Morphology control and electrochemical properties of nanosize LiFePO4 cathode material synthesized by co-precipitation combined with in situ polymerization

Nanosize carbon coated LiFePO4 cathode material was synthesized by in situ polymerization. The as-prepared LiFePO4 cathode material was systematically characterized by X-ray diffraction, thermogravimetric–differential scanning calorimetry, X-ray photo-electron spectroscopy, field-emission scanning electron microscopy, and transmission electron microscopy techniques. Field-emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) images revealed that the morphology of the LiFePO4 consists of primary particles (40–50 nm) and agglomerated secondary particles (100–110 nm). Each particle is evenly coated with an amorphous carbon layer, which has a thickness around 3–5 nm. The electrochemical properties were examined by cyclic voltammetry and charge–discharge testing. The as-prepared LiFePO4 can deliver an initial discharge capacity of 145 mAh/g, 150 mAh/g, and 134 mAh/g at 0.2 C, 1 C, and 2 C rates, respectively, and exhibits excellent cycling stability. At a higher C-rate (5 C) a slight capacity loss could be found. However after being charge–discharge at lower C-rates, LiFePO4 can be regenerated and deliver the discharge capacity of 145 mAh/g at 0.2 C.

Research highlights▶ Nanosize LiFePO4 was synthesized by co-precipitation combined with in situ polymerization. During the co-precipitation process, aniline monomers were polymerized and covered the surface of each newly formed FePO4 particle, thus hindering the further growth of nuclei. Even though the LiFePO4 was sintered at 650 °C for 15 h, the primary particle size of LiFePO4 is still controlled within 40–50 nm, with a continuous carbon coating layer. The as-prepared LiFePO4 can deliver an initial discharge capacity of 150 mAh/g at the rate of 1 C and exhibits excellent capacity retention and cycling stability at higher C-rates.