at 300 °C to 550 °C can be 2% or less, 1.5% or less, 1.3% or less, 1.2% or less, or 1% or less.

[0052] The weight change of single-walled carbon nanotubes measured by a thermogravimetric analyzer at 40 °C to 550 °C can be 2% or less than 2%, 1.98% or less than 1.98%, 1.97% or less than 1.97%, 1.96% or less than 1.96%, or 1.95% or less than 1.95%.

[0053] The initial temperature of thermal decomposition of single-walled carbon nanotubes measured by a thermogravimetric analyzer can be 500 °C to 700 °C, 520 °C to 700 °C, 530 °C to 650 °C, or 550 °C to 600 °C. The initial temperature of thermal decomposition can be obtained from the peak point obtained by differentiating the temperature-weight graph measured by a thermogravimetric analyzer.

[0054] The content of the residue in single-walled carbon nanotubes after completion of thermal decomposition measured using a thermogravimetric analyzer can 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.

[0055] When the weight change, initial thermal decomposition temperature, and residue of the single-walled carbon nanotubes are within the above ranges, impurities are minimized and purity is improved. When the single-walled carbon nanotubes are used as a conductive agent, the conductivity can be increased, enabling the performance of the secondary battery to be improved. In addition, the dispersibility can be increased, enabling the coating property and processability to be improved.

[0056] The single-walled carbon nanotubes can be in a bundle shape or rope-shaped bundle in which multiple single-walled carbon nanotubes are arranged in a certain direction, or the single-walled carbon nanotubes can also be in a spherical wound shape or potato-shaped wound shape in which multiple single-walled carbon nanotubes are wound together without a certain direction.

[0057] The single-walled carbon nanotubes can be manufactured by a step of synthesizing the single-walled carbon nanotubes and a step of purifying the synthesized single-walled carbon nanotubes.

[0058] The single-walled carbon nanotubes can be synthesized by a laser ablation method. The laser ablation method can refer to a process of irradiating a laser beam onto a mixture of a carbon-containing raw material and a catalyst in an inert gas atmosphere, and the single-walled carbon nanotubes can be synthesized by this process. The inert gas can be argon or nitrogen. The carbon-containing raw material can be graphite. The catalyst can be a metal catalyst. The intensity of the laser beam can be 100 mJ / cm 2 to 300 mJ / cm 2 、110 mJ / cm 2 to 300 mJ / cm 2 、110 mJ / cm 2 to 290 mJ / cm 2 、or 120 mJ / cm 2 to 280 mJ / cm 2 .

[0059] Single-walled carbon nanotubes can be synthesized by an arc discharge method. The arc discharge method may refer to the process of causing an arc discharge between paired electrodes to deposit the evaporated material generated from the anode, and single-walled carbon nanotubes can be synthesized by the above process. The anode may include a carbon-containing raw material. The carbon-containing raw material may be graphite. The anode may include a transition metal. The transition metal may include at least one of iron, cobalt, yttrium, and nickel. The graphite may be in the form of a rod with pores. The graphite pores may be mixed with a transition metal. The arc discharge method may be carried out in an inert gas atmosphere, or an inert gas and hydrogen atmosphere. The arc discharge method may be carried out in an atmosphere of a small amount of hydrocarbon gas. The hydrocarbon gas may include at least one of methane, ethylene, and acetylene. The paired electrodes may be spaced apart by a certain distance from each other. The paired electrodes may be spaced apart 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, and the DC power source in the DC arc discharge method may have a voltage range of 20 V to 70 V, 22 V to 70 V, 22 V to 65 V, or 25 V to 65 V. The DC power source in the DC arc discharge method may have a current range of 40 A to 120 A, 40 V to 115 V, 40 V to 100 V, or 45 V to 100 V.

[0060] Preferably, single-walled carbon nanotubes can be synthesized by a chemical vapor deposition method. The chemical vapor deposition method may refer to the process of thermally decomposing a gaseous hydrocarbon (such as methane, ethylene, or acetylene, benzene, toluene, or xylene) in the presence of a catalyst, and single-walled carbon nanotubes can be synthesized by this process. As the catalyst, nanoparticles loaded with iron, cobalt, nickel, molybdenum, etc. or alumina or silica loaded with nanoparticles can be used. The advantages of chemical vapor deposition are that it can conveniently control the diameter, length, density, structure, crystallinity, etc. of single-walled carbon nanotubes and can mass-produce high-purity single-walled carbon nanotubes.

[0061] The synthesized single-walled carbon nanotubes may include impurities. The impurities may include at least one of metal oxides, metals, and non-metals. The metal oxides may include cermets. The cermets may be derived from the catalyst support in the synthesis process of single-walled carbon nanotubes. The metals may include at least one of iron, cobalt, nickel, chromium, copper, manganese, nickel, and zinc. The non-metals may include sulfur. The metals and non-metals may be obtained from the catalyst in the synthesis process of single-walled carbon nanotubes.

[0062] Single-walled carbon nanotubes may be cut by nickel among impurities, the length of the single-walled carbon nanotubes may be shortened, or the surface of the single-walled carbon nanotubes may be oxidized, thereby deteriorating the electrical and mechanical properties. Nickel may damage the unique properties of single-walled carbon nanotubes. Therefore, it is more preferable to perform a process of purifying the synthesized single-walled carbon nanotubes to remove nickel. The BET specific surface area and nickel content in single-walled carbon nanotubes can be controlled not only according to the synthesis process of single-walled carbon nanotubes but also according to the process conditions for removing impurities.

[0063] The synthesized single-walled carbon nanotubes can be purified by physical or chemical methods.

[0064] Examples of physical methods include centrifugation, carbon nanotube dissolution, high-temperature annealing, and so on.

[0065] Centrifugation is a method of applying centrifugal force to a mixture of substances with different masses to separate the substances based on the difference in sedimentation rates. The amorphous carbon, carbon nanoparticles, and single-walled carbon nanotubes included in the synthesized single-walled carbon nanotubes can be separated by centrifugation.

