Journal
JOURNAL OF PHYSICAL CHEMISTRY C
Volume 117, Issue 22, Pages 11498-11505Publisher
AMER CHEMICAL SOC
DOI: 10.1021/jp401200u
Keywords
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Funding
- National Basic Research Program of China (973 program) [2011CB935903]
- National Natural Science Foundation of China [21233004, 21021002, 20873115]
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The reactions and structural evolution of FeF3 during cell cycling are investigated in an in situ cell by using Fe K-edge X-ray absorption fine-structure (XAFS) spectroscopy. The results of X-ray absorption near-edge structure spectroscopic analysis demonstrate that there are three stages in the reaction of FeF3 with Li: (1) a two-phase intercalation reaction in the range of x = 0 to 0.46 Li, (2) a single-phase intercalation reaction in the range of x = 0.46 to 0.92 Li, and (3) a conversion reaction in the range of x = 0.92 to 2.78 Li. The coordination numbers (CNs) and bond lengths of the Fe-F bonds or Fe-Fe bonds for the lithiated FeF3 are obtained by performing XAFS fitting. The splitting trends of the Fe-F bond lengths and the Fe-F CNs in the range of x = 0 to 0.92 Li support the proposal that R-3c-structured FeF3 is transformed into R3c-structured Li0.92FeF3 after the intercalation of 0.92 equiv. of Li, and that the intermediate Li0.46FeF3 may be R3-structured. The small Fe-Fe CN of Li2.78FeF3 indicates that the average diameter of the Fe crystallites formed during discharge is <1 nm.
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