SEM/EDX, XPS, and impedance spectroscopy of LiFePO4 and LiFePO4/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.