Characterization of carbon-coated LiFe0.3Mn0.7PO4 particles produced using a colloidal method for lithium batteries

Abstract

A convenient colloidal process for the preparation of LiFe0.3Mn0.7PO4/C nanocomposite cathode material for lithium batteries is reported. The process involves the use of lithium dihydrogen phosphate (LiH2PO4), ferrous chloride (FeCl2) and manganese chloride (MnCl2) as starting materials, with anhydrous N-methylimidazole (NMI) as the solvent and carbon source, followed by a 3 h annealing step at 650 °C. Carbonization of the molten salt NMIH+Cl− derived from NMI resulted in 3.0 wt% carbon content in the LiFe0.3Mn0.7PO4/C with 3–6 nm thick carbon coating. The material was characterized by thermogravimetric and differential thermal analysis, differential scanning calorimetry, powder X-ray diffraction, field-emission scanning electron microscopy, transmission electron microscopy, atomic absorption spectroscopy, Raman spectroscopy, four-point probe method, cyclic voltammetry and galvanostatic cycling experiments in coin cells. SEM analysis of the LiFe0.3Mn0.7PO4/C material revealed non-spherical agglomerates with average width and length of 50–70 nm and 120–150 nm, respectively. The electronic conductivity of carbon-coated LiFe0.3Mn0.7PO4 was found to be 9.7 × 10−2 S cm−1 at room temperature, and the discharge capacity reached 137 mAh g−1 measured at C/20 when the cell was cycled between 2.2 V and 4.2 V vs. Li+/Li, and 124 mAh g−1 at C/10 for the first cycle. The capacity dropped to 122 mAh g−1 at C/10 after the first 25 cycles and then stayed constant at 121 mAh g−1 until the 100th discharge cycle, making this cell to exhibit excellent cycling stability with only a 2.4% decrease.