Estimation of NCM111 /graphite acoustic properties under different lithium stoichiometry based on nondestructive acoustic in situ testing

Lithium (Li)-ion battery is an important energy storage for electronic production and electric vehicles. Battery aging is accompanied by a state change in the active material. The method of active material status evaluation in a nondestructive way has become a major topic in battery research. In this study, a battery in situ testing with multiple noncontact ultrasonic excitation signal methodology is proposed, and for the first time to use acoustic energy to analysis signal transmittance and reflectance. Based on a 1/20C charging and discharging experiment of commercial NCM111 pouch battery, the deformation, density, wave speed, acoustic impedance, and other parameters of NCM111/graphite material under different Li stoichiometry are estimated. Acoustic property of active material has been used as a medium to explain the mechanism of ultrasonic signal changes. The experiment result shows that acoustic energy is highly correlated with the calculated acoustic impedance of the active material, and there is no accurate correspondence with battery voltage and capacity. Ultrasonic is an effective method to study the status of Li battery.