[0066] Carbon nanotube dissolution can be carried out by introducing functional groups to the surface of single-walled carbon nanotubes, dissolving the single-walled carbon nanotubes in a solvent, and then separating the high-purity carbon nanotubes from impurities using filtration or chromatography.

[0067] High-temperature annealing is the following process in which, under inert gas or vacuum conditions, even at a high temperature of about 1500 °C or higher, carbon does not undergo a phase change, so that impurities formed on the single-walled carbon nanotubes can be removed by treating the single-walled carbon nanotubes at a high temperature higher than the vaporization temperature of the impurities under inert gas or vacuum conditions.

[0068] Examples of chemical methods include electrochemical oxidation, gas-phase oxidation, liquid-phase oxidation, etc.

[0069] Electrochemical oxidation can remove the amorphous carbon and impurities contained in the synthesized single-walled carbon nanotubes by electro-oxidizing the single-walled carbon nanotubes in a potassium hydroxide solution or a sulfuric acid solution.

[0070] Liquid-phase oxidation can react the synthesized single-walled carbon nanotubes with an oxidation solution to remove the amorphous carbon and impurities contained in the single-walled carbon nanotubes. As the oxidation solution, hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, etc. can be used. Liquid-phase oxidation can remove metal oxides and metals among the impurities contained in the single-walled carbon nanotubes. Liquid-phase oxidation can be carried out at about 20 °C to 25 °C. Previously, liquid-phase oxidation was carried out in a high-temperature range of about 50 °C to 70 °C, but during the purification process, the structure of the single-walled carbon nanotubes may be damaged (for example, the cut openings and end openings may be damaged), and there is a problem that the oxidation solution reactants exist as secondary impurities on the single-walled carbon nanotubes. Therefore, when liquid-phase oxidation satisfies this temperature range, the problem of secondary impurities appearing on the purified single-walled carbon nanotubes can be suppressed, and the structural stability of the purified single-walled carbon nanotubes can be improved.

[0071] Gas-phase oxidation can remove the amorphous carbon and impurities contained in the synthesized single-walled carbon nanotubes by performing heat treatment on the synthesized single-walled carbon nanotubes in an oxidation gas atmosphere at a temperature range of about 700 °C to 1000 °C. As the oxidation gas, air, chlorine gas, a mixture of water vapor and hydrogen chloride, hydrogen sulfide, argon, etc. can be used.

[0072] The step of performing purification 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.

[0073] The step of performing purification 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.

[0074] After the step of performing purification, the step of cooling to room temperature in a vacuum state can be carried out.

[0075] By the step of performing purification, the impurity - metal contained in the single-walled carbon nanotubes can be effectively removed.

[0076] The carbon nanotube dispersion according to the present invention includes a first dispersant surrounding the surface of the carbon nanotubes.

[0077] The first dispersant may include a nonionic polymer.

[0078] The first dispersant may include one or more of the groups selected from the following as the nonionic polymer: polyethylene glycol, polypropylene glycol, polybutylene glycol, polyvinyl alcohol, polyvinylpyrrolidone, polyacrylic hydrazide, poly-N-vinyl-5-methyloxazolidone, N-alkyl polyimine, N-acetyl polyimine, polyacrylamide, poly-L-lysine, polyethyleneimine, and polyethylene glycol - polypropylene glycol copolymer.

[0079] Preferably, the first dispersant may include polyvinylpyrrolidone as a nonionic polymer, and the polyvinylpyrrolidone has 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.

[0080] When this range is satisfied, the phenomenon that the first dispersant is eluted during electrode manufacturing can be suppressed, the blending with other materials in the carbon nanotube dispersion can be improved, the dispersibility can be enhanced, and the viscosity change caused by time variation can be minimized.

[0081] The nonionic polymer may be in the form of a random coil.

[0082] The nonionic polymer may be in the form of a random coil, and the random coil includes a main chain exhibiting hydrophobicity and side chains exhibiting hydrophilicity.

[0083] The first dispersant includes a nonionic polymer in the form of a random coil having hydrophobicity and hydrophilicity, thereby stably bonding to the carbon nanotubes and surrounding the surface of the carbon nanotubes. The cohesive force between the carbon nanotubes can be reduced by the first dispersant, enabling the carbon nanotubes to be smoothly dispersed.

[0084] The content of the first dispersant may account for 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% of the total weight of the carbon nanotube dispersion. When this range is satisfied, the dispersion effect of the carbon nanotubes can be enhanced, and the carbon nanotube dispersion can have an appropriate initial viscosity.

[0085] The carbon nanotube dispersion according to the present invention includes a second dispersant that introduces charges to the surface of the carbon nanotubes.

[0086] The second dispersant may include an ionic polymer.

[0087] The second dispersant may include a cationic polymer and / or an anionic polymer.

[0088] Preferably, the second dispersant may include an anionic polymer.

[0089] The second dispersant may include one or more of the groups selected from the following as an anionic polymer: polyacrylic acid (salt), polyacrylic acid maleic acid (salt), sulfonic acid (salt), sulfonate ester, phosphoric acid (salt), phosphate ester, acrylic acid-styrene copolymer, polyacrylic acid-styrene copolymer, polyacrylamide-acrylic acid copolymer, polyacrylic acid-sulfonic acid copolymer, and polyacrylic acid-maleic acid copolymer.

[0090] 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 preferred that the weight average molecular weight of the anionic polymer is less than the weight average molecular weight of the nonionic polymer included in the first dispersant.

[0091] When this range is satisfied, a strong interaction can be generated with the carbon nanotubes, so that charges can be smoothly introduced to the surface of the carbon nanotubes. Therefore, the dispersibility can be improved, and the viscosity change caused by the change over time can be minimized.

[0092] The second dispersant may include an anionic polymer having an aromatic ring.

