Aluminum doped Na3V2(PO4)2F3 via sol–gel Pechini method as a cathode material for lithium ion batteries

The solid solution series Na3V2-x Al x (PO4)2F3 (where x = 0, 0.02, 0.05, and 0.1) powders have been prepared using the Pechini method to study the effect of aluminum doping on the electrochemical properties of these cathode materials for lithium ion batteries. The structure, composition, and morphology of the compounds were investigated by X-ray diffraction, thermogravimetric and differential analysis, specific surface area, and pore size analysis using Brunauer-Emmett-Teller—Barret-Joyner-Halenda methods, scanning electron microscopy, elemental chemical analysis with induced coupled plasma-optical emission spectroscopy and charge/discharge galvanostatic experiments. X-ray diffraction indicates a tetragonal crystal structure for the Na3V2(PO4)2F3 phase, and all the Al compositions. The materials obtained have a microstructure consisting of nanoparticles (40–100 nm) with an average pore size 20 nm and 30 m2/g surface area. The phase with 0.05 moles of aluminum gave the best result electrochemical charge/discharge capacities of 123 to 101 mAh/g with cell voltage of 4.4 V vs. Li and a capacity retention of 82%, compared to undoped material which gave 128 to 63 mAh/g, and 49% capacity retention. Hence, Al-doped samples showed better electrochemical performance maybe attributable to improved structure stability compared to the undoped material. Those results suggest a promising material for lithium ion batteries.