Numerical Simulation of Quantitative Ultrasound Spectroscopy for State-of-Health and State-of-Charge Assessment in Lithium-Ion Batteries

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Abstract
The widespread use of lithium-ion batteries (LIBs) in energy storage systems has created a growing challenge in accurately determining their condition throughout their life through characterization such as State of Health (SOH) and State of Charge (SOC). This is critical to determine whether batteries are suitable for second-life applications or should be directed to recycling processes. Ultrasonic techniques have emerged as a non-destructive alternative to conventional electrochemical methods; however, the link between internal material properties and ultrasonic response remains insufficiently understood. This study employs numerical simulations to elucidate how mechanical variations affect Quantitative Ultrasound Spectroscopy (QUS) parameters in LIBs. The wave equation was solved using Local Radial Basis Function (L-RBF) methods and a two-dimensional model was also simulated with SimSonic to capture multi-layer interactions. The results demonstrate that increases in electrode thickness lead to decreased spectral slope and increased intercept and mid-band fit, consistent with enhanced ultrasonic attenuation and impedance mismatch. Moreover, two-dimensional analyses reveal energy gap dissipation and frequency shifts associated with evolving layer geometries. These findings confirm the feasibility of QUS-based ultrasonic metrics as reliable indicators of mechanical and electrochemical states in LIBs, offering a promising pathway for machine-learning (data-driven) SOH and SOC classification.