Carbon nanotube dispersion and method of making the same

Abstract

The present invention relates to a carbon nanotube dispersion and a method for producing the same. The carbon nanotube dispersion contains carbon nanotubes (CNTs), an amine-containing polymer dispersant, a phenolic compound containing two or more aromatic rings, and an aqueous solvent, wherein the polymer dispersant and the phenolic compound containing two or more aromatic rings are contained at a weight ratio of 100:1 to 100:90, and the carbon nanotube dispersion has a low viscosity and a small change in viscosity over time.

Description

[0001] This application is a divisional application of the invention patent application with application number 201980027612.0 (international application number: PCT / KR2019 / 006907), application date June 7, 2019, entitled "carbon nanotube dispersion and preparation method thereof". Technical Field

[0002] [Cross-references to related applications]

[0003] This application claims the benefit of Korean Patent Application No. 10-2018-0066857, filed on June 11, 2018, with the Korean Intellectual Property Office, the entire contents of which are incorporated herein by reference.

[0004] This invention relates to carbon nanotube dispersions and their preparation methods, and more specifically, to carbon nanotube dispersions having low viscosity and small viscosity changes over time, and their preparation methods. Background Technology

[0005] With technological advancements and increasing demands for mobile devices, the need for secondary batteries as an energy source has grown rapidly. Among these secondary batteries, lithium-ion batteries, characterized by high energy density and voltage, long cycle life, and low self-discharge rate, have been commercialized and are widely used. Furthermore, as electrodes for these high-capacity lithium-ion batteries, methods are being actively researched to manufacture electrodes with even higher energy density per unit volume by increasing electrode density.

[0006] Typically, high-density electrodes are formed by molding electrode active material particles with a size of a few micrometers to tens of micrometers using a high-pressure press. During the molding process, the particles may deform and the space between the particles may decrease, which can easily reduce the permeability to the electrolyte.

[0007] To address these issues, conductive agents with excellent conductivity and strength are used in the electrode manufacturing process. These conductive agents are located between the active material particles of the electrode and maintain the micropores between the particles even during the molding process, allowing the electrolyte to easily permeate and providing excellent conductivity, thereby reducing the resistance in the electrode. Among these conductive agents, the use of carbon nanotubes as fibrous carbon conductive agents, which can form conductive pathways in the electrode and further reduce electrode resistance, is increasing.

[0008] Carbon nanotubes, as a type of micro-carbon fiber, are thick tubular carbon fibers with a diameter of less than 1 μm. Due to their specific structure, they are expected to have applications and practical uses in various fields due to their high electrical conductivity, tensile strength, and heat resistance. However, due to their high specific surface area, carbon nanotubes suffer from problems such as low dispersibility and agglomeration caused by strong van der Waals interactions between them.

[0009] To address these issues, methods have been proposed for dispersing carbon nanotubes in a dispersion medium using mechanical dispersion processes such as ultrasonic treatment. However, in the case of mechanical dispersion methods, there is a problem that the carbon nanotubes aggregate once the ultrasonic irradiation is complete.

[0010] Therefore, there is a need to develop a method for preparing carbon nanotube dispersions that have improved carbon nanotube dispersibility, low viscosity, and inhibit viscosity increase over time. Summary of the Invention

[0011] Technical issues

[0012] One aspect of the present invention is to overcome the deficiencies of conventional technology and to provide a carbon nanotube dispersion comprising a polymeric dispersant containing an amine and a phenolic compound containing two or more aromatic rings, thereby exhibiting excellent dispersibility, low viscosity, and minimal viscosity change over time.

[0013] In addition, another aspect of the present invention is to provide a negative electrode slurry composition for lithium secondary batteries, comprising the carbon nanotube dispersion.

[0014] In addition, another aspect of the present invention is to provide a method for preparing the carbon nanotube dispersion.

[0015] Technical solution

[0016] According to one embodiment of the present invention, a carbon nanotube dispersion is provided, comprising carbon nanotubes (CNTs), an amine-containing polymeric dispersant, a phenolic compound containing two or more aromatic rings, and an aqueous solvent, wherein the polymeric dispersant and the phenolic compound containing two or more aromatic rings are contained in a weight ratio of 100:1 to 100:90.

[0017] According to another embodiment of the present invention, an electrode slurry composition for lithium secondary batteries is provided, comprising the carbon nanotube dispersion.

[0018] According to another embodiment of the present invention, a method for preparing a carbon nanotube dispersion is provided, comprising preparing a mixture by mixing carbon nanotubes, an amine-containing polymeric dispersant, a phenolic compound containing two or more aromatic rings, and an aqueous solvent; and grinding the mixture.

