Physical and electrochemical properties of LiFePO4/C composite cathode prepared from various polymer-containing precursors

The goal of this research was to study the effect of various polymer-containing precursors on the performance of LiFePO4/C composite. A coprecipitation method was applied to prepare a series of LiFePO4/C materials by calcinating amorphous LiFePO4 with various polymer compounds at 600 °C. The materials were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, particle size analysis, thermal analysis, BET specific surface area, Raman spectral analysis and electrochemical methods. The results showed that the structure of polymer precursors played an important role in improving the performance of LiFePO4/C composites. The residual carbon produced by the pyrolysis of polymers with functionalized aromatic groups exhibited a better capacity in the LiFePO4/C composites. A polyaromatic compound, e.g. polystyrene, with more functionalized aromatic groups displayed improved performance because its decomposition temperature was close to the temperature of the LiFePO4 phase transformation, which resulted in fine particle size and uniform carbon distribution on the composite surface. According to Raman spectral analysis, polystyrene with more aromatic groups has a lower ID/IG and sp3/sp2 peak ratio indicating more highly graphite-like carbon formation during polymer pyrolysis and exhibited a better capacity.