Electronic and structural properties of V$_2$O$_5$ layered polymorphs

Abstract

V$_2$O$_5$ is a promising battery electrode material that can intercalate not only Li, but also more abundant alkaline metals such as Na and K, and even multivalent ions such as Al, Ca, Cu, Mg, and Zn. V$_2$O$_5$ exhibits several different polymorphs, and phase transitions between the polymorphs can occur depending on intercalant or external conditions. At least 8 different layered polymorphs have been observed. However, detailed information about the energetics and structural properties of each polymorph is still lacking. To obtain a reliable computational reference, we use hybrid density functional theory calculations to investigate the properties of layered V$_2$O$_5$ polymorphs. We benchmarked several methods to include van der Waals interactions in combination with hybrid functionals, and found that the Grimme D3 method is most accurate. We obtain detailed information on the electronic properties and structures of the various unintercalated polymorphs and show that the main electronic effect of intercalants is a filling of the lowest conduction bands, as the intercalant contributions are well above the conduction-band minimum. Despite the structural differences between the unintercalated polymorphs, we find that they have very similar band gaps and band structures, with the exception of the high temperature and pressure phase $β$.