Correlative analysis of structure and chemistry of Li_xFePO₄ platelets using 4D-STEM and X-ray ptychography

Journal Article · 20 December 2021 · Materials Today

DOI: https://doi.org/10.1016/j.mattod.2021.10.031 · OSTI ID:1906821

Hughes, L. A. ^[1]; Savitzky, Benjamin H. ^[1]; Deng, Haitao D. ^[2]; Jin, Norman L. ^[2]; Lomeli, Eder G. ^[2]; Yu, Young-Sang ^[3]; Shapiro, David A. ^[3]; Herring, Patrick ^[4]; Anapolsky, Abraham ^[4]; Chueh, William C. ^[2]; Ophus, Colin ^[1]; Minor, Andrew M. ^[5]

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1. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Molecular Foundry
2. Stanford Univ., CA (United States)
3. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Advanced Light Source (ALS)
4. Toyota Research Institute, Los Altos, CA (United States)
5. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Molecular Foundry; Univ. of California, Berkeley, CA (United States)

Lithium iron phosphate (Li_xFePO₄), a cathode material used in rechargeable Li-ion batteries, phase separates upon de/lithiation under equilibrium. The interfacial structure and chemistry within these cathode materials affects Li-ion transport, and therefore battery performance. Here, correlative imaging of Li_xFePO₄ was performed using four-dimensional scanning transmission electron microscopy (4D-STEM), scanning transmission X-ray microscopy (STXM), and X-ray ptychography in order to analyze the local structure and chemistry of the same particle set. Over 50,000 diffraction patterns from 10 particles provided measurements of both structure and chemistry at a nanoscale spatial resolution (16.6–49.5 nm) over wide (several micron) fields-of-view with statistical robustness. Li_xFePO₄ particles at varying stages of delithiation were measured to examine the evolution of structure and chemistry as a function of delithiation. In lithiated and delithiated particles, local variations were observed in the degree of lithiation even while local lattice structures remained comparatively constant, and calculation of linear coefficients of chemical expansion suggest pinning of the lattice structures in these populations. Partially delithiated particles displayed broadly core–shell-like structures, however, with highly variable behavior both locally and per individual particle that exhibited distinctive intermediate regions at the interface between phases, and pockets within the lithiated core that correspond to FePO₄ in structure and chemistry. The results provide insight into the Li_xFePO₄ system, subtleties in the scope and applicability of Vegard’s law (linear lattice parameter-composition behavior) under local versus global measurements, and demonstrate a powerful new combination of experimental and analytical modalities for bridging the crucial gap between local and statistical characterization.

• Research Organization: Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)
• Sponsoring Organization: National Science Foundation (NSF); USDOE Office of Science (SC), Basic Energy Sciences (BES). Scientific User Facilities Division
• Grant/Contract Number: AC02-05CH11231
• OSTI ID: 1906821
• Journal Information: Materials Today, Journal Name: Materials Today Vol. 52; ISSN 1369-7021
• Publisher: ElsevierCopyright Statement
• Country of Publication: United States
• Language: English