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- Title
Room-temperature miscibility gap in LixFePO4.
- Authors
Yamada, Atsuo; Koizumi, Hiroshi; Nishimura, Shin-ichi; Sonoyama, Noriyuki; Kanno, Ryoji; Yonemura, Masao; Nakamura, Tatsuya; Kobayashi, Yo
- Abstract
The rechargeable lithium-ion cell is an advanced energy-storage system. However, high cost, safety hazards, and chemical instability prohibit its use in large-scale applications. An alternative cathode material, LiFePO4, solves these problems, but has a kinetic problem involving strong electron/hole localization. One reason for this is believed to be the limited carrier density in the fixed monovalent Fe3+PO4/LiFe2+PO4 two-phase electrode reaction in LixFePO4. Here, we provide experimental evidence that LixFePO4, at room temperature, can be described as a mixture of the Fe3+/Fe2+ mixed-valent intermediate LiαFePO4 and Li1−βFePO4 phases. Using powder neutron diffraction, the site occupancy numbers for lithium in each phase were refined to be α=0.05 and 1−β=0.89. The corresponding solid solution ranges outside the miscibility gap (0<x<α,1−β<x<1) were detected by the anomaly in the configurational entropy, and also by the deviation of the open-circuit voltage from the constant equilibrium potential. These findings encourage further improvement of this important class of compounds at ambient temperatures.
- Subjects
ENERGY storage; TEMPERATURE measurements; DENSITY; NEUTRON diffraction; LITHIUM cells
- Publication
Nature Materials, 2006, Vol 5, Issue 5, p357
- ISSN
1476-1122
- Publication type
Article
- DOI
10.1038/nmat1634