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The following quote was obtained by the news editors from the background information supplied by the inventors: "The present invention provides new nanocomposites comprising a graphitic matrix in which nanosized iron fluoride or iron oxide particles are embedded. The invention further comprises a one-step method for preparing said composites and their use as electrode material.
"Lithium ion batteries are key energy storage devices that power today's consumer electronics. However, their energy density still fall short for transportation and large scale power storage applications. One way to increase the energy density of battery is to use high energy density electrode materials. The present commercial Li-ion batteries use LiCoO.sub.2 or LiFePO.sub.4 based insertion positive electrode materials. While LiCoO.sub.2 is a layered compound with a specific capacity of 150 mAh/g, LiFePO.sub.4 is a framework compound whose capacity is 170 mAh/g. Even though both compounds show excellent reversibility with lithium, the specific capacity is limited by single electron redox reaction per molecule or even less.
"A valid approach to increase the energy density of electrode material is to utilize all possible redox states of metal ion. The best candidates for this purpose are metal fluorides as they reversibly react with lithium at relatively high voltage (
"Among various metal fluorides, iron fluorides are important class due to their low cost and low toxicity. In this context, FeF.sub.2 is an interesting cathode material which has a thermodynamic reduction potential of 2.66 V versus lithium and has a theoretical specific capacity of 571 mAh/g to a gravimetric energy density of 1519 Wh/kg. However, FeF.sub.2 is an electrical insulator and needs to stay in intimate contact with electronic conductors in order to become electrochemically active.
"To address these problems carbon-metal fluoride nanocomposites (CMFNCs) are proposed in U.S. 2004/0062994. These composites are prepared using mechanical high-energy milling of FeF.sub.2, FeF.sub.3, NH.sub.4FeF.sub.4, NiF, or CoF and activated carbon, carbon black, or expanded graphite. The total carbon content in the nanocomposites comprises about 5% to 50% by weight. Similar composites and a method for their preparation are described by Badway et al. (F. Badway,
"Plitz et al. presented a method for synthesising Carbon-Metal Fluoride Nanocomposites (CMFNCs) starting from insulative carbon fluoride (CF) as oxidizing agent and FeF.sub.2, NiF.sub.2, or CoF.sub.2 precursors (I. Plitz, F. Badway,
"A further disadvantage of the state of the art is the lack of an economic one-step synthesis which is easy to perform. The cited state of the art does not disclose iron nanoparticles or nanocomposites clamped into a highly conducting graphitic matrix."
In addition to the background information obtained for this patent application, VerticalNews journalists also obtained the inventors' summary information for this patent application: "To overcome the disadvantages of the state of the art, it is an objective of the present invention to provide a fabrication method which leads to a nanoscale dispersion and a stable anchoring of iron compounds, in particular FeF.sub.2 and Fe.sub.2O.sub.3 on or in a graphitic matrix. The nanomaterial is obtained by a reactive deposition of a volatile iron compound with chemically modified graphite which initially acts as an F.sup.- or O.sup.2- donor and transforms from a non-conducting graphite derivative into electrically conducting graphite during the process. The synthesis proceeds in one step and leaves no solid or liquid by-products.
"It is another objective of the present invention to provide a nanocomposite containing intercalated FeF.sub.2-- or Fe.sub.2O.sub.3-nanoparticles in a graphitic carbon matrix.
"It is a further objective of the present invention to provide an electrode material for its use in a battery cell. This battery material should be based on a nanocomposite containing intercalated FeF.sub.2-- or Fe.sub.2O.sub.3-nanoparticles in a graphitic carbon matrix. The material should overcome the problems of the poor electric conductivity due to a closer interface between the active iron material and the graphite conductor, and poor cycling stability resulting from significant volume expansion during the redox reaction.
"The invention provides a method to synthesize a nanocomposite containing intercalated FeF.sub.2-- or Fe.sub.2O.sub.3-nanoparticles in a graphitic carbon matrix by reaction of a volatile iron compound with a graphite fluoride (CF.sub.x) or a graphite oxide (CO.sub.x) in a hermetically closed vessel at a temperature from 100.degree. C. to 400.degree. C. Preferably, the reaction time is from 2 to 24 hours.
"During this bottom-up synthesis (pyrolysis), the volatile iron compound is dispersed in the graphite derivative where it reacts with the fluorine or oxygen atoms initially bound to the graphite and crystallises as nanoscale iron compound between the graphite sheets without defoliating them completely. The formerly insulating graphite fluoride or -oxide transforms into a highly conductive graphitic matrix by this reaction.
"Due to the extraordinary process of performing the reaction inside the graphite derivative, the product FeF.sub.2-nanoparticles are mechanically clamped inside the formed graphitic structure providing an excellent electrical contact between the constituents.
"Hence, the structure of the nanocomposite is made up of a graphitic carbon matrix which encapsulates the FeF.sub.2 nanoparticles. This encapsulation leads to a waved structure of the graphite sheets in between which the nanoparticles are embedded. In the case of Fe.sub.2O.sub.3, particles are also found at the outer surface which is not the case with FeF.sub.2.
