Ultrasonic characterization of multi-layered porous lithium-ion battery structure for state of charge.

A multi-layered porous finite element model of lithium-ion battery is proposed by using Voronoi polygons. The time domain simulation of ultrasonic transmission characteristics with different state of charge (SOC) are carried out, and the variation of acoustic parameters versus SOCs is explored. Then, in the experiment research, the ultrasonic transmission signals are obtained by employing piezoelectric ceramic transducers during the discharging step. By extracting the time domain characteristic parameters, it is discovered that the amplitude and time-of-flight (TOF) have a strong correlation with SOC, the slow pressure-wave (SPW) velocities of the experiments correspond well with the simulation results. In addition, the frequency domain analysis shows a linear link between the amplitude of the frequency spectrum and SOC. Moreover, via repeated experiments, it is found that the ultrasonic transmission method has good repeatability in probing the SOC, and the SPW velocities acquired by experiments can almost be covered by 95% confidence interval formed based on the results of the simulation. Furthermore, according to the results of the experiments, a gray model based on the particle swarm optimization-based-simulated annealing (GM-PSO-SA) is established, which realized the prediction of the SOC under the condition of small sample data. The research results can serve as a reference for creating a comprehensive finite element model of the multi-layered porous structure of lithium-ion battery. Meanwhile, it also provides a detection and evaluation tool for the monitoring of the SOC.