Highly dispersible non-oxidized carbon nanotube powder and manufacturing method therefor

Abstract

The present invention provides highly dispersible non-oxidized carbon nanotube powder comprising: a non-oxidized carbon nanotube bundle that is debundled as carbon nanotube flakes, in which carbon nanotube bundles are densely aggregated, are dispersed and spaced apart at predetermined intervals; and a polymer having a structure of wrapping at least one non-oxidized carbon nanotube bundle while forming a non-covalent bond with the non-oxidized carbon nanotube bundle, wherein, by means of the polymer, the non-oxidized carbon nanotube bundle has miscibility with a wet solvent or compatibility with dry particles, thereby enabling a wet or dry process. The highly dispersible carbon nanotube powder of the present invention is formed such that debundled carbon nanotubes are surrounded by a polymer, and the carbon nanotube bundles have a size of less than 100 nm. Therefore, the highly dispersible carbon nanotube powder has excellent dispersibility in a wet process using an aqueous or organic solvent, can be subjected to a dry process as it is, and provides high electrical conductivity and stability of a thick-film electrode. In addition, the preparation method of the present invention can obtain carbon nanotube powder having high dispersibility in a powder state by dispersing carbon nanotubes in an alcohol-based solvent containing a polymer and freeze-drying same.

Description

Highly dispersed non-oxidized carbon nanotube powder and method for manufacturing the same

[0001] The present invention relates to a highly dispersed non-oxidized carbon nanotube powder and a method for manufacturing the same.

[0002] A secondary battery is a battery that can be used repeatedly through a discharge process in which chemical energy is converted into electrical energy and a reverse charging process. A secondary battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator, and the positive and negative electrodes generally consist of an electrode current collector and an electrode active material layer formed on the electrode current collector. The electrode active material layer is manufactured by applying an electrode slurry composition containing an electrode active material, a conductive material, a binder, etc. onto the electrode current collector, drying it, and then rolling it.

[0003] Conductive materials are used to improve the conductivity of electrode active materials, and active attempts are being made to apply highly conductive carbon nanotubes (CNTs). Since carbon nanotubes can achieve high conductivity even in small amounts, using them offers the advantage of significantly reducing the conductive material content compared to using carbon black, thereby enabling an increase in electrical capacitance.

[0004] Carbon nanotubes are nanometer-sized particles with a high aspect ratio, making it difficult to disperse them uniformly. Therefore, to improve their low dispersibility, it is necessary to suppress aggregation by breaking the van der Waals bonds between the nanotubes. For example, silicon-based active materials are emerging for high-capacity cathode applications; however, since most cathode manufacturing processes are water-based, water-based dispersion technology for hydrophobic carbon nanotubes is required.

[0005] Carbon nanotubes are classified according to the number of synthesized layers into single-walled carbon nanotubes (1 to 3 nm), double-walled carbon nanotubes (3 to 4 nm), thin multi-walled carbon nanotubes (4 to 20 nm), and multi-walled carbon nanotubes (20 to 50 nm), and can also be distinguished by their diameter. In particular, single-walled carbon nanotubes are manufactured in the form of bundles due to van der Waals forces between tubes during synthesis, as their diameter is very small and their aspect ratio is very large. At this time, the diameter of the bundle is in the form of flakes of approximately several millimeters. To realize the excellent performance of carbon nanotubes, they must be manufactured into an intermediate form through debundling and dispersion in an appropriate solvent, which is a very important factor for application in products. Conventional methods proposed for the debundling and dispersion of carbon nanotubes are broadly divided into two types.

[0006] First, there is a chemical method that uses strong acids to introduce oxygen functional groups into carbon nanotubes and then debundles and disperses them. In other words, as a method for manufacturing oxidized carbon nanotubes, the debundling and dispersion of carbon nanotubes using strong acids or oxidizing agents is effective for ensuring dispersibility and minimizes bundle size, thereby improving the properties of the carbon nanotubes and facilitating dispersion. However, this method has disadvantages, such as the degradation of electrical properties due to defect formation during strong acid treatment, the need for an additional reduction process to remove oxygen functional groups, and issues regarding the treatment of acid wastewater resulting from the use of strong acids.

[0007] Second, there is a method using carbon nanotubes and a dispersant or binder. This is a method for manufacturing non-oxidized carbon nanotubes that involves debundling and dispersion using a dispersant or binder. Since acid treatment is not used, the formation of defects can be minimized; however, because a dispersant or binder must be infiltrated between the CNT bundles for debundling and dispersion, the length of the CNTs usually needs to be minimized through various mechanical crushing processes. At this time, the length of the CNTs becomes very short to sub-micron (< 1 μm) or less, and edge sites are exposed and defects are formed on the outer wall of the nanotubes, which reduces intrinsic electrical properties. Additionally, there is a disadvantage of forming high interfacial resistance because a large amount of dispersant must be used.

