SEM/EDX, XPS, and impedance spectroscopy of LiFePO<sub>4</sub> and LiFePO<sub>4</sub>/C ceramics

Abstract

The powders of LiFePO4 compounds have been synthesized by the solid state reaction, and LiFePO4/C composites were sintered in argon gas. The ceramics of LiFePO4 were sintered in air. The surfaces of the ceramics were investigated by a scanning electron microscope (SEM), energy dispersive X-ray spectrometer (EDX). The binding energies of the Fe 2p, P 2p, and O 1s core level of LiFePO4 ceramic and LiFePO4/C composite surfaces were determined by X-ray photoelectron spectroscopy (XPS). The deconvolutions of Fe 2p core level XPS are associated with Fe2+ and Fe3+ valence states of the ceramics. Impedance spectroscopy of the ceramics has been performed in the frequency range of 10 Hz to 3 GHz by low frequency and microwave impedance spectrometers. Two- and four-probe methods were used for measurements at low frequencies. The LiFePO4/C composite was investigated in nitrogen gas, and the measurements of LiFePO4 were conducted in air. The measurements of the electrical properties of the ceramics were carried out in the temperature interval of 300–500 K.