[0019] Beneficial effects

[0020] The carbon nanotube dispersion of the present invention comprises a polymeric dispersant containing an amine and a phenolic compound having a specific structure, and has excellent carbon nanotube dispersibility, low viscosity and small viscosity change over time. Therefore, the storage and use of the carbon nanotube dispersion are advantageous. Detailed Implementation

[0021] It will be understood that the words or terms used in the specification and claims of this invention should not be interpreted as having the meaning defined in a common dictionary, but rather will be further understood as having a meaning consistent with that in the context of the related art and the technical idea of ​​this invention, based on the principle that the inventors may appropriately define the meaning of words or terms to best interpret the invention.

[0022] The terminology used in this disclosure is for illustrative purposes only and is not intended to limit the invention. Unless the context clearly indicates otherwise, the singular form is intended to include the plural form as well.

[0023] It will be understood that when the terms “comprising” and / or “containing” are used in this disclosure, they specify the presence of the stated features, numbers, steps, elements or combinations thereof, but do not exclude the presence or addition of one or more other features, numbers, steps, elements or combinations thereof.

[0024] In this disclosure, unless the context clearly indicates otherwise, “%” refers to weight.

[0025] In this disclosure, the average particle size "D" 50 "" refers to the particle size corresponding to 50% of the volumetric accumulation. D 50 Laser diffraction, for example, can be used for measurement. Laser diffraction can typically measure particle sizes ranging from submicrometers to millimeters, and can yield results with high reproducibility and high resolution.

[0026] In this disclosure, the "specific surface area" is measured by the BET method, and in particular, it can be calculated using the BELSORP-mino II of BEL Japan Co. from the amount of nitrogen absorbed at liquid nitrogen temperature (77K).

[0027] The invention will be described in detail below.

[0028] The carbon nanotube dispersion according to the present invention comprises carbon nanotubes (CNTs), a polymeric dispersant containing an amine, a phenolic compound containing two or more aromatic rings, and an aqueous solvent, wherein the polymeric dispersant and the phenolic compound containing two or more aromatic rings are contained in a weight ratio of 100:1 to 100:90.

[0029] carbon nanotube dispersions

[0030] Each component of the carbon nanotube dispersion of the present invention will be described in detail below.

[0031] (1) Carbon nanotubes

[0032] The term "carbon nanotube" as used in this invention refers to a secondary structure formed by aggregating all or part of carbon nanotube units into a bundle, wherein the graphite sheet within the carbon nanotube unit has a cylindrical shape with a diameter at the nanometer scale and has sp 2 Bond structure. In this case, depending on the rolling angle and structure of the graphite sheet, it can exhibit conductor or semiconductor properties. Based on the number of bonds forming the walls, carbon nanotube units can be classified into single-walled carbon nanotubes (SWCNTs), double-walled carbon nanotubes (DWCNTs), and multi-walled carbon nanotubes (MWCNTs).

[0033] Unless otherwise specified, the term "bundle type" as used in this disclosure refers to an arrangement of multiple carbon nanotube units such that the longitudinal directions of the unit axes have substantially the same orientation, or to a secondary shape of bundle or rope in which the units are twisted or entangled after arrangement. "Non-bundle or entangled type" refers to an entangled state that does not have a specific shape such as a bundle or rope of carbon nanotube units.

[0034] Carbon nanotubes possess high electrical conductivity, but also exhibit high cohesion due to the van der Waals forces generated between them. If the conductive agent agglomerates, it may fail to properly form conductive pathways, requiring a relatively larger amount of conductive agent, and the reduced amount of active material significantly degrades electrode performance. Therefore, it is difficult to commercialize carbon nanotubes as conductive agents.

[0035] Because the carbon nanotube dispersion according to the present invention contains a polymeric dispersant containing an amine and a phenolic compound containing two or more aromatic rings, the viscosity of the aqueous carbon nanotube dispersion can be significantly reduced, and its change over time can be suppressed. Therefore, if it is applied to the electrode of a lithium secondary battery, it can exhibit high conductivity due to the high conductivity of the carbon nanotubes.

[0036] In particular, if the carbon nanotube dispersion according to the invention is applied to the preparation of electrode slurry, the carbon nanotubes can be uniformly positioned between the active materials. Therefore, during the manufacturing process of the electrode by applying the electrode slurry, drying, and pressing, the tiny spaces between the electrode active materials can be kept constant. Furthermore, since the carbon nanotubes are uniformly distributed without agglomeration, a small amount of carbon nanotubes can be used to sufficiently form conductive paths.