[0008] Generally, when carbon nanotubes are used in the anode / anode slurry process for secondary batteries, a pre-dispersion process is utilized. However, single-walled or double-walled carbon nanotubes have a high aspect ratio with small diameters and long lengths, resulting in very large bundle sizes during synthesis and purification processes. Consequently, there is a problem in minimizing bundle size when preparing slurries using solvents or when compounding with heterogeneous materials via dry processes. Furthermore, since solvents are essential for slurry preparation, adding an excess amount of carbon nanotube slurry leads to an excessive amount of solvent being added simultaneously, making it difficult to adjust the composition of the electrode slurry. Additionally, existing processes contain many additives, which poses a potential for problems when applied to secondary batteries.

[0009] Accordingly, the inventors developed a method for manufacturing highly conductive non-oxidized carbon nanotube powder capable of ensuring high dispersibility in the dry and solution processes of secondary batteries by mixing and dispersing carbon nanotubes and a polymer in a solvent containing an alcoholic solvent, and then maximizing the distance between bundles through freeze-drying, thereby completing the present invention.

[0010] The present invention was developed to resolve the above problems, and the technical problem is to provide a highly dispersed non-oxidized carbon nanotube powder that can form an electrode by directly adding it during the slurry and dry composite process in the secondary battery electrode manufacturing process, and a method for manufacturing the same.

[0011] To solve the above technical problem, the present invention comprises: non-oxidized carbon nanotube bundles spaced apart at predetermined intervals, wherein carbon nanotube flakes densely packed with carbon nanotube bundles are de-bundled and dispersed;

[0012] A polymer having a structure that winds at least one non-oxidized carbon nanotube bundle while forming a non-covalent bond with the above-mentioned non-oxidized carbon nanotube bundle; comprising

[0013] The non-oxidized carbon nanotube bundles are characterized by having miscibility with a wet solvent or compatibility with dry particles due to the above polymer, thereby enabling wet or dry processing.

[0014] Provides highly dispersed non-oxidized carbon nanotube powder.

[0015] Also, a first step of preparing a polymer solution by mixing a polymer in an alcoholic solvent;

[0016] A second step of preparing a carbon nanotube dispersion by adding carbon nanotube flakes densely packed with carbon nanotube bundles to the polymer solution and applying shear stress to cause the flakes to disperse and debundle, thereby dispersing the carbon nanotube bundles; and

[0017] A third step of freeze-drying the carbon nanotube dispersion to produce a carbon nanotube powder in which the polymer encapsulates the carbon nanotubes; wherein

[0018] The above carbon nanotube powder is,

[0019] A polymer having a structure comprising non-oxidized carbon nanotube bundles spaced apart at predetermined intervals and winding at least one non-oxidized carbon nanotube bundle while forming a non-covalent bond with said non-oxidized carbon nanotube bundles, wherein the non-oxidized carbon nanotube bundles have miscibility with a wet solvent or compatibility with dry particles due to said polymer, thereby enabling wet or dry processing.

[0020] A method for manufacturing highly dispersed non-oxidized carbon nanotube powder is provided.

[0021] The highly dispersed non-oxidized carbon nanotube powder of the present invention, according to the means for solving the above problem, is formed in a form in which debundled carbon nanotubes are surrounded by a polymer, and the carbon nanotube bundles are formed to be less than 100 nm, so that it has excellent dispersibility in wet processes using water-based or organic solvents, can be directly introduced into dry processes, and provides high electrical conductivity and stability of thick film electrodes.

[0022] In addition, the manufacturing method of the present invention can be stably and easily utilized in the manufacturing process of electrodes for secondary batteries through a dry process as well as a wet process in which carbon nanotubes are dispersed in an alcoholic solvent containing a polymer and freeze-dried to obtain carbon nanotube powder with high dispersibility and a slurry is prepared.

[0023] Figure 1 shows a schematic diagram of carbon nanotube powder before and after freeze-drying, prepared according to the manufacturing method of the present invention.

[0024] Figure 2 shows photographs of carbon nanotube powder before and after dispersion and freeze-drying according to one embodiment of the present invention.

[0025] Figure 3 is a photograph of carbon nanotube powder according to one embodiment and a comparative example of the present invention.

[0026] Figure 4 is an SEM image of carbon nanotube flakes before freeze-drying and carbon nanotube powder after freeze-drying according to one embodiment of the present invention.

[0027] Figure 5 shows the results of Raman spectroscopic analysis of carbon nanotube flakes before freeze-drying and carbon nanotube powder after freeze-drying according to one embodiment of the present invention.

[0028] Figure 6 shows the TEM photograph and elemental analysis image results of carbon nanotube powder after freeze-drying prepared according to one embodiment of the present invention.

[0029] FIG. 7 is a scanning electron microscope image of a cross-section of an electrode prepared including carbon nanotube powder according to one embodiment of the present invention.

