Comparative study of Na0.67Ni0.25Co0.17Mn0.58O2 P-Type cathode materials for sodium-ion batteries: Combustion synthesis and combined analysis of structural, electrical, and dielectric properties

In this study, we present a promising sodium-ion cathode material, Na0.67Ni0.25Co0.17Mn0.58O2, which was synthesized by combustion method, and subsequent heat treatment at various calcination temperatures (700 °C, 800 °C, and 900 °C). The samples underwent analysis using various techniques, including Thermogravimetric Analysis (TGA), Differential Thermal Analysis (DTA), Fourier Transform Infrared Spectroscopy (FT-IR), X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM) combined with Energy Dispersive X-ray Analysis (EDS), Specific Surface Area Measurements (BET), and Impedance Spectroscopy Measurements (EIS). The XRD pattern of the sample prepared at 700 °C reveals that the lower annealing temperature induces the formation of a new phase, P3. Indeed, the phase transition from the rhombohedral P3-phase to hexagonal P2-phase at 900 °C via mixed phases (P3/P2) yielded at 800 °C. Furthermore, Rietveld refinement using the hexagonal unit cell leads the calculation of the network parameters and the structural stacking, showing that the P2-phase exhibits a more pronounced two-dimensional character compared to the P3-phase. FT-IR spectra reveal that the lattice structures of the samples consist of NaO6 and MeO6 (Me = Ni, Co, Mn) octahedra. SEM-EDS analysis shows a homogeneous surface morphology in good agreement with the theoretical and experimental proportions of the elements constituting the three P-type phases. Subsequently, we extensively investigated the effect of our P-type materials on the electrical and dielectric properties of the cathodes using EIS measurements. Our findings suggest that the low-cost and eco-friendly P2–Na0.67Ni0.25Co0.17Mn0.58O2 phase shows promise as a cathode material for sodium-ion batteries and represents a competitive alternative to the P3/P2- and P3–Na0.67Ni0.25Co0.17Mn0.58O2 phases.