Li2-xFe0.5(VO)0.5(PO4)F0.5, a New Mixed Metal Phosphate Cathode Material

A new Fe-V mixed metal phosphate of the composition, Li2-xFe0.5(VO)(0.5)(PO4)F-0.5, has been synthesized and characterized as a single phase Li insertion/extraction cathode material for rechargeable lithium batteries. Its tetragonal crystal structure revealed from X-ray diffraction and absorption spectral data exhibits little change with Li extraction and subsequent Li insertion. The charge/discharge cycling capacities obtained from Li cells is consistent with the structure. The presence of F in the material is essential to prepare a mixed metal phosphate with equal amounts of Fe and V in the crystal structure and is probably the key to our success in preparing a single phase metal phosphate cathode material. (C) 2012 The Electrochemical Society. [DOI: 10.1149/2.030210jes] All rights reserved.