[0030] The present invention is capable of various modifications and may take various forms, and embodiments are to be described in detail in the text. However, this is not intended to limit the present invention to the specific disclosed forms, and it should be understood that it includes all modifications, equivalents, and substitutions that fall within the spirit and scope of the invention.

[0031] Throughout the specification, when a part is described as "including" a certain component, this means that, unless specifically stated otherwise, it does not exclude other components but may include additional components.

[0032] Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as generally understood by those skilled in the art to which the present invention pertains. Terms such as those defined in commonly used dictionaries should be interpreted as having a meaning consistent with their meaning in the context of the relevant technology, and should not be interpreted in an ideal or overly formal sense unless explicitly defined in this specification.

[0033] The terms used in this specification are used merely to describe specific embodiments and are not intended to limit the invention. Singular expressions include plural expressions unless the context clearly indicates otherwise.

[0034] In the specification of the present invention, 'carbon nanotube bundle' refers to a secondary shape in the form of a bundle or rope in which a plurality of carbon nanotube units are arranged in parallel with the axes along the length direction of the units in substantially the same orientation, or are twisted or entangled after being arranged.

[0035] Carbon nanotube monomers can be classified into single-walled carbon nanotubes (SWCNT), double-walled carbon nanotubes (DWCNT), and multi-walled carbon nanotubes (MWCNT) depending on the number of bonds forming the walls, and carbon nanotube monomers may be one or more of single-walled, double-walled, and multi-walled carbon nanotube monomers.

[0036]

[0037] According to one aspect of the present invention, a highly dispersed non-oxidized carbon nanotube powder is provided, comprising: non-oxidized carbon nanotube bundles spaced apart at a predetermined interval by debundling carbon nanotube flakes densely packed with carbon nanotube bundles while scattering; and a polymer having a structure that winds at least one non-oxidized carbon nanotube bundle while forming a non-covalent bond with the non-oxidized carbon nanotube bundles, wherein the non-oxidized carbon nanotube bundles have miscibility with a wet solvent or compatibility with dry particles through the polymer, thereby enabling wet or dry processing.

[0038] The carbon nanotube powder of the present invention comprises non-oxidized carbon nanotube bundles and a polymer having a structure that wraps the carbon nanotube bundles.

[0039] In the present invention, the polymer is a polymer that forms a non-covalent bond with the carbon nanotube bundle and is characterized by being one or more selected from the group comprising cellulose-based resin, polyvinylpyrrolidone (PVP), linear polyacrylic acid, branched polyacrylic acid, polyacrylic acid copolymer, linear polyethylene glycol, branched polyethyl glycol, polyethyl glycol copolymer, and amphiphilic copolymer.

[0040] The above-mentioned amphiphilic copolymers are polyacrylate-poly(2-vinylpyridinium) salt copolymers, polystyrene-poly(2-vinylpyridinium) salt copolymers, polyacrylic acid-polycaprolactone copolymers, polyethylene glycol-polyacrylate copolymers, polyethylene glycol-hydroxypolyethylene glycol methacrylate copolymers, poly(stearyl methacrylate)-poly(glycidyl methacrylate) copolymers, polystyrene-polyacrylic acid copolymers, polyvinylpyrrolidone-polyacrylate copolymers, polyvinylpyrrolidone-polyacrylic acid copolymers, and polyacrylic acid-poly Poly(ethylene glycol) monomethyl ether (meth)acrylate copolymers, etc., may be used.

[0041] The weight ratio of the carbon nanotubes and the polymer constituting the carbon nanotube powder may be 1:0.01 to 5. If the polymer is added at a ratio of 1:0.01 or less, it is difficult to control the bundle size to be sufficiently small during the process of dispersing carbon nanotubes in a solvent, which is the first step in the manufacturing process of highly dispersible carbon nanotube powder. Furthermore, since the non-covalent bonding of the polymer on the carbon nanotube bundles is lost after freeze-drying, it is not easy to disperse the solution using the manufactured powder. If the polymer is added at a ratio of 1:5 or more, an excess amount of polymer exists on the surface of the carbon nanotube bundles after freeze-drying, which may reduce electrical conductivity when used in slurry manufacturing and dry processes.

[0042] Conventional methods for introducing polymers onto the surface of carbon nanotubes involve dispersing carbon nanotubes in a solvent with an excess amount of polymer and removing polymers that cannot form non-covalent bonds with the carbon nanotubes through methods such as dialysis, filtration, and centrifugation to produce carbon nanotubes with surfaces modified by polymers. However, there is a disadvantage in that it is difficult to manufacture a structure with carbon nanotubes spaced apart at regular intervals by not undergoing a freeze-drying process or by using a solvent with uncontrolled solvent parameters. The carbon nanotube powder of the present invention is formed such that an appropriate amount of added polymer is completely encased on the surface of the carbon nanotube bundles.

