Microstructural Characteristics of Hydrothermally Synthesized LiFePO4 and Relevant Impacts on the Electrochemical Performance

Phospho-olivine LiFePO4 has been prepared using a facile hydrothermal method by optimizing the reaction temperatures. Structural and morphological properties of the as-prepared LiFePO4 powders are systematically characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), infrared spectra, UV-vis spectra, and Mossbauer spectroscopy. It is demonstrated that the samples prepared in the temperature range from 160 to 200 degrees C crystallize in a single phase of phospho-olivine structure. All particles are rod-like, showing dimensions of approximately 150 similar to 200 urn in width and 500 similar to 600 nm in length with a preferential growth direction of [001]. Within the lattice of LiFePO4 rods, Fe2+ ions partially disorderly occupy the Li+ sites, which increases the cell volume. The electrochemical performance of LiFePO4 is investigated by charge/discharge experiments. It is found that LiFePO4 rods prepared at 200 degrees C deliver a specific discharge capacity of 147 mAh g(-1), which is apparently superior to those prepared at lower reaction temperatures like 160 and 180 degrees C. This observation is explained in terms of the thinner surface noncrystalline layer and lower level of Fe2+ disorderly occupying the Li+ sites.