Lithium insertion chemistry of some iron vanadates

Lithium insertion into various iron vanadates has been investigated. Fe2V4O13 and Fe-4(V2O7)(3) center dot 3H(2)O have discharge capacities approaching 200 mAh g(-1) above 2.0 V vs. Li+/Li. Although the potential profiles change significantly between the first and subsequent discharges, capacity retention is unexpectedly good. Other phases, structurally related to FeVO4, containing copper and/or sodium ions were also studied. One of these, beta-Cu3Fe4(VO4)(6), reversibly consumes almost 10 moles of electrons per formula unit (ca. 240 mAh g(-1)) between 3.6 and 2.0 V vs. Li+/Li, in a non-classical insertion process. It is proposed that both copper and vanadium are electrochemically active, whereas iron(III) reacts to form (LiFeO2)-O-III. The capacity of the Cu3Fe4(VO4)(6)/Li system is nearly independent of cycling rate, stabilizing after a few cycles at 120-140 mAh g(-1). Iron vanadates exhibit better capacities than their phosphate analogues, whereas the latter display more constant discharge potentials. (c) 2006 Elsevier B.V. All rights reserved.