Effect of synthesis conditions on the properties of LiFePO4 for secondary lithium batteries

LiFePO4 is one of the promising materials for cathode of secondary lithium batteries due to its high energy density, low cost, environmental friendliness and safety. However, LiFePO4 has very poor electronic conductivity (~10−9 S cm−1) and Li-ion diffusion coefficient (~1.8 × 10−14 cm2 s−1) at room temperature. In an attempt to improve electrochemical properties, LiXFePO4 with various amounts of Li contents were investigated in this study. LiXFePO4 (X = 0.7–1.1) samples were synthesized by solid-state reaction. High resolution X-ray diffraction, Rietveld analysis, BET, scanning electron microscopy, and hall effect measurement system were used to characterize these samples. Electronic conductivities of the samples with Li-deficient and Li-excess in LixFePO4 were 10−3 to 10−1 S cm−1. Discharge capacities and rate capabilities of the samples with Li-deficient and Li-excess in LiXFePO4 were higher than those of stoichiometric LiFePO4 sample. Li0.9FePO4 samples fired at 700 °C had discharge capacity of 156 and 140 mAh g−1 at 0.1 C- and 2 C-rate, respectively.