The role of Li-based batteries in energy storage is unprecedented owing to their superior electrochemical performance, long-term stability and better controllability. The improved understanding of the structure-property relationship has helped to achieve the desired performance (capacity, power, electro-chemical stability) along with providing strong control on the long-term degradation issues. Recently, by use of advanced characterisation techniques, the structural degradation of cathodes has been identified to be either surface-specific or extended to the bulk of the cathode. To mitigate the degradation/reconstruction at the surface of cathode materials, the fabrication of a coating/artificial-interface is projected to be an effective remedy.  Traditionally metal oxides such as Al₂O₃ and ZrO₂ have been proposed as the coating/artificial-interface material. However, a recent report demonstrating the formation of lithiated phases at the interface, during the fabrication of coating or electrochemical cycling, has suggested a need for a pre-lithiated coating/artificial-interface layer. Due to sparse reports of electronically insulating Li-rich materials containing Group V d⁰ metal oxides, we explored the Li-rich side of Li-M-O phase diagrams (M being Ta and Nb) for their possible use as a coating/artificial-interface.  

     In the two-step solid-state method by tuning the Li-ion content in the precursor stoichiometry, we have successfully synthesised two new phases, Li₈M₂O₉ and Li₁₀M₂O₁₀. In order to identify the structures of these new phases and owing to the low X-ray scattering cross section of Li compared to Ta/Nb, we combined synchrotron X-ray diffraction (SXRD) and neutron diffraction (ND) revealing a layered structure with a complex superstructure. To get a full structural picture, local M-O distances and symmetries were assessed by Ta and Nb K edge extended X-ray absorption fine structure (EXAFS) analysis. We conducted in-depth Nb solid-state nuclear magnetic resonance (ssNMR) measurements on the known Nb compositions (LiNbO₃, Li₃NbO₄ and LiNb₃O₈) to develop a structural assignment of the different Nb sites in the Li-based oxides. Following this we recorded static and magic angle spinning (MAS) Nb ssNMR spectra on the two new Nb phases. From EXAFS analysis symmetric MO₆ featuring M-O distances and from ssNMR number and local structure of Nb sites were evaluated.  These results were feedback into the combined SXRD and ND analysis. We will summarise the synthesis optimisation and in-depth structural characterisation of the new phases using long-range (SXRD, ND) and short-range (EXAFS and ssNMR) analysis.