Catalyst for synthesising carbon nanotubes and method for producing carbon nanotubes using same

Abstract

The present invention relates to a catalyst for synthesising carbon nanotubes and a method for producing carbon nanotubes. The method for producing carbon nanotubes of the present invention comprises the steps of: obtaining a solution containing valuable metals recovered from a waste battery; adding a chelating agent to the solution containing the valuable metals; heat-treating the solution mixed with the chelating agent to produce a metal catalyst; and providing a carbon source to the metal catalyst and heat-treating same to synthesise carbon nanotubes, wherein the molar ratio of metal ions of the valuable metals to chelating agent ions (the number of moles of metal ions: the number of moles of chelating agent ions) is 1:1.28 or more.

Description

Catalyst for carbon nanotube synthesis and method for manufacturing carbon nanotubes using the same

[0001] The present invention relates to waste battery recycling, and more specifically to a catalyst for synthesizing carbon nanotubes produced from an alloy generated during the process of recycling waste batteries, and a method for manufacturing carbon nanotubes using the same.

[0002] This application claims priority to Korean Patent Application No. 10-2024-0141077 filed on October 16, 2024, the entire contents of which are incorporated herein by reference.

[0003] Carbon nanotubes possess excellent thermal conductivity and superior mechanical and electrical properties. For example, carbon nanotubes are not only used as reinforcements for composite materials by adding them to metals, ceramics, and polymers to enhance mechanical properties, but are also utilized in various fields such as nanobiosensors and battery anode materials.

[0004] Chemical Vapor Deposition (CVD) using metal catalysts is primarily used as a method for synthesizing the carbon nanotubes mentioned above. When a carbon source, such as CO, CH4, C2H2, or C2H4, is supplied to the metal catalyst at an appropriate temperature using CVD, the carbon nanotubes grow from the metal catalyst. The metal catalyst must possess high carbon solubility to grow the carbon nanotubes. Furthermore, the metal catalyst must have a rapid carbon diffusion rate on its surface to facilitate the growth of the carbon nanotubes.

[0005] Accordingly, transition metals are mainly used as metal catalysts for carbon nanotube synthesis. In particular, nickel is used as the main catalyst because it has an FCC structure, high solubility for carbon, and possesses an appropriate number of hole atoms in the outermost 3d orbitals, allowing it to properly capture and release carbon to grow carbon nanotubes. However, nickel single catalysts have the problem of reduced ability to decompose various carbon sources and low carbon solubility.

[0006] Furthermore, when growing carbon nanotubes using a metal catalyst, the size of the metal catalyst is a crucial factor, just as much as the composition. Specifically, carbon sources decompose on the catalyst surface and dissolve into the catalyst; as the temperature decreases, they precipitate back onto the surface to grow carbon nanotubes. At this stage, the catalyst size is critical for carbon nanotube growth, and a sufficient edge step is required for the precipitated carbon to develop into carbon nanotubes.

[0007] Specifically, when carbon precipitated at the unstable edge stage grows, carbon nanotubes grow in that part, and the edge stage is formed in large quantities when the surface of the catalyst is close to spherical and there are many unstable surfaces.

[0008] If the above edge step is small, it cannot grow into a carbon nanotube and is formed in the form of a carbon onion where carbon covers the catalyst surface. As such, the maximum size of the catalyst for forming carbon nanotubes is 50 nm, and in the range of 5 to 50 nm, it is formed as a multi-wall carbon nanotube (MW carbon nanotube), and in the range of 5 nm or less, as a single-wall carbon nanotube (SW carbon nanotube).

[0009] As such, it is important to form a transition metal catalyst of 50 nm or less to synthesize carbon nanotubes, and one method to grow it to 50 nm or less is to use Physical Vapor Deposition (PVD). Specifically, after depositing the catalyst via PVD onto a substrate that does not react with the transition metal catalyst, heat treatment is performed so that the catalyst coating layer on the surface aggregates, allowing nano-sized catalysts to be formed on the substrate according to the coating thickness.

[0010] However, this method requires a high vacuum and cannot be formed evenly within uneven materials. Accordingly, a nano-catalyst synthesis method utilizing a chelating agent is being employed as a means to effectively form a large amount of catalysts smaller than 50 nm. The chelating agent is a compound in which a single ligand forms two or more coordinate bonds with a metal ion in solution, which is referred to as a coordination compound. When the coordination compound is heat-treated, the metal ions do not aggregate but are well dispersed within a carbon matrix, thereby enabling the formation of nano-sized metal catalysts.

[0011] Accordingly, to manufacture a catalyst for carbon nanotube synthesis, metals must be dissolved in a solution. Generally, catalyst raw materials in the form of nitrates or sulfates that are highly soluble in solution are used as the metal catalyst raw materials. The present invention aims to utilize such catalyst raw materials extracted from spent batteries.

[0012] Battery demand is rapidly increasing as they are widely used not only in electronic devices such as smartphones and mobile devices but also in electric vehicles. The demand for these batteries is expected to rise further as the demand for electric vehicles increases as the next-generation mode of transportation.

[0013] Since the aforementioned electric vehicle requires a battery with a large electrical capacity, it is installed and used in the vehicle in units of multiple battery cells, modules composed of multiple battery cells, and packs composed of multiple modules. As the usage of the electric vehicle increases rapidly, the amount of waste generated from batteries used in the electric vehicle is also increasing.

[0014] Although various types of batteries are utilized, lithium-ion batteries are the most commonly used in the market due to their high energy density. The lithium-ion battery has a structure comprising a positive electrode, a negative electrode, a separator, and an electrolyte. In particular, since the positive electrode of the lithium-ion battery contains a large amount of valuable metals, research on recycling it is being actively conducted.

