Investigation of the change in the electronic properties of FeF₃ by the introduction of oxygen using a molecular orbital method

FeF₃ has attracted interest as a conversion-reaction-based positive electrode material in applications to lithium ion batteries. However, slow reaction kinetics is a major drawback due to its poor electrical conductivity. The electronic features of FeF₃ were examined using the DV-Xα molecular orbital method. This article reports the effects of oxygen doping on the bonding characteristics and electrical conductivity. An analysis of the bond overlap population and spatial distribution of electrons showed that the FeO bond has a more covalent nature than the FeF bond. New energy levels were generated in the original band gap region through an interaction between the Fe3d and O2p orbitals with the introduction of oxygen. The electrical conductivity of FeF₃ is expected to be increased by the partial substitution of oxygen for fluorine due to the higher covalent character and the formation of new energy levels.