Direct evidence of morphological changes in conversion type electrodes in Li-ion battery by acoustic emission

The charge and discharge of a Li-ion battery based on conversion type electrode material are investigated operando by acoustic emission (AE). The AE technique gives a direct evidence of both structural and morphological impacts of the electrochemical conversion reaction on the electrode. During the first discharge a huge AE energy is measured not only during the biphasic conversion process, but also during the SEI reaction. On first charge, the cumulated AE energy (CAEE) shows a significant increase, during the back conversion process, while upon further cycling the CAEE fluctuation is smoothed out, but very much reproducible. This demonstrates that a conversion reaction creates an “earthquake” in the electrode during conversion, which is correlated to a strong polarization of the electrochemical curve in the first discharge. More importantly, this study demonstrates that AE is a powerful tool to survey the real-time morphological changes and to discriminate the nature of electrochemical process in the electrode.