The cell finishing processes of lithium-ion batteries (soaking, formation, degassing, aging, end-of-line testing, grading) are time-, energy- and cost-intensive processes during the cell production. Common formation methods consist of several relatively slow constant charging and discharging cycles as it increases the probability of good performance of the Solid Electrolyte Interphase (SEI) on the negative electrode. The SEI has a significant impact on the performance, aging and safety of battery cells. Aiming for faster production times, cheaper production costs and better properties of lithium-ion batteries, the optimization of common cell finishing methods is necessary.
This contribution focuses on presenting an innovative cell finishing approach. More specifically, the Electrochemical Impedance Spectroscopy (EIS) is added at several phases during the cell finishing procedure. For example, the EIS is added before and after the soaking, pre-charging, degassing and aging, respectively. Moreover, several pulse-tests were integrated for every formation cycle. The EIS-data and pulse-test results are correlated with the final quality by the grading after the cell finishing process is finished. The grading is based on several parameters throughout the whole cell finishing process. By analyzing the change of the EIS and pulse-test data, the capability of an early cell quality assessment is evaluated. Based on these evaluations the formation process is shortened to save process time, energy expenses and production costs.