Electrochemically-Resolved Acoustic Emissions Analysis for Li-Ion Battery Materials
Authors: Samantaray Yash , Cogswell Daniel A. , Cohen Alexander E. , Bazant Martin Z. 
Published: December 2024

Operando non-destructive evaluation (NDE) techniques for Li-ion batteries are the gold standard for gaining physical insights into a cell. These methods have the potential to transform battery formation optimization, electrode and electrolyte characterization, and state-of-health (SoH) and remaining useable lifetime metrics by providing an orthogonal data stream to supplement conventional electrochemical data. A well-known NDE method is acoustic emission (AE) testing. AEs are elastic waves that are generated by a release of energy in a material due to an irreversible change in internal structure. Studies have documented the detection of AEs on the surface of Li-ion batteries during cycling1–3, but no clear connection has been established between AEs and SoH metrics due to low reproducibility from seemingly identical battery systems and poor interpretability of the acoustic activity.
Herein, we report the methodology for performing an electrochemically-resolved acoustic emissions analysis on Li-ion batteries to identify specific degradation mechanisms, using graphite and Ni0.8Mn0.1Co0.1O2 (NMC811) as case studies. First, careful identification and elimination of electromagnetic interference allowed for improved reproducibility in the number of AEs and cumulative energy per cycle. Next, our use of cyclic voltammetry as the simultaneous electrochemical method while measuring AEs allowed for a direct correlation between acoustic activity and specific degradation mechanisms, such as gas generation during SEI formation and particle fracture during NMC811 delithiation. The degradation mechanisms were confirmed using complementary destructive and non-destructive methods. Particle fracture was identified with ex-situ SEM imaging of electrodes and operando XRD during cyclic voltammetry. Gas generation was inferred by comparing to online electrochemical mass spectrometry (OEMS) data during battery formation in literature.4 Finally, a careful waveform analysis using the wavelet transform was capable of distinguishing AEs from different degradation mechanisms using multi-resolution features and identified these mechanisms during standard battery operation as well. Overall, acoustic emissions testing of Li-ion batteries represents a unique and promising methodology for identifying degradation mechanisms during normal battery operation and could offer a significant improvement to conventional health and lifetime prediction metrics.
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