Characterization of Carbonaceous Active Materials Used for the Negative Electrode of Li-Ion Batteries and Capacitors

During the course of investigating carbonaceous materials for the active materials of Li-ion batteries (LIB) or supercapacitors (SPC) we have found interesting properties and behaviors of the carbon in contact with an electrolyte containing Li+. In this article the author would like to exhibit these attractive matters. Especially use of carbon fiber (CF) attracted our attention since we can use a single fiber as the working electrode, which enables us to measure not only the conductivity change but also the volume change during Li insertion/extraction. Determination of the lithium diffusion coefficient in carbon could be performed with ease. Surprisingly propylene carbonate showed no decomposition during cathodic polarization of graphite in propylene carbonate electrolyte when we use a single graphitzed fiber. On the other hand, by the use of rounded graphite particle we suggested presence of holes on the graphene layer. We proved that homogeneous distribution of conductivity over the surface of coated electrode is the key factor to keep long cycle life. (C) The Electrochemical Society of Japan, All rights reserved.