Controlled Formation of Mixed Nanoscale Domains of High Capacity Fe<sub>2</sub>O<sub>3</sub>–FeF<sub>3</sub> Conversion Compounds by Direct Fluorination [electronic resource].
- Washington, D.C. : United States. Dept. of Energy. Office of Basic Energy Sciences, 2015.
Oak Ridge, Tenn. : Distributed by the Office of Scientific and Technical Information, U.S. Dept. of Energy
- Physical Description:
- pages 2,530-2,539 : digital, PDF file
- Additional Creators:
- Oak Ridge National Laboratory
United States. Department of Energy. Office of Basic Energy Sciences
United States. Department of Energy. Office of Scientific and Technical Information
- In this paper, we report a direct fluorination method under fluorine gas atmosphere using a fluidized bed reactor for converting nanophase iron oxide (n-Fe<sub>2</sub>O<sub>3</sub>) to an electrochemically stable and higher energy density iron oxyfluoride/fluoride phase. Interestingly, no noticeable bulk iron oxyfluoride phase (FeOF) phase was observed even at fluorination temperature close to 300 °C. Instead, at fluorination temperatures below 250 °C, scanning transmission electron microscopy coupled with electron energy loss spectroscopy (STEM-EELS) and X-ray photoelectron spectroscopy (XPS) analysis showed surface fluorination with nominal composition, Fe<sub>2</sub>O<sub>3-x</sub>F<sub>2x</sub> (x < 1). At fluorination temperatures of 275 °C, STEM-EELS results showed porous interconnected nanodomains of FeF<sub>3</sub> and Fe<sub>2</sub>O<sub>3</sub> coexisting within the same particle, and overall the particles become less dense after fluorination. We performed potentiometric intermittent titration and electrochemical impedance spectroscopy studies to understand the lithium diffusion (or apparent diffusion) in both the oxyfluoride and mixed phase FeF<sub>3</sub> + Fe<sub>2</sub>O<sub>3</sub> composition, and correlate the results to their electrochemical performance. Finally and further, we analyze from a thermodynamical perspective, the observed formation of the majority fluoride phase (77% FeF<sub>3</sub>) and the absence of the expected oxyfluoride phase based on the relative formation energies of oxide, fluoride, and oxyfluorides.
- Published through SciTech Connect.
ACS Nano 9 3 ISSN 1936-0851 AM
Hui Zhou; Rose E. Ruther; Jamie Adcock; Wu Zhou; Sheng Dai; Jagjit Nanda.
- Funding Information:
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