Is ultrasound suited to probe electrochemical processes in batteries? An operando multiprobe investigation of NMC/graphite commercial cell

Ultrasound technique has recently been employed to probe the internal dynamics of closed-form battery cells, offering a cost-effective means to gain real-time insights into electrochemical processes. It therefore has the potential to be a core part of the cell development process. However, existing literature has primarily focused on establishing superficial correlations between electrochemical and ultrasonic parameters, thereby severely constraining the interpretability of alterations of the ultrasound transmission properties of a cell upon cycling. This study aims to enhance the interpretability of these variations through simultaneous operando measurements of ultrasound and synchrotron X-rays diffraction (XRD) during electrochemical cycling and relaxation measurements. The results are further correlated to mechanical and electrochemical changes obtained through operando nano-dilatometry measurement. Thereby, we demonstrate the influence of both NMC and graphite on ultrasound features upon cycling. This work marks a significant advancement of the application of synchrotron XRD analysis to establish an understanding of ultrasound interactions with commercial cells.