[0015] Recycling technology for recovering valuable metals such as lithium, nickel, cobalt, and manganese from the aforementioned batteries is attracting attention as a promising method for supplying raw materials for lithium secondary batteries, and the wet process for recovering valuable metals from pretreated waste batteries has reached the commercialization stage. This process is carried out by discharging, crushing / grinding, and classifying / selecting waste batteries to form a black mass, followed by a leaching process in which valuable metals are dissolved in an acidic solution, and then undergoing separation / purification processes such as solvent extraction.

[0016] In this way, when the leaching process, which is a subsequent step in the aforementioned battery recycling process, is performed, a solution containing NCM is obtained. Since the catalyst for carbon nanotube synthesis does not require high purity, waste batteries can be recycled economically.

[0017]

[0018] The technical problem that the present invention aims to solve is to provide a catalyst for synthesizing carbon nanotubes that has high decomposition ability for various carbon sources and excellent carbon solubility, derived from raw materials obtained from waste batteries.

[0019] Another technical problem that the present invention aims to solve is to provide a method for synthesizing carbon nanotubes using a catalyst for carbon nanotube synthesis having the aforementioned advantages.

[0020]

[0021] A catalyst for carbon nanotube synthesis according to one embodiment of the present invention relates to a metal catalyst comprising a valuable metal, wherein Formula 1 below satisfies 9% or less.

[0022] <Equation 1>

[0023]

[0024] (In the above Equation 1, I net represents the area of ​​the XRD peaks of catalytic oxides, including the XRD peaks of Ni oxide, Co oxide, and Mn oxide, and I tot is the total XRD peak area and I bgr represents the XRD peak area of ​​the background regions)

[0025] In one embodiment, the catalyst for carbon nanotube synthesis may be derived from an aqueous transition metal solution recovered from a spent battery. In one embodiment, the average particle size (D50) may be 50 nm or less. In one embodiment, the valuable metal includes nickel, cobalt, and manganese, and the content of manganese may be 33 wt% or less based on 100 wt% of the catalyst for carbon nanotube synthesis.

[0026] In one embodiment, the particles of the valuable metal may be dispersed within a carbon matrix. In one embodiment, the XRD peak values ​​may not include at least one peak among the ranges 2θ = 15°±0.5°, 18°±0.5°, 37°±0.5°, 43°±0.5°, 63°±0.5°, 75°±0.5°, and 78°±0.5°.

[0027] A method for manufacturing carbon nanotubes according to another embodiment of the present invention comprises the steps of obtaining a solution containing a valuable metal recovered from a waste battery, adding a chelating agent to the solution containing the valuable metal, heat-treating the solution mixed with the chelating agent to produce a metal catalyst, and providing a carbon source to the metal catalyst and heat-treating it to synthesize carbon nanotubes, wherein the molar ratio of the metal ions of the valuable metal to the chelating agent ions (moles of metal ions:moles of chelating agent ions) may be 1:1.28 or higher.

[0028] In one embodiment, the step of adding a chelating agent to a solution containing the valuable metal may include the step of adding a pH adjuster to a solution mixed with the solution containing the valuable metal and the chelating agent. In one embodiment, the pH of the solution mixed with the solution containing the valuable metal and the chelating agent may be adjusted to 7 or higher.

[0029] In one embodiment, the step of preparing a metal catalyst by heat-treating a solution mixed with the chelating agent may include a drying step of gelling the solution mixed with the chelating agent and a first heat treatment step of heat-treating the gelled product to obtain a powder.

[0030] In one embodiment, the drying step may be performed at a temperature of 50°C or higher. In one embodiment, the first heat treatment step may be performed at 200°C or higher.

[0031] In one embodiment, the carbon source may include at least one of CO, CH4, C2H2, and C2H4. In one embodiment, the step of synthesizing carbon nanotubes by providing a carbon source to the metal catalyst and heat-treating it may be performed at 800°C or higher.

[0032] In one embodiment, the method may include the step of removing manganese from the solution containing the valuable metal after obtaining the solution containing the valuable metal recovered from the waste battery. In one embodiment, the step of obtaining the solution containing the valuable metal recovered from the waste battery may be such that the solution containing the valuable metal is obtained from black alloy or black mass.

[0033] In one embodiment, the step of obtaining a solution containing a valuable metal recovered from the waste battery may include the step of leaching lithium from the black alloy or the black mass, the step of obtaining a residue by solid-liquid separation of the product from which the lithium was leached, and the step of performing acid leaching on the residue. In one embodiment, after the first heat treatment step, a second heat treatment step of heat-treating the powder at a higher temperature than the first heat treatment step may be included.

[0034]

[0035] According to one embodiment of the present invention, a catalyst for carbon nanotube synthesis satisfies a crystallinity of 9% or less, thereby providing a catalyst for carbon nanotube synthesis that has high decomposition ability for various carbon sources and excellent carbon solubility. In addition, the catalyst for carbon nanotube synthesis is obtained from waste batteries, which has the advantage of being economically viable.

[0036] The present invention relates to a method for producing carbon nanotubes using a catalyst for carbon nanotube synthesis having the aforementioned advantages, according to another embodiment of the present invention.

[0037]

[0038] FIG. 1 is a flowchart of a method for manufacturing carbon nanotubes according to one embodiment of the present invention.

[0039] Figure 2 is a graph showing the degree of amorphousness of the catalyst according to the ratio of the chelating agent after the heat treatment process, according to the embodiments and comparative examples of the present invention.