[0093] The second dispersant may include an anionic polymer having an aromatic ring and a sulfonic acid (salt) group. The anionic polymer having a sulfonic acid (salt) group may include benzene.

[0094] The anionic polymer may have at least two or more aromatic rings.

[0095] The second dispersant may include an anionic polymer having at least two or more aromatic rings and a sulfonic acid (salt) group.

[0096] The anionic polymer having a sulfonic acid (salt) group may include one or more of the groups selected from the following: naphthalene, pyrene, anthracene, and phenanthrene.

[0097] The second dispersant may bind to the carbon nanotubes to change the electrical properties of the surface of the carbon nanotubes. Charges can be introduced to the surface of the carbon nanotubes through the second dispersant, and negative charges can be introduced to the surface of the carbon nanotubes through the second dispersant. Since charges are introduced to the surface of the carbon nanotubes through the second dispersant, the charges formed on the surface of the carbon nanotubes can generate an electrostatic repulsive force with the storage stabilizer described below.

[0098] In addition, due to the steric effect generated by the aromatic ring, the second dispersant can reduce the cohesive force between the carbon nanotubes bound with the second dispersant.

[0099] The content of the second dispersant can account for 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% of the total weight of the carbon nanotube dispersion. When this range is satisfied, the dispersion effect of the carbon nanotubes can be further improved.

[0100] The ratio of the content of the first dispersant to the content of the second dispersant can 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.

[0101] The ratio of the carbon nanotubes to the total content of the first dispersant and the second dispersant can 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.

[0102] When this range is satisfied, the charge caused by the second dispersant can be introduced onto the surface of the carbon nanotubes stabilized by the first dispersant in a balanced manner, so that the dispersibility of the carbon nanotubes can be improved, and the performance of the secondary battery including the carbon nanotubes can be improved.

[0103] The carbon nanotube dispersion according to the present invention includes a storage stabilizer that has an electrostatic repulsive force against the charge formed on the surface of the carbon nanotubes.

[0104] The storage stabilizer can inhibit the phenomenon that the first dispersant and the second dispersant not bonded to the carbon nanotubes aggregate with each other, and can inhibit the phenomenon that the carbon nanotubes bonded to the first dispersant and the second dispersant aggregate with each other.

[0105] The storage stabilizer can induce a repulsive force between the carbon nanotubes with surface-modified charges. The storage stabilizer can induce an electrostatic repulsive force between the following carbon nanotubes, the carbon nanotubes are dispersed by the first dispersant and the second dispersant and the surface of the carbon nanotubes is modified with negative charges.

[0106] The storage stabilizer can include phenolic compounds having two or more aromatic rings. The storage stabilizer can include phenolic single-molecule compounds containing two or more aromatic rings and carrying negative charges.

[0107] The negative charge carried by the phenolic compound has the same polarity as the negatively charged carbon nanotubes with surface modification, enabling the induction of electrostatic repulsion between the carbon nanotubes.

[0108] Therefore, the carbon nanotube dispersion can have an appropriate initial viscosity range and minimize the increase in viscosity over time, thereby enabling the improvement of long-term storage stability.

[0109] The phenolic compound can include one or more of the groups selected from the following: tannic acid, luteolin, baicalin, taxifolin, myricetin, quercetin, rutin, catechin, epigallocatechin gallate, epicatechin gallate, butane, and piceatannol.

[0110] The weight-average molecular weight of the phenolic compound can be 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.

[0111] When this range is satisfied, the phenomenon of elution of the storage stabilizer during electrode manufacturing can be inhibited, and the coatability and processability can be improved.

[0112] The content of the storage stabilizer can be 0.01 wt% to 0.1 wt%, 0.01 wt% to 0.08 wt%, 0.01 wt% to 0.07 wt%, or 0.02 wt% to 0.07 wt% of the total weight of the carbon nanotube dispersion. The content of the storage stabilizer can 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 of 100 parts by weight of the carbon nanotubes.

[0113] When this range is satisfied, the electrostatic repulsion between the carbon nanotubes can be induced more effectively, and thus the increase in viscosity over time can be minimized.

[0114] Relative to the total weight of the carbon nanotube dispersion, the total content of the first dispersant, the second dispersant, and the storage stabilizer can 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%.

[0115] When this range is satisfied, smooth dispersion between the high-content carbon nanotubes in the carbon nanotube dispersion can be achieved, enabling the further improvement of the performance of the secondary battery including the high-content carbon nanotubes.

[0116] The storage stabilizer can include silicate. The storage stabilizer can include layered silicate. When the storage stabilizer includes layered silicate, the dispersibility of the carbon nanotubes can be further improved.

[0117] The carbon nanotube dispersion according to the present invention may include a solvent. When the carbon nanotubes are mixed with an electrode active material or the like to be used as an electrode paste composition, the solvent can inhibit the aggregation between the carbon nanotubes or the aggregation between the carbon nanotubes and the electrode active material by pre-dispersing the carbon nanotubes.

[0118] The solvent may be an aqueous solvent. The aqueous solvent may be water.

[0119] The solvent may be an aqueous solvent, an organic solvent, or a mixture thereof.

[0120] Examples of the organic solvent may include: amide polar organic solvents such as dimethylformamide (DMF), diethylformamide, dimethylacetamide (DMAc), N-methylpyrrolidone (NMP); alcohols such as methanol, ethanol, 1-propanol, 2-propanol (isopropanol), 1-butanol (n-butanol), 2-methyl-1-propanol (isobutanol), 2-butanol (sec-butanol), 1-methyl-2-propanol (tert-butanol), pentanol, hexanol, heptanol, or octanol; diols such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, 1,3-propanediol, 1,3-butanediol, 1,5-pentanediol, or hexanediol; polyols such as glycerol, trimethylolpropane, pentaerythritol, or sorbitol; ethylene 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 isopropyl ketone, or cyclopentanone; esters such as ethyl acetate, γ-butyrolactone, and ε-propiolactone; and so on. A mixture of one or more of them may also be used.