[0037] The carbon nanotube dispersion according to embodiments of the present invention may contain one or more of single-walled, double-walled and multi-walled carbon nanotube units as carbon nanotubes, and may particularly contain multi-walled carbon nanotubes.

[0038] The specific surface area (BET) of carbon nanotubes can be 210 m². 2 / g or less, in particular, the specific surface area (BET) can be 30m². 2 / g to 200m 2 / g, and more specifically, 100m 2 / g to 200m 2 / g. If the specific surface area (BET) of carbon nanotubes meets the above range, the amount of carbon nanotubes contained in the carbon nanotube dispersion can be increased compared to the case of using carbon nanotubes with a specific surface area greater than the above range.

[0039] The average particle size (D) of carbon nanotubes 50 The diameter can be, for example, from 3 μm to 300 μm, particularly from 10 μm to 200 μm, and more particularly from 50 μm to 150 μm. To measure the average particle size of carbon nanotubes, the particle size of each carbon nanotube unit can be measured using laser diffraction.

[0040] Based on 100 parts by weight of the conductive agent dispersion, it may contain carbon nanotubes in amounts of 2 to 10 parts by weight, particularly 3 to 8 parts by weight, and more particularly 3 to 6 parts by weight.

[0041] Because carbon nanotubes can be uniformly dispersed in the carbon nanotube dispersion according to an embodiment of the present invention, a larger amount of carbon nanotubes can be present compared to the conventional application range of the aforementioned carbon nanotube dispersion. If a carbon nanotube dispersion with a smaller amount of carbon nanotubes is used to prepare an electrode slurry, the solid content of the electrode slurry thus produced may decrease, the thickness (wet thickness) after coating the electrode slurry and before its drying may increase, the calendering ratio measured after drying and calendering may increase, and there may be a large difference in the thickness ratio before and after drying and calendering. As mentioned above, if the calendering ratio is increased, the composition of the slurry containing the positive electrode active material may be disrupted during processing, thus potentially leading to defects that reduce battery performance.

[0042] (2) Polymer dispersants containing amines and phenolic compounds containing two or more aromatic rings.

[0043] The carbon nanotube dispersion according to the present invention comprises an amine-containing polymeric dispersant and a phenolic compound containing two or more aromatic rings to improve the dispersibility of carbon nanotubes. In the carbon nanotube dispersion, the amine-containing polymeric dispersant and the phenolic compound containing two or more aromatic rings act as dispersants and improve the dispersibility of carbon nanotubes, particularly exhibiting an effect of inhibiting viscosity changes over time.

[0044] According to the inventors' research, the dispersibility of carbon nanotube dispersions is improved compared to carbon nanotube dispersions using only conventional dispersants, due to the inclusion of phenolic compounds containing two or more aromatic rings in the carbon nanotube dispersions. Furthermore, the slurry compositions exhibit less particle agglomeration, lower settling velocity, and improved adhesion to the membrane.

[0045] When compared with conventional techniques, phenolic compounds containing two or more aromatic rings can reduce the viscosity of carbon nanotube dispersions, especially aqueous carbon nanotube dispersions, and significantly improve the increase of viscosity over time due to the large volume structure generated by the two or more aromatic rings and the hydroxyl groups contained in the phenolic groups.

[0046] When using phenolic compounds containing only one aromatic ring (e.g., dopamine, gallic acid, pyrogallol, catechol, etc.), the effect on improving viscosity and suppressing the change of dispersion viscosity over time is insufficient.

[0047] Furthermore, if a specific polymer dispersant containing an amine in the polymer structure is used as a polymer dispersant, it can exhibit further improved viscosity and inhibit viscosity changes over time. The amine-containing polymer dispersant is soluble in water and may include, for example, one or more selected from polyvinylpyrrolidone, polyacrylamide, poly-N-vinyl-5-methyloxazolinone, N-alkyl polyimide, N-acetyl polyimide, polyacrylamide, poly-L-lysine hydrobromide, benzyl-dodecyl-dimethylammonium chloride, and polyethyleneimine.

[0048] Furthermore, phenolic compounds containing two or more aromatic rings may include one or more structures selected from phenol, catechol, gallol, and naphthol structures within one or more of the aromatic rings. In particular, one or more structures selected from catechol and gallol structures may be included within one or more of the aromatic rings. A phenol structure is a single hydroxyl group bonded to a benzene ring; a catechol structure is a combination of two hydroxyl groups bonded to a benzene ring; a gallol structure is a combination of three hydroxyl groups bonded to a benzene ring; and a naphthol structure is a single hydroxyl group bonded to naphthalene.

