Axially and radially inhomogeneous swelling in commercial 18650 Li-ion battery cells

• Published in: Journal of energy storage 2022-08, Vol.52, p.104563, Article 104563
• Main Authors: Blazek, Pavel, Westenberger, Peter, Erker, Simon, Brinek, Adam, Zikmund, Tomas, Rettenwander, Daniel, Wagner, Nils Peter, Keckes, Jozef, Kaiser, Jozef, Kazda, Tomas, Vyroubal, Petr, Macak, Martin, Todt, Juraj
• Format: Article
• Language: English
• Subjects: Aging; Lithium-ion battery; Swelling; Virtual unrolling; X-ray computed tomography
• ISSN: 2352-152X; 2352-1538
• DOI: 10.1016/j.est.2022.104563

Aging of lithium-ion batteries is especially important for applications such as battery electric vehicles, where they constitute a major part of the total cost and practically determine product lifetime. One of the main problems during cycle aging is the swelling of the electrode stack, as this results in increased mechanical stresses inside batteries and can further accelerate aging. Earlier studies have used X-ray tomography to address this issue and were focused on the role of large aberrations in electrode geometry in rapid capacity fade. In this study, however, we focus on batteries not exhibiting such a rapid deterioration, where only small changes to electrode geometry can be expected. Helical trajectory micro-computed X-ray tomography and virtual unrolling were used to reveal axially and radially inhomogeneous swelling of the jelly-roll electrode windings inside commercial 18650 batteries. The results supported by mathematical-physical simulations demonstrate the efficacy of the employed methods in the analysis of minute volumetric changes and show that regions inside the batteries that are comparatively unconstrained mechanically experience accelerated swelling. In particular, the top and bottom of the jelly-roll showed an elevated thickness increase, especially within the innermost windings. [Display omitted] •X-ray computed tomography analysis of whole cylindrical cells.•Helical trajectory scanning provides high resolution.•Virtual unrolling is an effective tool for analysis.•Mild battery aging causes inhomogeneous swelling of electrodes.