[0043] The carbon nanotube powder of the present invention is characterized by the fact that the carbon nanotubes are in a debundled form so that the carbon nanotubes can be added to the electrode slurry as powder itself or directly introduced into the dry electrode process, and that they are wrapped in a polymer and functionalized by non-covalent bonding, thereby having excellent dispersibility without defects in the carbon nanotubes.

[0044] As the non-oxidized carbon nanotubes of the present invention are debundled without defects, the thickness of the carbon nanotube bundle is controlled to a maximum of 100 nm, and as the polymer forms a structure that surrounds and wraps the non-oxidized carbon nanotube bundle, the G peak of the Raman spectroscopy graph is at least 5 cm from the G peak of the aggregated flake-shaped carbon nanotube. -1 It can change beyond this.

[0045] When polymers possessing oxygen or nitrogen functional groups are wrapped around the surface of carbon nanotubes, they donate or receive electrons from the carbon nanotubes, causing the G peak resulting from Raman scattering to shift to a higher or lower wavenumber. Therefore, this makes it possible to determine the presence or absence of the polymer on the surface of non-oxidized carbon nanotube bundles.

[0046] As the polymer content increases and the bundle size decreases, the surface area of ​​the carbon nanotube bundle in contact with the polymer increases significantly, resulting in a larger change in the G peak; furthermore, the fact that the polymer encases the surface of the carbon nanotube bundle can be confirmed through transmission electron microscopy.

[0047] As described above, the carbon nanotube bundles with reduced size are encased by a polymer, and as the distance between the carbon nanotube bundles in the powder state is separated by more than a certain distance, the carbon nanotube powder of the present invention has miscibility with wet solvents, resulting in excellent dispersibility in water-based or organic solvents, and has compatibility with dry particles, making it possible to utilize it in dry processes.

[0048]

[0049] According to another aspect of the present invention, the method comprises: a first step of preparing a polymer solution by mixing a polymer in an alcoholic solvent; a second step of preparing a carbon nanotube dispersion by dispersing carbon nanotube bundles by adding carbon nanotube flakes densely packed with carbon nanotube bundles to the polymer solution and applying shear stress to cause the flakes to scatter and debundle; and a third step of preparing a carbon nanotube powder in which the polymer encapsulates the carbon nanotubes by freeze-drying the carbon nanotube dispersion; wherein the difference between the solubility parameter of the alcoholic solvent and the solubility parameter of the carbon nanotubes is 5 MPa 0.5 The present invention provides a method for manufacturing highly dispersed non-oxidized carbon nanotube powder, wherein the carbon nanotube powder comprises non-oxidized carbon nanotube bundles spaced apart at predetermined intervals and a polymer having a structure that wraps at least one non-oxidized carbon nanotube bundle while forming a non-covalent bond with the non-oxidized carbon nanotube bundles, and wherein the non-oxidized carbon nanotube bundles have miscibility with a wet solvent or compatibility with dry particles due to the polymer, thereby enabling wet or dry processing.

[0050] First, a polymer solution is prepared based on an alcoholic solvent (S1).

[0051] The carbon nanotube powder of the present invention is manufactured through freeze-drying, and it is necessary to control the type of solvent and the freeze-drying conditions to prevent deformation of the composition of the carbon nanotube powder dispersed in the solvent during freezing and to form a structure in which the polymer encases the carbon nanotubes.

[0052] In the present invention, the polymer solution is prepared by adding a polymer to an alcoholic solvent.

[0053] The difference between the solubility parameter of the above alcoholic solvent and the solubility parameter of the above carbon nanotube is 5 MPa 0.5It is characterized by the following: a difference in solubility parameters of 5 MPa 0.5 By doing so, the dispersibility of carbon nanotubes within the dispersion can be enhanced, and a structure can be realized in which the polymer penetrates the carbon nanotube flakes and envelops the carbon nanotube bundles. In particular, in the case of single-walled carbon nanotubes, they can be used as is without processing the longitudinal direction of a single strand; however, by reducing the thickness of the bundle to decrease its diameter, the bundle length can be reduced, and a dispersed state in which small bundles are unraveled can be realized.

[0054] The above alcoholic solvent comprises one or more of primary alcohols, secondary alcohols, and tertiary alcohols, and has a melting point of -90 o It is characterized by having a C or higher. Like ethanol, it has a melting point of -90 o If the temperature is below C, freeze-drying consumes a large amount of electrical energy, making it ineffective for reducing process costs.

[0055] By using an alcohol-based solvent, the difference in solubility parameters between the carbon nanotubes and the solvent is minimized during subsequent freeze-drying, thereby minimizing aggregation among the carbon nanotubes. Additionally, as polymers capable of forming non-covalent chemical bonds with the carbon nanotubes coat the surface of the nanotubes, the solvent can rapidly transform into a solid state. Consequently, deformation of the carbon nanotubes is suppressed, and the polymer-coated structure can be maintained intact.

