Evolution of Natural Graphite Morphology Through Sequential Spheroidization in the Impact Mill

Most commercial lithium‐ion batteries employ graphite as the active material of negative electrode (anode). If natural graphite is used, it should be preliminarily purified and spheroidized, i.e., crystalline graphite flakes should be converted into rounded particles. In this paper, the spheroidization process of natural graphite has been studied using advanced scanning electron microscopy and X‐ray powder diffraction. For the spheroidization, an impact mill equipped with three‐stage rotor of the original design has been employed, in which the rounding process occurs through the number of successive runs of the graphite material through the mill. The morphology study demonstrates that the most significant change in the particle morphology occurs within the first run, when the original flakes are crushed and split, and the “potato‐shape” particles are formed. During the subsequent mill runs, these rounded particles undergo compaction; their porosity decreases and sphericity increases, while the median size remains nearly constant. On the macroscopic scale, the repeated mill runs result in an increase in the graphite tap density. On the basis of the obtained experimental results, two‐stage scheme of the spheroidization process has been proposed.