[0121] 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 this range is satisfied, the aggregation phenomenon of the carbon nanotubes can be inhibited, and the process of repeatedly introducing and dispersing the carbon nanotubes can be minimized, so that the processing efficiency can be improved.

[0122] The viscosity can be measured using a B-type viscometer or a rotating cylinder viscometer, and specifically, a DV2TLV viscometer (Brookfield) can be used for measurement.

[0123] According to Equation 1 below, the viscosity change of the carbon nanotube dispersion can be 20% or less, 18% or less, 16% or less, 14% or less, 12% or less, or 5% or less. When this range is satisfied, the increase in viscosity of the carbon nanotube-containing dispersion over time can be minimized, thereby enabling the improvement of long-term storage stability.

[0124] [Equation 1]

[0125] Viscosity change rate (%) = (viscosity after 7 days - initial viscosity) / initial viscosity × 100

[0126] The pH of the carbon nanotube dispersion at room temperature can be 3 to 10, 4 to 10, 4 to 9, 5 to 9, 5 to 8, or 6 to 8. When this range is satisfied, aggregation due to hydrogen bonding can be inhibited.

[0127] The absorbance of the carbon nanotube dispersion can be measured. Absorbance is an index indicating the degree of light absorption. Absorbance is proportional to the concentration of the substance, and a high absorbance of the carbon nanotube dispersion can indicate that the carbon nanotubes capable of absorbing light are uniformly dispersed at a high concentration. That is, absorbance can be an index of the dispersibility of the carbon nanotubes included in the carbon nanotube dispersion.

[0128] The absorbance of the carbon nanotube dispersion can be 0.1 or greater to 10 or less, 0.15 or greater to 10 or less, 0.15 or greater to 5 or less, or 0.2 or greater to 5 or less. When this range is satisfied, the aggregates included in the carbon nanotube dispersion can be minimized, high-purity carbon nanotubes can be included in the carbon nanotube dispersion, and excellent dispersibility can be provided. The absorbance can be measured using a spectrophotometer in the wavelength range of 550 nm.

[0129] A method for preparing the carbon nanotube dispersion according to the present invention includes: a step of mixing carbon nanotubes, a first dispersant, a second dispersant, a storage stabilizer, and an aqueous solvent to prepare a mixture, wherein the first dispersant includes a nonionic polymer, the second dispersant includes an ionic polymer, and the storage stabilizer includes a phenolic compound having two or more aromatic rings; a step of grinding and pulverizing the mixture; and a step of dispersing the mixture.

[0130] The preparation method includes a step of mixing the carbon nanotubes, the first dispersant, the second dispersant, the storage stabilizer, and the aqueous solvent described above to prepare a mixture.

[0131] The step of preparing the mixture can be performed at a temperature at which the properties of the carbon nanotubes, the first dispersant, the second dispersant, and the storage stabilizer do not change.

[0132] The step of preparing 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.

[0133] The preparation method includes the step of grinding and pulverizing the mixture. Through this step, the particle size distribution of the carbon nanotubes included in the mixture can be arranged.

[0134] This step can be carried out using a high-shear stirrer. This step can use a stirrer at 1,000 rpm to 10,000 rpm, 2,000 rpm to 10,000 rpm, 5,000 rpm to 10,000 rpm or 7,000 rpm to 10,000 rpm for 5 minutes to 60 minutes, 5 minutes to 50 minutes, 10 minutes to 50 minutes or 10 minutes to 30 minutes.

[0135] Through this step, the mixture can be pulverized so that the average particle diameter becomes less than 100 μm, less than 95 μm, less than 90 μm, or less than 80 μm. When this range is satisfied, the dispersibility of the carbon nanotubes can be further improved.

[0136] The preparation method includes the step of dispersing the mixture.

[0137] This step can be a step of redispersing the pre-dispersed mixture through a pulverization process under high-pressure conditions.

[0138] In this step, the process of grinding the mixture using a ball mill, bead mill, disk mill, basket mill or high-pressure homogenizer can be repeatedly carried out. Preferably, a high-pressure homogenizer can be used to carry out the process.

[0139] The grinding using a high-pressure homogenizer can be carried out under pressure conditions of 200 bar to 3,000 bar, 500 bar to 3,000 bar, 1,000 bar to 3,000 bar, or 1,000 bar to 2,000 bar.

[0140] The step of dispersing the mixture can be carried out 1 time to 30 times, 2 times to 30 times, 5 times to 30 times, 5 times to 20 times, or 5 times to 10 times.

[0141] The electrode paste composition according to the present invention includes an electrode active material, a binder, and a carbon nanotube dispersion, and the carbon nanotube dispersion includes: carbon nanotubes; a first dispersant that surrounds the surface of the carbon nanotubes; a second dispersant that introduces charge to the surface of the carbon nanotubes; and a storage stabilizer that has an electrostatic repulsive force against the charge.

[0142] The carbon nanotube dispersion may be the same as the carbon nanotube dispersion described above.

[0143] The electrode active material may be a cathode active material.

[0144] The cathode active material is a compound capable of reversibly inserting and extracting lithium, and specifically may include a lithium composite metal oxide containing lithium and one or more metals (such as cobalt, manganese, nickel, or aluminum).

