Local structure of vanadium in doped LiFePO4.

LiFePO(4) composites with 5 at.% vanadium doping are prepared by solid state reactions. X-ray absorption fine-structure spectroscopy is used as a novel technique to identify vanadium sites. Both experimental analyses and theoretical simulations show that vanadium does not enter into the LiFePO(4) crystal lattice. When the vanadium concentration is lower then 1 at.%, the dopant remains insoluble. Thus, a single-phase vanadium-doped LiFePO(4) cannot be formed and the improved electrochemical properties of vanadium-doped LiFePO(4) previously reported cannot be associated with crystal structure changes of the LiFePO(4) via vanadium doping.