[0049] If a phenolic compound containing two or more aromatic rings includes the above-described structure, then the interaction between the aromatic rings and the carbon nanotubes in the carbon nanotube dispersion, as well as the interaction between the -OH groups of the phenolic compound and the polymer dispersant due to hydrogen bonding, can be properly balanced, and can exhibit the effect of suppressing the decrease and increase of the viscosity of the carbon nanotube dispersion over time.

[0050] Specific examples of phenolic compounds containing two or more aromatic rings may include one or more selected from baicalin, luteolin, taxifolin, myricetin, quercetin, lutine, catechin, epigallocatechin, gallate, butein, piceatannol, and tannic acid, preferably tannic acid, quercetin, or combinations thereof.

[0051] In one embodiment of the invention, the aromatic ring contained in a phenolic compound containing two or more aromatic rings may be an aromatic ring that is not fused with another aromatic ring or may be a structure in which two aromatic rings are fused with each other, but may not include a fused structure of three or more aromatic rings.

[0052] That is, within the range of phenolic compounds containing two or more aromatic rings, fused structures containing three or more aromatic rings in their molecular structure can be excluded.

[0053] When phenolic compounds containing two or more aromatic rings have a fused structure of three or more aromatic rings in their molecular structure, this fused structure can exhibit stronger-than-appropriate bonding forces with carbon nanotubes in the carbon nanotube dispersion, and can induce aggregation between carbon nanotubes. Therefore, the improvement in the dispersibility of carbon nanotubes is insufficient. Furthermore, in the aforementioned carbon nanotube dispersion, the balance between the interaction between the aromatic rings and the carbon nanotubes, and the hydrogen-bonded interaction between the -OH groups of the phenolic compound and the polymer dispersant, may be lost. Consequently, it may be difficult to achieve an appropriate reduction in the viscosity of the carbon nanotube dispersion and to suppress the increase in viscosity over time.

[0054] When a phenolic compound containing two or more aromatic rings and a polymeric dispersant are included in an appropriate weight ratio, both the viscosity-improving effect and the viscosity-inhibiting effect over time are observed. However, when the weight ratio of the phenolic compound containing two or more aromatic rings and the polymeric dispersant deviates from a specific weight ratio, although the viscosity-improving effect can be achieved, the viscosity-inhibiting effect over time is insufficient.

[0055] The polymeric dispersant and the phenolic compound containing two or more aromatic rings can be contained in a weight ratio of 100:1 to 100:90, particularly 100:10 to 100:80, and even more particularly 100:20 to 100:70. When the polymeric dispersant and the phenolic compound containing two or more aromatic rings are contained in the carbon nanotube dispersion in the aforementioned weight ratio, the carbon nanotubes are uniformly dispersed in the carbon nanotube dispersion, thus exhibiting low viscosity and maintaining the viscosity at a certain level over time.

[0056] Based on 100 parts by weight of carbon nanotubes, the carbon nanotube dispersion may contain a total amount of 11 to 100 parts by weight, particularly 11 to 70 parts by weight, and more particularly 15 to 50 parts by weight of a polymeric dispersant and a phenolic compound containing two or more aromatic rings.

[0057] If the content of polymer dispersant and phenolic compounds exceeds the above range, the conductivity of the electrode on which the carbon nanotube dispersion is applied may be reduced due to the excessive dispersant, and the polymer dispersant and phenolic compounds may act as impurities in the electrode. If the amount is less than the above range, the effect of improving dispersibility, reducing viscosity, and suppressing viscosity changes over time may be insufficient.

[0058] (3) Aqueous solvents

[0059] The solvent is a dispersion medium used to disperse carbon nanotubes, polymer dispersants, and phenolic compounds containing two or more aromatic rings, and is used for dispersion before being provided as a carbon nanotube dispersion to prevent agglomeration in the case of using powdered carbon nanotubes directly to prepare electrode slurry compositions.

[0060] The solvent can dissolve or disperse carbon nanotubes, polymer dispersants, and phenolic compounds containing two or more aromatic rings to a certain extent. The aqueous solvent can be, for example, water, and the amount of aqueous solvent included can provide an appropriate viscosity for the electrode paste composition, taking into account the coating properties of the electrode paste composition prepared later using the carbon nanotube slurry composition.

[0061] The carbon nanotube dispersions of the present invention containing such components exhibit excellent dispersibility, low viscosity, and minimal increase in viscosity over time.

[0062] If measured using a viscometer (TOKI Co. product, viscometer TV-22) at 25°C and 1 rpm, the viscosity of the carbon nanotube dispersion can be from 0.1 to 5 cps, particularly from 0.1 to 4 cps. If the carbon nanotube dispersion has a viscosity within this range, it can be used to prepare electrode slurries more smoothly and efficiently, and electrode slurries including carbon nanotube dispersions can have a suitable viscosity for electrode formation.

