Probing degradation of layered lithium oxide cathodes via multilength scaled X-ray imaging techniques

Layered lithium metal oxide (LLMO) cathode is widely used among the numerous cathode materials for providing high energy density and good reversibility in Li-ion batteries. However, the batteries still suffer from safety concerns and electrochemical performance decay during long-term cycling, which arises from the degradation of LLMO cathodes. In order to optimize the batteries, it becomes crucial to characterize and study the degradation mechanism of LLMO. X-ray imaging techniques have been intensively applied in this area. According to the different interactions between X-rays and matter, X-ray imaging techniques are divided into: X-ray projection imaging techniques; Transmission X-ray Imaging (TXM); Scanning Transmission X-ray Imaging (STXM), X-ray Fluorescence Imaging and X-ray Diffraction-based Imaging. These methods provide information related to the internal structure, morphology, chemical changes, and crystallization structure. The non-destructive and high penetration ability of X-rays also enables the in-situ experiments with multiscale spatial resolution, revealing the nature behind the LLMO cathode during the operation. In the review, we first overview the X-ray imaging techniques based on their function principle. A brief discussion of in-situ specialized designed cells and ex-situ samples is presented. Lateral, examples were discussed under different length scales. It is hoped the review can inspire a deeper consideration of the utilization of X-ray imaging techniques in detecting degradation of LLMO cathodes, paving new pathways to develop advanced LLMO cathodes with better cycling stability and practical capabilities.