[0040] Figure 3 shows TEM images of catalysts according to embodiments and comparative examples of the present invention.

[0041] FIG. 4 is a TEM image of a metal catalyst formed according to an embodiment of the present invention, and FIG. 5 is an elemental image of a metal catalyst prepared according to an embodiment of the present invention.

[0042] FIGS. 6 to 8 are structural photographs of carbon nanotubes synthesized according to embodiments and comparative examples of the present invention.

[0043]

[0044] Terms such as first, second, and third are used to describe various parts, components, regions, layers, and / or sections, but are not limited thereto. These terms are used solely to distinguish one part, component, region, layer, or section from another part, component, region, layer, or section. Accordingly, the first part, component, region, layer, or section described below may be referred to as the second part, component, region, layer, or section without departing from the scope of the present invention.

[0045] The technical terms used herein are for the reference of specific embodiments only and are not intended to limit the invention. The singular forms used herein include plural forms unless phrases clearly indicate otherwise. As used in the specification, the meaning of "comprising" specifies certain characteristics, areas, integers, steps, actions, elements, and / or components, and does not exclude the presence or addition of other characteristics, areas, integers, steps, actions, elements, and / or components.

[0046] When it is stated that one part is "above" or "on" another part, it may be directly above or on the other part, or other parts may be involved in between. In contrast, when it is stated that one part is "directly above" another part, no other parts are interposed in between.

[0047] Unless otherwise defined, all terms used herein, including technical and scientific terms, have the same meaning as generally understood by those skilled in the art to which this invention pertains. Terms defined in commonly used dictionaries are further interpreted to have meanings consistent with relevant technical literature and the present disclosure, and are not interpreted in an ideal or highly formal sense unless otherwise defined.

[0048] A catalyst for synthesizing carbon nanotubes according to one embodiment of the present invention is used to synthesize carbon nanotubes and may include a valuable metal. Specifically, the catalyst for synthesizing carbon nanotubes may be produced from a solution containing a valuable metal obtained from a battery recycling process. More specifically, the catalyst for synthesizing carbon nanotubes may be prepared using a solution containing a valuable metal extracted by acid leaching of an intermediate product obtained from a battery recycling process.

[0049] The above intermediate product may be black mass obtained by pre-treating crushed waste batteries or black alloy formed by high-temperature reduction heat treatment of the crushed waste batteries. Specifically, the above intermediate product may be obtained from waste batteries and may contain valuable metals.

[0050] The above valuable metal is extracted from waste batteries, for example, from the cathode material of the waste batteries. Specifically, the above valuable metal may include at least one of nickel (Ni), cobalt (Co), and manganese (Mn). More specifically, the catalyst for carbon nanotube synthesis may include nickel, cobalt, and manganese.

[0051] In one embodiment, the manganese content may be 33 weight% or less based on 100 weight% of the catalyst for carbon nanotube synthesis. Specifically, the manganese content may be 30 weight% or less, more specifically 20 weight% or less, and even more specifically 5 weight% or less.

[0052] By satisfying the aforementioned range for the manganese content, metal particles within the catalyst are properly dispersed, and carbon nanotubes can be easily formed during carbon nanotube synthesis. If the manganese content falls outside the aforementioned range, carbon onions formed by the aggregation of carbon are formed during carbon nanotube synthesis, which creates a problem in that carbon nanotubes cannot be easily formed.

[0053] In one embodiment, the catalyst for carbon nanotube synthesis may have particles of a valuable metal dispersed within a carbon matrix. Specifically, the catalyst for carbon nanotube synthesis may have a form in which particles containing nickel, cobalt, and manganese, which are valuable metals, are dispersed within a carbon matrix.

[0054] In one embodiment, the carbon nanotube synthesis catalyst may have an average particle size (D50) of 50 nm or less. By satisfying the aforementioned range, the average particle size of the carbon nanotube synthesis catalyst has the advantage of facilitating the synthesis of carbon nanotubes. If the average particle size of the carbon nanotube synthesis catalyst does not satisfy the aforementioned range, there is a problem in that carbon nanotubes cannot be formed.

[0055] In one embodiment, the crystallinity of the carbon nanotube synthesis catalyst may be 9% or less. Specifically, the crystallinity may be 8% or less. Specifically, the carbon nanotube synthesis catalyst may include an amorphous phase. By including an amorphous phase as described above, the carbon nanotube synthesis catalyst can promote the formation of a catalyst size of 50 nm or less. There is a problem in that the carbon nanotube synthesis catalyst has a crystallinity outside the aforementioned range and does not include an amorphous phase, so the catalyst size is not formed to be 50 nm or less.

[0056] In one embodiment, the catalyst for carbon nanotube synthesis may not include a peak of metal ions. Specifically, the aforementioned characteristics may be exhibited by mixing metal ions and a chelating agent in a predetermined ratio during the preparation of the catalyst. If the ratio of metal ions becomes excessively high during the process of preparing the catalyst for carbon nanotube synthesis, the catalyst for carbon nanotube synthesis may include a peak of metal ions.

[0057] In one embodiment, the catalyst for carbon nanotube synthesis may not include at least one peak among the ranges of 2θ = 15°±0.5°, 18°±0.5°, 37°±0.5°, 43°±0.5°, 63°±0.5°, 75°±0.5°, and 78°±0.5° in terms of XRD peak values. Specifically, the aforementioned XRD peak values ​​may refer to metal ion peak values. By not including the aforementioned peaks, the catalyst for carbon nanotube synthesis forms an amorphous catalyst, thereby allowing carbon nanotubes to be properly formed.