[0145] The lithium composite metal oxide is lithium manganese oxide (e.g., LiMnO2, LiMn2O4, etc.), lithium cobalt oxide (e.g., LiCoO2, etc.), lithium nickel oxide (e.g., LiNiO2, etc.), lithium nickel manganese oxide (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 oxide (e.g., LiNi 1-Y1 Co Y1 O2 (where 0 < Y1 < 1), etc.), lithium manganese cobalt oxide (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 oxide (e.g., Li(Ni p Co q Mn r1 )O2 (where 0 < p < 1, 0 < q < 1, 0 < r1 < 1, p + q + r1 = 1) or Li(Ni p1 Co q1 Mn r2 )O4 (where 0 < p1 < 2, 0 < q1 < 2, 0 < r2 < 2, p1 + q1 + r2 = 2), etc.) and 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.), or one or more compounds thereof. Among them, from the perspective of improving the capacity characteristics and stability of the battery, the lithium composite metal oxide may be LiCoO2, LiMnO2, LiNiO2, lithium nickel manganese cobalt oxide (e.g., Li(Ni 0.6 Mn0.2 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.), lithium nickel cobalt aluminum oxide (e.g., Li(Ni 0.8 Co 0.15 Al 0.05 )O2, etc.). Considering the obvious improvement effect according to the control of the types and content ratios of the constituent elements forming the lithium composite metal oxide, the lithium composite metal oxide can be 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 0.8 Mn 0.1 Co 0.1 )O2, or a mixture of one or more of them.

[0146] The electrode active material can be an anode active material.

[0147] Relative to the total weight of the electrode paste composition, the anode active material can include the following contents: 90 wt% to 99 wt%, 91 wt% to 99 wt%, 92 wt% to 99 wt%, 94 wt% to 99 wt%, or 95 wt% to 95 wt%. When this range is satisfied, the charge / discharge capacity of the secondary battery can be improved.

[0148] The anode active material can include a carbon-based material. The carbon-based material can include natural graphite particles and artificial graphite particles. The anode active material can include a silicon-based material.

[0149] The anode active material can include a silicon-graphite composite. The weight ratio of silicon in the silicon-graphite composite can be 1 wt% to 70 wt%, 5 wt% to 70 wt%, 5 wt% to 50 wt%, 5 wt% to 40 wt%, or 10 wt% to 40 wt%. When this range is satisfied, the deterioration of the life characteristics of the secondary battery can be minimized, and the charge / discharge capacity can be significantly improved.

[0150] The silicon-based material may include one or more of the groups selected from the following: metallic silicon (Si), silicon oxide (SiOx, 0 < x < 2), silicon carbide (SiC), and Si-Y alloy (wherein Y is an element of the group selected from the following: 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 a group selected from the following: 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.

[0151] The silicon-based material may exhibit higher capacity characteristics than the carbon-based material. When the silicon-based material is included in the anode active material, the capacity characteristics can be improved. However, the problem with the silicon-based material is that, compared with the carbon-based material, the silicon-based material has a larger volume change during charging and discharging, thereby deteriorating the cycle characteristics. Therefore, when the carbon nanotube according to the present invention is used as the conductive material, the high electron transport path is improved compared with the conventional conductive material, so that the conductivity can be improved. In addition, the dispersibility is improved, so that the structural stability is improved. Therefore, when the anode active material includes the silicon-based material, not only the capacity characteristics can be improved, but also the cycle characteristics can be improved.

[0152] The binder can improve the adhesion between the electrode active materials or improve the adhesion between the electrode active material and the current collector. The binder may be polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, or polyacrylic acid, or various types of binder polymers (such as polymers in which hydrogen is replaced by Li, Na, or Ca) or various copolymers may be used.

[0153] Relative to the total weight of the electrode paste composition, the binder may include the following contents: 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%. When this range is satisfied, the effect as a binder can be excellent, and the unit volume capacity will not be reduced due to the decrease in the relative content of the electrode active material.

[0154] The electrode paste composition may include a solvent.

[0155] The solvent may mix the components in the electrode paste composition and control the viscosity. The solvent may be an organic solvent or water. The organic solvent such as N-methylpyrrolidone (NMP), dimethylformamide (DMF), acetone or dimethylacetamide, and these solvents may be used alone or in combination of two or more of them. Considering the coating thickness and manufacturing yield of the electrode paste composition, the solvent may be used in an amount such that the electrode active material, binder and carbon nanotube dispersion can be dissolved and dispersed.

[0156] The carbon nanotube dispersion may serve as a conductive agent. The carbon nanotube dispersion may serve as a conductive agent, thereby improving the initial discharge capacity and high-rate characteristics of the secondary battery.

[0157] The conductive agent may improve the conductivity. The conductive agent may further include: graphite, such as natural graphite or artificial graphite; carbon black, such as acetylene black, Ketjenblack, channel black, furnace black, lamp black, or thermal black; metal powder, such as fluorocarbon, aluminum, or nickel powder; conductive whiskers, such as zinc oxide or potassium titanate; conductive metal oxides, such as titanium oxide; or conductive materials, such as polyphenylene derivatives.

[0158] 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 agent. The conductive agent is made of a carbon nanotube dispersion, and the carbon nanotube dispersion includes: 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 that has an electrostatic repulsive force against the charges.

[0159] The carbon nanotube dispersion may be the same as the carbon nanotube dispersion described above. The secondary battery includes carbon nanotubes as a conductive agent, and the carbon nanotubes are included in the carbon nanotube dispersion, so that the conductivity can be improved, and thus the initial efficiency, life characteristics and high-rate discharge characteristics of the secondary battery can be improved.

[0160] The electrode can be a cathode. The cathode can include the cathode active material, binder, and conductive agent described above. The cathode can be manufactured by applying a cathode slurry composition including the cathode active material onto a cathode current collector and then drying the cathode slurry composition to form a cathode active material layer. The cathode active material layer can be formed by applying the cathode slurry composition onto a cathode current collector and then drying the cathode slurry composition, or by applying the cathode slurry composition onto a separate support and then peeling the cathode slurry composition from the support and then laminating the obtained film onto the cathode current collector. After forming the cathode active material layer, a calendering process can be performed. Drying and calendering can be performed under appropriate conditions considering the properties of the electrode to be manufactured.

