Effect of Vanadium Modification on Electrochemical Performance of LiFePO4/C

摘要

A series of vanadium doped LiFePO4/C were synthesized by the carbothermal reduction method combining with balling technique. Results show that only a little of vanadium substitutes for iron site in the crystal lattice of olivine LiFePO4 and impurity phases are detected when the vanadium content is over 0.5 mol %. LiVOPO4, the first impurity phase, is discovered as vanadium content ranges from 1 mol to 5 mol % and disappears at high doping level. Li3V2(PO4)3 and vanadium oxide are gained when vanadium content is over 5 mol %. The special charge/discharge capacity and rate capability are enhanced on a certain extent by vanadium doping and LiFe_(0.975)V_(0.025)PO4 shows the most outstanding property among all samples. The improvement of electrochemical performance of LiFePO4 mainly resulted from the formation of impurity phases, LiVOPO4, instead of the vanadium doping into LiFePO4 lattice. Thus, excellent electrochemical performance can be achieved by optimizing the content of vanadium.