Anode characteristics of non-graphitizable carbon fibers for rechargeable lithium-ion batteries

Non-graphitizable carbon fibers heat-treated between 1000 and 1200 °C gave capacity higher than the capacity of LiC6 (372 mAh g−1) with a significant capacity below 0.1 V during oxidation. 7Li nuclear magnetic resonance (7Li-NMR) observation on lithium insertion into the carbon fibers suggested that lithium in the carbons are classified into two species. One of the lithium species was the same as that in graphitizable carbons. However, the other lithium species was quite different from that in graphitizable carbons, because the line shifts in the 7Li-NMR spectra of the carbon fibers fully lithiated to 0 V were between 80–110 ppm (versus LiCl); these shifts are larger than the maximum shift of lithium in graphitizable carbons (∼45 ppm). In particular, a significant capacity below 0.1 V corresponded to the formation of a new lithium species.