Redox Mechanisms upon the Lithiation of Wadsley–Roth Phases

Abstract

The Wadsley−Roth family of transition metal oxide phases are a promising class of anode materials for Li-ion batteries due to their open crystal structures and their ability to intercalate Li at high rates. Unfortunately, most early transition metal oxides that adopt a Wadsley−Roth crystal structure intercalate Li at voltages that are too high for most battery applications. Firstprinciples electronic structure calculations are performed to elucidate redox mechanisms in Wadsley−Roth phases with the aim of determining how they depend on crystal structure. A comparative study of two very distinct polymorphs of Nb 2 O 5 reveal two redox mechanisms: (i) an atom-centered redox mechanism at early stages of Li intercalation and (ii) a redox mechanism at intermediate to high Li concentrations involving the bonding orbitals of metal−metal dimers formed by edge-sharing Nb cations. Our study motivates several design principles to guide the development of new Wadsley−Roth phases with superior electrochemical properties.