Can Vanadium Be Substituted into LiFePO[subscript 4]?

Vanadium is shown to substitute for iron in the olivine LiFePO4 up to at least 10 mol %, when the synthesis is carried out at 550 degrees C. In the solid solution LiFe1-3y/2VyPO4, the a and b lattice parameters and cell volume decrease with increasing vanadium content, while the c lattice parameter increases slightly. However, when the synthesis is performed at 650 degrees C, a NASICON phase, Li3V2(PO4)(3), is also formed, showing that solid solution is a function of the synthesis temperature. X-ray absorption near-edge structure indicates vanadium is in the 3+ oxidation state and in an octahedral environment. Magnetic studies reveal a shift of the antiferromagnetic ordering transition toward lower temperatures with increasing vanadium substitution, confirming solid solution formation. The addition of vanadium enhances the electrochemical performance of the materials especially at high current densities.