[0063] In addition, if the carbon nanotube dispersion is placed at 25°C for 1 week, its viscosity can increase by less than 100%, especially less than 50%, and even more especially less than 20%.

[0064] Methods for preparing carbon nanotube dispersions

[0065] The method for preparing a carbon nanotube dispersion will be explained below. The method for preparing a conductive agent dispersion according to the present invention comprises: (1) preparing a mixture by mixing carbon nanotubes, a polymer dispersant, a phenolic compound containing two or more aromatic rings and an aqueous solvent; and (2) grinding the mixture.

[0066] In step (1), a mixture is prepared by mixing carbon nanotubes, a polymer dispersant, a phenolic compound containing two or more aromatic rings, and an aqueous solvent.

[0067] The preparation of the mixture can be carried out at temperatures where the physical properties of the mixture, including its viscosity, will not change due to the evaporation of the aqueous solvent. For example, this step can be carried out below 50°C, and more particularly, at temperatures between 5°C and 50°C.

[0068] In step (2), the mixture is dispersed to prepare a carbon nanotube dispersion.

[0069] Grinding can be performed using methods such as ball mills, bead mills, disc mills, basket mills, and high-pressure homogenizers. More specifically, grinding can be performed using disc mills or high-pressure homogenizers.

[0070] During the grinding process using a disc mill, the size of the beads can be appropriately determined according to the type and quantity of carbon nanotubes and the type of dispersant. In particular, the diameter of the beads can be from 0.1 mm to 5 mm, and more particularly from 0.5 mm to 4 mm. Furthermore, the bead milling process can be carried out at a rate of 2,000 rpm to 10,000 rpm, and more particularly at a rate of 5,000 rpm to 9,000 rpm.

[0071] The mixture can be pressurized by using a plunger pump, such as a high-pressure homogenizer, and extruded through the gap of a valve used for homogenization. While passing through the gap, the mixture is ground by cavitation force, shear force, impact force, explosive force, etc.

[0072] The grinding process can be carried out according to the dispersion of the carbon nanotube dispersion, and the grinding process can be carried out for 30 minutes to 120 minutes, and more specifically, for 60 minutes to 90 minutes.

[0073] Electrode paste composition

[0074] Furthermore, the present invention provides an electrode slurry composition for lithium secondary batteries, comprising the carbon nanotube dispersion and electrode active material.

[0075] Electrode slurry compositions for lithium secondary batteries can be positive electrode slurry compositions or negative electrode slurry compositions, especially negative electrode slurry compositions.

[0076] Electrode slurry compositions for lithium secondary batteries may include the carbon nanotube dispersion, a positive or negative electrode active material as an electrode active material, a binder, and solvents and / or other additives, if necessary.

[0077] As the positive electrode active material, any positive electrode active material known in the art can be used without limitation, such as lithium cobalt-based oxides, lithium nickel-based oxides, lithium manganese-based oxides, lithium iron phosphate oxides, lithium manganese cobalt-based oxides, or combinations thereof. In particular, as the positive electrode active material, LiCoO2, LiNiO2, LiMn2O4, LiCoPO4, LiFePO4, and LiNiO2MnBCO2 (wherein, 0...) can be used, but not limited to... <a<1,0<b<1,0<c<1)。

[0078] As the negative electrode active material, one or more of the following can be used: natural graphite, artificial graphite, carbonaceous materials; lithium-containing titanium oxide (LTO), metals (Me) of Si, Sn, Li, Zn, Mg, Cd, Ce, Ni or Fe; alloys composed of metals (Me); oxides of metals (MeOx); and composites of metals (Me) and carbon. Based on the total solid weight after removing the solvent from the negative electrode slurry, it may contain 60 to 98% by weight, more preferably 70 to 98% by weight of the negative electrode active material.

[0079] The adhesive is a component that assists in the adhesion of the active material to the conductive agent and to the current collector, and is typically added at a rate of 1 to 30% by weight based on the total weight of the mixture containing the electrode active material. Examples of such adhesives may include polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluororubber, or various copolymers.

[0080] As solvents, organic solvents including N-methylpyrrolidone (NMP), dimethylformamide (DMF), acetone, dimethylacetamide, etc., and water can be used. These solvents can be used alone or as a mixture of two or more. Considering the coating thickness and production yield of the slurry, the amount of solvent used is sufficient if it can dissolve and disperse the electrode active material, binder, and conductive agent.

