A GGA+U study of lithium diffusion in vanadium doped LiFePO4

Recent experiments showed beneficial influence of vanadium doping on the electrochemical performance of lithium iron phosphate (LiFePO4) cathode materials. First-principles calculations have been performed to investigate the stability, electronic structure and lithium diffusivity of vanadium-doped LiFePO4 and to elucidate the origin of such improvement. It is found that vanadium prefers occupying Fe sites and leads to additional density of states within the intrinsic bandgap. By the nudged elastic band method, we show that the barrier of Li ions diffusion along the one dimensional channel in both LiFePO4 and FePO4 phases can be effectively reduced by vanadium doping. Structural analysis shows the lower diffusion barrier ties closely to a volumetric expansion of the diffusion channel.

► We model vanadium doped lithium ion phosphates using GGA+U method.
► We theoretically determine the most energetically favorable site for phosphor dopant.
► Vanadium doping on iron site induces density of states within the bandgap.
► Vanadium is shown to reduce the lithium ion migration barrier.
► Reason for the reduced migration barrier is due to a volumetric expansion of the diffusion channel.