Using Rietveld-refined X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and electrochemical cycling, it was established that among sodium vanadium fluorophosphate compositions Na1+yVPO4F1+y (0 ≤ y ≤ 0.75), the single-phase material Na1.5VPO4F1.5 or Na3V2(PO4)2F3 with a tetragonal structure (the P42/mnm S.G.) is formed only for y = 0.5. The samples with y < 0.5 and y > 0.5 possessed different impurity phases. Na3V2(PO4)2F3 could be considered as a multifunctional cathode material for the fabrication of lithium-ion and sodium-ion high-energy batteries. The reversible discharge capacity of 116 mAh•g−1 was achieved upon cycling Na3V2(PO4)2F3 in a hybrid Na/Li cell. Decrease in discharge capacity for the other samples was in accordance with the amount of the electrochemically active phase Na3V2(PO4)2F3. Na3V2(PO4)2F3 showed good cycleability and a high rate of performance, presumably due to operation in the mixed Na/Li electrolyte. The study of the structure and composition of charged and discharged samples, and the analysis of differential capacity curves showed a negligible Na/Li electrochemical exchange, and a predominant sodium-based cathode reaction. To increase the degree of the Na/Li electrochemical exchange in Na3V2(PO4)2F3, it needs to be desodiated first in a Na cell, and then cycled in a lithium cell. In this case, the electrolyte would be enriched with the Li ions.

Lithium-excess oxides Li_1.2Ti_0.4Mn_0.4O₂ and Li_1.3Nb_0.3Mn_0.4O₂ with a disordered rock-salt structure and Mn³⁺/Mn⁴⁺ as a redox couple were compared to analyze the effect of different d⁰ metal ions on the local structure and Li⁺ ion migration.

A sample with a nominal composition ‘NaVPO₄F’ is prepared by mechanochemically assisted solid-state synthesis using quenching.