[0058] In one embodiment, the catalyst for carbon nanotube synthesis can satisfy the following Equation 1 in terms of XRD peak values.

[0059] <Equation 1>

[0060]

[0061] (In the above Equation 1, I net represents the area of ​​the XRD peaks of catalytic oxides, including the XRD peaks of Ni oxide, Co oxide, and Mn oxide, and I tot is the total XRD peak area and I bgr represents the XRD peak area of ​​the background regions)

[0062] Equation 1 above represents an indicator of the formation of an amorphous phase for a catalyst for carbon nanotube synthesis. Specifically, Equation 1 above represents the degree of crystallization of the catalyst for carbon nanotube synthesis. In Equation 1 above, I net represents the area of ​​the XRD peaks of catalyst oxides that includes all metal oxide peak areas such as 2θ = 15°±0.5°, 18°±0.5°, 37°±0.5°, 43°±0.5°, 63°±0.5°, 75°±0.5°, and 78°±0.5° among the XRD peaks of catalysts for carbon nanotube synthesis, and I totrepresents all peak areas excluding the background peak area, including the ranges 2θ = 15°±0.5°, 18°±0.5°, 37°±0.5°, 43°±0.5°, 63°±0.5°, 75°±0.5°, and 78°±0.5°, and the above I bgr The background peak area refers to the area of ​​the peak of diffracted X-rays originating from sources other than the crystal structure of the sample (amorphous or non-crystalline phase). Specifically, the background peak area can be calculated using spline or polynomial methods, or by using XRD data analysis programs such as Highscore plus or Smart lab studio.

[0063] The above Formula 1 may be 9% or less. Specifically, the above Formula 1 may be 8.95% or less, more specifically, 2 to 8.95% or less, 2 to 8.85% or less, or 2 to 8.75% or less. Specifically, by satisfying the above-mentioned range, when the amorphous carbon nanotube synthesis catalyst is heated to synthesize carbon nanotubes, it is formed into catalyst particles of 50 nm or less, which has the advantage of promoting the growth of carbon nanotubes.

[0064] If the above Equation 1 falls outside the aforementioned range, there is a problem in that when the temperature is raised for carbon nanotube synthesis, catalyst particles larger than 50 nm are formed, which cannot grow into carbon nanotubes and are formed into a carbon onion structure.

[0065] FIG. 1 is a flowchart of a method for manufacturing carbon nanotubes according to one embodiment of the present invention.

[0066] Referring to FIG. 1, a method for manufacturing carbon nanotubes comprises the steps of: obtaining a solution containing a valuable metal recovered from a waste battery; obtaining a solution containing a valuable metal recovered from a waste battery; adding a chelating agent to the solution containing the valuable metal; heat-treating the solution mixed with the chelating agent to produce a metal catalyst; and providing a carbon source to the metal catalyst and heat-treating it to synthesize carbon nanotubes. Specifically, the method for manufacturing carbon nanotubes according to the present invention involves synthesizing a metal catalyst obtained from a solution containing a valuable metal recovered from a waste battery to produce carbon nanotubes.

[0067] In the step of obtaining a solution containing valuable metals recovered from waste batteries, said solution containing valuable metals may be extracted by acid leaching of an intermediate product produced in a battery recycling process. Specifically, the valuable metals recovered from said waste batteries, for example, said solution containing valuable metals may include materials such as black mass supplied from discarded lithium-containing batteries, discarded parts of said batteries, and / or materials discarded from the battery production process, black powder obtained through pretreatment such as heat treatment of said black mass, anode scrap, and other alloys.

[0068] In one embodiment, the solution containing the valuable metal may be obtained from the intermediate product, which is black alloy or black mass. Specifically, the intermediate product may be black mass obtained by pre-treating crushed waste batteries or black alloy formed by high-temperature reduction heat treatment of the crushed waste batteries. More specifically, the intermediate product may be obtained from waste batteries and may contain a valuable metal. The valuable metal may be extracted from the waste batteries, for example, from the cathode material of the waste batteries. Specifically, the valuable metal may include at least one of nickel (Ni), cobalt (Co), and manganese (Mn).

[0069] In one embodiment, the waste battery crushed material is obtained from a waste battery, and the waste battery may satisfy NCM111 to NCM9½½ as a cathode material. This is because if the manganese content in the waste battery is excessively high, there is a problem in that the synthesis of carbon nanotubes is not easily performed.

[0070] In one embodiment, the step of obtaining a solution containing a valuable metal recovered from the waste battery may include the step of leaching lithium from the black alloy or the black mass. Specifically, the step of leaching lithium may be the step of leaching the black alloy or the black mass into an acidic solution. The acidic solution may be introduced to leach the solution containing the valuable metal into the solution phase. As a non-limiting example, the acidic solution may be an acidic aqueous solution such as sulfuric acid, nitric acid, hydrochloric acid, or methanesulfonic acid.

[0071] In one embodiment, the step of leaching the lithium may control the pH to 7 or higher by adding the acidic solution. Specifically, in the step of leaching the lithium, the concentration of the acidic solution may be 0.5 to 1.5 M, and the step of leaching the lithium may be performed within 1 to 3 hours. Through the step of leaching the lithium, a solution containing lithium and a residue containing valuable metals may be obtained.

