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Researchers Submit Patent Application, "Nanocomposite of Graphene and Metal Oxide Materials", for Approval

February 20, 2014



By a News Reporter-Staff News Editor at Politics & Government Week -- From Washington, D.C., VerticalNews journalists report that a patent application by the inventors Liu, Jun (Richland, WA); Aksay, Ilhan A. (Princeton, NJ); Choi, Daiwon (Richland, WA); Wang, Donghai (State College, PA); Yang, Zhenguo (Richland, WA), filed on October 1, 2013, was made available online on February 6, 2014.

The patent's assignee is The Trustees of Princeton University.

News editors obtained the following quote from the background information supplied by the inventors: "Graphene is generally described as a one-atom-thick planar sheet of sp2-bonded carbon atoms that are densely packed in a honeycomb crystal lattice. The carbon-carbon bond length in graphene is approximately 0.142 nm. Graphene is the basic structural element of some carbon allotropes including graphite, carbon nanotubes and fullerenes. Graphene exhibits unique properties, such as very high strength and very high conductivity. Those having ordinary skill in the art recognize that many types of materials and devices may be improved if graphene is successfully incorporated into those materials and devices, thereby allowing them to take advantage of graphene's unique properties. Thus, those having ordinary skill in the art recognize the need for new methods of fabricating graphene and composite materials that incorporated graphene.

"Graphene has been produced by a variety of techniques. For example, graphene is produced by the chemical reduction of graphene oxide, as shown in Gomez-Navarro, C.; Weitz, R. T.; Bittner, A. M.; Scolari, M.; Mews, A.; Burghard, M.; Kern, K. Electronic Transport Properties of Individual Chemically Reduced Graphene Oxide Sheets. and Nano Lett. 2007, 7, 3499-3503. Si, Y.; Samulski, E. T. Synthesis of Water Soluble Graphene. Nano Lett. 2008, 8, 1679-1682.

"While the resultant product shown in the forgoing methods is generally described as graphene, it is clear from the specific capacity of these materials that complete reduction is not achieved, because the resultant materials do not approach the theoretical specific capacity of neat graphene. Accordingly, at least a portion of the graphene is not reduced, and the resultant material contains at least some graphene oxide. As used herein, the term 'graphene' should be understood to encompass materials such as these, that contain both graphene and small amounts of graphene oxide.

"For example, functionalized graphene sheets (FGSs) prepared through the thermal expansion of graphite oxide as shown in McAllister, M. J.; LiO, J. L.; Adamson, D. H.; Schniepp, H. C.; Abdala, A. A.; Liu, J.; Herrera-Alonso, M.; Milius, D. L.; CarO, R.; Prud'homme, R. K.; Aksay, I. A. Single Sheet Functionalized Graphene by Oxidation and Thermal Expansion of Graphite. Chem. Mater. 2007, 19, 4396-4404 and Schniepp, H. C.; Li, J. L.; McAllister, M. J.; Sal, H.; Herrera-Alonso, M.; Adamson, D. H.; Prud'homme, R. K.; Car, R.; Saville, D. A.; Aksay, I. A. Functionalized Single Graphene Sheets Derived from Splitting Graphite Oxide. J. Phys. Chem. B 2006, 110, 8535-8539 have been shown to have tunable C/O ratios ranging from 15 to 500. The term 'graphene' as used herein should be understood to include both pure graphene and graphene with small amounts of graphene oxide, as is the case with these materials.

"Further, while graphene is generally described as a one-atom-thick planar sheet densely packed in a honeycomb crystal lattice, these one-atom-thick planar sheets are typically produced as part of an amalgamation of materials, often including materials with defects in the crystal lattice. For example, pentagonal and heptagonal cells constitute defects. If an isolated pentagonal cell is present, then the plane warps into a cone shape. Likewise, an isolated heptagon causes the sheet to become saddle-shaped. When producing graphene by known methods, these and other defects are typically present.

