Carbon nanotube hybrid materials and methods for manufacturing such hybrid materials

Abstract

Carbon nanotube (CNT) hybrid materials and methods for manufacturing such materials. The carbon nanotube (CNT) hybrid powder material comprises a CNT network in which particles of a second material are densely dispersed. In one example, the material comprises a blend of particles of a catalyst supported on a metal oxide and particles of a second material, and a CNT network grown on the supported catalyst within the blend. The CNT network is effective for dispersing the particles of the second material.

Description

[0001] Cross-references to related applications

[0002] This application claims priority to provisional patent application 63 / 146,980, filed on February 8, 2021, the entire disclosure of which is incorporated herein by reference for all purposes. Background Technology

[0003] This disclosure relates to carbon nanotube (CNT) hybrid materials and methods for manufacturing such hybrid materials.

[0004] There are numerous commercial applications utilizing the material properties of carbon nanotubes (CNTs). For example, carbon nanotubes have been used to enhance the electrical, thermal, and mechanical properties of various carbon and metal oxide materials. Carbon nanotubes blended with conductive carbon (carbon super-p) in lithium-ion battery cathodes or graphite in anodes can achieve the highest reversible energy capacity of any other carbon material for its use in lithium-ion batteries, while increasing the number of charge and discharge cycles without experiencing any energy capacity loss (longer durability). They are also outstanding materials for supercapacitor electrodes.

[0005] CNTs have also been used to improve the mechanical and thermal stability properties of thermoplastic and elastomer formulations for various commercial products, such as conductive polymers, plastics, tires, seals, gaskets, etc. Compared to other fillers widely used to reinforce the mechanical and final properties of rubber (such as carbon black and silica), the high aspect ratio of CNTs allows for lower loading concentrations. The degree of property improvement depends on the particle size, their structure, and surface activity. The key to the effectiveness of this filler is achieving sufficiently high dispersion using specific mixing techniques (such as optimized melt mixing or latex mixing techniques) combined with surface treatment or pre-preparation of the filler in suspension. The high aspect ratio of CNTs allows for lower loading concentrations of CNT filler, resulting in high effectiveness, thus reducing the density and weight of elastomer materials compared to carbon black (CB) fillers, chopped carbon fibers, silica, or stainless steel fiber materials. The reinforcing effects that improve elasticity, stiffness, toughness, and strength are generally attributed to strong rubber-filler interactions and their dispersibility.

[0006] Large CNT agglomerates are sometimes mechanically blended with different carbon or metal oxide materials. CNT agglomerates with a diameter of mm need to be milled before being mixed with carbon materials that generally have a very small particle size (a few micrometers), otherwise an inhomogeneous blend will be obtained. During the milling process, CNTs may break, which may negate the performance benefits of the blend relative to the carbon material.

[0007] Another method used in the prior art to prepare CNT-carbon hybrid materials is to load an active metal onto the surface of a carbon material and then grow CNTs to produce a "hairy" carbon hybrid. This method may have limitations when the primary particles of carbon black are comparable in size to the particles of the active phase.

[0008] Extensive research has focused on the dispersion of CNTs, including ball milling, ultrasonication, and physical and chemical modification. However, these methods generally require complex processing and may break CNTs into shorter segments. Summary of the Invention

[0009] In one instance, this disclosure relates to a novel method for producing CNT hybrid materials. This disclosure also relates to CNT hybrid materials. Compared to the physical mixing of pre-synthesized CNTs and other particulate materials, this method produces CNT hybrid materials in a safe, scalable, and cost-effective manner. In some instances, CNT hybrid materials are used to improve the mechanical, thermal, and / or electrical properties of different particulate materials. In some instances, the particulate materials include different forms of carbon (e.g., graphene, synthetic and natural graphite, carbon black, activated carbon, carbon fibers, etc.). In some instances, the particulate materials include one or more metal oxides, such as silicon dioxide and aluminum oxide. In some instances, CNT hybrid materials are used in electrode materials in battery applications. This includes active materials used in cathodes (including, but not limited to, lithium cobalt oxide or lithium cobalt, lithium manganese oxide (also known as spinel or lithium manganate), lithium iron phosphate, and lithium nickel manganese cobalt (or NMC) and lithium nickel cobalt aluminum oxide (or NCA)) and anodes.

[0010] In one example, a method for dispersing CNTs includes blending particles of a metal oxide-supported catalyst with particles of a second material. The blend does not require any particular degree of mixing or homogeneity. The components of the blend may be homogeneous or substantially homogeneous. Alternatively, the components of the blend do not need to be uniformly distributed in the blend. The particles of the second material are dispersed by CNTs grown on the metal oxide-supported catalyst. In some examples, the second material is a carbon material in varying proportions (in some examples, this can vary between 5 and 50 weight percent). In some examples, the second material comprises one or more metal oxides, such as silica and alumina. In one example, blending the different particles includes preparing a paste of the metal oxide-supported catalyst and the second material. In some examples, the paste is prepared using an organic solvent, such as an alcohol, in a high-speed mixer. The solvent is evaporated in an oven at atmospheric pressure or under vacuum. In some instances, CNT synthesis is carried out in fluidized bed or rotating tube reactors in the presence of a carbon source (C2H4, C2H2, CH4, CO, etc.) in H2 or an inert gas, at a total pressure from atmospheric pressure to 100 psig, and at temperatures between 400°C and 1000°C.