[0056] In the present invention, the polymer is a polymer that forms a non-covalent bond with the carbon nanotube bundle and may be one or more selected from the group comprising cellulose-based resin, polyvinylpyrrolidone (PVP), linear polyacrylic acid, branched polyacrylic acid, polyacrylic acid copolymer, linear polyethylene glycol, branched polyethyl glycol, polyethyl glycol copolymer, and amphiphilic copolymer.

[0057] The above-mentioned amphiphilic copolymers are polyacrylate-poly(2-vinylpyridinium) salt copolymers, polystyrene-poly(2-vinylpyridinium) salt copolymers, polyacrylic acid-polycaprolactone copolymers, polyethylene glycol-polyacrylate copolymers, polyethylene glycol-hydroxypolyethylene glycol methacrylate copolymers, poly(stearyl methacrylate)-poly(glycidyl methacrylate) copolymers, polystyrene-polyacrylic acid copolymers, polyvinylpyrrolidone-polyacrylate copolymers, polyvinylpyrrolidone-polyacrylic acid copolymers, and polyacrylic acid-poly Poly(ethylene glycol) monomethyl ether (meth)acrylate copolymers, etc., may be used.

[0058] Next, carbon nanotube flakes are added to the polymer solution to prepare a carbon nanotube dispersion (S2).

[0059] Carbon nanotube flakes containing densely packed carbon nanotube bundles are added to a polymer solution of the present invention, and then shear stress is applied. This causes the flakes to disperse and debundle within the polymer solution, thereby dispersing the carbon nanotube bundles to produce a carbon nanotube dispersion.

[0060] Specifically, a first debundling step is performed in which the carbon nanotube bundles of the densely packed carbon nanotube flakes are dispersed in a loosened form by the shear stress in the polymer solution, and then a second debundling step is performed in which the polymer is introduced between the carbon nanotube bundles to reduce the thickness of the bundles, thereby producing a carbon nanotube dispersion in which carbon nanotubes are uniformly dispersed.

[0061] In the present invention, the shear stress may be applied using one or more of the following equipment: horn sonication, homogenizer, inline mixer, and planetary mixer.

[0062] It is preferable that the solid content of the carbon nanotubes relative to the alcoholic solvent in the carbon nanotube dispersion be controlled to 0.1 to 5 weight%. If the solid content of the carbon nanotubes is controlled to 0.1 weight% or less, the distance between carbon nanotube bundles can be maintained to the maximum, but the freeze-drying time and solvent removal time will be longer, leading to increased manufacturing costs; if the solid content of the carbon nanotubes is controlled to 5 weight% or more, the distance between carbon nanotube bundles becomes too close, making it impossible to maintain high dispersibility during powder manufacturing.

[0063] Finally, the carbon nanotube dispersion is freeze-dried to produce carbon nanotube powder (S3).

[0064] In the present invention, freeze-drying is carried out by freezing at -50°C or lower and then vacuum drying.

[0065] In the above freeze-drying step, the freezing conditions of the carbon nanotube dispersion may vary depending on the freezing point of the alcoholic solvent; preferably, it is necessary to freeze at a temperature at least 20°C lower than the melting point of the alcoholic solvent to maximize the distance between carbon nanotubes. Otherwise, during the slow solidification process, the distance between carbon nanotubes narrows again, making redispersion difficult. During freeze-drying, the cooling chamber temperature was reduced to -120°C using a vacuum pump with a vacuum level of 1 torr or less. The vacuum level may vary depending on the saturated vapor pressure of the solvent.

[0066] The freeze-drying time must be sufficiently carried out for at least 12 hours to remove the solvent. When freeze-dried carbon nanotube powder is used in a secondary battery dry process, residual solvent may affect the characteristics of the electrode, so additional drying at room temperature under reduced pressure for at least 6 hours after freeze-drying may be required.

[0067] In the present invention, the carbon nanotube powder is composed of non-oxidized carbon nanotube bundles spaced apart at a predetermined interval and a polymer having a structure wrapped around at least one carbon nanotube bundle while forming a non-covalent bond with said carbon nanotube bundle, and is characterized in that said carbon nanotube bundles have dispersibility in an aqueous solvent or an organic solvent due to said polymer.

[0068] At this time, the weight ratio of the carbon nanotube to the polymer in the carbon nanotube powder may be 1:0.01 to 5.

[0069] When polymers are added at a ratio of 1:0.01 or less, it is difficult to control the bundle size to be sufficiently small during the process of dispersing carbon nanotubes in a solvent, which is the first step in the manufacturing process of highly dispersed carbon nanotube powder. Furthermore, after freeze-drying, the non-covalent bonding of the polymers on the carbon nanotube bundles is lost, making it difficult to disperse the powder in a solution. When polymers are added at a ratio of 1:5 or more, an excess amount of polymer exists on the surface of the carbon nanotube bundles after freeze-drying, which can reduce electrical conductivity when used in slurry manufacturing and dry processes.