[0072] Subsequently, the step of obtaining a solution containing valuable metals recovered from the waste battery may include a step of obtaining a residue by separating the lithium leaching product from solid and liquid. Specifically, solid and liquid separation may be performed on the lithium leaching product, which is a lithium-containing solution and a residue containing valuable metals, so that the lithium-containing solution is recovered separately and the residue is obtained separately. For example, the leached solution and the solid residue may be separated using a component such as a filter.

[0073] Afterward, the residue may undergo a drying step. The drying step may be performed at 50°C or higher, specifically at 50 to 200°C. By undergoing the drying step, the remaining solution material can be easily evaporated.

[0074] The dried residue may include a step of performing acid leaching. Specifically, the step of performing acid leaching may be a step for obtaining a solution containing a valuable metal from the residue. In one embodiment, the concentration of the acidic solution in the step of performing acid leaching may be 1 to 4 M. When acid leaching is performed within the concentration range, an aqueous solution containing a valuable metal can be easily obtained from the residue.

[0075] In one embodiment, after obtaining a solution containing a valuable metal recovered from the waste battery, the method may include a step of removing manganese from the solution containing the valuable metal. Specifically, the step of removing manganese may be a step of controlling the content of manganese in the solution containing the valuable metal to 33% by weight or less based on 100% by weight of the solution.

[0076] By satisfying the aforementioned range for the manganese content, metal particles within the catalyst are properly dispersed, and carbon nanotubes can be easily formed during carbon nanotube synthesis. If the manganese content falls outside the aforementioned range, carbon onions formed by the aggregation of carbon are formed during carbon nanotube synthesis, which creates a problem in that carbon nanotubes cannot be easily formed.

[0077] The step of adding a chelating agent to a solution containing the valuable metal may be a step of adding a chelating agent to a solution containing the valuable metal that has undergone an acid leaching process. For example, the chelating agent may be a substance such as Asparic acid (Asp), Lysine (Lys), EDTA, Citric acid, or Urea.

[0078] The molar ratio (moles of metal ions:moles of chelating agent ions) of the metal ions of the above-mentioned valuable metal and the chelating agent ions may be 1:1.28 or higher. Specifically, the molar ratio may be 1:1.30 or higher, more specifically, 1:1.4 or higher, and may be in the range of 1:1.4 to 1:1.6.

[0079] By satisfying the weight ratio of the metal ion and the chelating agent as described above, the metal catalyst is formed into a phase including an amorphous phase in the subsequent process, and there is an advantage that the synthesis of carbon nanotubes is easy.

[0080] If the weight ratio of the metal ions is higher than the aforementioned range, there is a problem of metal ion peaks forming within the metal catalyst during the subsequent process, which leads to the occurrence of carbon onion phenomena during carbon nanotube synthesis and a decrease in economic efficiency.

[0081] In one embodiment, the step of adding a chelating agent to a solution containing the valuable metal may include the step of adding a pH adjuster to a solution mixed with the solution containing the valuable metal and the chelating agent. Specifically, the pH adjuster may be a neutralizing agent containing OH. The step of adding the pH adjuster may be a step of controlling the pH of the solution to 7 or higher, specifically 8 or higher. As the pH is controlled to the aforementioned range, there is an advantage in that the degree of crystallinity is reduced.

[0082] The step of preparing a metal catalyst by heat-treating the solution mixed with the chelating agent may include a drying step of gelling the solution mixed with the chelating agent and a first heat treatment step of heat-treating the gelled product to obtain a powder. Specifically, a catalyst in which metal particles are dispersed within a carbon matrix may be prepared by heat-treating the solution mixed with the chelating agent.

[0083] In one embodiment, the drying step for gelling the solution mixed with the chelating agent may be a step of drying the solution at 60°C or higher to gel the solution in the form of an aqueous solution. Specifically, the drying step may be performed at 70°C or higher. As the drying step is performed within the above temperature range, there is an advantage that the aqueous solution is easily gelled. If the drying step is performed at a temperature lower than the above temperature range, there is a problem that the aforementioned gelling is not easily performed.

[0084] In one embodiment, the first heat treatment step of heat-treating the gelled product to obtain powder may be to pulverize the gelled product to form combustion powder.

[0085] In one embodiment, the first heat treatment step of heat-treating the gelled product to obtain powder may be performed at 200°C or higher. Specifically, the first heat treatment step may be performed at 250°C or higher, specifically in the range of 280 to 500°C, and more specifically in the range of 280 to 350°C. As the first heat treatment step is performed within the aforementioned range, the powdering of the gelled product can be easily performed.

[0086] In one embodiment, the first heat treatment step may be performed in an air atmosphere. Since the first heat treatment step is performed in an air atmosphere, the gelled powder expands easily upon combustion, and there is an advantage that the catalyst is easily dispersed within the carbon matrix.

[0087] The step of synthesizing carbon nanotubes by providing a carbon source to the metal catalyst and heat-treating it may be a step of synthesizing carbon nanotubes by supplying a carbon source, which is a carbon source, to the metal catalyst and heat-treating it. The carbon source may include at least one of CO, CH4, C2H2, and C2H4.

[0088] The step of synthesizing carbon nanotubes by providing a carbon source to the metal catalyst and heat-treating it can be performed at 800°C or higher. Specifically, the step of synthesizing carbon nanotubes can be performed at 900°C or higher. As carbon nanotubes are synthesized within the above temperature range, carbon nanotubes can be easily synthesized by a metal catalyst containing a valuable metal.

[0089] In the step of synthesizing the carbon nanotubes, the metal catalyst may utilize combustion powder that has undergone the first heat treatment step described above, or it may utilize combustion powder that has undergone both the first and second heat treatment steps described above. Thus, the carbon nanotube synthesis method of the present invention may synthesize carbon nanotubes by providing a carbon source to a powder-phase metal catalyst derived from a solution containing a valuable metal obtained from a waste battery and heat-treating it.

