High-rate characteristic of F-substitution Li3V2(PO4)3 cathode materials for Li-ion batteries

The effect of fluorine substitution on the electrochemical properties of Li3V2(PO4)(3) cathode materials was studied. Samples with stoichiometric proportions of Li3V2(PO4)(3-x)F-x (x = 0, 0.05, 0.10, 0.15) were prepared by adding LiF in the starting materials of Li3V2(PO4)(3). XRD studies showed that the F-substituted Li3V2(PO4)(3) had the same monoclinic structure as the un-substituted Li3V2(PO4)(3). SEM images showed that F-substitution Li3V2(PO4)(3) had a regular and uniform particles. The results of electrochemical measurement showed that F-substitution can improve the rate capability of these cathode materials. The Li3V2(PO4)(2.90)F-0.10 sample showed the best high rate performance. Its discharge capacity at 10 C rate was 117 mA h g(-1) with 30th capacity retention of about 90.60%. The electrode reaction reversibility and electronic conductivity was enhanced, and the charge transfer resistance was decreased through F-substitution. The improved electrochemical performance of F-substitution Li3V2(PO4)(3) cathode materials were attributed to the above factors. (C) 2009 Elsevier Ltd. All rights reserved.