Revisiting metal fluorides as lithium-ion battery cathodes

DOI: 10.1038/s41563-020-00893-1

Authors: Xiao Hua (University of Cambridge; University of Oxford) , Alexander S. Eggeman (University of Cambridge; University of Manchester) , Elizabeth Castillo-martinez (University of Cambridge; Universidad Complutense de Madrid) , Rosa Robert (University of Cambridge) , Harry S. Geddes (University of Oxford) , Ziheng Lu (University of Cambridge) , Chris J. Pickard (University of Cambridge; Tohoku University) , Wei Meng (University of Cambridge) , Kamila M. Wiaderek (Advanced Photon Source) , Nathalie Pereira (Rutgers University) , Glenn G. Amatucci (Rutgers University) , Paul A. Midgley (University of Cambridge) , Karena W. Chapman (SUNY Stony Brook) , Ullrich Steiner (Adolphe Merkle Institute) , Andrew L. Goodwin (University of Oxford) , Clare Grey (University of Cambridge)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Nature Materials , VOL 22

State: Published (Approved)
Published: January 2021
Diamond Proposal Number(s): 17315

Abstract: Metal fluorides, promising lithium-ion battery cathode materials, have been classified as conversion materials due to the reconstructive phase transitions widely presumed to occur upon lithiation. We challenge this view by studying FeF3 using X-ray total scattering and electron diffraction techniques that measure structure over multiple length scales coupled with density functional theory calculations, and by revisiting prior experimental studies of FeF2 and CuF2. Metal fluoride lithiation is instead dominated by diffusion-controlled displacement mechanisms, and a clear topological relationship between the metal fluoride F− sublattices and that of LiF is established. Initial lithiation of FeF3 forms FeF2 on the particle’s surface, along with a cation-ordered and stacking-disordered phase, A-LixFeyF3, which is structurally related to α-/β-LiMn2+Fe3+F6 and which topotactically transforms to B- and then C-LixFeyF3, before forming LiF and Fe. Lithiation of FeF2 and CuF2 results in a buffer phase between FeF2/CuF2 and LiF. The resulting principles will aid future developments of a wider range of isomorphic metal fluorides.

Journal Keywords: Batteries; Electrochemistry; Solid-state chemistry; X-ray diffraction

Subject Areas: Materials, Chemistry, Energy


Instruments: I15-1-X-ray Pair Distribution Function (XPDF)

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