The effect of cation ordering on the structure, electrical and electronic properties of cubic spinel LiNi₀.₅Mn₁.₅O₄

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.