Vacuum-assisted synthesis of Fe3(PO4)2·8H2o and its influence on structure, morphology and electrochemical performance of liFePO4/C

Abstract

A vacuum-assisted precipitation method was used to synthesize Fe3(PO4)2·8H2O (FP). The FP was then used to synthesize carbon-coated LiFePO4 (LFP/C) particles. The influence of FP on the structure, morphology, and electrochemical performance of LFP was investigated. The X-ray diffraction (XRD) patterns and molar ratio of Fe to P showed that the FP which was produced using a vacuum-assisted method was of high purity and gave highly crystalline, impurity-free LFP. Scanning electron microscopy (SEM) showed that the FP contained undeveloped particles. The undeveloped FP results in uniform LFP/C particles, without agglomeration. Transmission electron microscopy (TEM) showed that the LFP particles were coated with a homogeneous carbon layer. The LFP/C showed excellent discharge capacities of 140, 113, and 100 mAh·g-1 at 1C, 10C, and 20C rates, respectively. The cyclic voltammograms (CVs) of LFP showed a low polarization voltage and sharp redox peaks. The charge-discharge platform curves showed that LFP had an excellent high-rate capability. Electrochemical impedance spectroscopy (EIS) tests showed that the lithium-ion diffusion coefficients of LFP/C produced with and without vacuum assistance were 1.42×10-13 and 4.22×10-14 cm2·s-1, respectively, proving that vacuum assistance can improve the diffusion coefficients of LFP/C. © Editorial office of Acta Physico-Chimica Sinica.