In recent years, there has been a rapid growth in the development and application of Li-ion batteries in many aspects of daily life. From portable electronic devices to electric vehicles, global reliance on portable energy storage solutions is projected to continue growing throughout the next decade. To facilitate adoption of the Li-ion battery technologies, much of the current research is focused on improving electrode chemistries and developing novel cells, capable of lasting for longer time periods to reduce the need for frequent recharging. In spite of these developments, however, there exists little in the literature to show exactly how battery materials respond to charge cycling and why batteries ultimately fail.

Within the context of the present study, multi-length scale X-ray microscopy (XRM) was used to image a commercial 18650 Li-ion battery from the 20 µm length scale to the 0.1 µm length scale in 3D, to identify the relevant information observable at each resolution level. Correlative light- and scanning-electron microscopies were employed to provide additional information about the structure of the electrodes and to provide resolution down to the nanometer scale. The results revealed a complex, multi-scale structure to the battery electrodes, ranging from bulk defects (at the largest length scale) to porosity & tortuosity (at the hundred nanometer length scale) and sub-particle defects (on the 100 to sub-100 nm length scale).

One of the key advantages offered by X-ray imaging is the non-destructive nature of the 3D image-based characterization. With this in mind, the second part of the present study focused on utilizing this feature to perform a 3D imaging study before and after aging the battery, in a “4D” experimental design. Another sample from the same manufacturer was used for this study and imaged with 2 µm resolution in order to capture the finer cracks forming as a function of operation. The battery was imaged in its pristine state, charge cycled 100 times, and then the same specimen was imaged again using the same imaging conditions. From the 3D volumetric results, several cracks were observed to form on the outer side of the roll, following the capacity fade observed in the testing apparatus. This result has suggested the significance of microstructure-based degradation and pointed toward the importance of using image-based characterizations in Li-ion battery operational and lifetime studies.

In this presentation, we will present the study outlined here, both in terms of the 3D and the 4D investigations of the commercial 18650 Li-ion battery cells. The experimental design will be discussed in detail, including the imaging apparatus and the correlative imaging setup. Furthermore, the 3D imaging results will be shown alongside a discussion of the relevant geometric parameters at each length scale, and the results of the 4D investigation will be presented showing the defect formation as a functio