Synthesis of LiFePO₄ Cathode Materials by Mechanical-Activation-Assisted Polyol Processing

Abstract

A low-temperature approach for efficient preparation of LiFePO4 was developed. The rod-shaped [Fe3(PO4)2•8H2O + Li3PO4] precursor was prepared, using a mechanochemical liquid-phase activation technique, from LiH2PO4 and reduction iron powder. Pure LiFePO4 was then synthesized in boiling tetra(ethylene glycol) (TEG) by polyol processing with the as-prepared precursor. In order to improve the electrical conductivity, carbon coating of the pure LiFePO4 was carried out, using poly(vinyl alcohol) (PVA) as the carbon source. The products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), galvanostatic charge-discharge test and electrochemical impedance spectroscopy (EIS). The results show that well-crystallized LiFePO4 was successfully synthesized by polyol processing at low temperature. Carbon coating significantly improves the conductive properties of LiFePO4 and reduces charge-transfer impedance. The obtained LiFePO4/C composite delivers specific discharge capacities of 139.8 and 129.5 mAh•g-1 at 1C and 2C rates, respectively, displaying good cycling performance and rate capability.

Synthesis of Rod-Like LiFePO₄/C Materials with Different Aspect Ratios by Polyol Process

“…10 Recently, customizing particle morphologies is also becoming more and more prevalent because these factors are well-known to significantly influence electrochemical performance. 10,11 In order to synthesize homogenous nano-sized LiFePO4 and control its morphology at the same time, various synthesis technologies have been adopted such as the polyol process, [10][11][12]14 co-precipitation, 13,15 solid-state reactions, 16,17 hydrothermal synthesis, [18][19][20] solvothermal methods, 10,21,22 and the solgel process. 23 The polyol process is a new method to synthesize LiFePO4, in this process, the polyol medium acts not only as a solvent, but also as a stabilizer and a deoxidizer.…”