Preparation and Electrochemical Properties of Carbon-Coated LiMn0.6Fe0.4PO4 Cathode Material for Lithium-Ion Batteries

The LiMn x Fe 1− x PO 4 /C ( x = 0.5, 0.6, and 0.7) cathode materials for lithium-ion batteries were synthesized by polyethylene glycol (PEG) 400 as the carbon source via a combination of wet ball-milling and high-temperature solid-state reaction. The analysis results of X-ray diffraction (XRD), scanning electron microscopy (SEM), and high-resolution transmission electron microscopy (HRTEM) indicate that the as-prepared LiMn 0.6 Fe 0.4 PO 4 /C sample has a single-phase orthorhombic olivine structure, and the majority of particle sizes range from 100 to 200 nm with a ∼2–3 nm carbon coating layer. The electrochemical measurements demonstrate that the obtained LiMn 0.6 Fe 0.4 PO 4 /C composite possesses preferable Li-ion storage properties, and the discharge capacity of 137.7 mAh g −1 at 1 C rate, which is 83.6% of that at 0.1 C rate. The composite also exhibits outstanding cycling stability, with a capacity retention of 98.2% after 100 cycles at 0.2 C rate. And the differential capacity analysis (dQ/dV) reveals that the dominating degradation of LiMn 0.6 Fe 0.4 PO 4 /C is caused by the Mn 2+ /Mn 3+ redox capacity loss which is located at ∼4.12/3.96 V, whether during the charge or discharge process. Moreover, the LiMn 0.6 Fe 0.4 PO 4 /C sample delivers excellent high-temperature performance (45 °C), with improved reversible capacity and capacity retention of 148.7 mAh g −1 and 99.3% after 80 cycles at 0.5 C rate, respectively.