[0070] The present invention first prepares a carbon nanotube dispersion in which a polymer and dense carbon nanotube flakes are added, and then freeze-dries it to form a powder with a structure in which the polymer expands the spacing between carbon nanotube bundles. At this time, the spacing between carbon nanotube bundles can be expanded by at least five times the distance between carbon nanotube bundles in the carbon nanotube powder prepared in the third step compared to the distance between carbon nanotube bundles in the dense carbon nanotube flakes added in the second step.

[0071] In addition, the thickness of the carbon nanotube bundle is reduced to a maximum of 100 nm, and then dried in a loosened state, thereby forming a carbon nanotube powder in which the polymer is wrapped around the carbon nanotube by non-covalent bonds with a reduced diameter of the carbon nanotube bundle.

[0072] As such, the present invention is characterized by the ability to secure high dispersibility in the dry and solution processes of secondary batteries by preparing a powder in which a polymer encapsulates the surface of carbon nanotubes through non-covalent bonds, mixing carbon nanotubes in a polymer solution containing an alcohol solvent and a polymer, and maximizing the distance between bundles through freeze-drying after dispersion.

[0073] The embodiments of the present invention will be described in more detail below. However, the following embodiments are provided merely to aid in understanding the present invention and do not limit the scope of the present invention.

[0074]

[0075] <Example>

[0076] Example 1: Preparation of freeze-dried carbon nanotube powder (CMC)

[0077] 2 g of single-walled carbon nanotubes and 0.5 g of carboxymethyl cellulose (CMC) were added to 500 mL of a solution of H2O and butanol mixed in a 7:3 ratio at a weight ratio of 1:0.25. The single-walled carbon nanotubes were dispersed in the solvent by applying mechanical stress, such as using a homo mixer or an ultrasonic disperser, to the single-walled carbon nanotube / CMC mixture. The dispersion was -50 o Single-walled carbon nanotube powder was prepared by freezing at C and then vacuum drying at a vacuum of 1 torr or less for more than 12 hours. Depending on the application, this can be used after further crushing using a powder mixer, etc.

[0078]

[0079] Example 2: Preparation of freeze-dried carbon nanotube powder (PVP)

[0080] 2 g of single-walled carbon nanotubes and 0.5 g of polyvinylpyrrolidone (PVP) were added to 500 mL of butanol in a weight ratio of 2:1. The single-walled carbon nanotubes were dispersed in the solvent by applying mechanical stress, such as with a homo mixer or an ultrasonic disperser, to the single-walled carbon nanotube / PVP mixture. The dispersion was -90 o Single-walled carbon nanotube powder was prepared by freezing at a temperature below C and vacuum drying at a vacuum of 1 torr or less for more than 12 hours. Depending on the application, this can be used after further crushing using a powder mixer, etc.

[0081]

[0082] Comparative Example 1: Preparation of carbon nanotube powder using an aqueous solution

[0083] SWCNT and CMC were dispersed in an aqueous solution at a ratio of 10:1 using only water as the dispersion solvent, which has a large difference in solubility parameters from carbon nanotubes, without adding an alcoholic solvent, and the solution was freeze-dried at -50 ℃ to obtain single-walled carbon nanotube powder.

[0084]

[0085] Comparative Example 2: Preparation of carbon nanotube powder without polymer

[0086] Single-walled carbon nanotube powder was obtained by processing in the same manner as in Example 2, but without adding a polymer (PVP), dispersing, and freeze-drying.

[0087]

[0088] <Results and Evaluation>

[0089] Form of carbon nanotube powder

[0090] Figure 1 shows a schematic diagram of carbon nanotube powder before and after freeze-drying, manufactured according to the manufacturing method of the present invention. Referring to Figure 1, conventional carbon nanotubes are in an aggregated form, with thick bundles and narrow spacing between bundles, exhibiting a flake shape. In contrast, when prepared as powder according to the present invention, a polymer is introduced between the bundles to reduce the thickness of the bundles and expand the spacing between bundles, thereby forming a flake shape that has been loosened. Consequently, the volume of carbon nanotube powder of the same mass increases, resulting in an expanded form.

[0091]

[0092] This can be confirmed in Figure 2, which shows photographs of carbon nanotube powder before and after dispersion and freeze-drying according to one embodiment of the present invention. (a) is a photograph of the single-walled carbon nanotube powder before treatment, and (b) is a photograph of the single-walled carbon nanotube powder after dispersion and freeze-drying treatment according to the embodiment.

[0093] Referring to Figure 2, it can be seen that the volume of carbon nanotube powder of the same weight (0.1 g) expanded by more than five times after undergoing the process of preparing a dispersion and freeze-drying. This is because the polymer is introduced between the carbon nanotube flakes, reducing the thickness of the carbon nanotube bundles and widening the spacing between the carbon nanotube bundles, thereby forming empty spaces and increasing the volume.