"In a preferred embodiment, the reaction is performed under inert gas atmosphere. Inert gas such as argon may prevent any side reactions leading to a product of a lower purity or a poorer yield.
"In another preferred embodiment, the volatile iron compound is Fe(CO).sub.5. By using this educt, the only side product is CO which leaks upon opening of the reaction vessel after the reaction and the crude product of this reaction can be used as such without further purification.
"In yet another preferred embodiment the graphitic educt, graphite fluoride (CF.sub.x) or the graphite oxide (CO.sub.x), are milled at ambient or cryogenic temperatures prior to the pyrolysis reaction. One example of milling is ball milling.
"The crystallite size of formed iron fluoride nanoparticles lies in a narrow range between 8 and 12 nm, proved with TEM and XRD measurements. The nanoparticles are clamped or embedded in or on the surface of the graphitic carbon matrix, such that an agglomeration of the particles is prevented and electrical contact of the insulating active material is provided.
"The present invention further provides a nanocomposite containing intercalated FeF.sub.2-- or Fe.sub.2O.sub.3-nanoparticles in a graphitic carbon matrix synthesised by a method described in this invention.
"The present invention provides also a nanocomposite containing intercalated FeF.sub.2-nanoparticles in a graphitic carbon matrix, wherein the nanoparticles have a diameter from 8 nm to 12 nm. In a preferred embodiment, the nanocomposite contains 75 to 85 wt % of iron fluoride particles and 15 to 25 wt % of carbon.
"Due to its particular graphitic nature, the composite exhibits a considerably lower resistivity than other materials described in the state of the art. This nanocomposite reveals a resistivity of 120-150 .OMEGA.*cm at a density of 2.5-3.5 g/cm.sup.3. In the cited literature (Plitz et al. see above), pellets of a composite consisting of iron fluoride and carbon produced by ball milling showed a resistivity of 1500 .OMEGA.*cm with a specific weight of the pellet of 0.5 cm.sup.3/g.
"One advantage of the nanocomposite with the embedding graphitic carbon matrix is that an agglomeration of the particles is impeded or prevented. The iron salt crystallites remain well dispersed in the matrix during cycling.
"Another advantage of the composite is the strong binding forces between the particles and the graphitic surface due to the widening and bending of the graphite sheets. The binding forces of the graphitic structure lead to an intimate contact of the particles to the graphite. As a consequence, the particles which are electrically insulating by nature are embedded in an electrically conducting environment (graphite) with electronic conductors and thus become electrochemically active.
"A further advantage of the nanocomposites according to the present invention is the large amount of the active iron compound inside the graphitic matrix. There is no need to purify the nanocomposites or add additional carbon after the pyrolysis when using as electrochemically active material in batteries. About 80 wt % of the obtained crude composite is active material, and, when used in an electrochemical storage cell such as a lithium battery, the active material yields to an amount of 72 wt % active material on the electrode upon adding 10 wt % of binder.
"Hence, the invention also provides electrochemically active material material containing a nanocomposite with intercalated FeF.sub.2-- or Fe.sub.2O.sub.3-nanoparticles in a graphitic carbon matrix as described in the invention. In a preferred embodiment, this electrochemically active material is for use in an electrochemical storage cell.
BRIEF DESCRIPTION OF THE DRAWINGS
"The following figures and examples are presented to provide a better understanding of the description of procedures and conceptual aspects of the invention.
"FIG. 1 show diagraoms of powder XRD patterns of Pristine CF.sub.1.1, C(FeF.sub.2).sub.0.55, ball milled CF.sub.1.1 and BM-C(FeF.sub.2).sub.0.55.
"FIG. 2 show diagrams of FT-IR spectra of CF.sub.1.1 pristine, ball milled CF.sub.1.1, C(FeF.sub.2).sub.0.55 and BM-C(FeF.sub.2).sub.0.55
"FIG. 3a is a TEM image and FIG. 3b is a schematic structure of C(FeF.sub.2).sub.0.55
"FIG. 4 is show powder XRD patterns of graphite oxide and graphite Fe.sub.2O.sub.3 nanocomposite.
"FIG. 5 shows electrochemical discharge/charge curves of C(FeF.sub.2).sub.0.55 (a) at 25.degree. C. (b) at 40.degree. C. and © corresponding differential capacity plot for the first three cycles; discharge/charge curves of BM-C(FeF.sub.2).sub.0.55 (d) at 25.degree. C. (e) at 40.degree. C. and (f) corresponding differential capacity plot for first three cycles.
"FIG. 6 shows electrochemical cycling of C(FeF.sub.2).sub.0.55 and BM-C(FeF.sub.2).sub.0.55 at 25.degree. C. and 40.degree. C.
"FIG. 7 shows electrochemical discharge/charge curves of C(Fe.sub.2O.sub.3)."
URL and more information on this patent application, see: Munnangi,
Keywords for this news article include: Anions, Carbon, Patents, Graphite, Minerals, Chemistry, Fluorides, Nanoscale, Nanoparticle, Nanotechnology, Electrochemical, Hydrofluoric Acid, Emerging Technologies.
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