Effect of chromium doping on Na3V2(PO4)2F3@C as promising positive electrode for sodium-ion batteries

Cr-doped Na3V2(PO4)2F3@C samples, obtained by a one-step sol-gel method, are studied as cathode materials for sodium-ion batteries. Their structural and morphological properties induced by Cr incorporation are determined by powerful solid-state techniques including X-ray diffraction, electron microscopy, and Raman and XPS spectroscopies. Galvanostatic tests reveal the beneficial effects of low-level Cr doping in Na3V2(PO4)2F3, mainly improving the kinetic response of the electrode materials at the highest studied rates. These results are correlated to low cell internal resistances and cell polarization between charge and discharge. Eventually, a full sodium-ion cell is essayed as a proof of concept to evidence the reliability of these cathode materials in practical conditions.