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Researchers Submit Patent Application, "Graphene Materials Having Randomly Distributed Two-Dimensional Structural Defects", for Approval

February 6, 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 Kung, Harold H. (Wilmette, IL); Zhao, Xin (Evanston, IL); Hayner, Cary M. (Evanston, IL); Kung, Mayfair C. (Wilmette, IL), filed on September 12, 2013, was made available online on January 23, 2014.

The patent's assignee is Northwestern University.

News editors obtained the following quote from the background information supplied by the inventors: "The proliferation of mobile devices with large numbers of increasingly sophisticated and powerful functions has led to a rapidly increasing demand for high-power, high-capacity electrical energy storage devices. The situation will become even more acute when hybrid and battery-powered electric vehicles become a preferred mode of transportation. Currently, the combined need for high capacity and high power is met by two separate devices: a rechargeable battery for capacity and an ultracapacitor for power. A single device, such as a rechargeable battery that can operate at high power, is highly desirable because it would be lighter, simpler to control, and able to provide sustained high power.

"Graphene, a two-dimensional aromatic monolayer graphite has recently been investigated with respect to rate capability and cycling stability when used in conventional electrochemical energy storage devices. The excellent tensile modulus and mechanical durability of self-supporting graphene materials eliminate the requirement for traditional inactive additives and metal foil current collectors. In addition, charge storage materials made by sandwiching high-capacity metallic or redox materials between graphene sheets have shown improved cycling stability.

"Unfortunately, the practical charge storage capability of graphene based anodes in Li ion batteries at high charge/discharge rates has been constrained by the structure of graphene, which has a very high aspect ratio (i.e., it is wide, but very thin). In order to access the interior of a graphene stack, Li ions need to enter the structure at the edge of the stack and travel distances of the order of microns. Thus, at high power, when fast Li exchange between the electrolyte solution and the electrode is required, only the regions near the edge of the graphene stack are accessible"

As a supplement to the background information on this patent application, VerticalNews correspondents also obtained the inventors' summary information for this patent application: "Graphene-based materials, electrodes made from the materials, batteries incorporating the electrodes, and methods for making the electrode materials are provided.

"One aspect of the invention provides graphene-based materials comprising a plurality of graphene sheets disposed in a vertical stack, wherein graphene sheets within the vertical stack comprise randomly-distributed defect pores formed by in-plane carbon vacancies. In some embodiments of the materials, the graphene sheets are part of a structure comprising a continuous network of graphitic regions comprising crystalline portions of the vertical stack of graphene sheets. In these embodiments, the continuous network of graphitic regions is integrated with a composite comprising: (a) disordered portions of the vertical stack of graphene sheets; and (b) an electrochemically active material, such as silicon nanoparticles, in contact with the graphene sheets in the disordered portions of the vertical stack.

"Another aspect of the invention provides lithium ion batteries comprising a cathode, an anode and a non-aqueous electrolyte comprising a lithium salt disposed between the cathode and the anode, wherein the anode comprises a plurality of graphene sheets disposed in a vertical stack, and further wherein graphene sheets within the vertical stack comprise randomly-distributed defect pores formed by in-plane carbon vacancies. In some embodiments of the batteries, the graphene sheets are part of a structure comprising a continuous network of graphitic regions comprising crystalline portions of the vertical stack of graphene sheets, wherein the continuous network of graphitic regions is integrated with a composite comprising: (a) disordered portions of the vertical stack of graphene sheets; and (b) an electrochemically active material, such as silicon nanoparticles, in contact with the graphene sheets in the disordered portions of the vertical stack.

"Yet another aspect of the invention provides methods for making an electrode material, the method comprising the steps of: exposing a suspension of exfoliated, oxidized graphene sheets to an acid at an acid concentration high enough, and an exposure time long enough, to generate defect pores formed from carbon vacancies in the oxidized graphene sheets; removing the oxidized graphene sheets from the suspension; and reducing the oxidized graphene sheets to form a vertical stack of graphene sheets having a random distribution of defect pores distributed therein.

"Some embodiments of the methods also include the step of mixing the oxidized graphene sheets in suspension with electrochemically active nanoparticles, such that the nanoparticles are dispersed between the graphene sheets. In these embodiments of the present methods, when the oxidized graphene sheets are removed from the suspension and reduced, the resulting material comprises a network of graphitic regions comprising crystalline portions of the vertical stack of graphene sheets integrated with a composite comprising disordered portions of the vertical stack of graphene sheets and nanoparticles of the electrochemically active material dispersed between the graphene sheets in the disordered portions of the vertical stack, the graphene sheets having a random distribution of defect pores distributed therein.

"Other principal features and advantages of the invention will become apparent to those skilled in the art upon review of the following drawings, the detailed description, and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

"Illustrative embodiments of the invention will hereafter be described with reference to the accompanying drawings, wherein like numerals denote like elements.

"FIG. 1. is a schematic diagram of the cross-section of (A) a vertical stack made of graphene sheets with randomly distributed two-dimensional defect pores and (B) a vertical stack of graphene sheets that includes disordered portions, wherein Si nanoparticles are disposed between graphene sheets, and crystalline portions of ordered graphene sheets. Structural defects in the form of carbon vacancies are distributed through the three-dimensional network. Each broken line represents a single-atom thick graphene sheet with defects (deG). Each group of gray lines represents crystalline portions of the vertical stack. Circles represent Si nanoparticles sandwiched between disordered portions of the graphene sheets, represented by black lines. The disordered portions are structurally connected to the crystalline portions, providing both electrical conductivity and mechanical integrity.

"FIG. 2. Transmission electron microscope (TEM) images of Pd-stained samples (see Example): (A) GO, (B) deGO-I, (C) deGO-II, (D) deGO-III, and (E) deGO-IV. (F) A high magnification image of a highlighted region in D, showing .about.3 nm Pd particles in ring-like arrangements, a result of Pd ion binding to carboxylate at defect perimeters.

"FIG. 3. (A) Scanning electron microscope (SEM) image of the top surface of a Si-deG-III paper (see Example). Circles in the inset highlight in-plane defects. (B) SEM image of the cross-section of a Si-deG-III paper. Insets show Si nanoparticles embedded between graphene sheets uniformly."

For additional information on this patent application, see: Kung, Harold H.; Zhao, Xin; Hayner, Cary M.; Kung, Mayfair C. Graphene Materials Having Randomly Distributed Two-Dimensional Structural Defects. Filed September 12, 2013 and posted January 23, 2014. Patent URL: http://appft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&u=%2Fnetahtml%2FPTO%2Fsearch-adv.html&r=4987&p=100&f=G&l=50&d=PG01&S1=20140116.PD.&OS=PD/20140116&RS=PD/20140116

Keywords for this news article include: Chemistry, Nanoparticle, Nanotechnology, Electrochemical, Emerging Technologies, Northwestern University.

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Source: Politics & Government Week


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