Preparation, dielectric and conductivity studies of LiNi1-xMgxO2 cathode materials for lithium-ion batteries

Abstract

A layered structure cathode materials LiNi1-xMgxO2 (where x = 0.0 and 0.02) were prepared by solid state reaction from Li2CO3, MgO and NiO. The thermal analysis of the precursor materials up to 750 °C showed the weight loss of about 30%. The X-ray diffraction patterns of the synthesized samples confirmed the presence of α-NaFeO2 structure with the rhombohedral-hexagonal symmetry (space group, R3m) and no evidence of any impurities. The peaks intensity ratio I003/I104 increased with Mg concentration, which indicates the cation mixing within transition metal layer and lithium layer. The Fourier transform infrared spectroscopy showed the presence of two broad vibrational bands between 400 and 1000 cm-1 and corresponding bands for the 3a and 3b octahedral sites of LiO6 and MO6 units. The scanning electron microscopy analyses showed that the prepared samples have porous and relatively uniform distribution of grain sizes in the range 0.4–3µm. The complex impedance spectroscopy studies of the samples sintered at 850 °C were done in the frequency range from 42 Hz to 1 MHz with temperature variation from 30 to 100 °C. The results revealed that the total electrical conductivity increases with temperature and frequency and at 100 °C it is 7.06×10-6 and 9.00×10-6 S/cm for the LiNiO2 and LiNi1-xMgxO2 materials, respectively. The obtained relatively high conductivity and low dielectric constant confirmed that the prepared ceramics can be used as cathode materials for Li-ion batteries.

Keywords

• LiNiO2
• layered structure
• XRD
• FESEM
• FT-IR
• dielectric constant
• conductivity