[0011] In some instances, the blending of these two materials can be achieved by preparing an organic paste containing both a metal oxide-supported catalyst and a carbon material in a high-speed mixer, evaporating the organic solvent, and then synthesizing carbon nanotubes in a rotating tube or fluidized bed reactor using different carbon sources (CO, CH4, C2H2, C2H4, etc.) and process conditions (T = 400-1000 °C, P = ambient pressure up to 100 psi) to form a hybrid material. By using a supported metal catalyst, the morphological properties (diameter and length) of CNTs and the size of CNT agglomerate particles can be controlled. When a metal oxide-supported catalyst is combined with a carbon material (or a different second material), CNTs tend to separate large agglomerate particles, allowing for good dispersion of smaller second material (e.g., carbon) aggregate particles. The particle size of the carbon powder is less than 100 micrometers, which represents a limitation for the use of these materials in conventional fixed-bed and moving-bed reactors. Compared to other catalytic reactors, fluidized bed and rotary kiln reactors have demonstrated numerous advantages when operating with fine powders; for example, excellent heat transfer and contact between gaseous and solid particles, especially when both density and reactor volume change during CNT growth. Products can be manufactured in continuous or semi-continuous operation modes, enabling the production of hundreds of metric tons of CNT-carbon hybrid materials annually.

[0012] In one instance, the method of this disclosure: i) increases the dispersion of a second (e.g., carbon) material, thereby enabling CNTs to separate coarse agglomerated carbon particles; ii) creates a closer contact between the particles of the CNTs and the second material; iii) increases the surface area and pore volume of the hybrid material; and iv) enhances the density properties of the product.

[0013] The result is a more compact mixture of CNTs and the second material. Another result is that the electrical and mechanical properties of the hybrid material can be increased beyond those available in the second material itself. Yet another result is that composite materials can be formulated at a wider range of CNT loading levels compared to materials in which CNTs are physically mixed. Furthermore, the surface of the particles of the second material is not covered by CNTs, and therefore can be used to contribute to the properties of the hybrid material.

[0014] This CNT-carbon dispersion method is far more efficient than mechanically mixing CNTs and carbon materials. For example, when synthesizing multi-walled carbon nanotubes (MWCNTs), the particles can grow to diameters of several millimeters, requiring the agglomerated MWCNTs to be broken into smaller particles before being mixed with other carbon materials, such as graphite or carbon black particles with particle sizes of tens of micrometers. During this process, the CNT tubes may break, resulting in a reduced aspect ratio and mitigating the properties of the carbon hybrid material.

[0015] Another example considers growing carbon nanotube (CNT) networks on metal oxide catalyst supports. Colloidal particles such as silica, alumina, magnesium, or titanium are deposited on the surface of a metal oxide substrate along with an active metal via an impregnation technique, followed by drying and calcination steps. The active metal refers to a transition metal, such as Co, Fe, Ni, Cu, Ru, Pd, Mo, W, etc., which is deposited on the surface of a metal oxide (e.g., silica (SiO2), alumina (Al2O3), magnesium oxide (MgO), titanium dioxide (TiO2), or mixtures thereof, such as a catalyst support comprising up to about 5% magnesium oxide and about 80% to about 98% alumina or carbon (e.g., natural or synthetic graphite or graphene)) support by an impregnation method. The amount of active metal is controlled to avoid the formation of a dense CNT blanket on the metal oxide / substrate surface (which occurs when the active metal is deposited on the substrate surface), and CNT growth is controlled. This technique forms a network of long SWCNTs (CNT length typically ≥ 5 μm) covering the outer surface of the silica particles. When carbon nanotubes grow in a network form on the surface of silica particles, the agglomerated silica particles separate and disperse from each other. This creates greater contact between the surface of these particles and molecules of other present substances, such as elastomers. A smaller amount of filler is then required to achieve the greater benefits of the elastomer's mechanical properties. In one example, this CNT-silica hybrid material thus reduces or eliminates the need for, for example, using a combination of carbon black and silica for reinforcing tires.

[0016] In some examples of CNT-metal oxide hybrid materials, an impregnation technique is used to deposit a solution containing an active metal and colloidal particles (preferably silica or alumina) onto a metal oxide substrate. The material is then dried and calcined to form a metal oxide active phase precursor. The colloidal particles alter the surface roughness of the metal oxide substrate. The active metal is preferentially loaded onto the surface of the colloidal particles. Compared to conventional catalyst preparation methods, a network of long, straight CNTs is observed on the synthesized, surface-modified metal oxide substrate. This CNT structure is expected to provide better performance in tire reinforcement and conductive coatings compared to forming a thick CNT surface blanket with shorter, entangled tubes.

[0017] In some examples of the preparation of SWCNT networks on silica or graphite supports, the support surface is impregnated with an aqueous solution of colloidal silica particles containing salts of Co and Mo, as well as surface modifiers, additives, and nonionic surfactants (only when graphite or other hydrophobic catalyst supports are used). After calcination of the catalyst, the metal salt deposited on the surface is converted into a metal oxide active phase precursor. The metal oxide precursor (Co) is converted into metal nanoparticles during the activation step (i.e., reduction in H₂). During the synthesis of SWCNTs at high temperatures in the presence of CO, the reduced Mo oxide is converted into molybdenum carbides loaded with Co nanoparticles.

[0018] In some examples of preparation of CNT-carbon networks, a metal oxide-supported catalyst (e.g., a combination of Fe, Co, Ni, Mo, or W supported on Al2O3 or a mixed oxide containing Al2O3-TiO2, Al2O3-MgO, Al2O3-ZrO, Al2O3-SiO2) is blended with a carbon material (graphite, carbon black, activated carbon, etc.). In some examples, blending is performed in a mixer apparatus using an organic solvent to form a paste. The solvent is removed by evaporation at a controlled temperature and can be collected using a vacuum apparatus. The dried material blend is then used to synthesize the CNT-carbon hybrid material. The desired combination of metal oxide-supported catalyst and carbon material depends on the specific application (tires, energy storage, other materials for conduction or reinforcement applications, etc.).

[0019] In some instances, the carbon nanotube (CNT) hybrid powder material comprises a CNT network in which particles of a second material are intimately dispersed. In some instances, the hybrid material further comprises particles of a first material different from the second material. In some instances, the first material comprises metal oxide support particles. In some instances, the first material also contains a catalyst on at least some of the metal oxide support particles.

[0020] In some instances, carbon nanotube (CNT) hybrid materials comprise blends of particles containing a first material and particles of different second materials. A network of CNTs is coupled to the particles of the first material. The CNT network is effective for dispersing the particles of the second material. In some instances, the first material comprises metal oxide support particles. In some instances, the first material further comprises a catalyst on at least some of the metal oxide support particles.

