Local structure of vanadium in doped LiFePO₄

LiFePO₄ 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 LiFePO₄ crystal lattice. When the vanadium concentration is lower then 1 at.%, the dopant remains insoluble. Thus, a single-phase vanadium-doped LiFePO₄ cannot be formed and the improved electrochemical properties of vanadium-doped LiFePO₄ previously reported cannot be associated with crystal structure changes of the LiFePO₄ via vanadium doping.