Electrochemical insertion properties of lithium vanadium titanate, LiVTiO4

The electrochemical insertion properties of the novel spinel phase, lithium vanadium titanate, LiVTiO4 (Fdm, a=8.236 A) have been evaluated in non-aqueous lithium cells. LiVTiO4 is a member of the general series, LiMTiO4 where M represents a 3d transition metal and was synthesized by a simple solid-state ceramic approach involving lithium carbonate, V2O3 and TiO2. The lithium insertion behavior in the LiVTiO4 relies on the reversibility of the V3+/V4+ redox couple and preliminary electrochemical evaluation indicates a reversible specific capacity of around 90 mA h/g, which represents the cycling of just over half the available lithium in the structure. High-resolution measurements reveal a structureless and sloping voltage profile consistent with the lithium insertion reactions proceeding via a single-phase mechanism. The lithium extraction and insertion reactions are located at 3.16 and 2.85 V vs. Li, respectively, while the symmetrical nature of the differential capacity data confirms the electrochemical reversibility. By comparison, the structurally related LiCrTiO4 phase demonstrates redox activity in the potential range 4.5-4.8 V vs. Li, although this behavior is accompanied by significant irreversibility. Constant current cycling of representative Li//LiVTiO4 cells indicates moderate insertion stability characterized by about 15% capacity fade over the initial 20 cycles.