A simple preparation method for spherical carbons and their anodic performance in lithium secondary batteries

This work reports a simple preparation method for spherical hard carbons and graphites. The phenolic resin and methylnaphthalene-derived mesophase pitch (MNMP) powders are employed as the precursor for hard carbon and graphite, respectively. The irregular-shaped precursor powders are converted to spherical carbons by first coating with fine-grained fumed silica powder and carbonizing/graphitizing under an argon atmosphere. Two characteristic features are observed in this preparation. First, among the used silica powders, only those having a hydrophobic surface group are effective for the irregular to sphere conversion. Second, the conversion takes place near the glass transition temperature of the resin and the softening point of the pitch, respectively. Based on these observations, an irregular to sphere conversion mechanism has been proposed. The spherical carbon powders exhibit a higher tap density and smaller surface area than those of the irregular-shaped ones, which is an advantageous feature for practical lithium batteries.