Bismuth Fluoride Nanocomposite as a Positive Electrode Material for Rechargeable Lithium Batteries

摘要

The electrochemical activity of BiF_3 has been enabled in a BiF_3/C nanocomposite prepared by high-energy milling. It has been demonstrated that a 3 V reversible conversion reaction occurs in the BiF_3/C nanocomposite with the formation of Bi metal and LiF during lithiation and the reformation of BiF_3 during delithiation. When discharged at room temperature to 2 V at rates ranging from C/30 to C the BiF_3/C nanocomposite exhibited a specific capacity of 230 mAh/(g of composite), which corresponds to 90 percent utilization of the active material. The composites retained a specific capacity of 65 percent of the theoretical capacity when the rate was elevated to 4C. Two polymorphs of BiF_3 were studied, a hexagonal P-3cl 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-3cl structure after initial conversion.