In Situ X-Ray Diffraction during Lithium Extraction from Rhombohedral and Monoclinic Li[sub 3]V[sub 2](PO[sub 4])[sub 3]

Abstract

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 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 (R-3, led to NaSICON (R-3c, isotypical with in a single two-phase process. Monoclinic showed a much more complicated series of four successive two-phase transitions on Li extraction to between 3.4 and 4.6 V vs. Li. Each pattern of the intermediate compositions was fully indexed in the monoclinic space group with a unit-cell contraction of between and and a slight increase upon further oxidation to Despite these numerous phase transitions and non-negligible volume changes, the monoclinic system is structurally highly reversible. © 2003 The Electrochemical Society. All rights reserved.