[0090] In one embodiment, after the first heat treatment step, a second heat treatment step may be included in which the combustion powder that has undergone the first heat treatment step is heat-treated at a higher temperature than the first heat treatment step before synthesizing carbon nanotubes. The second heat treatment step may be a step of applying heat to the combustion powder to control the formation of a catalyst in which a metal catalyst is dispersed within a carbon matrix.

[0091] Specifically, the second heat treatment step may be performed at 500 ℃ or higher. Specifically, the second heat treatment step may be performed in the range of 500 ℃ to 800 ℃, more specifically, in the range of 600 ℃ to 700 ℃. As the heat treatment is performed in the above temperature range, a metal catalyst in which metal particles are appropriately dispersed within a carbon matrix may be formed.

[0092] If the above temperature range exceeds the upper limit of the aforementioned range, there is a problem in that the carbon is excessively carbonized due to excessive heat supply. If the above temperature range exceeds the lower limit of the aforementioned range, there is a problem in that the metal particles are not easily dispersed within the carbon matrix.

[0093]

[0094] Preferred embodiments and comparative examples of the present invention are described below. However, the following examples are merely preferred embodiments of the present invention, and the present invention is not limited to the following examples.

[0095]

[0096] <Experimental Example 1>: Preparation of Catalyst and Carbon Nanotubes from NCM Extraction Solution

[0097] <Example 1>:

[0098] Preparation of metal catalysts for carbon nanotube synthesis

[0099] (Raw material preparation stage)

[0100] In order to prepare the raw material, Black Alloy or Black Mass, NCM 622 waste batteries were prepared. The waste batteries were crushed and subjected to high-temperature reduction heat treatment to produce 15 kg of Black Alloy.

[0101]

[0102] (Lithium leaching and solid-liquid separation step)

[0103] The above black alloy was leached in sulfuric acid (H2SO4) at a concentration of 1.5 M for about 2 hours, and the residue obtained through filtration was dried at 100 ℃.

[0104]

[0105] (NCM leaching step)

[0106] The above dried residue was added to 2 M sulfuric acid for NCM leaching and leached for approximately 4 hours to obtain an NCM solution.

[0107]

[0108] (Step of adding chelating agent and pH adjuster)

[0109] Ethylenediaminetetraacetic acid (EDTA), a chelating agent, was added to the above NCM solution, and subsequently, an ammonia solution, a pH adjuster, was added to maintain the pH at 10. At this time, the ratio of metal ions to chelating agent was added to be 1:1.5.

[0110]

[0111] (Drying stage)

[0112] After mixing a chelating agent and an ammonia solution with the above NCM solution, the solution was gelled by undergoing a drying step at 90°C.

[0113]

[0114] (1st heat treatment step)

[0115] The above gelled product was heat-treated at 300°C in an air atmosphere to obtain combustion powder.

[0116]

[0117] Preparation of metal catalysts for carbon nanotube synthesis

[0118] (Carbon Source Supply and Heat Treatment Steps)

[0119] Carbon nanotubes were formed by supplying CO gas, a carbon source, at a flow rate of 1 L / min to 100 g of combustion powder, which is a metal catalyst prepared by the above-described method, and heat-treating it at 900 ℃.

[0120]

[0121] <Comparative Example 1>

[0122] The procedure was carried out in the same manner as Example 1, except that NCM 111 waste batteries were used in the raw material preparation step.

[0123]

[0124] <Example 2>

[0125] In the raw material preparation step, NCM 111 waste batteries were used, and the procedure was carried out in the same manner as Example 1, except that Mn was removed by performing a solvent extraction process on the NCM solution obtained through the NCM leaching step using a cation extractant (solvent) containing D2EHPA.

[0126]

[0127] <Experimental Example 2>: Control of Metal:Chelating Agent Ratio

[0128] <Comparative Example 2>

[0129] The procedure was carried out in the same manner as Example 1, except that the ratio of metal ions to chelating agent was 1:1 in the step of adding chelating agent and ammonia.

[0130]

[0131] <Comparative Example 3>

[0132] The procedure was performed in the same manner as Example 1, except that the ratio of metal ions to chelating agent was 1:1.25 in the step of adding chelating agent and ammonia.

[0133]

[0134] Table 1 below shows the characteristics of catalysts and carbon nanotubes prepared according to the embodiments and comparative examples of the present invention. Specifically, the following conditions, catalyst characteristics, and carbon nanotube characteristics were measured by the following method.

[0135] NCM Ratio: Indicates the NCM ratio (Ni:Co:Mn) in the waste battery during the raw material preparation stage.

[0136] Degree of Crystallinity: Calculated using the formula (Crystallinity) explained below.

[0137] Peak ratio: Calculated based on XRD peak intensity measured using an XRD SLS2 device.

[0138] Catalyst particle size: The average particle size (D50) of the catalyst particles was measured using a FE-TEM device.