[0161] The cathode current collector is a metal having high conductivity to which the slurry of the cathode active material can easily adhere, and there is no particular limitation as long as it has high conductivity and does not cause chemical changes in the secondary battery. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. can be used. In addition, by forming fine irregularities on the surface of the cathode current collector, the adhesion of the cathode active material can be increased. The cathode current collector can be used in various forms such as a film, sheet, foil, net, porous body, foam, non-woven fabric, etc., and the cathode current collector can have a thickness of 3 μm to 500 μm.

[0162] The electrode can be an anode. The anode can include the anode active material, binder, and conductive agent described above. The anode can be manufactured by applying an anode slurry composition containing the anode active material onto an anode current collector and then drying the anode slurry composition to form an anode active material layer.

[0163] There is no particular limitation on the anode current collector as long as it has conductivity and does not cause chemical changes in the secondary battery, and for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., aluminum cadmium alloy, etc. can be used. In addition, the bonding force of the anode active material can be enhanced by forming fine irregularities on its surface, and the anode active material can be used in various forms such as a film, sheet, foil, net, porous body, foam, non-woven fabric, etc.

[0164] The separator can be disposed between the anode and the cathode. The separator can be configured to prevent an electrical short circuit between the cathode and the anode and to allow ion flow. The separator can include a porous polymer membrane or a porous non-woven fabric. The porous polymer membrane can be composed of a single layer or multiple layers, which includes an olefin polymer, such as an ethylene polymer, a propylene polymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, or an ethylene / methacrylate copolymer. The porous non-woven fabric can include high melting point glass fibers and polyethylene terephthalate fibers. However, the present invention is not limited thereto, and depending on the embodiment, the separator can be a high temperature resistant separator including ceramics (ceramic coated separator; CCS).

[0165] The electrolyte can be a non-aqueous electrolyte. The electrolyte can include a lithium salt and an organic solvent. The organic solvent can include 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, γ-butyrolactone, propylene sulfide, and tetrahydrofuran.

[0166] The cathode, anode, and separator can be made into an electrode assembly by winding, laminating, folding, or zigzag stacking processes. The electrode assembly can be provided together with the electrolyte and can be made into a secondary battery. The secondary battery can be any one of cylindrical, square, pouch-shaped, and button-type using a canister, but is not limited thereto.

[0167] The secondary battery can be used for high-power, large-capacity secondary batteries that require long life and excellent durability, or for modules or groups including multiple secondary batteries as unit cells.

[0168] Multiple secondary batteries can be made into a module. Multiple modules can be made into a group.

[0169] The group can be used as a power source for medium and large-sized devices that require high temperature stability, long cycle characteristics, high rate characteristics, etc. Examples of medium and large-sized devices include: power tools driven by an electric motor; electric vehicles, which include electric vehicles (EV), hybrid electric vehicles (HEV), and plug-in hybrid electric vehicles (PHEV); electric two-wheel vehicles, which include electric bicycles (E-bike) and electric scooters (E-scooter); electric golf carts; electric trucks; electric commercial vehicles and power storage systems. Detailed Description

[0170] Hereinafter, the present invention will be described in more detail based on examples and comparative examples. However, the following examples and comparative examples are only examples for more detailed explanation of the present invention, and the present invention is not limited by the following examples and comparative examples.

[0171] Preparation Example

[0172] Preparation Example 1

[0173] 200 mg of single-walled carbon nanotubes were prepared by chemical vapor deposition (CVD) using a catalyst. Next, the single-walled carbon nanotubes were loaded into a reactor.

[0174] Next, the reactor was purified at about 1000 °C for 60 minutes under an argon atmosphere and vacuum conditions, and then cooled to room temperature, thereby preparing single-walled carbon nanotubes having a specific surface area of about 1557 m 2 / g.

[0175] Using water as a solvent, the following mixture was prepared, in which single-walled carbon nanotubes: first dispersant (polyvinylpyrrolidone, Mw 17,000 g / mol): second dispersant (polynaphthalenesulfonate, Mw 5,000 g / mol): storage stabilizer (tannic acid, Mw 1,700 g / mol) were mixed at a weight ratio of 26:19.5:19.5:1.

[0176] Next, the mixture was treated with a stirrer at 8,000 rpm for 20 minutes, and the particles included in the mixture were crushed so that the average particle size of the particles included in the mixture was less than about 100 μm.

[0177] Next, a carbon nanotube dispersion was prepared by treating 10 times under a pressure condition of 1,200 bar using a high-pressure homogenizer.

[0178] Preparation Example 2

[0179] A carbon nanotube dispersion was prepared in the same manner as Preparation Example 1, except that tannic acid at a weight ratio of 0.6 was used instead of tannic acid at a weight ratio of 1 used in Preparation Example 1 as a storage stabilizer.

[0180] Preparation Example 3

[0181] A carbon nanotube dispersion was prepared in the same manner as Preparation Example 1, except that tannic acid at a weight ratio of 0.4 was used instead of tannic acid at a weight ratio of 1 used in Preparation Example 1 as a storage stabilizer.

[0182] Preparation Example 4

[0183] A carbon nanotube dispersion was prepared in the same manner as in Preparation Example 1, except that tannic acid was used at a weight ratio of 1.2 as a storage stabilizer instead of tannic acid used at a weight ratio of 1 in Preparation Example 1.

[0184] Preparation Example 5

[0185] A carbon nanotube dispersion was prepared in the same manner as in Preparation Example 1, except that tannic acid was used at a weight ratio of 1.4 as a storage stabilizer instead of tannic acid used at a weight ratio of 1 in Preparation Example 1.

[0186] Preparation Example 6

[0187] A carbon nanotube dispersion was prepared in the same manner as in Preparation Example 1, except that epigallocatechin gallate was used as the storage stabilizer instead of tannic acid in Preparation Example 1.

[0188] Preparation Example 7

[0189] A carbon nanotube dispersion was prepared in the same manner as in Preparation Example 1, except that epicatechin gallate was used as the storage stabilizer instead of tannic acid in Preparation Example 1.

