Patent Publication Number: US-2021167364-A1

Title: System and method of producing a composite product

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The present Application is a divisional of U.S. patent application Ser. No. 15/452,500, filed Mar. 7, 2017, which claims priority to U.S. Provisional Application No. 62/308,480, filed Mar. 15, 2016. The disclosures of both applications are incorporated herein by reference in their entirety. 
    
    
     BACKGROUND 
     Carbon nanotubes are small tube-shaped structures essentially having a composition of a graphite sheet in a tubular form. Carbon nanotubes feature diameters less than 100 nanometers, and large aspect ratios, where the length is much greater than is the diameter. For example, a length of the CNT may be more than 1000 times the diameter. Single-walled carbon nanotubes (SWNT) are increasingly becoming of interest for various applications in nanotechnology because of their unique electronic structures, which gives them exceptional thermal, mechanical, and electrical properties. For example, SWNTs can be used in electronics, energy devices, medicine, and composite materials in order to obtain desirable physical and chemical properties. These uses require methods for producing significant quantities of SWNTs. 
     Processes for producing SWNTs include, but are not limited to, physical methods (e.g., electrical arc, laser ablation) and chemical methods (e.g., pyrolysis, chemical vapor deposition). Once formed, the SWNTs are sometimes distributed within a matrix material, which modifies the thermal, mechanical, and electrical properties of the matrix material. However, the enhancement of electrical or mechanical properties of matrix material by nanotube additives requires very homogeneous dispersion, no agglomeration and fine control over the nanotube/matrix ratios. Attempts have been made following the synthesis of nanotubes to disperse the nanotubes in various solvents (e.g. via surface functionalization) followed by mixing of the nanotubes with the matrix (e.g. by ball milling, sonication etc.). However, such attempts have failed to provide satisfactory dispersion of the nanotubes in the matrix as they lead to the reduction of aspect ratio, damage the nanotubes, and increase the cost of the processed material. 
     BRIEF DESCRIPTION 
     In an aspect, a method of producing a composite product is provided. The method includes fluidizing an amount of metal oxide particles within a fluidized bed reactor, providing a catalyst or catalyst precursor in the fluidized bed reactor, providing a carbon source to a carbon nanotube growth zone of the fluidized bed reactor, growing carbon nanotubes in the carbon nanotube growth zone, and providing a flow of carrier gas to the fluidized bed reactor and carrying a composite product comprising carbon nanotubes and metal oxide particles through the fluidized bed reactor. 
     In an aspect, a system for use in producing a composite product is provided. The system includes a fluidized bed reactor comprising an amount of metal oxide particles contained therein, an outlet, a catalyst or catalyst precursor source in fluid communication with the fluidized bed reactor to provide a flow of catalyst or catalyst precursor in the fluidized bed reactor, and a carrier gas source in fluid communication with the fluidized bed reactor to carry a composite product comprising metal oxide particles and carbon nanotubes grown in the fluidized bed reactor. 
     In an aspect, a method of producing a composite product is provided. The method includes providing a fluidized bed of metal oxide particles in a fluidized bed reactor, providing a catalyst or catalyst precursor in the fluidized bed reactor, providing a carbon source in the fluidized bed reactor for growing carbon nanotubes, growing carbon nanotubes in a carbon nanotube growth zone of the fluidized bed reactor, and collecting a composite product comprising metal oxide particles and carbon nanotubes. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic illustration of an exemplary system that may be used to produce a composite product in an aspect of the disclosure. 
         FIG. 2  is a thermogravimetric analysis (TGA) for lithium nickel manganese cobalt oxide heated to 750° C. in air. 
         FIG. 3  is a TGA for lithium nickel manganese cobalt oxide heated to 750° C. in nitrogen. 
         FIG. 4  is an x-ray powder diffraction (XRD) spectra for lithium nickel manganese cobalt oxide (a) as received, (b) after heating to 750° C. in air, and (c) after heating to 750° C. in nitrogen. 
         FIG. 5  is a portion of a view of the XRD spectra of  FIG. 4  enlarged for magnification purposes. 