[0094] Meanwhile, it can be seen in FIG. 3, which shows photographs of carbon nanotube powder before and after freeze-drying according to one embodiment and a comparative example of the present invention. FIG. 3 (a) is the result of Example 1, (b) is the result of Comparative Example 1, and (c) is the result of Comparative Example 2.

[0095] Referring to Fig. 3, it can be seen that when a dispersion solvent containing a polymer is used as in Fig. 2 (a), the distance between carbon nanotube bundles increases, the bundle size decreases, and a powder in a form that can be immediately used in both wet and dry processes is produced.

[0096] On the other hand, referring to Figure 3(b), if only water, which has a large difference in solubility parameters from carbon nanotubes as in Comparative Example 1, is used as the dispersion solvent, ice crystals are formed upon freezing, causing aggregation between carbon nanotubes. This results in the distance between carbon nanotube bundles becoming closer and large flakes being formed, which reduces dispersibility. In this case, a structure unsuitable for dry processing is formed.

[0097] Referring to Figure 3 (c), when a polymer is not used as in Comparative Example 2, the bundle size of single-walled carbon nanotubes in the solvent is not reduced, and only the twisted bundles are untwisted during freeze-drying, so it can be confirmed that the effect of reducing bundle size is minimal.

[0098] Figure 4 is a scanning electron microscope (SEM) image of carbon nanotube flakes before freeze-drying and carbon nanotube powder after freeze-drying according to an embodiment of the present invention. Referring to Figure 4, the size of the carbon nanotube bundles and the presence or absence of polymer coating can be observed depending on the process of preparing a dispersion containing a polymer and freeze-drying. While the flakes appear in an aggregated form before freeze-drying, the powder after treatment shows that the carbon nanotube bundles constituting the flakes have unraveled, resulting in a decrease in thickness and the creation of empty spaces.

[0099] FIG. 5 shows the results of Raman spectroscopic analysis of carbon nanotube flakes before freeze-drying and carbon nanotube powder after freeze-drying according to one embodiment of the present invention. The samples are pristine SWCNT powder before pretreatment and powder samples with SWCNT / PVP weight ratios of 10 / 1 and 4 / 1, respectively, in which PVP polymer is wrapped. (a) is a Raman spectroscopic analysis graph showing the D-, G-, and G'- bands of carbon nanotube powder using PVP as the polymer, and (b) is a Raman spectroscopic analysis graph showing an enlarged G-band of (a). (c) is a Raman spectroscopic analysis graph of carbon nanotube powder using CMC as the polymer.

[0100] The shift of the Raman spectral G-peak position to a lower wavenumber is a phenomenon resulting from the elevation of the Fermi level of the carbon nanotubes due to the electron donating effect, caused by the non-covalent introduction of PVP containing numerous nitrogen atoms onto the SWCNT surface. Referring to Fig. 4, the absence of a change in the D-band magnitude in (a) indicates that no defects were formed on the SWCNT surface during the pretreatment process, and in (b) and (c), the G-band is 5 cm⁻¹ -1 Through abnormal changes, it can be confirmed that a structure in which the polymer wraps around the carbon nanotube has been formed.

[0101] Figure 6 shows the TEM photograph and elemental analysis image results of carbon nanotube powder after freeze-drying prepared according to one embodiment of the present invention. Referring to Figure 6, it can be seen that the PVP used as a polymer surrounds the carbon nanotube bundles, and through the uniform distribution of each element, it can be confirmed that the polymer uniformly coated the carbon nanotube bundles through the freezing process.

[0102] Meanwhile, the manufactured single-walled carbon nanotube powder was mixed with NCM811 cathode material, PTFE binder, carbon black, and single-walled carbon nanotubes in a ratio of 96:2:1.5:5 using a kneader, and the dispersibility was tested in a dry process. To apply the carbon nanotube powder of the present invention to the dry process of a secondary battery cathode, a secondary battery cathode was manufactured by physically mixing and compressing the NCM811 cathode material, PTFE binder, carbon black, and single-walled carbon nanotubes. Fig. 7 is a scanning electron microscope image of a cross-section of an electrode manufactured including carbon nanotube powder according to one embodiment of the present invention. Referring to Fig. 7, it can be seen that small single-walled carbon nanotube bundles of 100 nm or less are evenly distributed within the electrode and connect each material, confirming that it can be directly applied to a dry process without additional processes.

[0103]

[0104] As such, the highly dispersed non-oxidized carbon nanotube powder of the present invention is formed in a form in which debundled carbon nanotubes are surrounded by a polymer, and the carbon nanotube bundles are formed to be less than 100 nm, so it has the characteristic of having excellent dispersibility in wet processes using water-based or organic solvents and can be directly introduced into dry processes. It is excellent in that it can provide a carbon nanotube powder with excellent dispersibility and stability through a simple process of dispersing carbon nanotubes in an alcoholic solvent containing a polymer and freeze-drying the same.

