High Resolution 3-Dimensional Chemical and Morphological Imaging of Single LixFePO4 Particles

Understanding chemical and morphological transitions within single nanoparticles of electrochemically active materials is crucial to overcome the performance limitations and degradation of batteries. Techniques that afford high chemical resolution at the nanoscale are ideally suited for this goal. Soft X-ray ptychographic microscopy combined with X-ray absorption spectroscopy (XAS) is a powerful suite which affords chemical and structural information on large volumes of material at spatial resolutions better than 5 nm.¹ However, to date, this technique has been intrinsically limited to 2 dimensional observations in transmission mode, which causes complications during interpretation, especially in the case of overlapped particles, because the projection images represent an average over the X-ray penetration path within the crystals.

In this study, soft X-ray tomography combined with ptychography, developed at beamline 5.3.2.1 at the Advanced Light Source (Berkeley, CA) is applied to assess the chemical and morphological consequences of electrochemical delithiation of aggregated nano-sized lithium iron phosphate (LiFePO₄) plates (Figure 1). Our work provides quantitative analysis of oxidation states in 3 dimensions at the 10 nm scale. After segmentation, statistical analysis of the chemical phase for any given individual particle was achieved, and information was extracted of the particle interior. The ability to visualize the nanoscale chemical state distribution over functional volumes will revolutionize the study of energy storage materials and enable the design of optimized morphologies for the next generation of devices.

Figure 1. 3 dimensional chemical volume rendering of Li_xFePO₄ crystals. Chemical phase information were extracted from 3 dimensional volumes collected at 708.25 eV and 710.25 eV. The red and blue areas indicate the highest content of LiFePO₄ and FePO₄, respectively.

1. D. A. Shapiro, Y.-S. Yu, T. Tyliszczak, J. Cabana, R. Celestre, W. Chao, K. Kaznatcheev, A. L. D. Kilcoyne, F. Maia, S. Marchesini, Y. S. Meng, T. Warwick, L. L. Yang, H. A. Padmore, Nat Photon 8, 765 (2014).