Comprehensive Insights into the Structural and Chemical Changes in Mixed-Anion FeOF Electrodes by Using Operando PDF and NMR Spectroscopy

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• 作者：Kamila M. Wiaderek ; Olaf J. Borkiewicz ; Elizabeth Castillo-Mart铆nez ; Rosa Robert ; Nathalie Pereira ; Glenn G. Amatucci ; Clare P. Grey ; Peter J. Chupas ; Karena W. Chapman
• 刊名：The Journal of the American Chemical Society
• 出版年：2013
• 出版时间：March 13, 2013
• 年：2013
• 卷：135
• 期：10
• 页码：4070-4078
• 全文大小：454K
• 年卷期：v.135,no.10(March 13, 2013)
• ISSN：1520-5126

文摘

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鈥揷harge) differs from the pristine uncycled electrode material. Instead, the 鈥渁ctive鈥?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.