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Journal of the Electrochemical Society, Vol.159, No.8, A1171-A1175, 2012
Lithium Insertion or Extraction from/into Tavorite-Type LiVPO4F: An In Situ X-ray Diffraction Study
The Tavorite-type composition LiVPO4F undergoes a complex series of phase transformations upon Li+ electrochemical extraction or insertion at similar to 4.25 V (V4+/V3+ redox couple) and 1.8 V vs. Li (V3+/V2+ redox couple), respectively. In all the reactions involved, followed by in-house in situ X-Ray diffraction, two-phase topotactic mechanisms are systematically encountered, without noticeable modification of the [VPO4F] framework besides significant unit-cell contractions/expansions and overall shifts in symmetry from triclinic P-1 to monoclinic C2/c. Two electrochemical oxidation reactions occur at 4.24 V and 4.28 V vs. Li due to the formation of the intermediate phase Li0.67VPO4F, isolated for the first time. Noticeably, this peculiar composition is not encountered upon reduction from VPO4F to LiVPO4F. (C) 2012 The Electrochemical Society. [DOI: 10.1149/2.022208jes] All rights reserved.