[0021] Some examples include one or any combination of the above and / or below features. In one example, the second material comprises carbon. In one example, the second material comprises at least one of carbon black, graphite, and graphene. In one example, the second material comprises one or more metal oxides, such as silicon dioxide and / or alumina. In one example, the catalyst support comprises at least one of alumina, silicon dioxide, and magnesium oxide. In one example, the CNT comprises at least one of single-walled CNTs (SWCNTs), few-walled CNTs (FWCNTs), and many-walled CNTs (MWCNTs). In one example, the material comprises from about 5% by weight to about 50% by weight of CNTs. In one example, the material comprises from about 10% by weight to about 50% by weight of a catalyst.

[0022] Some examples include one or any combination of the above and / or below features. In one example, at least some of the CNTs are directly coupled to particles of the first material and are adjacent to, but not directly coupled to, particles of the second material. In one example, at least some of the CNTs are directly coupled to particles of the first material and also directly coupled to particles of the second material. In one example, the material has a thickness of at least about 140 μm. 2 / g BET surface area. In one example, the material has a pore volume of at least about 0.43 ml / g. In one example, the material has a tap bulk density of about 0.102 g / ml or less. In one example, the material has an average particle size of at least about 42 micrometers.

[0023] In other examples, carbon nanotube (CNT) hybrid materials comprise a substrate containing both a colloidal material and a catalyst precursor supported on a support surface, and CNTs on both the support surface and the colloidal material.

[0024] Some examples include one or any combination of the above and / or below features. In one example, the carrier surface comprises silica or carbon. In one example, the colloidal material comprises colloidal silica.

[0025] In other examples, methods for forming carbon nanotube (CNT) hybrid materials include forming a blend of particles comprising a catalyst supported on a metal oxide and a second material, and synthesizing CNTs on the blend to produce the CNT hybrid material.

[0026] Some examples include one or any combination of the above and / or below features. In one example, the second material includes at least one of carbon black, graphite, graphene, and silicon dioxide. In some examples, at least some of the metal oxide catalyst support is removed from the CNT hybrid material. In one example, the metal oxide catalyst support is removed by chemical purification of the hybrid material.

[0027] In other examples, methods for forming carbon nanotube (CNT) hybrid materials include preparing a substrate comprising both a colloidal material and a catalyst precursor supported on a support surface, and synthesizing CNTs on both the support surface and the colloidal material to produce the CNT hybrid material.

[0028] Some examples include one or any combination of the above and / or below features. In one example, the carrier surface comprises silica or carbon. In one example, the colloidal material comprises colloidal silica. Attached Figure Description

[0029] The following discussion of at least one example, with reference to the accompanying drawings, is not intended to be drawn to scale. The drawings are included to provide illustration and further understanding of the various aspects and examples, and are incorporated into and constitute a part of this specification, but are not intended to be a definition of limitation of the invention. In the drawings, the same or substantially the same components shown in the various figures may be represented by the same reference numerals or numbers. For clarity, not every component may be labeled in every figure. In the drawings:

[0030] Figure 1A Figure 1B shows four stages of carbon deposition in the tip-growth CNT growth model, where the active metal-substrate interaction is weak, and Figure 2B shows three stages of carbon deposition in the base-growth CNT growth model, where the active metal-substrate interaction is strong.

[0031] Figure 2 This is a model for the growth of MWCNTs on supported metal oxide catalysts.

[0032] Figure 3 A model for the formation of CNT network carbon black hybrid materials.

[0033] Figures 4A-4C SEM images of SWCNTs synthesized using a conventional CoMo / SiO2 catalyst, taken at different magnifications.

[0034] Figures 5A-5DSEM images of catalyst particles, SWCNT networks formed on silica nanoparticles, SWCNT networks on SiO2 substrates, and individual SWCNT bundles at different magnifications. Figure 5E-5G SEM images of SWCNT networks formed on smaller silica aggregates at different magnifications.

[0035] Figure 6A and 6B SEM images of long and straight SWCNT networks formed on silica nanoparticles by colloidal silica additives at different magnifications.

[0036] Figure 7A and 7B SEM images of carbon black starting material at different magnifications.

[0037] Figures 8A-8C SEM images of the metal oxide-supported catalyst at different magnifications.

[0038] Figures 9A-9C SEM images of catalyst-carbon black blends supported on metal oxides at different magnifications.

[0039] Figures 10A-10C SEM images of MWCNT-carbon black hybrid materials obtained by using 15% metal oxide catalyst in the blend at different magnifications.

[0040] Figure 11A and 11B SEM images of MWCNT-carbon black hybrid materials obtained by using 15% metal oxide catalyst in the blend at different magnifications. Figure 11C and 11D Comparative SEM images of MWCNT-carbon black hybrid materials obtained by using 25% metal oxide catalyst in the blend at the same magnification, and Figure 11E and 11F SEM images of MWCNT-carbon black hybrid materials obtained by using 50% metal oxide catalyst in the blend at the same magnification.

[0041] Figure 12A-12D Thermogravimetric (TGA) analyses were performed on carbon black, MWCNT-carbon black hybrids obtained by using 15% metal oxide catalyst in the blend, MWCNT-carbon black hybrids obtained by using 25% metal oxide catalyst in the blend, and MWCNT-carbon black hybrids obtained by using 50% metal oxide catalyst in the blend.

[0042] Figures 13A-13DSEM images of MWCNT-carbon black hybrid material at different magnifications after purification.

[0043] Figure 14 TGA analysis of purified MWCNT-carbon black hybrid material.

[0044] Figure 15 To display a TEM image of a metal encapsulated by a graphite coating.

[0045] Figures 16A-16D TEM images of MWCNT-graphite hybrid materials at different magnifications.

[0046] Figure 17 TGA analysis of MWCNT-graphite hybrid materials.

