Preparation and electrochemical studies of Fe-doped Li_3V_2(PO_4)_3 cathode materials for lithium-ion batteries

摘要

The Fe-doped Li_3V_2(PO_4)_3 cathode materials for Li-ion batteries were synthesized by a conventional solid-state reaction, and the Fe-doping effects on the Li electrochemical extraction/insertion performance of Li_3V_2(PO_4)_3 were investigated by galvanostatic charge/discharge and cyclic voltammetry measurements. The optimal Fe-doping content x is 0.02-0.04 in Li_3Fe_x-V_(2-x)(PO_4)_3 system. The Fe-doped Li_3V_2(PO_4)_3 samples showed a better cyclic ability between 3.0 and 4.9 V, for example, the discharge capacity of Li_3Fe_(0.02)V_(1.98)(PO_4)_3 was 177 mAh g~(-1) in the 1st cycle and 126 mAh g~(-1) in the 80th cycle. The retention rate of discharge capacity is about 71 percent, much higher than 58 percent of the undoped system. The improved electrochemical performances of the Li_3V_2(PO_4)_3 could be attributed to the increased electrical conductivity and structural stability deriving from the incorporation of the Fe~(3+) ions.