Benefits of molybdenum substitution in Na3V2(PO4)3 cathode material for sodium ion batteries: A first principles study

Abstract

The first principles study on the structural and electronic properties of Na3V2(PO4)3 (NVP) was performed using first principles calculation. Results on lattice constant, Mulliken analysis and density of state are discussed in this paper. Overall, lattice parameter calculation obtained using GGA-PBEsol functional is in better agreement with the experimental result. Based on atomic population, Na2 is expected to be sodiated first compared to Na1. From the bond order calculation, it was shown that the P-O bond provided thermal stability and contributed to the long-life cycle of the battery. The Na-O bond showed that the ionic character is essential for ion migration. From the Density of state, the overlapping between O 2p and P 3p orbitals forms a strong bond which supports the bond order result. In this study, the calculated band gap value was 2.06 eV and which then decreased to 0.4 eV upon desodiation. The effect of Molybdenum (Mo) substitution on NVP was also studied using virtual crystal approximation method. The volume of NVP increases with increasing amount of Mo6+ substitution which eases the migration of ions and this will be beneficial to the electrochemical performance. Thus, this substituted NVP with Mo (Na3V2-xMox(PO4)3) cathode material could be a potential candidate for sodium ion batteries.