Highly reversible Li insertion at 4 V in ε-VOPO4/α-LiVOPO4 cathodes

Electrochemical (and chemical) lithium intercalation into a new vanadium phosphate, epsilon-VOPO4, is a two-phase process involving reduction of V-V to V-IV at an attractive potential (3.95V). X-ray diffraction shows that this material and that obtained from LiI reduction are structurally similar to high-temperature alpha-LiVOPO4. Increased stability and capacity are achieved with chemically lithiated epsilon-VOPO4 when contact with the conductive additive is enhanced by mechanical grinding. Following the first charge cycle, reversible electrochemical lithium extraction/insertion at a cycling rate of C/10 affords a specific capacity of over 100 mAh/g (3.0-4.5 V window) that is stable for at least 100 cycles. This material demonstrates the best overall properties, thus far, of any polyanionic vanadium phosphate structure. (C) 2000 The Electrochemical Society. S1099-0062(00)05-069-0. All rights reserved.