         FIG. 6  is a flow diagram illustrating an exemplary series of process steps that may be used in producing a composite product in an aspect of the disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The embodiments described herein relate to a composite product, and systems and methods for making the composite product. In general, the systems and methods provide for the in-situ dispersion of carbon nanotubes into a metal oxide matrix material in the course of carbon nanotube growth in a reactor. The reactor may be a fluidized bed reactor capable of aerosolization or fluidization of the metal oxide matrix material with a fluidization gas flowing from a gas distributor, such as a porous frit, from the bottom of the reactor. One or more injectors may be provided in the middle of the reactor to supply catalyst and carbon precursors for growing of the carbon nanotubes. Hence, carbon nanotubes may be grown in a cloud of fluidized metal oxide matrix material to provide in-situ mixing and, as a result, improved homogeneity of the resulting composite product containing carbon nanotubes and metal oxide matrix material. The composite product may be used in an electrode. In a non-limiting example, the composite product may be used in a cathode of a secondary lithium battery. 
       FIG. 1  is a schematic illustration of an exemplary system  100  that may be used to produce a composite product  102  comprising carbon nanotubes and metal oxide matrix materials. In the exemplary embodiment, system  100  includes a fluidized bed reactor  104  having an amount of metal oxide matrix material contained therein. The matrix material may be any solid, metal oxide particle that is capable of being suspended in a fluidized bed. An exemplary metal oxide includes, but is not limited to, any metal oxide that may be used in an electrode. In an illustrative example, the metal oxide is a material for use in the cathode of the battery. Non-limiting examples of metal oxides include Ni, Mn, Co, Al, Mg, Ti and any mixture thereof. The metal oxide may be lithiated. In an illustrative example, the metal oxide is lithium nickel manganese cobalt oxide (LiNiMnCoO 2 ). The metal oxide particles can have a particle size defined within a range between about 1 nanometer and about 100 microns. In a non-limiting example, the metal oxide particles have an average particle size of about 1 nanometer to about 10 nanometers. 
     In an illustrative example, the fluidized bed reactor  104  includes a reaction chamber  108 , and a gas distributor that may comprise a porous frit  110  coupled to reaction chamber  108  and a gas plenum  112  coupled to porous frit  110 . Porous frit  110  includes a plurality of flow apertures  114  defined therein such that gas plenum  112  is coupled in fluid communication with reaction chamber  108 . Gas plenum  112  receives a flow of fluidizing gas from a first gas source  118 . The flow of fluidizing gas is routed through plenum  112  and the porous frit  110  to fluidize the metal oxide particles in the reaction chamber  108 . The fluidizing gas may be any gas capable of fluidizing the metal oxide particles to form a fluidized bed  109  of metal oxide particles. Exemplary fluidizing gases include, but are not limited to, argon, helium, nitrogen, hydrogen, carbon dioxide, and ammonia. 
     As shown in  FIG. 1 , the fluidized bed  104  may include one or more heat sources  119  for heating the reaction chamber  108  to the desired reaction temperature. For example, the reaction chamber  108  may be heated with the heat source  119  to a temperature in the range of about 450° C. to about 1100° C. depending on the catalyst or catalyst precursor and the type of nanotube desired. In one embodiment, especially to accommodate sensitive cathode materials, the reactor can be operated closer to the lower end of this temperature (e.g. ˜500° C.) and in the presence of hydrogen in order to avoid converting the cathode material. In an alternative embodiment, the reactor can be operated closer to the higher end of the aforementioned temperature range (e.g. ˜750° C. and above) and in the absence of hydrogen). The products obtained from operating the reactor whether at the lower or higher temperatures are not necessarily limited to SWNTs. Typically, single-walled nanotubes (SWNTs) require higher temperatures (&gt;750° C.) while multi-walled nanotubes (MWNTs) can be grown as low as about 450° C. In a non-limiting example, the reactor his heated to a temperature of about 450° C. to about 850° C. As shown in  FIGS. 2, 3, 4, and 5 , lithium nickel manganese cobalt oxide is thermally stable up to at least 850° C. via TGA ( FIG. 2  in air and  FIG. 3  in nitrogen) and XRD ( FIG. 4  and  FIG. 5 ) measurements. Therefore, such a lithiated mixed metal oxide can be provided in a fluidized bed reactor at temperatures suitable for the growth of carbon nanotubes. 