[0081] Viscosity control agents can be carboxymethyl cellulose or polyacrylic acid, and can control the viscosity of the electrode paste, making the preparation of the electrode paste and the coating process on the electrode current collector easier with the addition of viscosity control agents.

[0082] The filler is a component that suppresses electrode expansion and is optional. Any filler can be used without specific limitations, as long as it is a fibrous material that does not cause chemical changes in the battery. For example, olefin-based polymers such as polyethylene and polypropylene, and fibrous materials such as glass fiber and carbon fiber can be used.

[0083] If the electrode slurry composition is a positive electrode slurry composition for forming a positive electrode, the positive electrode can be formed by coating the positive electrode slurry composition onto a positive electrode current collector, drying, and calendering. Alternatively, the positive electrode can be formed by casting the positive electrode slurry onto a separate support and pressing the film layer obtained by peeling it from the support onto the positive electrode current collector.

[0084] The thickness of the positive electrode active material layer formed by the positive electrode slurry can be changed according to the loading amount, loading rate, etc. of the positive electrode slurry used for application.

[0085] The thickness of the positive electrode current collector typically ranges from 3 μm to 500 μm. There are no limitations on the type of positive electrode current collector; it can be any material with high conductivity that will not cause chemical changes in the 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. Additionally, a rough surface can be formed on the surface of the positive electrode current collector to improve the bonding strength of the positive electrode active material. Positive electrode current collectors can be used in various shapes, such as films, sheets, foils, meshes, porous bodies, foams, nonwoven fabrics, etc.

[0086] If the electrode paste composition is a negative electrode paste composition for forming a negative electrode, the negative electrode can be formed by coating the negative electrode paste composition onto a negative electrode current collector, drying, and calendering. Alternatively, the negative electrode can be formed by casting the negative electrode paste onto a separate support and pressing the film layer obtained by peeling it from the support onto the negative electrode current collector.

[0087] The thickness of the negative electrode active material layer formed by the negative electrode slurry can be changed according to the loading amount, loading rate, etc. of the negative electrode slurry used for application.

[0088] The thickness of the negative electrode current collector typically ranges from 3 μm to 500 μm. There are no limitations on the type of negative electrode current collector; it can be any material with high conductivity that will not cause chemical changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, or copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., or aluminum-cadmium alloys can be used. Furthermore, as in the positive electrode current collector, a rough surface can be formed on the surface of the negative electrode current collector to improve the bonding strength of the negative electrode active material, and the negative electrode current collector can be used in various shapes, such as films, sheets, foils, meshes, porous bodies, foams, nonwoven fabrics, etc.

[0089] Lithium secondary batteries

[0090] A lithium-ion secondary battery includes a positive electrode, a negative electrode, a separator disposed between the positive and negative electrodes, and an electrolyte. The descriptions of the positive and negative electrodes are the same as above, therefore their specific details will be omitted.

[0091] The separator separates the negative and positive electrodes and provides channels for the movement of lithium ions. Any separator used in typical secondary batteries can be used without specific limitations. In particular, separators with low resistance to the movement of electrolyte ions and excellent electrolyte wetting ability are preferred. Specifically, porous polymer membranes can be used, for example, porous polymer membranes made from polyolefin-based polymers such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers, or laminated structures with two or more layers can be used. Furthermore, typical porous nonwoven fabrics can be used, such as nonwoven fibers formed from high-melting-point glass fibers or polyethylene terephthalate fibers. Additionally, to ensure heat resistance or mechanical strength, separators coated with ceramic components or polymer materials can be used, optionally in single-layer or multi-layer structures.

[0092] Electrolytes can be organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel polymer electrolytes, solid inorganic electrolytes, molten inorganic electrolytes, etc., and there are no restrictions on their use in manufacturing lithium secondary batteries. In particular, electrolytes can include organic solvents and lithium salts.

[0093] Organic solvents can be used without restriction, as they can act as a medium through which ions participating in the electrochemical reaction of the battery can move. In particular, ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether and tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic solvents such as benzene and fluorobenzene; carbonate solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol solvents such as ethanol and isopropanol; nitriles such as R-CN (where R is a C2 to C20 hydrocarbon group with a straight-chain, branched, or cyclic structure); amides such as dimethylformamide; dioxolane, such as 1,3-dioxolane; or sulfolane. Preferably, a carbonate solvent is used, and more preferably, a mixture of cyclic carbonates (e.g., ethylene carbonate or propylene carbonate) with high ionic conductivity and high dielectric constant, and linear carbonate compounds (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) with low viscosity, which can increase the charge and discharge capacity of the battery. In this case, the cyclic carbonate and the linear carbonate are used in a volume ratio of about 1:1 to about 1:9 to exhibit excellent electrolyte performance.