"The IUPAC compendium of technology states: 'previously, descriptions such as graphite layers, carbon layers, or carbon sheets have been used for the term graphene . . . it is not correct to use for a single layer a term which includes the term graphite, which would imply a three-dimensional structure. The term graphene should be used only when the reactions, structural relations or other properties of individual layers are discussed'. Accordingly, while it should be understood that while the terms 'graphene' and 'graphene layer' as used in the present invention refers only to materials that contain at least some individual layers of single layer sheets, the terms 'graphene' and 'graphene layer' as used herein should therefore be understood to also include materials where these single layer sheets are present as a part of materials that may additionally include graphite layers, carbon layers, and carbon sheets.

"The unique electrical and mechanical properties of graphene have led to interest in its use in a variety of applications. For example, electrochemical energy storage has received great attention for potential applications in electric vehicles and renewable energy systems from intermittent wind and solar sources. Currently, Li-ion batteries are being considered as the leading candidates for hybrid, plug-in hybrid and all electrical vehicles, and possibly for utility applications as well. However, many potential electrode materials (e.g., oxide materials) in Li-ion batteries are limited by slow Li-ion diffusion, poor electron transport in electrodes, and increased resistance at the interface of electrode/electrolyte at high charging-discharging rates.

"To improve the charge-discharge rate performance of Li-ion batteries, extensive work has focused on improving Li-ion and/or electron transport in electrodes. The use of nanostructures (e.g., nanoscale size or nanoporous structures) has been widely investigated to improve the Li-ion transport in electrodes by shortening Li-ion insertion/extraction pathway. In addition, a variety of approaches have also been developed to increase electron transport in the electrode materials, such as conductive coating (e.g., carbon), and uses of conductive additives (e.g., conductive oxide wires or networks, and conductive polymers). Recently, TiO.sub.2 has been extensively studied to demonstrate the effectiveness of nanostructures and conductive coating in these devices.

"TiO.sub.2 is particularly interesting because it is an abundant, low cost, and environmentally benign material. TiO.sub.2 is also structurally stable during Li-insertion/extraction and is intrinsically safe by avoiding Li electrochemical deposition. These properties make TiO.sub.2 particularly attractive for large scale energy storage.

"Another way to improve the Li-ion insertion properties is to introduce hybrid nanostructured electrodes that interconnect nanostructured electrode materials with conductive additive nanophases. For example, hybrid nanostructures, e.g., V.sub.2O.sub.5-- carbon nanotube (CNT) or anatase TiO.sub.2-CNT hybrids, LiFePO.sub.4--RuO.sub.2 nanocomposite, and anatase TiO.sub.2--RuO.sub.2 nanocomposite, combined with conventional carbon additives (e.g., Super P carbon or acetylene black) have demonstrated an increased Li-ion insertion/extraction capacity in the hybrid electrodes at high charge/discharge rates.

"While the hybrids or nanocomposites offer significant advantages, some of the candidate materials to improve the specific capacity, such as RuO.sub.2 and CNTs, are inherently expensive. In addition, conventional carbon additives at high loading content (e.g., 20 wt % or more) are still needed to ensure good electron transport in fabricated electrodes. To improve high-rate performance and reduce cost of the electrochemically active materials, it is important to identify high surface area, inexpensive and highly conductive nanostructured materials that can be integrated with electrochemical active materials at nanoscale.

"Those having ordinary skill in the art recognize that graphene may be the ideal conductive additive for applications such as these hybrid nanostructured electrodes because of its high surface area (theoretical value of 2630 m.sup.2/g), which promises improved interfacial contact, the potential for low manufacturing cost as compared to CNTs, and high specific capacity. Recently, high-surface-area graphene sheets were studied for direct Li-ion storage by expanding the layer spacing between the graphene sheets as described in Yoo, E.; Kim, J.; Hosono, E.; Zhou, H.-s.; Kudo, T.; Honma, I. Large Reversible Li Storage of Graphene Nanosheet Families for Use in Rechargeable Lithium Ion Batteries, Nano Lett. 2008, 8, 2277-2282. In addition to these studies, graphene has also been used to form composite materials with SnO.sub.2 for improving capacity and cyclic stability of the anode materials as described in Paek, S.-M.; Yoo, E.; Honma, I. Enhanced Cyclic Performance and Lithium Storage Capacity of SnO.sub.2/Graphene Nanoporous Electrodes with Three-Dimensionally Delaminated Flexible Structure, Nano Lett. 2009, 9, 72-75.

