LiFePO4–carbon composites obtained by high-pressure technique: Synthesis and studies on their structure and physical properties

LiFePO4 samples were prepared in a modified sol–gel process. The resulting LiFePO4 xerogels were ground and mixed with 2 wt.% of selected carbon components (graphite flakes and carbon nanotubes) in a ultrasonic cleaner. As-prepared composite samples were isostatically pressed at ca. 8 GPa and elevated temperatures (400, 800 or 1000 °C) in order to provide more intimate contact between small grains of LiFePO4 and the carbon components. The as-synthesized LiFePO4 material and its composites with carbon were characterized by a number of methods: X-ray diffractometry (XRD), differential scanning calorimetry–thermogravimetry (DSC–TGA), scanning electron microscopy (SEM), Raman spectroscopy, Mössbauer spectroscopy and impedance spectroscopy (IS). It was confirmed that synthesized material contains only a triphylite phase. The presence of carbon does not affect the crystalline structure of the parent material. The conductivity of such composites was high — over 10− 3 S cm− 1 at room temperature. The composites have not been tested yet in electrochemical cells.