Laboratory X-ray Microscopy Study of Microcrack Evolution in a Novel Sodium Iron Titanate-Based Cathode Material for Li-Ion Batteries

Abstract

The long-term performance of batteries depends strongly on the 3D morphology of electrode materials. Morphological changes, i.e., particle fracture and surface deterioration, are among the most prominent sources of electrode degradation. A profound understanding of the fracture mechanics of electrode materials in micro- and nanoscale dimensions requires the use of advanced in situ and operando techniques. In this paper, we demonstrate the capabilities of laboratory X-ray microscopy and nano X-ray computed tomography (nano-XCT) for the non-destructive study of the electrode material’s 3D morphology and defects, such as microcracks, at sub-micron resolution. We investigate the morphology of Na0.9Fe0.45Ti1.55O4 sodium iron titanate (NFTO) cathode material in Li-ion batteries using laboratory-based in situ and operando X-ray microscopy. The impact of the morphology on the degradation of battery materials, particularly the size- and density-dependence of the fracture behavior of the particles, is revealed based on a semi-quantitative analysis of the formation and propagation of microcracks in particles. Finally, we discuss design concepts of the operando cells for the study of electrochemical processes.

Laboratory X-ray computed tomography imaging protocol allowing the operando investigation of electrode material evolution in various environments

“…There are many publications reporting on the electrode morphology of different materials examined by laboratory X-ray computed tomography (XCT). Unfortunately, most of the operando investigations had to significantly reduce the acquisition frequency 26 , 27 , 28 or spatial resolution 29 , 30 due to insufficient flux.…”

“…Using laboratory XCT, Shapovalov et al., 27 managed to visualize in operando , the crack formation in sodium iron titanate cathode, which is remarkable, especially that nano-XCT system was used, which is characterized by very limited room for the sample. Single CT however took around 20 h and was done with an experiment on hold, at fully charged or discharged states.…”