"While these results were promising, they fell short of producing materials exhibiting specific capacity approaching the theoretical possibilities. For example, while it has been shown that graphene may be combined with certain metal oxides, the graphene materials in these studies fall far short of the theoretical maximum conductivity of single-sheet graphene. Further, those having ordinary skill in the art recognize that the carbon:oxygen ratio and the specific surface area of graphene provide an excellent proxy to measure the relative abundance of high conductivity single-sheets in a given sample. This is because the C:O ratio is a good measure of the degree of 'surface functionalization' which affects conductivity, and the surface area conveys the percentage of single-sheet graphene in the synthesized powder.

"Accordingly, those having ordinary skill in the art recognize that improvements to these methods are required to achieve the potential of using graphene nanostructures in these and other applications. Specifically, those skilled in the art recognize the need for new methods that produce nanocomposite materials of graphene and metal oxides that exhibit greater specific capacity than demonstrated in these prior art methods.

"The present invention fulfills that need, and provides such improved composite nanostructures of graphene layers and metal oxides that exhibit specific capacities heretofore unknown in the prior art. The present invention further provides improved and novel methods for forming these composite nanostructures, and improved and novel devices that take advantage of the new and unique properties exhibited by these materials. The present invention meets these objectives by making nanostructures of graphene layers and metal oxides where the C:O ratio of the graphene layers in these nanostructures is between 15-500:1, and preferably 20-500:1, and the surface area of the graphene layers in these nanostructures is 400-2630 m2/g, and preferably 600-2630 m2/g, as measured by BET nitrogen adsorption at 77K. While those having ordinary skill in the art have recognized the desirability of having C:O ratios and surface areas this high in the graphene of nanostructures of graphene and metal oxides, the prior art methods have failed to produce them."

As a supplement to the background information on this patent application, VerticalNews correspondents also obtained the inventors' summary information for this patent application: "The present invention thus includes a nanocomposite material comprising a metal oxide bonded to at least one graphene layer. The metal oxide is preferably M.sub.xO.sub.y, and where M is selected from the group consisting of Ti, Sn, Ni, Mn, V, Si, Co and combinations thereof. The nanocomposite materials of the present invention are readily distinguished from the prior art because they exhibit a specific capacity of at least twice that of the metal oxide material without the graphene at a charge/discharge rate greater than about 10 C.

"For example, while not meant to be limiting, an example where titania is used as the metal oxide, the resulting nanocomposite material has a specific capacity at least twice that of a titania material without graphene at a charge/discharge rate greater than about 10 C. Continuing the example, where titania is used as the metal oxide, the titania may be provided in a mesoporous form, and the mesoporous titania may further be provided in a rutile crystalline structure, or in an anatase crystalline structure.

"The nanocomposite material of the present invention preferably is provided as graphene layers with metal oxides uniformly distributed throughout the nanoarchitecture of the layers. Preferably, but not meant to be limiting, the nanocomposite material of the present invention provides a metal oxide bonded to at least one graphene layer that has a thickness between 0.5 and 50 nm. More preferably, but also not meant to be liming, the nanocomposite material of the present invention provides a metal oxide bonded to at least one graphene layer that has a thickness between 2 and 10 nm. Preferably, the carbon to oxygen ratio (C:O) of the graphene in the nanostructures of the present invention is between 15-500:1, and more preferably between 20-500:1. Preferably, the surface area of the graphene in the nanostructures of the present invention is between 400-2630 m2/g, and more preferably between 600-2630 m2/g, as measured by BET nitrogen adsorption at 77K.

"Another aspect of the present invention is a method for forming the nanocomposite materials of graphene bonded to metal oxide. The method consists of the steps of providing graphene in a first suspension; dispersing the graphene with a surfactant; adding a metal oxide precursor to the dispersed graphene to form a second suspension; and precipitating the metal oxide from the second suspension onto at least one surface of the dispersed graphene. In this manner, a nanocomposite material of at least one metal oxide bonded to at least one graphene layer is thereby formed. The nanocomposite materials formed in this manner are readily distinguished from materials formed by prior art methods because they exhibit a specific capacity of at least twice that of the metal oxide material without the graphene at a charge/discharge rate greater than about 10 C.

