Bismuth fluoride nanocomposite as a positive electrode material for rechargeable lithium batteries

The electrochemical activity of BiF3 has been enabled in a BiF3/C nanocomposite prepared by high-energy milling. It has been demonstrated that a 3 V reversible conversion reaction occurs in the BiF3/C nanocomposite with the formation of Bi metal and LiF during lithiation and the reformation of BiF3 during delithiation. When discharged at room temperature to 2 V at rates ranging from C/30 to C the BiF3/C nanocomposite exhibited a specific capacity of 230 mAh/(g of composite), which corresponds to 90% utilization of the active material. The composites retained a specific capacity of 65% of the theoretical capacity when the rate was elevated to 4C. Two polymorphs of BiF3 were studied, a hexagonal P-3c1 high pressure form of Tysonite structure and the more common orthorhombic Pnma form isolated by an HF induced reaction. Both are shown to reconvert to the hexagonal P-3c1 structure after initial conversion. (C) 2005 The Electrochemical Society.