Building a Fast Lane for Mg Diffusion in α-MoO3 by Fluorine Doping

Abstract

Following previous experimental work examining a layered oxyfluoride as cathode material for Mg-ion batteries [Incorvati et al., Chem. Mater. 2016, 28, 17], we study the role of fluorination on the structural and electronic properties of molybdenum trioxide and its impact on Mg intercalation and diffusion using first-principles methods. Although bulk α-MoO3 is a 2D layered compound, we find that it provides 3D channels for Mg diffusion. When F atoms are incorporated into the α-MoO3 lattice, they replace the O atoms sitting at a specific crystallographic site that is linked by two nearest Mo atoms within a single Mo–O layer. As a consequence of F substitution, the local Mo-anion bonds are distorted, which leads to closure of the electronic band gap. From the analysis of zone center phonon vibrational frequencies, it is found that the local Mo-anion bonding strength is weakened by replacing O2– with F–, which ultimately facilitates Mg diffusion through the F-substituted lattice. For example, it is shown tha...