Excitability, attenuation and mode identification of guided waves in multilayer lithium-ion pouch cells

Guided-wave inspection of lithium-ion pouch cells has been reported with strongly inconsistent phase velocities and mode assignments, complicating reliable interpretation of ultrasonic measurements in these complex multilayer structures. In particular, the fundamental quasi-antisymmetric mode (qA 0 ) has been reported both at low frequencies with velocities on the order of 100 - 200 m s −1 and at higher frequencies with velocities close to 1000 m s −1 , raising concerns regarding incorrect mode identification in non-destructive evaluation. Such ambiguities can influence the sensitivity and spatial interpretation of guided-wave-based diagnostics, and thereby affect their consistent application. In this work, we systematically investigate the physical origin of this discrepancy by combining controlled guided-wave experiments with a fully three-dimensional multiphysics simulation framework that explicitly models wave excitation, propagation, and attenuation in a multilayer lithium-ion pouch cell. The anode and cathode are effectively described as homogenised, fluid-saturated slurries in the long-wavelength regime and augmented with viscoelastic damping to reproduce the experimentally observed frequency-dependent attenuation. The model is parametrised using effective mechanical properties to quantitatively reproduce measured acceleration time signals in the 3 kHz - 15kHz band, capturing propagation velocity, the dominant out-of-plane flexural response, and amplitude attenuation along the propagation path. Building on this validated model, dispersion characteristics, mode attenuation, and guided-wave excitability are computed and experimentally verified. The results demonstrate that under normal out-of-plane excitation, the qA 0 mode is the predominantly excitable and observable guided-wave mode in thick pouch cells at low frequencies, while higher frequency measurements primarily excite faster higher-order modes due to strong attenuation of qA 0 . Mode excitability analysis further reveals the decisive role of transducer forcing direction in governing observable wave content. The presented results establish a physically consistent framework for guided-wave mode identification and interpretation in lithium-ion pouch cells, providing essential guidance for the design and reliable application of guided-wave-based non-destructive evaluation in complex multilayer energy-storage structures.