Suppression of FeLi• antisite defects in fluorine-doped LiFePO4

We report on the suppression of Fe-Li(center dot) antisite defects in LiFe(PO4)(1-x)F-3x with 0 <= x <= 0.4 prepared by sol-gel and hydrothermal methods. Evidence for a systematic suppression of antisite defects upon fluorine doping in LiFePO4 is inferred from Fourier transform infrared spectra, wherein a noticeable red shift in the symmetric P-O stretching vibrational mode of (PO4)(3-) polyanion from 970 to 957 cm(-1) was observed. We report detailed structural and compositional studies of LiFe(PO4)(1-x)F-3x, and discuss the implications for the performance of LiFePO4 cathodes in lithium ion batteries. (C) 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.