Theoretical calculations of the performance of Li₇NbO₆ and its doped Phases as solid electrolytes

Materials with Hexagonal Close Packed (HCP) anionic configuration contain promising lithium-ion conductors. In the HCP anionic structure, when the non-lithium cations occupy the octahedral sites (the important diffusion channels for lithium ions), it is not known whether the nature of fast lithium-ion diffusion will be retained. This work systematically studied the lithium-ion diffusion properties of Li₇NbO₆ as well as its doped phases on the basis of first-principles calculations. The calculation results show that the lithium-ion conductivity of Li₇NbO₆ is 0.008 mS cm^-1 at room temperature, while the doped phase Li₅₅Nb₇WO₄₈ with W⁶⁺ doping at the Nb sites possesses a higher lithium-ion conductivity of 0.28 mS cm^-1 at room temperature and an activation energy of 0.34 eV. The lithium-ion diffusion mechanism in Li₇NbO₆ and its doped phase involves concerted migration; besides, they are poor conductors of electrons regardless of whether doping is applied. In addition, W⁶⁺ doping increases the reduction limit of the electrochemical window due to its strong oxidizing property; therefore, an artificial SEI film needs to be applied to reduce interfacial decomposition. The discovery and characterization of the new fast lithium-ion conductor Li₅₅Nb₇WO₄₈ provide theoretical guidance for the development of new solid electrolytes.