Polyanion compounds offer a playground for designing prospective electrode active materials for sodium-ion storage due to their structural diversity and chemical variety. Here, by combining a NaVPO₄F composition and KTiOPO₄-type framework via a low-temperature (e.g., 190 °C) ion-exchange synthesis approach, we develop a high-capacity and high-voltage positive electrode active material. When tested in a coin cell configuration in combination with a Na metal negative electrode and a NaPF₆-based non-aqueous electrolyte solution, this cathode active material enables a discharge capacity of 136 mAh g⁻¹ at 14.3 mA g⁻¹ with an average cell discharge voltage of about 4.0 V. Furthermore, a specific discharge capacity of 123 mAh g⁻¹ at 5.7 A g⁻¹ is also reported for the same cell configuration. Through ex situ and operando structural characterizations, we also demonstrate that the reversible Na-ion storage at the positive electrode occurs mostly via a solid-solution de/insertion mechanism.

The effect of the cation nature is explored for the reaction of alkali metal ions intercalation into the AVPO₄F material. Application of electrochemical methods allowed determining the key diffusional and kinetic parameters for Li⁺, Na⁺ and K⁺ intercalation reactions. The obtained formal redox potential values, apparent diffusion coefficients and charge transfer resistance values are contrasted, providing the possibility to assess the variation in the reaction energetics for metal ion insertion/extraction. The observed differences in reaction rates are rationalized in terms of different contributions of ion desolvation and transition through adsorbate layer/electrode interface for various ions.