Li / β ‐ VOPO 4: A New 4 V System for Lithium Batteries

Lithium intercalation into has been performed, both chemically and electrochemically, with X‐ray diffraction characterization of the resulting phases at various levels of intercalation‐deintercalation. It is shown that intercalation occurs through a first‐order transition at 3.98 V vs. , which leads to a ‐like structure but with lithium ordering which doubles the a and b unit cell parameters. Starting from chemically intercalated , the reversible process involves 0.55 electron per transition metal, i.e. , 90 mAh/g, at a C/50 rate which owing to the 3.95 V potential plateau, gives an attractive specific energy of 355 Wh/kg. Fundamentally, it is shown herein that the redox energy of couple in an octahedral coordination involving unit is included between those observed in oxides and in compounds with oxo‐anions. © 1999 The Electrochemical Society. All rights reserved.