Antisite Defects in Sol‐Gel‐Synthesized LiFePO 4 at Higher Temperature: Effect on Lithium‐Ion Diffusion

In the present work, the study of atomic defects in LiFePO 4 is achieved by Rietveld refinements. Several LiFePO 4 samples are synthesized by using a sol‐gel process with varying calcination times and argon flow rates. Quantitative analysis of XRD patterns through Rietveld refinements confirms 2 % antisite defects in the LiFePO 4 sample. However, for the first time, we have observed antisite defects in LiFePO 4 prepared through a sol‐gel process at a higher temperature of 700 °C. Two samples identified as LFP−A and LFP−B are further studied by electrochemical analysis and electrochemical impedance spectroscopy to examine the effect of the antisite defects on the electrochemical performances and Li‐ion diffusion of LiFePO 4 . Sample LFP−B with 2 % antisite defects shows, at 0.1 C rate, a lower discharge capacity of 138 mAh g −1 as compared to 150 mAh g −1 for LFP−A. LFP−B also shows shorter cycle life as well as rate capability at all of the C rates studied. Li‐ion diffusion coefficients of LFP−A and LFP−B in initially prepared electrodes are found to be 1.669×10 −13 and 1.198×10 −13  cm 2  s −1 , respectively, whereas the diffusion coefficients after 200 cycles are 0.968×10 −13 and 0.436×10 −13  cm 2  s −1 , respectively.