     Fluidized bed reactor  104  may also include one or more inlets for introduction of the metal oxide particles, the catalyst or catalyst precursor, a carrier gas  127 , and the carbon precursor for the carbon nanotubes. As shown in  FIG. 1 , an inlet  120  is provided for the introduction of the metal oxide particles from a metal oxide particle source  106  into the reaction chamber  108 . It is to be understood that any method or device may be used to introduce the metal oxide particles into the reaction chamber  108  via the inlet  120 . In a non-limiting example, the metal oxide particles may be fed into the reaction chamber  108  with a screw feeder, belt feeder, vibratory feeder, or a rotary (bulk solid) feeder. In addition, or alternatively, the metal oxide particles may be conveyed pneumatically into the reaction chamber  108 . Non-limiting examples include pressure vessel conveyors, pressurized screw conveyor, airlifts, blow-through feeders, and jet feeders. The conveying gas may the same as or different than the fluidizing gas. Exemplary gases include, but are not limited to, argon, nitrogen, helium, hydrogen, carbon dioxide, and ammonia. It is to be understood that the metal oxide particles may be continuously fed into the reaction chamber  108  so that the system operates in a continuous operation of the reaction chamber  108 , the metal oxide particles may be introduced in a single charge for batch operation of the reaction chamber  108 , or the metal oxide particles may be intermittently added for semi-batch operation of the reaction chamber  108 . 
     The carbon nanotubes can be synthesized using carbon precursors, such as one or more carbon-containing gases, one or more hydrocarbon solvents, and mixtures thereof. Examples of carbon-containing precursors include carbon monoxide, aliphatic hydrocarbons, both saturated and unsaturated, such as methane, ethane, propane, butane, pentane, hexane, ethylene, acetylene and propylene; oxygenated hydrocarbons such as acetone, and methanol; aromatic hydrocarbons such as benzene, toluene, and naphthalene; and mixtures of the above, for example carbon monoxide and methane. In general, the use of acetylene promotes formation of multi-walled carbon nanotubes, while CO and methane are preferred feed gases for formation of single-walled carbon nanotubes. Specifically, hydrocarbon solvents may include, but are not limited to, alcohols such as methanol, ethanol, and isopropanol. The carbon precursor may optionally be mixed with a diluent gas such as hydrogen, helium, argon, neon, krypton and xenon or a mixture thereof. As shown in  FIG. 1 , a carbon precursor may be included in a carrier gas  127  (e.g. via carrier gas source  126 ) and introduced to the reaction chamber  108  via inlet  128 . 
     The catalyst or catalyst precursors may include any catalyst or catalyst precursor that may be used in the production of carbon nanotubes. The catalyst or catalyst precursor may be one or more of an acetylacetonate, a metallocene, an acetate, a nitrate, a nitride, a sulfate, a sulfide, an oxide, a halide, a chloride, and the like. Illustrative metals for use as the catalyst include, but are not limited to, iron, nickel, cobalt, molybdenum, or a mixture thereof. Non-limiting examples of catalyst precursors include iron (III) acetylacetonate, ferrocene, iron acetate, iron nitrate, iron sulfate, and iron chloride. It is to be understood that the catalyst or catalyst precursor source may be a solid powder, a solid dispersed in a liquid, or dissolved in a solvent. As shown in  FIG. 1 , a catalyst or catalyst precursor source  130  may be provided in communication with the reaction chamber  108  via inlet  132  to introduce the catalyst or catalyst precursor to a carbon nanotube growth zone  150  of the reaction chamber  108 . A pump, solids feeder, syringe, or any other device or method known to one of ordinary skill in the art may be used to introduce the catalyst or catalyst precursor into the carbon nanotube growth zone  150 . It is to be understood that the carbon precursor may be mixed with the catalyst or catalyst precursor and introduced with the catalyst or catalyst precursor via inlet  132 . 