[0047] Figure 18A For FWCNT's TGA analysis, and Figure 18B TGA analysis of FWCNT-graphite hybrid material after purification.

[0048] Figure 19A and 19B SEM images of the original and purified FWCNT-graphite hybrid materials, respectively.

[0049] Figure 20A and 20B TGA analysis of CNT-carbon black hybrid materials and CNT-graphite hybrid materials, respectively.

[0050] Figure 21A and 21B SEM images of MWCNT-carbon black hybrid material and MWCNT-graphite hybrid material, respectively.

[0051] Figure 22A SEM images of graphene nanosheets, and Figure 22B and 22C The images are SEM images of the MWCNT-graphene nanosheet hybrid material taken at low and high magnification, respectively. Detailed Implementation

[0052] The examples of materials and methods discussed herein are not limited in application to the details set forth in the following description or shown in the accompanying drawings. The materials and methods described can be implemented in other examples and can be practiced or performed in various ways. The specific examples of implementations provided herein are for illustrative purposes only and are not intended to be limiting. In particular, the functions, elements, and features discussed in conjunction with any one or more examples are not intended to exclude similar roles in any other examples.

[0053] The instances disclosed herein may be combined with other instances in any manner consistent with at least one of the principles disclosed herein, and references to “instance,” “some instances,” “alternative instances,” “various instances,” “an instance,” etc., are not necessarily mutually exclusive and are intended to indicate that a particular feature, structure, or property described may be included in at least one instance. The appearance of such terms in this document does not necessarily refer to the same instance.

[0054] Furthermore, the wording and terminology used herein are for descriptive purposes and should not be considered restrictive. Any reference to examples of materials and methods, materials, elements, actions, or functions mentioned herein in the singular may also cover plural embodiments, and any reference in the plural form may also cover singular examples. Therefore, references in either the singular or plural form are not intended to limit the materials or methods, their components, actions, or elements currently disclosed. The use of “comprising,” “including,” “having,” “containing,” “involving,” and variations thereof herein is intended to cover the items listed thereafter and their equivalents, as well as additional items. References to “or” may be interpreted as inclusive, and any term described using “or” may refer to any of the single, more than one, or all of the described terms.

[0055] This disclosure relates in part to a novel method for dispersing carbon nanotube (CNT) materials when they are used as additives to improve the mechanical, thermal, and / or electrical properties of various carbon and metal oxide materials. The resulting novel hybrid materials can be used in desired applications, including, but not limited to, electrode materials in battery and supercapacitor applications (both cathode and anode) and elastomeric formulations for various commercial products (tires, sealants, gaskets, etc.).

[0056] One of the main challenges in blending CNT materials with carbon, metals, or metal oxides is the difference in particle size and density between the two materials. In-situ or purified multi-walled carbon nanotubes have particles several millimeters in size and can reach 50 to 80 kg / m³. 3 The tap packing density varies between these values. Single-walled carbon nanotubes have particle sizes between 100 and 500 micrometers and a density of 40-90 kg / m³. 3 Density ranges between 100 and 400 kg / m³. Carbon black and graphite materials have particles of a few micrometers (typically between 5 and 50 micrometers for electrode applications) and density ranges between 100 and 400 kg / m³. 3 The tap packing density within a certain range. Silica has a size of tens of micrometers and a density of 50 to 120 kg / m³. 3Particles within a certain range. Due to differences in particle size and density between CNTs and carbon, as well as between metal oxide fillers, CNTs typically undergo grinding and sieving processes before being blended with carbon or metal oxide materials. During this process, tube breakage can occur, and the aspect ratio of the CNTs can be significantly reduced, thereby inhibiting the intended performance benefits.

[0057] One way to address this technical problem is to blend the metal oxide-supported catalyst with a carbon material or a different second material. The blend is in powder form. The synthesis of CNTs is carried out in a rotating tube reactor or fluidized bed reactor at moderately high temperatures and pressures between atmospheric pressure and 100 psi in the presence of a carbon source. The carbon source can be in an inert gas (e.g., N2, Ar) or diluted with H2. When the carbon source gas comes into contact with the catalyst particles at the synthesis temperature, the metal oxide is converted into active metal nanoparticles supported on a metal carbide substrate. For single-walled carbon nanotubes (SWCNTs), the minimum metal agglomerate cluster size is approximately 0.5 nm, while for MWCNTs, the critical metal cluster size is approximately 12 nm. Below these sizes, it is impossible to grow CNTs and form other types of carbon.

[0058] Figure 1 illustrates the different CNT growth mechanisms proposed in the literature. The mechanism depends on the interaction between the active metal catalyst and the substrate surface. When the active metal-surface interaction is weak, the surface contact is low (metal particles exhibit high contact angles), and CNT growth follows a tip growth mechanism. Figure 1A Large-diameter and short CNTs are formed. Conversely, when the interaction between the active metal and the surface is strong, the contact angle of the metal particles is low, resulting in higher surface contact, and CNT growth follows a bottom-growth mechanism. Figure 1B In this case, long CNTs with a smaller diameter are obtained.

[0059] Figure 2 This paper proposes a multi-walled carbon nanotube (MWCNT) growth mechanism when using metal-supported catalysts at different carbon source-catalyst contact times. Reactant molecules decompose at the catalyst active sites, leading to carbon deposition, and the product properties begin to change as a function of carbon accumulation. CNT growth primarily occurs via a bottom-mode mechanism. Figure 1B During the first 5 minutes of the reaction, the surface host catalyst particles, with dimensions of a few micrometers, begin to separate from each other due to CNT growth. A series of reactions occur, starting from the surface and proceeding to the nuclei of the catalyst grains; the particle size increases while the density decreases sharply. At a reaction time of 10 minutes, sheet-like CNTs are visible agglomerating together, forming nano-agglomerated cotton balls or ribbon-like structures with high carbon yields. CNT rods with a diameter of 10 nm and a length of approximately 5 micrometers were observed by TEM and SEM analysis.

