The effect of cation ordering on the structure, electrical and electronic properties of cubic spinel LiNi0.5Mn1.5O4
Abstract
In this paper, we present the investigation of the impact of cation ordering on the structural, electrical, and electronic properties of a cubic spinel LiNi0.5Mn1.5O4. Rietveld refinement using X-ray diffraction (XRD) data reveals that LiNi0.5Mn1.5O4 annealed at 700 °C adopts a well-ordered atomic arrangement in cubic spinel (SG = P4332). Then, it is transformed to a disordered cubic spinel (SG = Fd-3m) at higher temperatures (> 800 °C). Impedance spectroscopy is employed to evaluate the dielectric and electrical properties in the temperature range of 0 to 25oC within the frequency range between 10 Hz and 100 kHz. The Cole-Cole plot indicates that grain boundaries contribute significantly to electrical conductivity and that bulk resistance decreases with increasing temperature. The AC conductivity analysis shows that the electrical conductivity of well-ordered and disordered cubic spinel LiNi0.5Mn1.5O4 exhibits thermal activation and obeys Jonscher's universal power law. Furthermore, the electronic properties of cubic spinel LiNi0.5Mn1.5O4 with the space groups of Fd-3m and P4332 are investigated using the density functional theory (DFT) plane-wave method. The electronic analysis of the cubic spinel LiNi0.5Mn1.5O4 (SG = Fd-3m) indicates stronger bonding between oxygen and transition metal elements compared to the LiNi0.5Mn1.5O4 (SG = P4332) structure. Therefore, LiNi0.5Mn1.5O4 with the Fd-3m space group exhibits high structural stability, making it a favourable cathode material for high-voltage rechargeable lithium-ion batteries.
