A Study on the Kinetics and Structural Changes of Silicon during Ball Milling

Enhancing our understanding of the ball milling process is important to optimize silicon amorphization, a key factor in improving the performance of lithium-ion battery anodes. To improve this understanding, we quantitatively studied the kinetics of silicon amorphization during ball milling using x-ray diffraction (XRD) and electrochemical methods, among other methods. The percentage of amorphous and crystalline silicon was deduced by fitting the XRD data and electrochemical results. The resulting trend versus ball milling time was then fitted using the Avrami model. The material resulting from ball milling was further studied using scanning and transmission electron microscopy (SEM/TEM). Under extended milling times, we found that a maximum of 86% of the silicon became amorphous. Similarly, the grain size of the crystalline silicon phase could not be reduced below 6 nm. Our observations suggest that amorphization results from defects creation during ball milling. Amorphization then stops when the grain size reaches a limit where defects are no longer formed.