[0060] Figure 3 This disclosure illustrates a CNT network-carbon hybrid material concept. Catalyst grains supported on metal oxides in powder form (<30 micrometer size) are blended with carbon black agglomerates, also in powder form, having a size of hundreds of nanometers to micrometers. The elementary carbon particles exhibit a size of approximately 20 to 80 nm and form aggregates with a size of several hundred nm. When this powder blend is fed into a reactor at high temperature and then contacted with a carbon source, the elementary catalyst particles forming the grains, with a size of several micrometers, begin to separate from each other, and deagglomeration of the carbon black particles occurs due to the formation of the CNT network. As the MWCNT yield increases, the density and size of the carbon particle agglomerates in the hybrid material continuously decrease. The degree of dispersion of the carbon black agglomerates is higher in the CNT-carbon black hybrid material than in carbon black itself. This same concept can be applied to graphite and activated carbon, as well as other materials such as metal oxides.

[0061] The formation of CNT networks grown on the supported catalyst enables the deagglomeration of particles of a second material (e.g., different forms of carbon or metal oxides) to which the metal oxide-supported catalyst (i.e., the first material) has been blended. This deagglomeration of the second material results in an expanded network comprising a CNT network in which less dense agglomerates of the second material are dispersed. The CNT network is densely dispersed among particles of the second material. In some instances, the CNTs are located close to the surface of the dispersed particles of the second material. In some instances, the CNTs are directly coupled to the particles of the second material. These expanded networks or hybrid materials can be mixed with polymers and elastomers to produce other hybrid materials. These hybrid materials may have properties different from those of the polymers or elastomers. For example, the conductivity of the material may be increased, or conductivity may be maintained but at lower CNT loadings. Furthermore, the expanded network can enhance the hybrid material. Higher conductivity and / or increased strength can be achieved with these hybrid materials compared to materials in which CNTs are physically dispersed in the second material. Furthermore, the method of this disclosure avoids the mixing constraints, effort, and health risks associated with physically dispersing CNTs in a second material, where the CNTs are grown on a metal oxide-supported catalyst that has been mixed with the second material.

[0062] In some instances, CNT-metal oxide hybrid materials are developed by growing carbon nanotubes on a metal oxide-supported catalyst, which is used to initiate growth in the presence of a carbon source (ethylene, acetylene, methane, carbon monoxide, etc.) using catalytic chemical vapor deposition (CCVD) in a fluidized bed, moving bed, or rotating tube reactor at temperatures ranging from 300 to 1000 °C. In some examples, the catalyst active metal consists of a combination of transition elements from Group VIII and / or VLB of the periodic table. In some instances, catalyst preparation involves impregnating a catalyst support in the presence of an aqueous solution containing iron, cobalt, nickel, molybdenum, or tungsten and colloidal particles of silica, alumina, or titanium hydroxide. The type of carbon nanotubes synthesized (SWCNT, FWCNT, and MWCNT) depends on the type of active metal, the carbon source used, and the reaction temperature. Compared to conventional carbon materials used in lithium-ion batteries, supercapacitors, etc., the MWCNT-graphite hybrid material obtained in this disclosure provides superior battery performance when used as an electrode, while the MWCNT-carbon black hybrid material enhances the mechanical properties of elastomers, rubbers, thermoplastics, etc.

[0063] The following are non-restrictive illustrative examples:

[0064] Example 1: SWCNT networks were synthesized on a SiO2 support.

[0065] Comparative Example

[0066] The catalyst was prepared by impregnating a silica support with a solution containing cobalt and ammonium heptamolybdate. The impregnated material was aged at room temperature under controlled humidity for 3 hours, then dried at 120°C for 3 hours and calcined at 450°C for 4 hours. The Co / Mo molar ratio was 0.5. SWCNT synthesis was carried out in a fluidized bed reactor using CO as the carbon source, operated at 760°C, 40 psi, and a reaction time of 50 minutes. Prior to SWCNT synthesis, the metal oxide precursor catalyst was activated by reduction at 680°C in the presence of H₂.

[0067] Figures 4A-4C SEM images of SWCNTs synthesized using a CoMo / SiO2 catalyst, taken at magnifications of 25 kx, 10 kx, and 100 kx, respectively. A dense blanket of entangled SWCNTs is observed. The tubes are short (<3 μm in length) and difficult to disperse in aqueous surfactant solutions or organic solvents using sonication techniques.

[0068] This public information

[0069] This embodiment describes a method for preparing SWCNT-SiO2 and SWCNT-graphite hybrid materials, and the resulting materials. In some instances, the method considers the use of surface-modifying agents (e.g., colloidal silica). The active metal is loaded onto the substrate by impregnation with colloidal silica.

[0070] To control the growth of CNTs on a silica support, a metal oxide-supported catalyst was prepared by impregnating the silica support with an aqueous solution containing cobalt and molybdenum salts in the same proportions as in the comparative examples above. Commercially available colloidal silica was mixed with the metal oxide-supported catalyst. Aging, drying, and calcination steps, as well as SWCNT synthesis, were performed under the same experimental conditions as described above.

[0071] Figure 5A-5G To correspond to the catalyst particles synthesized using the catalyst preparation method described above ( Figure 5A SEM images of SWCNT taken at different magnifications (40x and 50kx). Figure 5B This image shows a network of SWCNTs formed on silica nanoparticles. Photographed at 50 kx. Figure 5C This image shows a network of SWCNTs on a SiO2 substrate. Photographed at 75 kx. Figure 5D The SWCNT bundle is shown. Figure 5E , 5F The image shows the formation of a network on smaller silica aggregate particles, captured at increased magnification, using 5G. (As shown in...) Figure 5A-5G As can be observed, a network of SWCNTs forms on silica nanoparticles derived from colloidal silica additives and on a silica support. This network is formed from individual long SWCNT bundles having a length of ≥7 micrometers. In some embodiments, and in contrast to the comparative examples above, the SWCNTs of this disclosure are more readily dispersed in organic and aqueous surfactant solutions after purification, even when using lower sonic breaking power and less time.

