Novel vanadium-doped olivine-like nanomaterials with high electronic conductivity

Olivine-like lithium iron phosphate (LiFePO4) is the most studied cathode material for a new generation of commercial Li-ion batteries. In this work we have studied the effect of thermal nanocrystallization on the electronic conductivity of the LiFe0.75V0.10PO4 glasses. The electrical conductivity of the as-prepared glass extrapolated to room temperature was as low as 10− 12 S · cm− 1. An appropriate thermal treatment of the glass led, however, to an immense increase in its electrical conductivity (up to 10− 3 S · cm− 1) and to a decrease in the activation energy from 1.0 eV for a freshly synthesized material to 0.17 eV after heat treatment. In the best conducting sample a large number of 5 ÷ 10 nm nanocrystallites of LiFePO4 were observed by SEM, STEM and HRTEM techniques. We ascribe the immense increase in the conductivity to especially advantageous conditions for polaron hopping between aliovalent iron and/or vanadium ions, created during the thermally induced microstructural changes. No traces of metallic impurities (such e.g., Fe2P) were found, but some presence of an electrochemically active Li3V2(PO4)3 phase was detected by XRD.