title: Comprehensive insights into the structural and chemical changes in mixed-anion FeOF electrodes by using operando PDF and NMR spectroscopy.
abstract: In-depth analysis of operando X-ray pair distribution function (PDF) data is combined with Li NMR spectroscopy to gain comprehensive insights into the electrochemical reaction mechanism of high-performance iron oxyfluoride electrodes. While the full discharge capacity could be recovered upon charge, implying reversibility of the electrochemical reaction, the atomic structure of the electrode formed after cycling (discharge-charge) differs from the pristine uncycled electrode material. Instead, the "active" electrode that forms upon cycling is a nanocomposite of an amorphous rutile phase and a nanoscale rock salt phase. Bond valence sum analysis, based on the precise structural parameters (bond lengths and coordination number) extracted from the in situ PDF data, suggests that anion partitioning occurs during the electrochemical reaction, with the rutile phase being F-rich and the rock salt phase being O-rich. The F- and O-rich phases react sequentially; Fe in a F-rich environment reacts preferentially during both discharge and charge.
authors: X-ray Science Division, Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439, USA.
authors: Kamila M
authors: KM
authors: Wiaderek
authors: Olaf J
authors: OJ
authors: Borkiewicz
authors: Elizabeth
authors: E
authors: Castillo-Martínez
authors: Rosa
authors: R
authors: Robert
authors: Nathalie
authors: N
authors: Pereira
authors: Glenn G
authors: GG
authors: Amatucci
authors: Clare P
authors: CP
authors: Grey
authors: Peter J
authors: PJ
authors: Chupas
authors: Karena W
authors: KW
authors: Chapman
mesh_terms: D000838:Anions / Q000737:chemistry; D004566:Electrodes; D005296:Ferrous Compounds / Q000737:chemistry*; D007501:Iron / Q000737:chemistry*; D008094:Lithium / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy; D015394:Molecular Structure; D009010:Monte Carlo Method; D011789:Quantum Theory
chemical_list: D000838:Anions; D005296:Ferrous Compounds; D008094:Lithium; D007501:Iron