[0190] Preparation Example 8

[0191] A carbon nanotube dispersion was prepared in the same manner as Preparation Example 1, except that polyacrylic acid having a weight average molecular weight of about 1,500 g / mol at a weight ratio of 19.5 was used as the second dispersant instead of polynaphthalenesulfonate having a weight average molecular weight of about 5,000 g / mol at a weight ratio of 19.5 used in Preparation Example 1.

[0192] Preparation Example 9

[0193] A carbon nanotube dispersion was prepared in the same manner as Preparation Example 1 except that polyvinyl pyrrolidone having a weight average molecular weight of about 30,000 g / mol was used as the first dispersant instead of polyvinyl pyrrolidone having a weight average molecular weight of about 17,000 g / mol in Preparation Example 1.

[0194] Preparation Example 10

[0195] In addition to using 1160m 2 A carbon nanotube dispersion was prepared in the same manner as in Preparation Example 1, except that single-walled carbon nanotubes having a specific surface area of ​​200 Å / g (TUBALL, OCSiAl Corporation) were used instead of the single-walled carbon nanotubes prepared in Preparation Example 1.

[0196] Preparation Example 11

[0197] A carbon nanotube dispersion is prepared in the same manner as Preparation Example 1, except that tannic acid at a weight ratio of 0.16 is used instead of tannic acid at a weight ratio of 1 used in Preparation Example 1 as a storage stabilizer.

[0198] Preparation Example 12

[0199] A carbon nanotube dispersion is prepared in the same manner as Preparation Example 1, except that tannic acid at a weight ratio of 3 is used instead of tannic acid at a weight ratio of 1 used in Preparation Example 1 as a storage stabilizer.

[0200] Preparation Example 13

[0201] A carbon nanotube dispersion is prepared in the same manner as Preparation Example 1, except that polyvinylpyrrolidone having a weight average molecular weight of about 30,000 g / mol at a weight ratio of 29.26 is used instead of polyvinylpyrrolidone having a weight average molecular weight of about 17,000 g / mol at a weight ratio of 19.5 used in Preparation Example 1 as the first dispersant, and polynaphthalenesulfonate at a weight ratio of 9.74 is used instead of polynaphthalenesulfonate at a weight ratio of 19.5 used in Preparation Example 1 as the second dispersant.

[0202] Comparative Preparation Example 1

[0203] A carbon nanotube dispersion is prepared in the same manner as Preparation Example 1, except that tannic acid (storage stabilizer) of Preparation Example 1 is not used.

[0204] Comparative Preparation Example 2

[0205] A carbon nanotube dispersion is prepared in the same manner as Preparation Example 1, except that polyvinylpyrrolidone (first dispersant) and tannic acid (storage stabilizer) of Preparation Example 1 are not used, and polyacrylic acid having a weight average molecular weight of about 1,500 g / mol at a weight ratio of 19.5 is used instead of polynaphthalenesulfonate having a weight average molecular weight of about 5,000 g / mol at a weight ratio of 19.5 used in Preparation Example 1 as the second dispersant.

[0206] Comparative Preparation Example 3

[0207] A carbon nanotube dispersion is prepared in the same manner as Preparation Example 1, except that polyvinylpyrrolidone (first dispersant) and tannic acid (storage stabilizer) of Preparation Example 1 are not used, and polynaphthalenesulfonate at a weight ratio of 60 is used instead of polynaphthalenesulfonate at a weight ratio of 19.5 used in Preparation Example 1 as the second dispersant.

[0208] Comparative Preparation Example 4

[0209] A carbon nanotube dispersion was prepared in the same manner as Preparation Example 1, except that the polynaphthalenesulfonate (second dispersant) in Preparation Example 1 was not used.

[0210] Comparative Preparation Example 5

[0211] A carbon nanotube dispersion was prepared in the same manner as Preparation Example 1, except that polyvinylpyrrolidone used at a weight ratio of 40 was used instead of the polyvinylpyrrolidone used at a weight ratio of 19.5 in Preparation Example 1 as the first dispersant, and the polynaphthalenesulfonate (second dispersant) of Preparation Example 1 was not used.

[0212] Comparative Preparation Example 6

[0213] A carbon nanotube dispersion was prepared in the same manner as Preparation Example 1, except that the polyvinylpyrrolidone (first dispersant) in Preparation Example 1 was not used.

[0214] [Table 1]

[0215]

[0216] Example Example 1

[0217] <Anode manufacturing>

[0218] An anodic active material slurry comprising a silicon-graphite composite material, a carbon nanotube dispersion of Preparation Example 1, a carboxymethyl cellulose (CMC) thickener, and a styrene-butadiene rubber (SBR) binder at a weight ratio of 96.5:0.1:1.2:2.2 (silicon-graphite composite material: carbon nanotube dispersion of Preparation Example 1: carboxymethyl cellulose (CMC) thickener: styrene-butadiene rubber (SBR) binder) was coated on a Cu foil current collector having a thickness of about 10 μm to a thickness of about 30 μm, and then dried at 100 °C for about 12 hours to fabricate an anode.

[0219] <Secondary battery (button half-cell) manufacturing>

[0220] A metallic lithium foil of about 0.3 mm was used as the cathode, and a polyethylene separator was placed between the cathode and the anode. Next, EC and EMC were mixed at a ratio of 3:7 (EC:EMC), and 1 M LiPF6 (non-aqueous electrolyte) was injected therein to fabricate a button half-cell.

[0221] Examples 2 to 13 and Comparative Examples 1 to 6

[0222] A button half-cell was fabricated in the same manner as Example 1, except that each of the carbon nanotube dispersions shown in Table 2 below was used instead of the carbon nanotube dispersion in Preparation Example 1.

