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

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.