Improved electrochemical properties in the Li3Fe2(PO4)3 by titanium and vanadium doping

摘要

The nominal Li3-xFe2-xTix(PO4)2.55(VO4)0.45 (x =0~0.3) compounds were synthesized by a sol-gel process. Different from the single VO43 doping, further introduction of Ti4+ion was easy to result in precipitation of a little secondary phases, besides the main NASICON products. The simultaneous substitution of Ti4+and VO43 for Fe3+and PO43 , respectively, in the Li3Fe2(PO4)3 resulted in a net improvement in the rate capability and cycling performance, as compared with the single Ti4+or VO43 -substituted compound. The sample with x=0.2 presented a high initial discharging capacity of 125.4 mAh/g at the rate of 0.5C, about 25% higher than the Ti4+-substituted Li2.8Fe1.8Ti0.2(PO4)3, and 102.6 mAh/g after 60 cycles at 2C, about 12% higher than the single VO43 -substituted one. The high rate performance between 0.5C to 10C suggested that this sample had a good stability and reversibility. These results proved that the combination of the Ti4+ substitution for Fe3+ with the VO43 substitution for PO43 was a promising method of improving electrochemical performance of the studied Li3Fe2(PO4)3 cathode material.