A Novel CNT Anode Material for Li Battery Applications

Carbon nanotubes hold excellent promise for lithium based energy storage and conversion applications. The use of typical nanophase sp² carbon as a host material has two principal disadvantages, chief of which is the substantial presence of electrochemical impurities and low lithium storage ability when compared with metallic lithium. A process is shown that produces electrochemically clean, high defect rate carbon nanotubes through the corrosion of silicon carbide fibers to produce a low internal resistance, high activity anode material for Li battery applications. This material is shown to be superior to conventional chemical vapor deposition grown CNTs electrochemically and physically. Residual material present in carbide derived CNTs are electrochemically inert carbides and oxides. The resulting CNT bundles are more consistent in chirality, as well as defect rate and physical dimension than the CVD grown counterparts.

Under optimal conditions Li intercalates into graphitic material in the form of LiC₆, which leads to a specific capacity reduction from 3860 mAh/g for metallic Li to 372 mAh/g for the graphitic anodes. We describe a process, carbothermal carbide conversion, for the production of a uniquely valuable carbon nanotube material for electrochemical applications comprised of bundles of SWCNTs of high defect rate. As carbide conversion nanotubes form, the CNTs aggregate into bundles which consist of single-wall nanotubes held together by van der Waals forces roughly equivalent to graphitic sheet spacing, approximately 5 angstrom. These ropes display increased energy storage capabilities as Li ions can intercalate both into the channels between the nanotubes, and into the interior of the nanotubes themselves. This gives an anode stoichiometry of approximately LiC2, which is considerably higher than the value of conventional Li-graphite anodes. Studies have shown that the entry of Li ions preferentially enter through defects such as kinks or open ends of nanotubes. We show higher edge plane character of carbide derived CNTs via Raman spectroscopy, transmission electron microscopy and electrochemical deposition of nickel.