[0072] To demonstrate the effectiveness of adding colloidal particles along with a metal salt to the impregnation solution to control SWCNT growth, another catalyst was prepared following the same procedure, but this time using graphite as the catalyst support. SWCNT synthesis was carried out in a rotating tube reactor at the same reduction and reaction temperatures and times used in the aforementioned examples. SEM images corresponding to the obtained SWCNT-graphite products are shown below. Figure 6A and 6B The image shows a network of long, straight SWCNTs formed on silica nanoparticles due to the addition of colloidal silica additives, wherein... Figure 6A It was shot at 50kx, and Figure 6B Close-up views at higher magnification. These images clearly show the formation of a network of long, straight SWCNTs on SiO2 nanoparticles derived from colloidal silica aggregates.

[0073] SWCNT-silica nanohybrids are suitable for conductive silica, as fillers for mechanical reinforcement of carbon black, and other applications.

[0074] Example 2: Synthesis of CNT-carbon black mixtures.

[0075] This embodiment (and Example 4 below) describes a method for preparing MWCNT-carbon black and MWCNT-graphite using a metal oxide-supported catalyst. In this case, fine particles of a pre-prepared metal oxide-supported catalyst are blended with carbon material in varying proportions to customize the MWCNT composition in the hybrid material. In some instances, a volatile organic solvent (preferably an alcohol) is used to prepare a paste containing both carbon and the fine catalyst powder. The dried powder is then fed into a reactor for MWCNT synthesis. MWCNTs grow to form as shown in the example. Figures 10A-10C and Figure 11A-11F The extended mesh-like structure is shown in the SEM image.

[0076] As described above, existing technologies disclose blends of carbon nanotubes with polymers, thermoplastics, and elastomers (to enhance their mechanical strength properties) and with graphite or conductive carbon (carbon super-P) (to improve battery energy capacity). Due to differences in particle size and density between the two types of carbon blends, this approach cannot guarantee optimal contact between CNTs and carbon materials.

[0077] These technical limitations are addressed in this paper by blending fine powders (<70 micrometer particle size) of metal oxide-supported catalysts with graphite, carbon black, or activated carbon in different catalyst / carbon material ratios, and then synthesizing CNTs in a catalytic reactor (fluidized bed or rotary tube reactor) using ethylene as a carbon source at T = 675 °C and different catalyst / gas flow contact times.

[0078] Figure 7A and 7B Here is a SEM image of carbon black, where Figure 7A Shot at 50kx, and Figure 7B Shot at 800x. Spherical primary particles with dimensions ranging from 20 to 65 nm can be observed. Figure 7B The low-magnification SEM image shows carbon black agglomerate particles with a size of a few micrometers.

[0079] SEM images corresponding to catalysts supported on metal oxides ( Figures 8A-8CThis displays particles smaller than 10 micrometers. Primary particles are smaller than 1 micrometer. Figure 8A Shot at 2.5kx Figure 8B Shot at 5kx, and Figure 8C Shot at 60kx.

[0080] Figures 9A-9C SEM images of the catalyst-carbon black blends supported on metal oxides at different magnifications (150x, 5kx, and 7.5kx, respectively). The images show aggregates with sizes ranging from 15 to 40 micrometers. Catalyst particles are observed to be attached to carbon black particles.

[0081] Figures 10A-10C SEM images of the MWCNT-carbon black hybrid material were taken at 100x, 1.25kx, and 10kx, respectively. The catalyst composition in the blend was 15% by weight. Aggregates of MWCNT-carbon black with a size range of 20 to 60 micrometers were observed. Sheets of MWCNTs with diameters of 8-15 nm were formed. As MWCNTs began to grow, the carbon black agglomerates began to separate from each other, and the particle density decreased significantly. Thus, high dispersion of the carbon black aggregates was achieved.

[0082] Figure 11A-11F The catalyst composition in the blend is 15% by weight. Figure 11A and 11B (Photographed at 10kx and 25kx respectively), the blend contains 25% by weight catalyst ( Figure 11C and 11D The catalyst composition consisted of 50% by weight in the blend and (photographed at 10 kx and 25 kx respectively). Figure 11E and 11F SEM images of the MWCNT-carbon black hybrid material at different magnifications (photographed at 10kx and 25kx, respectively). Increasing the catalyst composition in the blend resulted in greater dispersion of the carbon black aggregates and also achieved closer contact between the MWCNT-carbon black particles.

[0083] Table 1 provides some properties of carbon black and MWCNT carbon black hybrids synthesized using different catalyst compositions in the blends. Several effects were observed when the catalyst composition in the blends was increased. First, the MWCNT content in the product increased, and both the BET surface area and pore volume values ​​also increased significantly. Furthermore, the tap packing density decreased, and the size of the MWCNT-carbon black agglomerates increased. In some instances, one or more of the following parameters were determined using standard testing methods: BET surface area, pore volume, tap packing density, residual mass, weight percentage of CNTs and the second material, TGA results, and average particle size (and other qualities of the hybrids).

[0084] Figure 12A-12D To use different catalyst compositions ( Figure 12B 15% catalyst, Figure 12C 25% catalyst, and Figure 12D Carbon black obtained by 50% catalyst Figure 12A TGA analysis of MWCNT-carbon black hybrids was performed. Two distinct signals were distinguishable between the MWCNT-carbon black hybrids, with their relative intensities varying as a function of the catalyst composition in the blend. The low-temperature signal was attributed to the MWCNT combustion mode, while the high-temperature signal corresponded to the carbon black. The low-temperature signal consistently increased with increasing catalyst content in the blend, indicating that more catalyst resulted in more MWCNTs.

[0085] Table 1: Properties of MWCNT-carbon black hybrid materials under different catalyst compositions

[0086]

[0087] In some instances, analytical techniques used to determine the size of catalysts, carbon black, and hybrid material aggregates include light scattering, such as laser diffraction. Laser diffraction is used to determine the average particle size. This technique allows for the determination of the size of carbon black aggregates and nano-aggregates formed when CNTs are grown using different catalyst / carbon black compositions. Therefore, this technique enables the measurement of the size of the formed CNT-carbon black network. When more catalyst is used, the CNT-carbon black network is larger due to the growth of a greater number of high aspect ratio MWCNTs.

