Integrating high-purity NASICON-type Na₃V₂(PO₄)₃ cathodes and ionic liquid gel electrolytes for sodium-ion energy storage

The deployment of sustainable sodium-ion energy storage systems demands the parallel development of structurally stable cathodes and non-volatile, safe electrolytes. Herein, we demonstrate a synergetic dual innovation: the synthesis of highly crystalline, phase-pure nanocrystalline Na 3 V 2 (PO 4 ) 3 (NVP) via a tailored sol–gel route, integrated with a thermally robust, fumed silica-reinforced ionic liquid gel electrolyte (NaFSI - C 3 mpyrFSI). X-ray diffraction and structural refinement confirm that the NVP crystallizes cleanly into a rhombohedral NASICON-type structure ( ̅ R 3 ̅ c space group) with a mean crystallite size of 58.01 nm and no detectable secondary phase impurities. FE-SEM analysis reveals a highly porous, three-dimensional skeletal framework consisting of interconnected sub-micron grains with prominent thermal sintering and necking boundaries, which optimizes electrolyte wetting. Quantitative EDX evaluation confirms the uniform presence of the constituent elements (13.2 wt% Na, 35.5 wt% V, 22.5 wt% P, and 28.8 wt% O), yielding an experimental framework P/V atomic ratio of 1.48 that aligns exceptionally well with the ideal stoichiometric ratio of 1.50. At room temperature, the optimized low-concentration (1.6 m) gel electrolyte architecture exhibits a superior ionic conductivity of 7.48 mS.cm −1 , drastically outperforming its high-concentration (4.0 m) counterpart due to suppressed ion-pairing and aggregate formation. This gel framework retains complete structural and mechanical stability up to 100 °C without leakage. Cyclic voltammetry (CV) analysis validates the electrochemical robustness of the gel electrolytes. Both formulations exhibit clear plating and stripping behavior of sodium, as evidenced by well-defined cathodic and anodic peaks. When evaluated in coin-cell prototypes at 50 °C, the NVP cathode operating with the 1.6 m NaFSI gel electrolyte delivers a stable specific discharge capacity of 83.9 mAh.g −1 at 0.05 C, demonstrating excellent structural reversibility and reliable sodium-ion transport kinetics. This strategy provides an effective, scalable pathway toward fabricating high-safety and high-performance polyanionic sodium-ion batteries for elevated-temperature operations.