Effect of aluminum doping on carbon loaded Na3V2(PO4)3 as cathode material for sodium-ion batteries

Aluminum-doped Na3V2-xAlx(PO4)3/C (0 ≤ x ≤ 0.3) samples were synthesized and characterized as cathode materials for sodium-ion batteries. X-ray diffraction, electron microscopy and Raman spectroscopy data unveiled high purity NASICON phosphate phases and amorphous carbon forming a homogenous matrix that enhances the electron conducting properties of the composite electrode material. For x ≥ 0.2, the occurrence of a new voltage plateau at ca. 4.0 V contributed favorably to the overall capacitance. The good kinetic response detected on galvanostatic cycling was interpreted in terms of low internal resistances at the cycled cells. Thus, Na3V1.8Al0.2(PO4)3 performed 96.8 mA h g­−1 at 6C and preserved 103 mA h g­−1 after decreasing to C/2 after 60 cycles.