279954 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.
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