High rate performance of hard carbons as a lithium-ion battery anode material

By using carbon spherules as raw material, spherical hard carbons were pyrolyzed in a tube furnace at a constant temperature of 900°C in an argon atmosphere. The crystallite structure and surface morphology of the hard carbons were characterized by X-ray powder diffraction (XRD) and scan electronic microscope (SEM), and the electrochemical performance at high current density was investigated by using three different charge/discharge modes. The results show that the speed of lithium ion intercalation is very slow, which limits the whole reaction. As the current density increases, the slow intercalation limits the capacity of hard carbon. However, the step of deintercalation is comparatively quicker, which only has a little influence on high rate performance of the hard carbons.