[0105]

[0106] The foregoing description is merely an illustrative explanation of the technical concept of the present invention, and those skilled in the art to which the present invention pertains will be able to make various modifications and variations within the scope of the essential characteristics of the present invention. Accordingly, the embodiments disclosed in the present invention are intended to explain, not to limit, the technical concept of the present invention, and the scope of the technical concept of the present invention is not limited by such embodiments. The scope of protection of the present invention shall be interpreted by the claims, and all technical concepts within an equivalent scope shall be interpreted as being included within the scope of rights of the present invention.

Claims

1. Non-oxidized carbon nanotube bundles spaced apart at predetermined intervals as carbon nanotube flakes densely packed with carbon nanotube bundles are dispersed and de-bundled; and A polymer having a structure that forms a non-covalent bond with the above-mentioned non-oxidized carbon nanotube bundle and winds at least one non-oxidized carbon nanotube bundle; wherein The non-oxidized carbon nanotube bundles are characterized by having miscibility with a wet solvent or compatibility with dry particles due to the above polymer, thereby enabling wet or dry processing. Highly dispersed non-oxidized carbon nanotube powder.

2. In Paragraph 1, A highly dispersed non-oxidized carbon nanotube powder characterized by the above non-oxidized carbon nanotube bundles having a maximum thickness of 100 nm.

3. In Paragraph 1, The above polymer is, A highly dispersed non-oxidized carbon nanotube powder characterized by being one or more polymers selected from the group comprising cellulose-based resins, polyvinylpyrrolidone (PVP), linear polyacrylic acid, branched polyacrylic acid, polyacrylic acid copolymers, linear polyethylene glycol, branched polyethyl glycol, polyethyl glycol copolymers, and amphiphilic copolymers, as polymers that non-covalently bond with the carbon nanotube bundles.

4. In Paragraph 1, A highly dispersed non-oxidized carbon nanotube powder characterized by a weight ratio of the carbon nanotube to the polymer of 1:0.01 to 5.

5. A first step of preparing a polymer solution by mixing a polymer in an alcoholic solvent; A second step of preparing a carbon nanotube dispersion by adding carbon nanotube flakes densely packed with carbon nanotube bundles to the polymer solution and applying shear stress to cause the flakes to disperse and debundle, thereby dispersing the carbon nanotube bundles; and A third step of freeze-drying the carbon nanotube dispersion to produce a carbon nanotube powder in which the polymer encapsulates the carbon nanotubes; wherein The difference between the solubility parameter of the above alcoholic solvent and the solubility parameter of the above carbon nanotube is 5 MPa 0.5 The following, The above carbon nanotube powder is, It is composed of non-oxidized carbon nanotube bundles spaced apart at predetermined intervals, and a polymer having a structure that winds at least one non-oxidized carbon nanotube bundle while forming non-covalent bonds with said non-oxidized carbon nanotube bundles, and The non-oxidized carbon nanotube bundles are characterized by having miscibility with a wet solvent or compatibility with dry particles due to the above polymer, thereby enabling wet or dry processing. Method for manufacturing highly dispersed non-oxidized carbon nanotube powder.

6. In Paragraph 5, A method for manufacturing highly dispersed non-oxidized carbon nanotube powder, characterized in that the above non-oxidized carbon nanotube bundles have a maximum thickness of 100 nm.

7. In Paragraph 5, The above alcoholic solvent has a melting point of -90 o A method for manufacturing highly dispersed non-oxidized carbon nanotube powder characterized by having a C or higher.

8. In Paragraph 5, The above second step is, A first debundling step in which carbon nanotube bundles of the dense carbon nanotube flakes are dispersed in the polymer solution; and The method is characterized by proceeding to include a secondary debundling step in which the polymer is introduced between the carbon nanotube bundles to reduce the thickness of the bundles. Method for manufacturing highly dispersed non-oxidized carbon nanotube powder.

9. In Paragraph 5, The above polymer is, A method for producing highly dispersed non-oxidized carbon nanotube powder, characterized by comprising one or more polymers selected from the group comprising cellulose-based resins, polyvinylpyrrolidone (PVP), linear polyacrylic acid, branched polyacrylic acid, polyacrylic acid copolymers, linear polyethylene glycol, branched polyethyl glycol, polyethyl glycol copolymers, and amphiphilic copolymers, as polymers that non-covalently bond with the carbon nanotube bundles.

10. In Paragraph 5, A method for manufacturing highly dispersed non-oxidized carbon nanotube powder, characterized in that the distance between carbon nanotube bundles in the carbon nanotube powder manufactured in the third step is extended by at least five times compared to the distance between carbon nanotube bundles in the dense carbon nanotube flakes added in the second step.

11. In Paragraph 5, In the second step above, A method for manufacturing highly dispersed non-oxidized carbon nanotube powder, characterized in that the shear stress is applied using one or more of the following equipment: horn sonication, homogenizer, inline mixer, and planetary mixer.

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