Experimental and computational study of binary transition metal oxides NaNi1/2 X1/2 O2 (X=Cr, Fe, Co and Cu) for energy storage applications

For novel applications as cathodes in sodium-ion batteries, layered transition metal oxides have been reported to have an appropriate voltage window that results higher specific capacity and energy density. In the present work, a series of binary layered transition metal oxides: NaNi1/2Cr1/2O2, NaNi1/2Fe1/2O2, NaNi1/2Co1/2O2, and NaNi1/2Cu1/2O2 were prepared using sol-gel technique. XRD analysis confirmed that all the synthesized materials stabilize a hexagonal structure with an R3m space group. SEM micrographs showed the formation of well-separated particles of varying shapes. FTIR spectra indicated the presence of metal oxygen absorption bands. Using density functional theory (DFT), crystal structure was generated using the lattice parameters worked out using XRD. The spin polarized electronic band structures and density of states (DOS) computed for all four compounds revealed half metallic character. Average intercalation voltages (AIV) were calculated theoretically from the total energies of the optimized compounds and their de-sodianted phases. Volume changes were also calculated to study its minimal values for the compounds, to identify them as of good structural stability. Both experimental findings and theoretical calculations show that the investigated binary layered transition metal oxides are suitable cathode materials for coin cell fabrications.