The formation of lithium-ion batteries is an important and time-consuming process step in battery production. Good formation can positively influence cell properties and save process time. Within the scope of the investigations, tests will be carried out on special three-electrode cells. Among other things, the effects of the separators and electrolyte quantities used will be examined. In particular, the effects on the performance of the battery cells and any lithium plating that may occur will be analyzed by measurement. In addition, the assumptions made regarding the occurrence of lithium plating will be verified with post-mortem analyses. Based on the findings, optimized formation profiles will be developed and validated by means of further three-electrode cells.
Another aspect of the investigations is the experimental system integration of electrochemical impedance spectroscopy (EIS) already during formation for early diagnosis and prediction of electrochemical cell properties. In detail, EIS measurements are performed at different times before and during formation and the effects on the cells are presented. A critical issue with this measurement methodology is the feedback effects of the measurement on the battery cell being formed. The battery cells may already be partially formed by the current excitation during the measurement. With the help of the knowledge gained here, the metrological analysis of battery cells should already be possible during the forming process and thus optimized with regard to the reject rate.
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