A dual vanadium substitution strategy for improving NASICON-type cathode materials for Na-ion batteries

The effect of the Al/Cr proportion in six carbon-containing Na3VAlxCr1−x(PO4)3 (0 ≤ x ≤ 1) samples is evaluated to unveil the influence on their performance as positive electrodes for sodium-ion batteries. For this purpose, solid-state techniques such as XRD diffraction, electron microscopy, and XPS and Raman spectroscopies are helpful to untangle the structural and textural properties of the raw materials. Sodium half-cells assembled with the studied material as the positive electrode are subjected to voltammetric and galvanostatic tests to unveil the insertion mechanism and electrochemical performance. The better reversibility of the high voltage plateau, for the sample with the highest Al content, may explain its good kinetic response when subjected to the highest rate. These results are correlated with the measurements of apparent diffusion coefficients and cell internal resistance.