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Researchers Submit Patent Application, "Lignin-Based Active Anode Materials Synthesized from Low-Cost Renewable Resources", for Approval

February 27, 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 RIOS, Orlando (Knoxville, TN); TENHAEFF, Wyatt Evan (Knoxville, TN); DANIEL, Claus (Knoxville, TN); DUDNEY, Nancy Johnston (Knoxville, TN); JOHS, Alexander (Knoxville, TN); NUNNERY, Grady Alexander (Rock Hill, SC); BAKER, Frederick Stanley (Malulani Gardens, HI), filed on August 6, 2012, was made available online on February 13, 2014.

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 Oak Ridge National Laboratory (ORNL) has shown that good performance can be achieved on the cathode side by replacing the binder and current collector with highly conductive graphitic carbon fibers. In this work, particles of the cathode active material were coated directly onto the carbon fiber; the carbon fibers were the backbone of the electrode architecture and conduit for electron transport to the active material but did not participate in lithium intercalation. Attempts have been made to utilize these carbon fibers as the active material on the anode side, but low capacities were realized due to alignment of the basal planes of graphite crystallites parallel to the carbon fiber axis. The basal plane is effectively a barrier to lithium diffusion; lithium insertion is limited to defect sites in the plane. Researchers at the U.S. Army Research Laboratory recently presented results from their characterization of commercially available carbon fibers and related structures as anodes in lithium ion batteries. The best reversible electrochemical capacity was 158 mAh g.sup.-1, less than half the theoretical capacity of graphite. The authors note that carbon fibers for the composite industries typically consist of a disordered carbon core surrounded by a graphitic sheath, which may explain the low capacities obtained in the study.

"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 (

"Carbon fibers are mixed ionic/electronic conductors that can have relatively high electrical conductivities >10-50 S/cm. The microstructure and graphitic content of carbon fibers are critical for effective insertion of lithium into carbon fibers; the microstructure should be controlled such that the graphene planes of graphite crystallites are oriented off-parallel to the fiber axis. Charge storage capacities in carbon fibers derived from mesophase pitch with a radial texture are comparable to those of graphite, but pitch-based fibers are expensive. Pyrolytic carbons from rice husks have been shown to have reversible capacities over 700 mAh g.sup.-1 for several hundred cycles; however, the additional processing steps required for binding the powder form graphite dominates its cost. Previous studies on the pyrolysis of epoxy for battery applications have shown that turbostratic disorder and crystallite size significantly increase the specific capacity from under 200 mAh g.sup.-1 to over 700 mAh g.sup.-1."

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, Orlando; TENHAEFF, Wyatt Evan; DANIEL, Claus; DUDNEY, Nancy Johnston; JOHS, Alexander; NUNNERY, Grady Alexander; BAKER, Frederick Stanley. Lignin-Based Active Anode Materials Synthesized from Low-Cost Renewable Resources. Filed August 6, 2012 and posted February 13, 2014. Patent URL: http://appft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&u=%2Fnetahtml%2FPTO%2Fsearch-adv.html&r=3057&p=62&f=G&l=50&d=PG01&S1=20140206.PD.&OS=PD/20140206&RS=PD/20140206

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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Source: Politics & Government Week


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