Ultrasonic testing-based method for segmental calibration and quantitative estimation of the electrolyte content in lithium-ion batteries

Nondestructive testing and quantitative estimation of the electrolyte content in seal-packed lithium-ion batteries (LIBs) have remained a major technological challenge. This study developed a non-contact, multi-channel ultrasonic testing solution for nondestructive, in situ testing and quantitative estimation of the electrolyte content in LIBs. First, sample batteries with different electrolyte contents were prepared. Then, the electrolyte contents in different local areas of the sample batteries were calibrated based on the corresponding mass ratios of characteristic elements obtained using energy-dispersive spectroscopy and scanning electron microscopy; thereby, the mapping relationship between the ultrasonic propagation properties and the electrolyte content of the batteries was established. Finally, a method for segmental quantitative electrolyte content estimation with thickness-based corrections was proposed and verified experimentally. The experimental results showed that the magnitude of through-transmission ultrasonic signals and the electrolyte content of the cells were strongly correlated. The error of the electrolyte content estimation method was within 3% for cells with adequate electrolyte content, and the error of electrolyte content was smaller than 6% even for batteries with a low electrolyte content.