(503d) Electrode Designs Incorporating Low Cost Carbon Fibers to Eliminate Inactive Components in Lithium Ion Battery Anodes

For high energy density lithium ion batteries required for transportation
applications, electrode designs that increase the mass and volume fraction of
active material in the cells while maintaining rate performance are needed. Cost
is also a critical factor. The electrochemical properties of lignin-derived
carbon fibers (LCFs) pertinent to their implementation as anodic active materials
in lithium ion batteries have been characterized. LCFs were synthesized through
industrially scalable melt-spinning and melt-blowing processes at Oak Ridge
National Laboratory. Engineering studies predict that LCFs can be manufactured
at $3/lb using these technologies, which compares favorably to $12/lb for
battery grade graphite. The LCFs were coated onto copper current collectors with
PVDF binder and conductive carbon additive through conventional slurry
processing. Galvanostatic cycling of the LCFs against Li revealed reversible capacities
greater than 300 mAh/g.  The coulombic efficiencies were over 99.8%. To eliminate
the inactive components in the slurry-coated electrodes, LCF processing
parameters were modified to produce monolithic mats where the fibers were electrically
interconnected.  These mats were several hundreds of micrometers thick, and the
fibers functioned as both current collector and active material by virtue of
their mixed ionic/electronic conductivities. The mats were galvanostatically cycled
in half cells against Li. Specific capacities as high as 250 mAh/g were
achieved ? approximately 17% lower than the capacities of the same fibers in
slurries. Here, however, there were no inactive materials reducing the
practical specific capacity of the entire electrode construction. Lithiation
and delithiation of the LCFs proceeded with coulombic efficiencies greater than
99.9%, and the capacity retention was greater than 99% over 100 cycles at a rate
of 15 mA/g. Research sponsored by the Laboratory Directed Research and
Development Program of Oak Ridge National Laboratory, managed by UT-Battelle,
LLC, for the U. S. Department of Energy.