"Preferably, but not meant to be limiting, the first suspension is, at least in part, an aqueous suspension and the surfactant is an anionic surfactant. Also not meant to be limiting, a preferred anionic sulfate surfactant is sodium dodecyl sulfate. The method of the present invention may further comprise the step of heating the second suspension from 50 to 500 degrees C. to condense the metal oxide on the graphene surface. The method of the present invention may also further comprise the step of heating the second suspension from 50 to 500 degrees C. to remove the surfactant.

"The present invention also encompasses an energy storage device comprising a nanocomposite material having an active metal oxide compound and one graphene layer arranged in a nanoarchitecture. The energy storage devices of the present invention are readily distinguished from prior art energy storage devices because they exhibit a specific capacity of at least twice that of the metal oxide material without the graphene at a charge/discharge rate greater than about 10 C.

"For example, while not meant to be limiting, an example where titania is used as the metal oxide, the energy storage device of the present invention has a specific capacity at least twice that of a titania material without graphene at a charge/discharge rate greater than about 10 C.

"Preferably, but not meant to be limiting, the energy storage device of the present invention is provided as having at least one component having a nanocomposite material having graphene layers with metal oxides uniformly distributed throughout the nanoarchitecture of the layers. Also preferably, but not meant to be limiting, the energy storage device of the present invention is an electrochemical device having an anode, a cathode, an electrolyte, and a current collector, wherein at least one of the anode, cathode, electrolyte, and current collector is fabricated, at least in part, from a nanocomposite material having graphene layers with metal oxides uniformly distributed throughout the nanoarchitecture of the layers.

"In embodiments where the energy storage device of the present invention includes a cathode fabricated, at least in part, from a nanocomposite material having graphene layers with metal oxides uniformly distributed throughout the nanoarchitecture of the layers, the graphene in the cathode is preferably, but not meant to be limiting, 5% or less of the total weight of the cathode, and more preferably, but also not meant to be limiting, 2.5% or less of the total weight of the cathode. In this manner, the energy storage devices of the present invention are distinguished from prior art devices which are characterized by having more than 5% of the total weight of the cathode as carbon with no graphene.

"In embodiments where the energy storage device of the present invention includes an anode fabricated, at least in part, from a nanocomposite material having graphene layers with metal oxides uniformly distributed throughout the nanoarchitecture of the layers, the graphene in the anode is preferably, but not meant to be limiting, 10% or less of the total weight of anode, and more preferably, but also not meant to be limiting, 5% or less of the total weight of anode. In this manner, the energy storage devices of the present invention are distinguished from prior art devices which are characterized by having more than 10% of the total weight of the anode as carbon with no graphene.

"One embodiment where the present invention is an energy storage device is as a lithium ion battery. In this embodiment, the lithium ion battery has at least one electrode with at least one graphene layer bonded to titania to form a nanocomposite material, and the nanocomposite material has a specific capacity at least twice that of a titania material without graphene at a charge/discharge rate greater than about 10 C. The electrode of this lithium ion battery may further have multiple nanocomposite material layers uniformly distributed throughout the electrode.

BRIEF DESCRIPTION OF THE DRAWINGS

"The following detailed description of the embodiments of the invention will be more readily understood when taken in conjunction with the following drawing, wherein:

"FIG. 1 is a schematic illustration of the present invention showing anionic sulfate surfactant mediated stabilization of graphene and growth of TiO.sub.2-FGS hybrid nanostructures.

"FIG. 2 is a graph showing high energy resolution photoemission spectra of the C 1s region in functionalized graphene sheets (FGS) used in one embodiment of the present invention.

"FIG. 3 are Raman spectra of rutile TiO.sub.2-FGS and FGS in one embodiment of the present invention.

"FIG. 4(a) is a photograph of FGS (left) and SDS-FGS aqueous dispersions (right); FIG. 4(b) is a graph of the UV-Vis absorbance of the SDS-FGS aqueous dispersion.

