Acoustic reflection and transmission at the interface between two-phase porous lithium-ion battery and liquid media

Based on the combination of transfer matrix method and Biot theory, the acoustic wave reflection and transmission coefficients was theoretically calculated at the liquid/solid interfaces between two-phase porous lithium-ion battery and liquid media. Meanwhile, the influence of the swing characteristics of lithium-ion on the mechanical properties of electrode was considered, and the theoretical prediction of electrode density and elastic modulus under different states of charge is realized. The angle spectrum and frequency spectrum of reflection and transmission coefficients for corresponding state lithium-ion battery can be obtained by the proposed method. Then, a frequency domain simulation model of the multi-layered porous lithium-ion battery was established, and the reflection and transmission coefficients obtained by finite element method for lithium-ion battery are consistent with those results by the proposed approach. For the case of multi-cell lithium-ion battery, the relationship between reflection/transmission coefficients, oblique incident angle or frequency under different azimuth angles are analyzed. The shift law of the characteristic point curves in the angle spectrum and frequency spectrum with the change of the state of charge of the lithium-ion battery is analyzed. It provides a theoretical basis for the ultrasonic measurement of the state of charge of lithium-ion batteries.