Evaluating Long-Term Cycling Degradation in Cylindrical Li-Ion Batteries Using X-ray Tomography and Virtual Unrolling

Abstract

Lithium-ion (Li-ion) batteries have undergone a multitude of improvements and achieved a high level of technological maturity. To further optimise cell performance, an understanding of the failure mechanisms is important. Forty-eight state-of-the-art cylindrical cells in the 21700 format, suitable for electric vehicles, are studied at the beginning-of-life (BOL) and end-of-life (EOL) by X-ray computed tomography (X-ray CT) and image analysis. The results indicate that shifting current collecting tabs closer to the centre of the cell and including a mandrel is likely to supress the propagation of capacity depleting deformations. It is recommended that manufacturers also try to improve cell assembly processes to form a more uniformly circular jelly roll and use tapered electrodes to minimise the nucleation of deformations.