Fe excess in hydrothermally synthesized LiFePO4

Olivine lithium iron phosphate (LiFePO4) is synthesized by a typical hydrothermal route. Although X-ray diffraction (XRD) shows no detectable impurities, inductively coupled plasma-atomic emission spectroscopy (ICP-AES) demonstrates extra iron (Fe) in the sample which is further indicated as crystallographic defects occupying lithium sites and a small amount of surface amorphous Fe3+ impurities by Rietveld refinement of high resolution synchrotron XRD and Raman spectroscopy, respectively. The latter possibility is also verified by high resolution transmission electron microscopy (HRTEM) and galvanostatic discharge/charge measurements between 2.0 and 3.2 V (vs. Li/Li+). In addition, the influence of Fe excess on the electrochemical performance of LiFePO4 as a cathode material for lithium ion batteries (LIBs) is discussed.

► Fe excess is indicated by ICP-AES in as-prepared LiFePO4 by hydrothermal synthesis.
► Rietveld refinement of high resolution synchrotron XRD indicates crystallographic defects occupying Li sites.
► Raman spectroscopy demonstrates amorphous surface Fe3+ impurities which are also verified by galvanostatic discharge/charge technique.
► The influence of Fe excess on battery performance of olivine LiFePO4 is discussed as well.