     As shown in  FIG. 1 , a collection vessel  170  is provided for collecting the composite product of metal oxide particles and carbon nanotubes. The composite product exits the reactor  104  at outlet  175  and is collected in the vessel  170 . The vessel  170  may include a porous filter or membrane  176  that collects the composite product  102  in the vessel  170 , but allows the gases leaving the fluidized bed reactor  104  through the exit  175  to be exhausted from the system via outlet  177 . In a non-limiting example, the porous membrane may be a porous quartz frit. However, the present disclosure is not limited to such a collection vessel  170  and porous filter or membrane  176 , as any collection system may be used that is capable of separating solid particles from a gas stream. Non-limiting examples include one or more cyclone separators and bag houses. 
     In a non-limiting example, the metal oxide particles can be provided with a catalyst or catalyst precursor deposited thereon prior to introduction of the metal oxide particles in the reaction chamber  108 . 
     In operation, the growth rate of carbon nanotubes and the weight percentage of carbon nanotubes relative to the metal oxide particles in the composite product is controlled by the feed rates of the metal oxide particles, the catalyst or catalyst precursor, and the carbon precursor into the reaction chamber  108 . These feed rates can be tailored to produce the desired ratio of carbon nanotubes to metal oxide particles in the composite product to meet the needs of a desired application. 
     In an illustrative example as shown in  FIG. 2 , a method of making the composite product comprises providing a fluidized bed of a metal oxide particles (step  200 ), providing a catalyst or catalyst precursor in the fluidized bed (step  300 ), introducing a carbon source in the fluidized bed (step  400 ), growing carbon nanotubes in the fluidized bed (step  500 ), and collecting the composite product comprising metal oxide particles and carbon nanotubes (step  600 ). In a non-limiting example, at least some of the catalyst or catalyst precursor is deposited on the surface of the metal oxide particles and the carbon nanotubes are grown on the surface of the metal oxide particles. 
     Example: Production of Composite Product 
     To demonstrate the method of producing a composite product comprising carbon nanotubes and metal oxide particles, the following experiment was conducted. 
     A quartz tube having a 2 inch diameter was provided as the reaction chamber  108  for the fluidized bed reactor  104  and a tube furnace was used as the heat source  119 . The quartz tube was aligned vertically with a lower end closed with the porous frit  114 . Two tubes were provided at the center of the porous frit  114  for the carrier gas inlet  128  and the catalyst/catalyst precursor inlet  132 . Both inlets  128 / 132  were positioned below the section of the reaction chamber  108  heated by the heat source  119 . Lithium nickel manganese cobalt oxide particles were used as the metal oxide particles and were poured onto the porous frit  114  to a height of about 10 millimeters. The fluidizing gas, argon, was then provided at a rate of about 350 sccm (standard cubic centimeters per minute) through the porous frit  114  at the lower end of the quartz tube to fluidize the metal oxide particles. The reactor chamber  108  was heated to a temperature of about 800° C. The carrier gas  127  included a mixture of argon (about 850 sccm) and hydrogen (about 300 sccm) and was provided to the reaction chamber  108  via inlet  128 . The catalyst precursor was a solution of ferrocene (0.4 wt %) and thiophene (0.2 wt %) in ethanol. The ethanol functioned as both a solvent for the ferrocene and the carbon source for growing the nanotubes. The catalyst precursor solution was injected at a rate of 6 ml/hr via the inlet  132  into the carbon nanotube growth zone  150  where the ferrocene decomposed to iron catalyst particles having a diameter of about one nanometer, and the ethanol was converted to a carbon source for the growth of single walled nanotubes on the iron catalyst particles. The carrier gas  127  transported the composite product  102  from the nanotube growth zone  150  through the reactor outlet  175  and to the collection vessel  170 . The composite product included SWCNTs and lithium nickel manganese cobalt oxide particles and comprised approximately 0.7 wt % SWCNTs. 
     This written description uses examples to disclose various implementations, including the best mode, and also to enable any person skilled in the art to practice the various implementations, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the disclosure is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.