Electrochemical lithium insertion properties of carbon nanotubes produced by catalytic pyrolysis of acetylene

Carbon nanotubes are synthesized in catalytic pyrolysis of acetylene over Co/SiO2 at 650, 700, and 750 degrees C. The first-charge capacities are 436, 303, and 205 mA h/g for samples produced at 650, 700, and 750 degrees C. The capacity of the 650 degrees C sample shows is higher than that of LiC6 (372 mA h/g), but the voltage profile shows a large hysteresis (lithium is inserted below 0.25 V and removed above 1 V). The capacity below 1 V may be related to lithium intercalated into the interlayer of graphite planes, and that above 1 V, to accommodation of lithium at vacancies and nanoscopic cavities. With increasing preparation temperature, the cavities and vacancies are annihilated and the first-charge capacity above 1 V decreases.