Enhanced electrochemical properties of LiFePO4/C synthesized with two kinds of carbon sources, PEG-4000 (organic) and Super p (inorganic)

Olivine structured LiFePO4/C cathode was synthesized via a freeze-drying route and followed by microwave heating with two kinds of carbon sources: PEG-4000 (organic) and Super p (inorganic). XRD patterns indicate that the as-prepared sample has an olivine structure and carbon modification does not affect the structure of the sample. Image of SEM shows a uniform and optimized particles size, which greatly improves the electrochemical properties. TEM result reveals the amorphous carbon around the surface of the particles. At a low rate of 0.1 C, the LiFePO4/C sample presents a high discharge capacity of 157.8 mAh g−1 which is near the theoretical capacity (170 mAh g−1), and it still attains to 149.1 mAh g−1 after 200 cycles. It also exhibits an excellent rate capacity with high discharge capacities of 143.2 mAh g−1, 137.5 mAh g−1, 123.7 mAh g−1 and 101.6 mAh g−1 at 0.5 C, 1.0 C, 2.0 C and 5.0 C, respectively. EIS results indicate that the charge transfer resistance of LiFePO4 decreases greatly after carbon coating.