Modeling Ultrasonic Wave Propagation in Prismatic Li-ion Battery Cells

Accurate in-situ monitoring of key states in prismatic Li-ion battery cells, such as temperature, state of charge (SoC), and state of health (SoH), is critical for ensuring the safety and performance of electric transportation. Since these states are closely linked to the cells’ internal mechanical properties, ultrasonic non-destructive testing (NDT) has emerged as a promising diagnostic approach. However, practical implementation remains challenging due to the complex nature of ultrasonic wave propagation within the cells’ internal structure, which comprises stacked layers of porous electrodes and separators. While analytical methods like the transfer matrix method and Biot theory are widely used to model wave propagation in layered and porous media, they fall short in capturing the behavior of porous layers with heterogeneous solid frames. To address this, the present study develops finite-difference time-domain (FDTD) models that account for both inter-layer wave interactions and micro-scale fluid-solid coupling within the porous layers, enabling simulation of wave propagation through the thickness and along the plane of the cell layers. The simulation results are analyzed and compared with experimental data, and the resulting insights provide a deeper understanding of ultrasonic wave behavior in battery cells, laying a solid foundation for advancing ultrasonic-based battery state monitoring.