title: Lithium Insertion Mechanism in Iron-Based Oxyfluorides with Anionic Vacancies Probed by PDF Analysis.
abstract: The mechanism of lithium insertion that occurs in an iron oxyfluoride sample with a hexagonal-tungsten-bronze (HTB)-type structure was investigated by the pair distribution function. This study reveals that upon lithiation, the HTB framework collapses to yield disordered rutile and rock salt phases followed by a conversion reaction of the fluoride phase toward lithium fluoride and nanometer-sized metallic iron. The occurrence of anionic vacancies in the pristine framework was shown to strongly impact the electrochemical activity, that is, the reversible capacity scales with the content of anionic vacancies. Similar to FeOF-type electrodes, upon de-lithiation, a disordered rutile phase forms, showing that the anionic chemistry dictates the atomic arrangement of the re-oxidized phase. Finally, it was shown that the nanoscaling and structural rearrangement induced by the conversion reaction allow the in situ formation of new electrode materials with enhanced electrochemical properties.
authors.affiliation: Sorbonne Universités, UPMC, Univ. Paris 06, UMR 8234, PHENIX 75005, Paris, France ; CNRS, UMR 8234, PHENIX 75005, Paris, France.
authors.forename: Damien
authors.initials: D
authors.lastname: Dambournet
authors.affiliation: X-ray Science Division, Advanced Photon Source, Argonne National Laboratory Argonne, IL, 60439, USA.
authors.forename: Karena W
authors.initials: KW
authors.lastname: Chapman
authors.affiliation: Sorbonne Universités, UPMC, Univ. Paris 06, UMR 8234, PHENIX 75005, Paris, France ; CNRS, UMR 8234, PHENIX 75005, Paris, France ; CNRS, Univ. Bordeaux, ICMCB, UPR 9048 33600, Pessac, France.
authors.forename: Mathieu
authors.initials: M
authors.lastname: Duttine
authors.affiliation: X-ray Science Division, Advanced Photon Source, Argonne National Laboratory Argonne, IL, 60439, USA.
authors.forename: Olaf
authors.initials: O
authors.lastname: Borkiewicz
authors.affiliation: X-ray Science Division, Advanced Photon Source, Argonne National Laboratory Argonne, IL, 60439, USA.
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Chupas
authors.affiliation: Sorbonne Universités, UPMC, Univ. Paris 06, UMR 8234, PHENIX 75005, Paris, France ; CNRS, UMR 8234, PHENIX 75005, Paris, France.
authors.forename: Henri
authors.initials: H
authors.lastname: Groult
keywords: anionic partitioning; cathode materials; ferric fluoride; pair distribution function