[0094] Lithium salts can be any compound that provides lithium ions for use in lithium secondary batteries, without specific limitations. In particular, lithium salts can include LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, LiB(C2O4)2, etc. Lithium salts are preferably used in a concentration range of 0.1M to 2.0M. If the concentration of the lithium salt is within the above range, the electrolyte can have suitable conductivity and viscosity and exhibit excellent electrolyte properties, and lithium ions can move efficiently.

[0095] In addition to the electrolyte components, the electrolyte may contain one or more additives, such as materials based on alkylene carbonate halides (e.g., difluoroethylene carbonate), pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glycol dimethyl ether, triamide hexaphosphate, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolides, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, to improve battery life characteristics, suppress battery capacity reduction, and improve battery discharge capacity. In this case, the additives may be included in an amount from 0.1% to 5% by weight, based on the total weight of the electrolyte.

[0096] In lithium secondary batteries comprising electrodes formed using the carbon nanotube dispersion according to the invention, particularly in lithium secondary batteries comprising a negative electrode formed using the carbon nanotube dispersion, the carbon nanotubes are uniformly dispersed in the negative electrode, and compared to cases comprising conventional conductive agents such as carbon black, the amount of carbon nanotubes can be reduced, thereby consistently exhibiting excellent discharge capacity and output performance. As a result, lithium secondary batteries can be effectively used in portable devices including mobile phones, laptops, and digital cameras, as well as in electric vehicles including hybrid electric vehicles (HEVs).

[0097] Therefore, according to another embodiment of the present invention, a lithium secondary battery, a battery module including a lithium secondary battery as a unit battery, and a battery pack including the same can be provided.

[0098] Battery modules and battery packs can be used as a power source for medium and large devices of any of the following: power tools; electric vehicles, including electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PEHVs); or power storage systems.

[0099] The invention will be described in more detail below with reference to embodiments. However, the embodiments are for illustrative purposes only, and the scope of the invention is not limited thereto.

[0100] Example

[0101] Example 1:

[0102] With a specific surface area of ​​4% by weight, the surface area is 185 m². 2 / g and average particle size (D 50A mixture of 93 μm multi-walled carbon nanotubes (MWCNT, LG Chem Co.), 0.6 wt% polyvinylpyrrolidone (PVP, Zhangzhou Huafu Chemical Co.) as a polymer dispersant, 0.2 wt% tannic acid (Sigma-Aldrich Co.) as a phenolic compound containing two or more aromatic rings, and water as a solvent was prepared to produce 200 g of the mixture. Then, 700 g of zirconia beads were mixed with the mixture and milled for 1 hour at 8,000 rpm using a disc mill (Dispermat-CC, VMA-Getzmaan Co.) to prepare a carbon nanotube dispersion.

[0103] Example 2

[0104] Except that the amount of multi-walled carbon nanotubes in Example 1 was changed to 5.14% by weight, the amount of polyvinylpyrrolidone was changed to 1.03% by weight, and the amount of tannic acid was changed to 0.51% by weight, the carbon nanotube dispersion was prepared according to the same method as in Example 1.

[0105] Example 3

[0106] Except that the amount of polyvinylpyrrolidone in Example 1 was changed to 0.75% by weight and the amount of tannic acid was changed to 0.05% by weight, the carbon nanotube dispersion was prepared according to the same method as in Example 1.

[0107] Example 4

[0108] Except that the amount of polyvinylpyrrolidone in Example 1 was changed to 0.45% by weight and the amount of tannic acid was changed to 0.35% by weight, the carbon nanotube dispersion was prepared according to the same method as in Example 1.

[0109] Comparative Example 1

[0110] Except for excluding tannic acid and changing the amount of polyvinylpyrrolidone to 0.8% by weight in Example 1, carbon nanotube dispersions were prepared according to the same method as in Example 1.

[0111] Comparative Example 2

[0112] Except that the amount of polyvinylpyrrolidone and tannic acid in Example 1 were changed to 0.4% by weight, the carbon nanotube dispersion was prepared according to the same method as in Example 1.

[0113] Comparative Example 3

[0114] The carbon nanotube dispersion was prepared according to the same method as in Example 1, except that the same amount of carboxymethyl cellulose (Daicel Co.) was used instead of polyvinylpyrrolidone in Example 1.

[0115] Experimental Example

[0116] The viscosity of the carbon nanotube dispersions of Examples 1 to 4 and Comparative Examples 1 to 3 was measured, and the viscosity was measured again after they were left to stand at 25°C for one week. The results are shown in Table 1 below.

