Electrochemical voltage spectroscopy (EVS) was utilized to compare the graphitization tendency of two needle cokes at 2000 to 3000 °C. Of the two precursors, the NC-A-1000 has a higher density and lower impurity than NC-B-1000. The polarized optical microscopic pictures revealed that the NC-A-1000 has a flow-type texture whereas the NC-B-1000 a mixed (flow and mosaic) one, indicative of a better molecular ordering in the former. Both the X-ray and SEM (scanning electron microscopy) analysis on the resulting carbons indicated that the NC-A has a higher graphitizability, which likely stems from the higher molecular ordering (mesophase development) in the precursor states. The EVS study also supported the easier graphitization in the NC-A series, where it was found that the onset temperature for graphitization is lower in the NC-A series, and their EVS profiles look closer to those observed with natural graphites. The staging phenomenon involved in the resulting graphitized materials was analyzed by the EVS technique with a high potential resolution. Here, the intensity and location of the discharging EVS peaks was so sensitively affected by the degree of graphitization that it could be used as a probe for estimating the graphitizability. In particular, the peak labeled C in this report decreases in intensity with graphitization and the peak position steadily moves to the negative direction in the potential range of 0.16 to 0.25 V (versus Li/Li+).
All Science Journal Classification (ASJC) codes
- Materials Science(all)