The patent's assignee is
News editors obtained the following quote from the background information supplied by the inventors: "Silicon is a promising high capacity anode material for Li ion batteries. However, the large volume fluctuation upon Li.sup.+ insertion/extraction can fracture the material, leading to fast capacity fading due to the loss of electrical continuity. Another problem is that cracking exposes new surface of Si to the electrolyte solvents, which can decompose at low potential to deposit a solid electrolyte interface (SEI) layer of lithiated compounds on the new Si surface. During charge/discharge cycling, the insulating SEI layer can grow thicker, which further degrades the capacity and cycling stability of the Si anode. In an operating battery cell, continuous growth of SEI layer will also gradually deplete the available Li.sup.+ and the amount of electrolytes, thus deteriorating the overall performance.
"Theoretical and in-situ transmission electron microscopy (TEM) studies have shown that the strain induced by the expansion/contraction can be accommodated in Si nanoparticles with diameters Yoshio, M.; Wang, H. Y.;
As a supplement to the background information on this patent application, VerticalNews correspondents also obtained the inventors' summary information for this patent application: "Materials comprising sub-micron sized capsules comprising crumpled graphene sheets that form a graphene shell encapsulating an internal cargo comprising nanostructures of a second component are provided. Also provided are anodes comprising the capsules, lithium ion batteries incorporating the anodes and methods of making the capsules.
"One embodiment of the present materials comprises a layer of capsules, the capsules comprising: a crumpled graphene shell comprising graphene sheets having a crumpled morphology; and silicon nanostructures encapsulated within the crumpled graphene shell; wherein the average size of the capsules is less than 1 .mu.m.
"One embodiment of a lithium ion battery comprises an anode comprising the material described above; a counter electrode; and an electrolyte in electrical communication with the anode and the counter electrode. Embodiments of batteries having this construction are characterized by a coulombic efficiency reaching 99% after 20 cycles, or better at a charge voltage of about 2 V and a current density of about 1 A/g.
"An embodiment of a method of making sub-micron sized capsules comprises the steps of: forming an aqueous dispersion comprising graphene oxide sheets and silicon nanostructures; forming aerosol droplets from the aqueous dispersion; and heating the aerosol droplets to evaporate water from the aerosol droplets, whereby the resulting compression induces the formation of the capsules. The resulting capsules comprise crumpled graphene oxide shells comprising the graphene oxide sheets having a crumpled morphology and silicon nanostructures encapsulated within the crumpled graphene oxide shells. In this method, the temperature at which the aerosol droplets are heating is sufficiently high to produce capsules having an average size of less than 1 .mu.m.
"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. Schematic drawing illustrating a method and apparatus for the aerosol assisted capillary assembly of crumpled graphene wrapped Si nanoparticles.
"FIG. 2A. SEM image showing a low-magnification image of crumpled capsules of graphene-wrapped Si. FIG. 2B. SEM image showing a single capsule. FIG. 2C. STEM image of a single capsule under scanning mode. FIG. 2D. STEM image of a single capsule under Z-contrast transmission mode, clearly showing encapsulated Si nanoparticles. FIG. 2E. EELS elemental mapping for carbon. FIG. 2F. EELS elemental mapping for EDX mapping of element Si of the same capsule as FIG. 2C.
"FIG. 3. Coulombic efficiency of an anode comprising crumpled graphene wrapped Si nanoparticles in comparison to an anode comprising unwrapped Si nanoparticles at a constant current density of 1 A/g.
"FIG. 4. Charge/discharge cycling capacity of an anode comprising crumpled graphene wrapped Si nanoparticles in comparison to an anode comprising unwrapped Si nanoparticles at a constant current density of 1 A/g.
"FIG. 5. SEM image of the capsules after 250 cycles showing that Si nanoparticles were still encapsulated in the crumpled graphene.
"FIG. 6. Galvanostatic charge/discharge profiles of an anode comprising crumpled graphene wrapped Si nanoparticles at current densities ranging from 0.2 to 4 A/g."
For additional information on this patent application, see: Huang, Jiaxing; Jang, Hee Dong; Luo, Jiayan. Crumpled Graphene-Encapsulated Nanostructures and Lithium Ion Battery Anodes Made Therefrom. Filed
Keywords for this news article include: Silicon, Electrolytes, Nanoparticle, Nanostructural, Nanostructures, Nanotechnology, Inorganic Chemicals, Emerging Technologies,
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