Redox Mechanisms, Structural Changes, and Electrochemistry of the Wadsley-Roth LiTiNb₂O₇ Electrode Material

The TiNb₂O₇ Wadsley-Roth phase is a promising anode material for Li-ion batteries, enabling fast cycling and high capacities. While already used in commercial batteries, many fundamental electronic and thermodynamic properties of LiTiNb₂O₇ remain poorly understood. We report on an in-depth first-principles study of the redox mechanisms, structural changes, and electrochemical properties of LiTiNb₂O₇ as a function of Li concentration. First-principles electronic structure calculations reveal an unconventional redox mechanism upon Li insertion that results in the formation of metal-metal bonds. This metal dimer redox mechanism has important structural consequences as it results in a shortening of cation-pair distances, which in turn affects lattice parameters of the host and thereby alters Li site preferences as the Li concentration is varied. The new insights about redox mechanisms in TiNb₂O₇ and their effect on the structure and Li site preferences provide guidance on how the electrochemical properties of a promising class of anode materials can be tailored by exploiting the tremendous structural and chemical diversity of Wadsley-Roth phases.