The patent's assignee is Ut-battelle, Llc.
News editors obtained the following quote from the background information supplied by the inventors: "Lithium-ion battery packs in hybrid electric vehicles (HEVs) and fully electric vehicles (EVs) in the near term will contain carbon-based active materials in the anode. However, full market penetration will require further non-incremental improvements in cyclic capacity at lower costs. Typical state of the art lithium battery anodes are composites of 90% (by mass) graphitic carbon and 10% polymeric binder coated onto metallic copper current collectors.
"Previous work at the
"The intercalation compound of lithium with graphite with a stoichiometry of LiC.sub.6 corresponds to a theoretical charge capacity of 372 mAhg.sup.-1. It has been demonstrated that it is possible to surpass this capacity using several modifications of carbon and graphite, many of which do exceed the theoretical charge capacities. However, in many cases of high capacity carbons (hard carbons and disordered carbons), the stability upon cycling is limited. Activated carbons containing micropores (
As a supplement to the background information on this patent application, VerticalNews correspondents also obtained the inventors' summary information for this patent application: "A method of making an anode includes the step of providing fibers from a carbonaceous precursor. The carbonaceous fibers have a glass transition temperature T.sub.g. The carbonaceous fibers are placed into a layered fiber mat. The fiber mat is fused by heating the fiber mat in the presence of oxygen to above the Tg but no more than 20% above the T.sub.g to fuse fibers together at fiber to fiber contact points and without melting the bulk fiber mat to create a fused fiber mat through oxidative stabilization. The fused fiber mat is carbonized by heating the fused fiber mat to at least 650.degree. C. under an inert atmosphere to create a carbonized fused fiber mat.
"The carbonaceous precursor fibers can be lignin fibers. The lignin fibers can be melt spinnable, or blowable, or formed from the carbonaceous lignin precursor by any suitable method. The fibers can have a diameter between 1 and 300 .mu.m.
"The fusing step can include heating the fiber mat at heating rates of from 0.03.degree. C./min to 10.degree. C./min. The fusing step can include heating the carbon fiber to between about 180 and about 300.degree. C. The carbonizing step can include heating the fused fiber mat at a rate of between 0.5.degree. C./min and 500.degree. C./min. The carbonizing step can include heating the fused fiber mat to between 650.degree. C. and 3000.degree. C. The carbonizing step can include determining a desired level of graphitization in the anode, and adjusting the carbonization temperature depending on the degree of carbonization, increasing graphitization being attained by increasing the carbonization temperature.
"The step of providing carbon fibers can include mixing carbon nanotubes with the carbonaceous precursor to generate carbon nanotube composite fibers. The carbon nanotubes can comprise between about 0.2% and about 10%, by weight.
"The step of providing carbon fibers comprises chemically modifying functional groups on the carbonaceous precursors. The chemical modification step can comprise reacting the precursors with at least one selected from the group consisting of acetic anhydride, succinic anhydride, maleic anhydride and phthalic anhydride.
"The step of providing carbon fibers can comprise providing a lignin precursor, and forming fibers from the lignin precursor. The lignin precursor is ground to produce a lignin powder. The lignin powder is extruded and cut into pellets, and the pellets are subjected to one of melt spinning and melt blowing to produce lignin fibers.
"The carbonized fused fiber mat can be incorporated as the anode of a battery. The anode can have capacity of over 100 mAh g.sup.-1 for at least 10 cycles. The anode can have a reversible capacity of at least 100 mAh g.sup.-1. The anode can have a reversible capacity of at least 150 mAh g.sup.-1.
"A lithium ion battery can include a cathode layer, a lithium salt electrolyte disposed in operable relationship with the cathode layer; and a carbon fiber mat anode layer disposed in operable relationship with the lithium salt electrolyte layer. The carbon fiber mat anode layer can have a carbon fiber mat that has been fused at fiber to fiber contact points and carbonized.
"The carbon fiber mat anode layer can also comprise the anode current collector. The carbon fiber can be derived from lignin. The anode can have a specific charge capacity of over 100 mAh g.sup.-1 for at least 10 cycles. The anode can have a reversible charge capacity of at least 100 mAh g.sup.-1. The anode can have a reversible charge capacity of at least 150 mAh g.sup.-1.
"An anode for a battery, comprising a carbon fiber mat anode layer, the carbon fiber mat anode layer comprising a carbon fiber mat that has been fused at fiber to fiber contact points and carbonized.
BRIEF DESCRIPTION OF THE DRAWINGS
"There are shown in the drawings embodiments that are presently preferred it being understood that the invention is not limited to the arrangements and instrumentalities shown, wherein:
"FIG. 1 is A) a schematic cross-sectional view of a conventional anode design for lithium ion batteries; B) a schematic of an anode design according to the invention; and C) an optical micrograph of lignin fibers, thermally fused during the early stages of stabilization.
"FIG. 2 is a plot of specific capacity and coulombic efficiency vs. cycle # for given lithium insertion rates for a lignin fiber cell with a binder.
"FIG. 3 is a plot of specific capacity vs cycle # for LCF mats carbonized at various temperatures.
"FIG. 4 is a plot of specific capacity and coulombic efficiency vs cycle # for an LCF mat carbonized at 2000.degree. C. against Li metal in 1M LiPF.sub.6 in PC.
"FIG. 5 is a plot of derivative weight (%/min) and temperature difference (.degree. C./mg) vs. temperature (.degree. C.) for lignin fiber mats.
"FIG. 6 are scanning electron microscopy (SEM) images of high density (right--10% open volume) and low density (left--80% open volume) lignin fiber electrodes.
"FIG. 7 is an X ray diffraction (XRD) plot of intensity vs 2.theta. (deg.) for lignin carbon fiber samples.
"FIG. 8 are transmission electron microscopy (TEM) images of lignin fiber samples.
"FIG. 9 is a plot of resistivity (mOhmcm) vs. max pyrolysis temperature (.degree. C.) for a conventional lignin carbon fiber and for a carbon nanotube (CNT) composite carbon fiber.
"FIG. 10 are SEM images of carbon fiber electrodes coated onto copper current collectors using slurry processing.
"FIG. 11 are .sup.13C CP-MAS NMR spectra of unmodified Alcell lignin and Alcell lignin chemically modified using acetic anhydride, succinic anhydride and phthalic anhydride.
"FIG. 12 are Thermogravimetric Analysis (TGA) plots of oxidation and carbonization data for unmodified Alcell lignin and Alcell lignin chemically modified using acetic anhydride, succinic anhydride and phthalic anhydride.
"FIG. 13 is a plot of coulombic efficiency vs. cycle # of lignin-based carbon fibers fused into mats. Three different carbonization temperatures were characterized."
For additional information on this patent application, see: RIOS,
Keywords for this news article include: Graphite, Minerals, Nanotube, Succinates, Acetic Acids, Nanotechnology, Phthalic Acids, Succinic Acids, Ut-battelle Llc, Acetic Anhydrides, Organic Chemicals, Dicarboxylic Acids, Phthalic Anhydrides, Succinic Anhydrides, Emerging Technologies.
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