Soft‐Chemistry Synthesis and Characterization of Bismuth Oxyfluorides and Ammonium Bismuth Fluorides

Abstract

Two bismuth oxyfluorides, BiOF and BiO0.5F2, have been prepared by soft chemistry. These two compounds are of interest for application as new type of positive electrode active materials in secondary lithium battery. BiOF was obtained directly from the fluorination of Bi2O3 by a saturated aqueous solution of NH4F. BiO0.5F2 was obtained by the hydrolysis of β‐NH4BiF4 at 70°C. The ammonium bismuth fluoride β‐NH4BiF4, which is a new orthorhombic form of NH4BiF4, was obtained by reacting BiF3 in a saturated aqueous solution of NH4F. Two other ammonium bismuth fluorides, (NH4)0.5BiF3.5 and NH4Bi3F10, were also prepared by annealing β‐NH4BiF4 at a relatively low temperature under inert atmosphere. The existence of the fluorite (NH4)0.5BiF3.5 is reported for the first time in this paper.