Nano-structural and electrochemical characteristics of low crystalline carbonaceous materials and carbonized non-graphitizable carbons as negative electrodes of rechargeable lithium-ion cells

Electrochemical characteristics of low crystalline carbonaceous materials and carbonized non-graphitizable carbons as negative electrodes of rechargeable lithium-ion cells are reviewed, particularly from the viewpoint of the relationship linking the electrochemical characteristics and nano-structural features of these materials. These low crystalline materials show very attractive characteristics for negative electrodes of lithium-ion cells, e. g., reversible capacity higher than that of graphite (LiC6, 372mAh/g). In addition, carbonized non-graphitizable carbons display a significant capacity below 0.1V (vs. Li/Li+). These features are very important to improve specific energy of lithium-ion cells. 7Li-nuclear magnetic resonance (7Li-NMR) observation on lithium insertion into those materials suggested that lithium species in those materials are quite different from that in graphite. Lithium species in low crystalline carbonaceous materials have an ionic character. On the other hand, lithium in carbonized non-graphitizable carbons is classified into two species. One of the lithium species is the same as that in graphitizable carbons. However, the other lithium species are inferred to be lithium clusters, which gave 7Li-NMR peaks at 190 and 280ppm (vs. aq. LiCl) at -130°C. The structural characteristics, which form ionic lithium species and lithium clusters, are discussed.