[0223] Experimental Example

[0224] Experimental Example 1 - Initial Viscosity

[0225] For each of the carbon nanotube dispersions of Preparation Examples 1 to 13 and Comparative Preparation Examples 1 to 6, the initial viscosity was measured at room temperature using a DV2T LV viscometer (Brookfield). The results are shown in Table 2 below.

[0226] Experimental Example 2 - Viscosity Change Rate

[0227] For each of the carbon nanotube dispersions of Preparation Examples 1 to 13 and Comparative Preparation Examples 1 to 6, the viscosity after 7 days was measured under the same conditions as in Experimental Example 1, and the viscosity change rate was calculated according to Equation 1 below. The results are shown in Table 2 below:

[0228] [Equation 1]

[0229] Viscosity change rate (%) = (Viscosity after 7 days - Initial viscosity) / Initial viscosity × 100 Experimental Example 3 - Dispersibility

[0230] For each of the carbon nanotube dispersions of Preparation Examples 1 to 13 and Comparative Preparation Examples 1 to 6, the zeta potential was measured. The evaluation was carried out according to the following criteria, and the results are shown in Table 2 below:

[0231] - ○: Absolute value exceeds 30 mV.

[0232] - △: Absolute value is 10 mV to 30 mV.

[0233] - ×: Absolute value is less than 10 mV.

[0234] Experimental Example 4 - Dispersion Stability

[0235] The carbon nanotube dispersions of each of Preparation Examples 1 to 13 and Comparative Preparation Examples 1 to 6 were placed in glass bottles, and then the presence or absence of aggregation was measured within 120 days. The evaluation was carried out according to the following criteria, and the results are shown in Table 2 below.

[0236] - ○: Aggregation occurs after 2 weeks

[0237] - △: Aggregation occurs within 1 to 2 weeks

[0238] - ×: Aggregation occurs within 1 week

[0239] Experimental Example 5 - Evaluation of Initial Discharge Capacity of Button Half-Cell Batteries

[0240] For each button half-cell battery in Examples 1 to 13 and Comparative Examples 1 to 6, charge it at a constant current (CC) mode with a current of 0.1C to 0.01V at room temperature, and then switch to constant voltage (CV) and cut off at 0.01C, and discharge it at a constant current (CC) mode with a current of 0.1C to 1.5V.

[0241] Under the above charging and discharging conditions, after performing charging and discharging up to the second cycle, measure the discharge capacity of the second cycle, and the results are shown in Table 2 below.

[0242] Experimental Example 6 - High-rate Characteristic Evaluation

[0243] For the button half-cell batteries in Examples 1 to 13 and Comparative Examples 1 to 6, charge them under the conditions of constant current (0.2C) and constant voltage (0.01V, cut off at 0.01C) at room temperature, and then let them stand for 10 minutes, and discharge them under the condition of constant current (3.0C) until reaching 1.5V.

[0244] Measure the discharge capacity and capacity retention rate after performing charging and discharging, and the results are shown in Table 2 below.

[0245] [Table 2]

[0246]

[0247] As shown in Table 1 and Table 2, it is confirmed that compared with Comparative Preparation Examples 1 to 6, the carbon nanotube dispersions (including the first dispersant, the second dispersant, and the storage stabilizer) according to Preparation Examples 1 to 13 have excellent dispersibility and long-term storage stability.

[0248] In addition, it is confirmed that compared with the secondary batteries of Comparative Examples 1 to 6 including the carbon nanotube dispersions according to Comparative Preparation Examples 1 to 6, the secondary batteries of Examples 1 to 13 including the carbon nanotube dispersions according to Preparation Examples 1 to 13 have excellent initial discharge capacity and high-rate characteristics.

Claims

1. A carbon nanotube dispersion, comprising: Carbon nanotubes; a first dispersant, the first dispersant surrounding the surface of the carbon nanotube; a second dispersant, the second dispersant being used to introduce charges to the surface of the carbon nanotubes; as well as A storage stabilizer having an electrostatic repulsive force to the electric charges.

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

3. The carbon nanotube dispersion according to claim 1, wherein The storage stabilizer may be present in an amount of 0.01 wt % to 0.1 wt % based on the total weight of the carbon nanotube dispersion.

4. The carbon nanotube dispersion according to claim 1, wherein The storage stabilizer is present in an amount of 1 to 10 parts by weight based on 100 parts by weight of the carbon nanotubes.

5. The carbon nanotube dispersion according to claim 1, wherein The first dispersant includes a nonionic polymer.

6. The carbon nanotube dispersion according to claim 1, wherein The second dispersant includes an ionic polymer.

7. A method for preparing a carbon nanotube dispersion, the method comprising: mixing carbon nanotubes, a first dispersant, a second dispersant, a storage stabilizer and an aqueous solvent to prepare a mixture, wherein the first dispersant includes a nonionic polymer, the second dispersant includes an ionic polymer, and the storage stabilizer includes a phenolic compound having two or more aromatic rings; grinding and pulverizing the mixture; as well as The mixture was dispersed.

8. The method according to claim 7, wherein: The mixture is pulverized so that the average particle diameter of the mixture is less than 100 μm.

9. An electrode slurry composition, comprising: Electrode active materials; Adhesives; as well as Carbon nanotube dispersion, The carbon nanotube dispersion comprises: carbon nanotubes; a first dispersant, which surrounds the surface of the carbon nanotubes; a second dispersant, which is used to introduce charges to the surface of the carbon nanotubes; and a storage stabilizer, which has an electrostatic repulsive force on the charges.

10. A secondary battery, comprising: electrode; Diaphragm; as well as Electrolyte, Wherein, the electrode comprises an electrode active material, a binder and a conductive agent, Wherein, the conductive agent is made of carbon nanotube dispersion, The carbon nanotube dispersion comprises: carbon nanotubes; a first dispersant, which surrounds the surface of the carbon nanotubes; a second dispersant, which is used to introduce charges to the surface of the carbon nanotubes; and a storage stabilizer, which has an electrostatic repulsive force on the charges.

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