[0088] Example 3 Properties of CNT-carbon black hybrid materials after purification.

[0089] To investigate the effect of chemical purification on the structure and morphological properties of MWCNT-carbon black hybrid materials, samples obtained by using a 50% catalyst composition in the blend were treated with a solution containing an acid mixture of 3M H2SO4 and 3M HCl at 85°C for 3 hours to remove the metal oxide catalyst support and any unencapsulated active metal catalyst particles from the product. An alternative method is to use HF solution for purification. Figures 13A-13D SEM images of the purified MWCNT-carbon black product, taken at 2.5 kx, 12 kx, 20 kx, and 60 kx, are shown. The purified MWCNT-carbon black product retains the same network structure as the unpurified sample. No carbon nanotubes were observed to separate from the carbon black aggregates. Figure 14TGA analysis confirmed these results, with labeled data points on the weight % curve from left to right at 213.64℃ and 98.97%, 606.99℃ and 51.01%, 640.89℃ and 25.44%, and 843.56℃ and 2.199%. The residue consisted primarily of metals encapsulated in a graphite coating, such as... Figure 15 As shown in the TEM image. The BET surface area and pore volume of the purified product are 266 m². 2 / g and 1.18cc / g, which is comparable to the unpurified sample (Table 1).

[0090] MWCNT-carbon black can also be purified using chlorine gas and / or high-temperature heat treatment. This procedure breaks down the graphite coating encapsulating the metal catalyst particles, which are then removed from the solid under vacuum at very high temperatures (greater than 1000°C). This purification method may be more effective than chemical digestion methods for removing metal carbide impurities from a sample.

[0091] Example 4: Synthesis of CNT-graphite hybrids.

[0092] In this embodiment, a metal oxide-supported catalyst was blended with natural graphite particles (50 wt% / 50 wt%) with a size of 5 to 30 micrometers. CNT synthesis was carried out under the same experimental conditions as used in Example 2. Figure 16A-16D SEM images corresponding to the MWCNT-graphite hybrid materials are shown at different magnifications (400x, 10kx, 4kx, and 100kx, respectively). Graphite particles with sizes ranging from 13 to 45 micrometers were observed to be covered by a network of MWCNTs with diameters from 7 to 15 nm. Table 2 shows the properties of the graphite used and the synthesized CNT-graphite hybrid materials. The estimated MWCNT content in the stock-produced product was approximately 44% by weight, with BET values ​​and pore volumes ranging from 18 m³. 2 / g and 0.069cc / g increased to approximately 285m 2 / g and 0.97cc / g, while the tapped bulk density decreased from 0.18cc / g to approximately 0.050cc / g. TGA analysis ( Figure 17 The graph shows two separate signals with maximum combustion temperature rates of 570°C and 716°C, corresponding to MWCNT and graphite, respectively, marked on the wt% curves from left to right at 212.93°C and 99.95%, 569.73°C and 72.06%, 636.95°C and 52.17%, 716.33°C and 39.34%, and 843.63°C and 27.81%. The average particle size increases after MWCNT deposition on the graphite particle surface.

[0093] Table 2: Properties of graphite and MWCNT-graphite hybrids

[0094]

[0095] Example 5: Low-walled carbon nanotube-carbon hybrid materials

[0096] This embodiment describes a method for manufacturing few-walled carbon nanotubes (FWCNTs) using various carbon materials (graphite, graphene, carbon black, activated carbon, etc.). FWCNTs are defined by the CNT family, which has 1 to 4 walls, with most having between 2 and 3 walls. The method described above involves blending a metal oxide-supported catalyst with a carbon material comprising 5 to 50% by weight. The hybrid FWCNT-carbon material is manufactured in a rotating tube reactor or fluidized bed reactor using various carbon sources (e.g., acetylene, methane, aromatic compounds, alcohols, etc.), H2, and / or inert gases at temperatures between 400°C and 1000°C. The active metal oxide precursor and catalyst support are as described above.

[0097] FWCNTs were synthesized in a rotary tube reactor using a FeMo / MgO catalyst at T = 950 °C, a gas composition of 20 vol% CH4 in H2, a catalyst weight / gas flow rate ratio of 1 g catalyst / L, and a reaction time of 5 minutes. The FWCNT product was purified by digestion of residual catalyst particles in 3M nitric acid prior to characterization. TGA analysis of the purified FWCNTs is shown below. Figure 18A As shown in the figure. A single signal was observed at approximately 565°C, which corresponds to the temperature of maximum combustion rate. Marked data points are found on the wt% curve from left to right at 213.64°C and 93.80%, 565.32°C and 42.07%, and 844.98°C and 16.38%.

[0098] In the next experiment, following the procedure described in Example 2, fine particles of the FeMo / MgO catalyst were blended with graphite powder in a 50 / 50 weight ratio. The FWCNT-graphite hybrid material was synthesized and purified under the same conditions described above. Figure 18B The TGA analysis of the FWCNT-graphite hybrid material after purification is shown, where two well-separated signals were observed at 573 °C and 737 °C. These correspond to FWCNT and graphite, respectively. The estimated FWCNT content in the hybrid material is approximately 15% by weight. Labeled data points are shown on the wt% curve from left to right at 211.52 °C and 99.18%, 573.09 °C and 89.72%, 611.23 °C and 83.91%, 737.64 °C and 30.72%, and 844.98 °C and 0.1496%.

[0099] Figure 19A and19B SEM images of the unprocessed and purified FWCNT-graphite hybrid materials are shown, respectively. In both cases, a CNT network covering the graphite particles was observed.

[0100] Example 6: CNT-carbon black and CNT-graphite hybrid materials were synthesized in a fluidized bed reactor.

