On the improvement of Li charge/discharge cyclability of carbon fibers by making a C/C composite with thermosetting resins

The charging capacity of the anode of Li-ion secondary batteries is based on the insertion of Li ions into the internal structure of carbonaceous materials. Low temperature mesophase carbon gives rise to an extraordinary capacity up to 900 mAh/g which is over two times that of graphitic carbon now utilized. However, the serious issue of its low cyclability prevents its actual application. In an attempt to improve the low cyclability of a mesophase carbon fiber, C/C composites have been prepared with an epoxy or a phenolic resin. The cyclability was found to be considerably improved by making the fiber felt into a C/C composite. The cyclability is dependent on how each individual fiber is bound together by the binder carbon, as well as how the electrical conductivity of the consisting material is increased. Epoxy resin created difficulty in forming a smooth binding but it still gave an improved cyclability as compared to the unbound fiber. Phenolic resin of resol type showed a very smooth binding, giving rise to a more stabilized cyclability. The importance of the binding of individual active material particles with an electroconductive material for obtaining a long cycle life has been shown.