Tracking the Lifecycle of a 21700 Cell: A 4D Tomography and Digital Disassembly Study

Abstract

Extending the lifetime of commercial Li-ion cells is amongst the most important challenge to facilitate the continued electrification of transport as demonstrated by the substantial volume of literature dedicated to identifying degradation mechanisms in batteries. Here, we conduct a long-term study on a cylindrical Li-ion cell, tracking the evolution of the structure of the cell using X-ray computed tomography. By evaluating the internal geometry of the cell over several hundreds of cycles we show a causal relationship between changes in the electrode structure and the capacity fade associated with cell ageing. The rapid aging which occurs as cells reach their end-of-life condition is mirrored in a significant acceleration in internal architecture changes. This work also shows the importance of consistent and accurate manufacturing processes with small defects in the jelly-roll being shown to act as nucleation sites for the structural degradation and by extension capacity fade.