[0101] This embodiment describes a method for producing CNT-carbon black and CNT-graphite hybrid materials in a fluidized bed reactor. Following the procedure described in Example 2, metal oxide-supported catalyst precursors were blended with carbon materials at a ratio of 40 / 60% by weight, respectively.

[0102] CNT / carbon black and CNT / graphite hybrid materials were synthesized in a fluidized bed reactor at a temperature of 675 °C, a gas composition of 75% C2H4 in H2, a catalyst / gas flow rate ratio of 1.3 g catalyst / L, and a reaction time of 10 minutes.

[0103] Figure 20A and 20B TGA analysis of CNT / carbon black and CNT / graphite hybrid materials, respectively. Figure 20A Two distinguishable signals were observed at approximately 577 °C and 682 °C, corresponding to MWCNT / carbon black, respectively. The estimated MWCNT content in the hybrid material is approximately 53% by weight. Marked data points are found on the wt% curve from left to right at 210.81 °C and 99.87%, 576.62 °C and 66.23%, 624.64 °C and 47.31%, 681.85 °C and 29.83%, and 843.56 °C and 15.48%. Figure 20B In the figure, the maximum oxidation rate signals corresponding to MWCNT and graphite are located at approximately 545 °C and 714 °C, respectively. In this case, the estimated MWCNT content in the hybrid material is approximately 30% by weight. Marked data points are found on the weight % curve from left to right at 212.22 °C and 99.95%, 5444.84 °C and 82.99%, 618.29 °C and 70.91%, 713.62 °C and 50.43%, and 844.98 °C and 32.80%.

[0104] Figure 21A and 21B SEM images of MWCNT-carbon black and MWCNT-graphite hybrid materials synthesized in a fluidized bed reactor are shown. The SEM images reveal smaller carbon black aggregates separated from each other by the MWCNT network. Figure 21A ) and graphite flake particles ( Figure 21B ).

[0105] Example 7: Synthesis of CNT-graphene nanosheets

[0106] This embodiment describes a method for fabricating CNT / graphene nanosheet hybrid materials. In some instances, these materials are fabricated in a fluidized bed reactor. Following the procedure described in Example 2, a metal oxide-supported catalyst precursor is mixed with graphene nanosheets of approximately 1-4 micrometers in size (in... Figure 22A The graphene nanosheets (shown as 25KX) were blended at a ratio of 30% and 70% by weight, respectively.

[0107] CNT / graphene nanosheet hybrid materials were synthesized in a fluidized bed reactor at a temperature of 675 °C, a gas composition of 75% C2H4 in H2, a catalyst / gas flow rate ratio of 1.3 g catalyst / L, and a reaction time of 10 minutes.

[0108] Figure 22A This is a SEM image of graphene nanosheets. Figure 22B and 22C SEM images were taken at low (5KX) and high (25KX) magnifications, respectively. A fine network of MWCNTs can be observed around the surface of the graphene nanosheets.

[0109] In Table 3, it was observed that the MWCNT / graphene nanosheet hybrid material has a significantly higher surface area and pore volume compared to the graphene nanosheet material itself.

[0110] Table 3: Texture properties corresponding to MWCNT / graphene nanosheet hybrid materials

[0111] sample <![CDATA[BET surface area (m 2 / g)]]> Pore ​​volume (cc / g) Graphene nanosheets 131 0.25 MWCNT / graphene nanosheet hybrid materials 352 1.34

[0112] Having described various aspects of at least one embodiment above, it will be understood that various changes, modifications, and improvements will readily occur to those skilled in the art. These changes, modifications, and improvements are intended to be part of this disclosure and are intended to be within the scope of the invention. Therefore, the foregoing description and drawings are merely illustrative, and the scope of the invention should be determined by the appropriate construction of the appended claims and their equivalents.

Claims

1. A carbon nanotube (CNT) hybrid powder material derived from a blend of metal oxide-supported catalyst grains with agglomerated particles of different second materials, wherein the catalyst grains are formed by the aggregation of multiple basic catalyst particles. include: CNT networks, at least some of which are directly coupled to the basic catalyst particles, and at least some of which are adjacent to but not directly coupled to the particles of the second material. The basic catalyst particles are separated from each other, and the second material depolymerizes due to the formation of the CNT network.

2. The material of claim 1, wherein the second material comprises carbon.

3. The material of claim 1, wherein the second material comprises at least one of carbon black, graphite, and graphene.

4. The material of claim 1, wherein the second material comprises a metal oxide.

5. The material of claim 4, wherein the second material comprises at least one of silicon dioxide and aluminum oxide.

6. The material of claim 1, wherein the CNT comprises at least one of single-walled CNT (SWCNT), few-walled CNT (FWCNT), and multi-walled CNT (MWCNT).

7. The material of claim 1, comprising 5% to 50% by weight of CNTs.

8. The material of claim 1, wherein at least some of the CNTs are directly coupled to particles of the second material.

9. The material of claim 1, wherein the blend comprises 10% to 50% by weight of catalyst particles.

10. The material of claim 1, wherein the metal oxide comprises at least one of aluminum oxide, silicon dioxide, and magnesium oxide.

11. The material of claim 1, having a particle size of at least 140 μm 2 / g BET surface area.

12. The material of claim 1, having a pore volume of at least 0.43 ml / g.

13. The material of claim 1, having a tap packing density of 0.102 g / ml or less.

14. The material of claim 1, having an average particle size of at least 42 micrometers.

15. A method for forming the carbon nanotube (CNT) hybrid material of claim 1, comprising: A blend comprising catalyst grains supported on metal oxides and aggregated particles of a second material is formed. and CNTs are synthesized on a catalyst supported in the blend to produce a CNT hybrid material.

16. The method of claim 15, wherein the second material comprises at least one of carbon black, graphite, graphene, and metal oxide.

17. The method of claim 16, wherein the second material comprises at least one of silicon dioxide and aluminum oxide.

18. The method of claim 15, further comprising removing at least some of the metal oxide catalyst support from the CNT hybrid material.

19. The method of claim 18, wherein the metal oxide catalyst support is removed by chemical purification of the CNT hybrid material.

Images