"FIG. 5 is an XRD pattern of one embodiment of the present invention, an anatase TiO.sub.2-FGS and rutile TiO.sub.2-FGS hybrid material. Standard diffraction peaks of anatase TiO.sub.2 (JCPDS No. 21-1272) and rutile TiO.sub.2 (JCPDS No. 21-1276) are shown as vertical bars.

"FIG. 6(a)-(g) are TEM and SEM images of the nanocomposite materials of various embodiments of the present invention at selected magnifications.

"FIG. 7(a)-(f) are graphs showing the electrical performance of one embodiment of the present invention. FIG. 7(a) shows the voltage profiles for control rutile TiO.sub.2 and rutile TiO.sub.2-FGS (0.5 wt % FGS) hybrid nanostructures at C/5 charge-discharge rates. FIG. 7(b) shows the specific capacity of control rutile TiO.sub.2 and the rutile TiO.sub.2-FGS hybrids at different charge/discharge rates;

"FIG. 7 shows the cycling performance of the rutile TiO.sub.2-FGS up to 100 cycles at 1 C charge/discharge rates after testing at various rates shown in FIG. 7(b). FIG. 7(d) shows the voltage profiles for control anatase TiO.sub.2 and anatase TiO.sub.2-FGS (2.5 wt % FGS) hybrid nanostructures at C/5 charge-discharge rates. FIG. 7(e) shows the specific capacity of control anatase TiO.sub.2 and the anatase TiO.sub.2-FGS hybrids at different charge/discharge rates; FIG. 7(f) shows the cycling performance of the anatase TiO.sub.2-FGS up to 100 cycles at 1 C charge/discharge rates after testing at various rates shown in FIG. 7(e).

"FIG. 8 is a graph showing a plot of coulombic efficiency versus cycle number of TiO.sub.2-FGS hybrids of one embodiment of the present invention at various charge/discharge rate between 1.about.3 V vs. Li/Li.sup.+.

"FIG. 9 is a graph showing the capacity of functionalized graphene sheets of one embodiment of the present invention as function of cycling numbers between 1.about.3 V vs. Li/Li.sup.+.

"FIG. 10(a) is a graph showing the impedance measurement of coin cells using the electrode materials of control rutile TiO.sub.2 and rutile TiO.sub.2-FGS hybrids with different weight percentage of FGSs. FIG. 10(b) is a graph showing the specific capacity of rutile TiO.sub.2-CNT and rutile TiO.sub.2-FGS at 30 C rate with different percentages of graphene.

"FIG. 11 is a graph showing the specific capacity of control rutile TiO.sub.2 (10 wt % Super P) and rutile TiO.sub.2-FGS hybrids (10 wt % FGS) at different charge/discharge rates. The rutile TiO.sub.2-FGS hybrid electrode was prepared by mixing the calcined hybrid with PVDF binder at a mass ratio of 90:10. The control TiO.sub.2 electrode was prepared by mixing control TiO.sub.2 powder, Super P and PVDF binder at a mass ratio of 80:10:10.

"FIG. 12 is an SEM image of TiO.sub.2/FGS hybrid materials made in one embodiment of the present invention without using SDS as a stabilizer. As shown, TiO.sub.2 and FGS domains are separated from each other with minor TiO.sub.2 coated on FGS."

For additional information on this patent application, see: Liu, Jun; Aksay, Ilhan A.; Choi, Daiwon; Wang, Donghai; Yang, Zhenguo. Nanocomposite of Graphene and Metal Oxide Materials. Filed October 1, 2013 and posted February 6, 2014. Patent URL: http://appft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&u=%2Fnetahtml%2FPTO%2Fsearch-adv.html&r=3207&p=65&f=G&l=50&d=PG01&S1=20140130.PD.&OS=PD/20140130&RS=PD/20140130

Keywords for this news article include: Anions, Carbon, Oxides, Graphite, Minerals, Chemistry, Nanoscale, Nanoporous, Electrolytes, Nanotechnology, Electrochemical, Oxygen Compounds, Inorganic Chemicals, Emerging Technologies, The Trustees of Princeton University.

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