Density functional theory calculations applied to olivine-like NaMnPO₄ with transition metal substitutions for energy storage applications

Abstract

In this study, Density Functional Theory (DFT) calculations are applied to evaluate the structural and thermodynamic properties of MPO 4 and NaMPO 4 as cathode materials for sodium-ion batteries (SIBs). Using the modified Perdew-Burke-Ernzerhof (PBE) method and the projector augmented wave (PAW) method, the effect of metal substitution in MPO 4 and NaMPO 4 lattices (M = Mn, Fe, Co, Ni,), as well as Fe-Ni substituted NaMnPO 4 was examined for its structural and electrochemical characteristics. As NaMnPO 4 has less ionic and electronic conductor, the partial substitution of Mn by simultaneous Ni and Fe gives good physicochemical properties useful for good cathode materials in SIBs. For NaMn 0.5 Ni 0.25 Fe 0.25 PO 4 , its optimal values of gravimetric capacity (154 mAh.g −1 ), bandgap energy (0.45 eV) and intercalation potential (3.54 V) appeared very interesting to be an attractive cathode material for SIBs. Na + diffusion required less energy in NaFePO 4 , NaMnPO 4 , and Fe-Ni co-doped NaMnPO 4 systems, promoting a rapid recharge rate and good ionic conductivity thanks to the desodiation process in creating a mixed oxidation state particularly for Fe and Mn atoms.