Electrochemically Stable In Situ Dilatometry of NMC, NCA and Graphite Electrodes for Lithium-Ion Cells Compared to XRD Measurements
Franz B. Spingler, Simon Kücher, R. F. Phillips, Erfan Moyassari, Andreas Jossen
Abstract
Virtually all types of electrodes used in lithium-ion batteries expand and contract during cycling, which poses an engineering and design challenge. Information provided by X-ray diffraction (XRD) about alterations in the crystal structure of active materials may be insufficient to inform these engineering tasks. This is because it is unclear how these evolutions of the crystal structure translate into the measurable thickness changes at the electrode or cell level. In this study we investigate the thickness changes of electrodes during cycling using a dilatometry setup and compare them to XRD-measured crystal structure changes from scientific literature. Both the reliability of the dilation measurement and the electrochemical performance of the dilatometry setup are thoroughly validated and significantly exceed those of related studies that have been published in recent years. Various laboratory-made graphites as well as LiNi 1/3 Co 1/3 Mn 1/3 O 2 (NMC111), LiNi 0.6 Co 0.2 Mn 0.2 O 2 (NMC622), LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NMC811) and LiNi 0.8 Co 0.15 Al 0.05 O 2 (NCA) electrodes and the positive electrode from a Kokam SLPB356495 pouch cell are investigated. The results show that electrode expansion does not necessarily correlate with the unit cell volume changes of its active materials in any meaningful way and thus only by measuring the expansion of the full electrode can we fully understand and predict its behavior during cycling.