[0139] Conditions Catalyst Characteristics Carbon Nanotube Characteristics NCM ratio in black alloy (Ni:Co:Mn) Ratio of Mn in Ni:Co:Mn in leaching solution Metal ion:chelating agent ratio Degree of crystallinity [%] Average catalyst particle size [nm] Synthesis status Shape Example 1 6:2:2 16.8 1:1.5 8.7 7 21.20 Metal dispersion in carbon nanotubes Comparative Example 1 1:1:1 26.1 1:1.5 9.1 23 5.3X Carbon Onion Example 2 1:1:1 10.6 1:1.5 8.9 5 23.50 Metal dispersion in carbon nanotubes Comparative Example 2 6:2:2 16.2 1:1 37.25 76.2X Carbon Onion Comparative Example 3 6:2:2 15.2 1:1.25 17.8 44 5.8△ Metal dispersion in carbon nanotubes, but growth length decreases

[0140] Looking at Table 1 above, it can be seen that when the Mn content in the leaching solution is high, as in Example 1 and Comparative Example 1, the degree of crystallization and catalyst particle size fall outside the scope of the present invention, and when carbon nanotubes are synthesized using the catalyst, the metal within the carbon nanotubes is not dispersed and grows as carbon onions. In contrast, as in Example 2, even if the NCM ratio in the Black Alloy is the same as in Comparative Example 1, if a separate process to remove manganese is performed, the degree of crystallization and the average catalyst particle size fall within the scope of the present invention, and accordingly, it was confirmed that carbon nanotube synthesis is easy. Specifically, it was confirmed that when the doping amount of manganese is high, it strongly binds to carbon, so even if the particle size is 50 nm or less, it does not grow into carbon nanotubes but grows as carbon onions. Furthermore, when the average particle size approaches 50 nm, although carbon nanotubes grow, there is a problem in that the growth amount and length are reduced, making it impossible to grow the target carbon nanotubes. Looking at Example 1, Comparative Example 2, and Comparative Example 3, it can be seen that when the ratio of metal ions to chelating agent is 1:1.5, the dispersion of metal within carbon nanotubes is facilitated. In contrast, Comparative Example 2, in which the ratio of chelating agent is excessively lower than the range of the present invention, shows that the metal within the carbon nanotubes is not dispersed and forms carbon onions. Comparative Example 3 shows that regarding the catalyst, the degree of crystallinity is excessively high, and during carbon nanotube synthesis, although the metal within the carbon nanotubes is dispersed, the growth length decreases, resulting in a problem where carbon nanotubes are not easily formed.

[0141]

[0142] <Evaluation Example 1>: Amorphousness of catalyst according to the ratio of metal ions to chelating agents

[0143] Figure 2 is a graph showing the degree of amorphousness of the catalyst according to the ratio of the chelating agent after the heat treatment process, according to the embodiments and comparative examples of the present invention.

[0144] Figure 3 shows TEM images of catalysts according to embodiments and comparative examples of the present invention.

[0145] FIG. 2 is a graph showing the degree of amorphousness of catalysts prepared according to Example 1 and Comparative Example 2 of the present invention. In the case of Example 1, where the ratio of metal ions to chelating agents satisfies the aforementioned range, it can be confirmed that no metal ion peak is expressed. In contrast, in the case of Comparative Example 2, it can be confirmed that peaks are expressed at approximately 15°, approximately 18°, approximately 37°, approximately 43°, approximately 63°, approximately 75°, and approximately 78°, which confirms that a metal ion peak is expressed.

[0146] Specifically, crystallinity was calculated using the following formula through Figure 3.

[0147] [ceremony]

[0148]

[0149] When examining the crystallinity of the catalyst according to the above formula, it can be confirmed that Comparative Example 2 is higher than 9%, and Example 1 is 9% or less in terms of crystallinity. This indicates that it is amorphous.

[0150] In FIG. 3, (a) is a TEM image of the catalyst prepared according to Comparative Example 1, and (b) is a TEM image of the catalyst prepared according to Example 1. Referring to FIG. 3, it can be seen that in the case of Comparative Example 1, unlike Example 1, a crystal shape is visible.

[0151]

[0152] <Evaluation Example 2>: Comparison of Carbon Nanotube Synthesis Results According to Mn Content in Raw Materials

[0153] FIG. 4 is a TEM image of a metal catalyst formed according to an embodiment of the present invention, and FIG. 5 is an elemental image of a metal catalyst prepared according to an embodiment of the present invention.

[0154] Referring to Fig. 4, when a second heat treatment process is performed on the combustion powder at around 500°C, it can be seen that a catalyst in which metal particles are dispersed in a carbon matrix having particles of 50 nm or less is realized. At this time, the left side of Fig. 4 is observed at a 200 nm scale, and the right side of Fig. 4 is observed at a 20 nm scale.

[0155] Referring to FIG. 5, it can be seen that an amorphous phase is easily formed in the combustion powder prepared according to Example 1 of the present invention, even if it contains impurities such as manganese. At this time, the left side of FIG. 5 is a TEM image of the combustion powder prepared at 300 nm, and the right side (Ni, Co, C, Mn) is a photograph showing the ratios for each element separately.

[0156] FIGS. 6 to 8 are structural photographs of carbon nanotubes synthesized according to embodiments and comparative examples of the present invention. In this case, the left figure of FIGS. 6 to 8 is a TEM photograph of a carbon nanotube prepared at 200 nm, and the right figure (Ni, Co, C, Mn) is a photograph showing the ratio of each element separately.

[0157] Referring to FIGS. 6 to 8, FIG. 6 shows a carbon nanotube synthesized according to Example 1, FIG. 7 shows a carbon nanotube synthesized according to Comparative Example 1, and FIG. 9 shows a carbon nanotube synthesized according to Example 2. FIG. 6 can be seen to show a form in which a 50 nm metal catalyst containing nickel, cobalt, and manganese is present inside the carbon nanotube. FIG. 7 shows that carbon nanotubes are not formed, and a carbon onion structure in which carbon is aggregated around the catalyst is present.

