Theoretical calculations of the performance of Li 7 NbO 6 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 Li ₇ NbO ₆ as well as its doped phases on the basis of first-principles calculations. The calculation results show that the lithium-ion conductivity of Li ₇ NbO ₆ is 0.008 mS cm ^-1 at room temperature, while the doped phase Li ₅₅ Nb ₇ WO ₄₈ with W ⁶⁺ 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 Li ₇ NbO ₆ and its doped phase involves concerted migration; besides, they are poor conductors of electrons regardless of whether doping is applied. In addition, W ⁶⁺ 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 Li ₅₅ Nb ₇ WO ₄₈ provide theoretical guidance for the development of new solid electrolytes.