First-principles study of the change in the electronic properties of NiF2 by the introduction of oxygen

• Effect of O-doping on electronic state of NiF2 is studied with first-principle method.
• Introduction of O increases covalent nature of NiF2.
• New energy levels are formed in band gap region by interaction of Ni3d–O2p orbitals.
• The results support O-doping increases electrical conductivity of metal fluorides.

NiF2 is investigated as a conversion-reaction-based positive electrode material in applications to lithium ion batteries. Despite high discharge capacity, slow reaction kinetics due to poor electrical conductivity is a general drawback of the conversion reaction. The electronic features of NiF2 were investigated using the DV-Xα molecular orbital method in this study. The effects of oxygen doping on the bonding characteristics and electrical conductivity were examined in particular. An analysis of the bond overlap population and spatial distribution of electrons showed that the Ni–O bond has a more covalent nature than the Ni–F bond, and doping of oxygen increases the covalent characteristics of Ni–F bond. New energy levels were generated in the band gap region through an interaction between the Ni3d and O2p orbitals with the introduction of oxygen. The electrical conductivity of NiF2 is expected to be increased by the substitution of fluorine by oxygen owing to the higher covalent character and the formation of new energy levels.