High-rate characteristic of F-substitution cathode materials for Li–ion batteries

The effect of fluorine substitution on the electrochemical properties of Li3V 2(PO4)3 cathode materials was studied. Samples with stoichiometric proportions of Li3V 2(PO4)3−xFx ( x = 0 , 0.05 , 0.10 , 0.15 ) were prepared by adding LiF in the starting materials of Li3V 2(PO4)3. XRD studies showed that the F-substituted Li3V 2(PO4)3 had the same monoclinic structure as the un-substituted Li3V 2(PO4)3. SEM images showed that F-substitution Li3V 2(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 Li3V 2(PO4)2.90F0.10 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 Li3V 2(PO4)3 cathode materials were attributed to the above factors.