In situ X-ray diffraction during lithium extraction from rhombohedral and monoclinic Li3V2(PO4)3

A comparative in situ X-ray diffraction (XRD) study of phase transitions and volume variations that occur during lithium extraction from the rhombohedral and monoclinic forms of Li3V2(PO4)(3) is presented. For this purpose, a new in situ XRD cell configuration was designed that enabled us to extract lithium at high voltages (up to 4.65 V vs. Li) without cell deterioration. A thin film of aluminum was deposited onto the surface of a beryllium window as a protective layer to avoid direct electronic contact with the positive electrode. Lithium extraction from NaSICON Li3V2(PO4)(3) (R-3, c/a = 2.709) led to NaSICON LiV2(PO4)(3) (R-3c, c/a = 2.427) isotypical with LiTi2(PO4)(3) in a single two-phase process. Monoclinic Li3V2(PO4)(3) showed a much more complicated series of four successive two-phase transitions on Li extraction to Li0.1V2(PO4)(3) between 3.4 and 4.6 V vs. Li. Each pattern of the intermediate compositions was fully indexed in the monoclinic space group P2(1) /n, with a unit-cell contraction of DeltaV/V = 26.8% between Li3V2(PO4)(3) and LiV2(PO4)(3) and a slight increase upon further oxidation to Li0.1V2(PO4)(3). Despite these numerous phase transitions and non-negligible volume changes, the monoclinic Li3V2(PO4)(3) system is structurally highly reversible. (C) 2003 The Electrochemical Society.