[0117] Viscosity was measured at 25°C and 1 rpm using a viscometer (TV-22, manufactured by TOKI Co.).

[0118] [Table 1]

[0119]

[0120]

[0121] Referring to the results in Table 1 above, compared to the carbon nanotube dispersion of Comparative Example 1, which only contained polyvinylpyrrolidone as a polymer dispersant, the carbon nanotube dispersions of Examples 1-4, which contained phenolic compounds with two or more aromatic rings and polymer dispersants, exhibited lower viscosity immediately after the carbon nanotubes were dispersed in an aqueous solvent. In particular, the increase in viscosity of the carbon nanotube dispersion over time could be suppressed very effectively. Furthermore, when comparing the results of Examples 1 to 4 with those of Comparative Example 2, it was confirmed that the weight ratio and total amount of the polymer dispersant containing amines and the phenolic compounds with two or more aromatic rings in the carbon nanotube dispersion affected the viscosity of the carbon nanotube dispersion and its change over time. Specifically, Comparative Example 2 included a polymer dispersant containing amines and phenolic compounds with two or more aromatic rings in a weight ratio of 1:1. In this case, compared to using only the polymer dispersant containing amines, the initial viscosity could be reduced, but the effect of suppressing the increase in viscosity over time could not be practically achieved.

[0122] Meanwhile, Comparative Example 3 included carboxymethyl cellulose instead of polyvinylpyrrolidone as the polymer dispersant, and included a polymer dispersant different from those containing amines, as well as a phenolic compound containing two or more aromatic rings. It showed a slight decrease in viscosity and a minor effect in inhibiting viscosity increase over time, but these were negligible compared to the results of Comparative Example 1. The difference in results compared to Example 1, which included the same amount of polymer dispersant and a phenolic compound containing two or more aromatic rings, was significant.

[0123] Therefore, it can be confirmed that only when the carbon nanotube dispersion in which carbon nanotubes are dispersed in an aqueous solvent contains a polymer dispersant and a phenolic compound containing two or more aromatic rings in a certain weight ratio can low viscosity and inhibition of viscosity increase over time be achieved.

Claims

1. A carbon nanotube dispersion comprising: Carbon nanotubes (CNTs), amine-containing polymer dispersants, phenolic compounds containing two or more aromatic rings, and aqueous solvents. in, Based on 100 parts by weight of the dispersion, the carbon nanotubes are contained in 2 to 10 parts by weight. The polymer dispersant and the phenolic compound containing two or more aromatic rings are contained in a weight ratio of 100:1 to 100:

90. The polymer dispersant is selected from one or more of polyvinylpyrrolidone, polyacrylamide, poly-N-vinyl-5-methyloxazolinone, N-alkyl polyimide, N-acetyl polyimide, polyacrylamide, poly-L-lysine hydrobromide, benzyl-dodecyl-dimethylammonium chloride, and polyethyleneimine. The phenolic compound containing two or more aromatic rings includes one or more structures selected from phenol, catechol, gallol, and naphthol in one or more aromatic rings.

2. The carbon nanotube dispersion according to claim 1, wherein, The specific surface area of ​​the carbon nanotubes, measured by the BET method, is 210 m². 2 / g or less.

3. The carbon nanotube dispersion according to claim 1, comprising the polymer dispersant and the phenolic compound containing two or more aromatic rings in a weight ratio of 100:10 to 100:

90.

4. The carbon nanotube dispersion according to claim 1, wherein, The phenolic compounds containing two or more aromatic rings do not contain a fused structure of three or more aromatic rings in their molecular structure.

5. The carbon nanotube dispersion according to claim 1, wherein, The phenolic compound containing two or more aromatic rings is selected from one or more of baicalin, luteolin, sphagnum mossin, myricetin, quercetin, rutin, catechin, epigallocatechin, gallic acid ester, zeaxanthin, tetrahydroxytrans-zirconia, and tannic acid.

6. The carbon nanotube dispersion according to claim 1, wherein, Based on 100 parts by weight of carbon nanotubes, the carbon nanotube dispersion comprises a total amount of 11 to 100 parts by weight of the polymer dispersant and the phenolic compound containing two or more aromatic rings.

7. An electrode slurry composition for lithium secondary batteries, comprising an electrode active material and a carbon nanotube dispersion according to claim 1.

8. A method for preparing the carbon nanotube dispersion of claim 1, the method comprising: (1) A mixture is prepared by mixing carbon nanotubes, an amine-containing polymer dispersant, a phenolic compound containing two or more aromatic rings, and an aqueous solvent; and (2) Grind the mixture.

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