[0158] This is related to the bonding strength between manganese and carbon, and since all five electrons in the outermost d orbitals of manganese are unpaired electrons, the bonding strength with carbon is very strong. Accordingly, when the proportion of manganese increases, the bonding strength with carbon increases, so the manganese cannot properly release the carbon and cannot grow into a carbon nanotube, and it can be confirmed that a structure in which the carbon surrounds the metal catalyst is realized. Through this, it was confirmed that the concentration of manganese is preferably about 33% or less based on 100 wt% of the metal catalyst.

[0159] In contrast, as shown in Fig. 8, in Example 2, where the ratio of nickel to cobalt was controlled to 1:1 by reducing the concentration of manganese in the NCM solution, it was confirmed that the synthesis of carbon nanotubes was easily performed. In the case of cobalt, there are 8 outermost electrons in the d orbitals, and the number of unpaired electrons is 3. Accordingly, since there is no significant difference from nickel, which has 2 unpaired electrons, it was confirmed that carbon nanotubes were easily synthesized.

[0160]

[0161] The present invention is not limited to the above embodiments and can be manufactured in various different forms, and those skilled in the art will understand that the invention can be implemented in other specific forms without changing the technical concept or essential features of the invention. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive.

Claims

1. The invention relates to a metal catalyst containing a valuable metal, A catalyst for carbon nanotube synthesis satisfying the following formula 1 at 9% or less. <Equation 1> (In the above Equation 1, I net represents the area of ​​the XRD peaks of catalytic oxides, including the XRD peaks of Ni oxide, Co oxide, and Mn oxide, and I tot is the total XRD peak area and I bgr represents the XRD peak area of ​​the background regions) 2. In Paragraph 1, The above catalyst for carbon nanotube synthesis is a catalyst for carbon nanotube synthesis derived from an aqueous transition metal solution recovered from spent batteries.

3. In Paragraph 1, A catalyst for synthesizing carbon nanotubes with an average particle size (D50) of 50 nm or less.

4. In Paragraph 1, The above valuable metals include nickel, cobalt, and manganese, and A carbon nanotube synthesis catalyst having a manganese content of 33 wt% or less based on 100 wt% of the carbon nanotube synthesis catalyst.

5. In Paragraph 1, A catalyst for synthesizing carbon nanotubes in which particles of the above-mentioned valuable metal are dispersed within a carbon matrix.

6. In Paragraph 1, A catalyst for carbon nanotube synthesis that, in terms of XRD peak values, does not include at least one peak among 2θ = 15°±0.5°, 18°±0.5°, 37°±0.5°, 43°±0.5°, 63°±0.5°, 75°±0.5°, and 78°±0.5°.

7. A step of obtaining a solution containing valuable metals recovered from waste batteries; A step of adding a chelating agent to a solution containing the above valuable metal; A step of preparing a metal catalyst by heat-treating a solution mixed with the above chelating agent; and The method includes the step of synthesizing carbon nanotubes by providing a carbon source to the metal catalyst and heat treating it. A method for manufacturing carbon nanotubes in which the molar ratio of the metal ion of the above-mentioned valuable metal to the chelating agent ion (moles of metal ion:moles of chelating agent ion) is 1:1.28 or higher.

8. In Paragraph 7, The step of adding a chelating agent to the solution containing the above valuable metal is, A method for manufacturing carbon nanotubes comprising the step of adding a pH adjuster to a solution mixed with the above-mentioned valuable metal and the above-mentioned chelating agent.

9. In Paragraph 8, A method for manufacturing carbon nanotubes by adjusting the pH of a solution mixed with the above-mentioned valuable metal and the above-mentioned chelating agent to 7 or higher.

10. In Paragraph 7, The step of preparing a metal catalyst by heat-treating the solution mixed with the above chelating agent is: A drying step for gelling the solution mixed with the above chelating agent; and A method for manufacturing carbon nanotubes comprising a first heat treatment step of heat-treating the gelled product above to obtain a powder.

11. In Paragraph 10, A method for manufacturing carbon nanotubes in which the above drying step is performed at a temperature of 50°C or higher.

12. In Paragraph 10, A method for manufacturing carbon nanotubes in which the first heat treatment step is performed at 200 ℃ or higher.

13. In Paragraph 7, A method for manufacturing carbon nanotubes in which the carbon source comprises at least one of CO, CH4, C2H2, and C2H4.

14. In Paragraph 7, A method for manufacturing carbon nanotubes in which the step of synthesizing carbon nanotubes by providing a carbon source to the metal catalyst and heat treating it is performed at 800°C or higher.

15. In Paragraph 7, After obtaining a solution containing valuable metals recovered from the above waste battery, A method for manufacturing carbon nanotubes comprising the step of removing manganese from a solution containing the above-mentioned valuable metal.

16. In Paragraph 7, The step of obtaining a solution containing valuable metals recovered from the above waste battery is, A method for manufacturing carbon nanotubes obtained from black alloy or black mass using a solution containing the above-mentioned valuable metal.

17. In Paragraph 7, The step of obtaining a solution containing valuable metals recovered from the above waste battery is, A step of leaching lithium from the black alloy or the black mass; A step of obtaining a residue by separating the solid and liquid of the product obtained by leaching the lithium above; and A method for manufacturing carbon nanotubes comprising the step of performing acid leaching on the above residue.

18. In Paragraph 10, A method for manufacturing carbon nanotubes, comprising a second heat treatment step of heat-treating the powder at a higher temperature than the first heat treatment step after the first heat treatment step.

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