Calorimetric heat flux analysis as an accelerated alternative to OCV drop screening for end-of-line testing of lithium-ion battery cells

Open-circuit voltage (OCV) drop analysis is the most widely used end-of-line (EOL) quality-control method for lithium-ion battery cells due to its low implementation cost and proven ability to identify defective cells. However, the method requires storage periods of up to two weeks, making it a significant bottleneck in battery manufacturing. In this work, calorimetric heat flux analysis is investigated as an accelerated and potentially more sensitive alternative for EOL battery cell screening. More than 300 cylindrical lithium-ion cells produced at the BMW Battery Cell Competence Center (BCCC) are characterized by quasi-isothermal calorimetry and conventional OCV drop testing in parallel. The results demonstrate a strong correlation between heat flux and OCV drop measurements, with Pearson correlation coefficients consistently exceeding 0.8. Beyond reproducing the cell identification by conventional OCV drop testing, the calorimetric approach detected additional abnormal cells through the combined analysis of multiple heat-flux-derived features, indicating an increased sensitivity to latent defects. The findings suggest that calorimetric heat flux analysis represents a promising method for EOL battery cell testing. By reducing testing time from several days to approximately 24 h while simultaneously enhancing anomaly detection capabilities without substantially increasing the false rejection of cells.