Synthesis and characterization of nano-sized LiFePO4 by using consecutive combination of sol-gel and hydrothermal methods

Lithium iron phosphate (LiFePO4) was synthesized by means of a new route which is based on the combination of sol-gel and hydrothermal methods (HY-SO-LiFePO4). The results of HY-SO-LiFePO4 were compared with those of LiFePO4 which was synthesized by using only hydrothermal method (HY-LiFePO4). The crystalline structure and morphology of LiFePO(4 )nanoparticles were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Based on XRD data, LiFePO4 powders have a well olivine crystal structure with a space group of Pnma. The slight decrease of crystalline lattice parameters in HY-SO-LiFePO4 was observed compared to that of HY-LiFePO4. LiFePO4 powders have homogeneous distribution of nanoparticles with a plate-like morphology. Also, the plate length decreases from 300-500 nm to 150-350 nm if sol-gel and hydrothermal methods are consecutively used together. The as-prepared LiFePO4 coin cells were characterized via cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), and their charge/discharge experiments were performed at different current rates in a range of 2.5-4.2V vs. Li/Li+. The discharge capacities of HY-SO-LiFePO4 were found as 126 mAhg(-1) at 0.2C and 70 mAhg(-1) at 3C. Meanwhile, HY-SO-LiFePO4 cathode exhibits a stable charge/discharge cycle ability (>97.5% capacity retention after 100 charge/discharge cycles compared with HY-LiFePO4 cathode which is 77.7% at 0.5C). The overall experimental results revealed the idea that positioning the wet gel inside reactor may impede the growth of grains and lead to the formation of smaller LiFePO4 nanoparticles with a narrow size distribution during reactive synthesis procedure. Hence, these results improve the electrochemical performance of cathode material. (C) 2020 Elsevier Ltd. All rights reserved.

Automated summary

A new route combining sol-gel and hydrothermal methods was used to synthesize LiFePO4, which showed well olivine crystal structure with nanoparticles homogeneously distributed and smaller size when compared with traditional hydrothermal method. The electrochemical performance of the cathode material was improved with the new synthesis method.