Investigating the influence of sodium sources towards improved Na3V2 (PO4)3 cathode of sodium-ion batteries

Abstract Sodium-ion batteries have been regarded as one of next promising alternatives for large scale energy storage originated from its resource abundance, low cost and environmental benignity. Sodium vanadium phosphates (Na3V2(PO4)3) owing to its robust structure, three-dimensional diffusion channels, and satisfactory energy density have been extensively studied. Herein, Na3V2(PO4)3 samples have been prepared by solid state method and post heat treatment employing two kinds of sodium source (Na2CO3 and NaOH). Furthermore, the related solid-state reaction mechanism and corresponding electrochemical properties have been investigated in detail. It turned out that sodium source has important effect on the crystal structure and morphology, which would influence the (de)insertion reaction of sodium-ion during cycling process. Na3V2(PO4)3 synthesized at 750 °C with Na2CO3 shows better electrochemical performance. And the original capacity is 114.8 mA h g−1 at 0.1C with following capacities of 104.6, 95.2 and 71.6 mA h g−1 at 5, 10 and 20 C delivered, respectively. Moreover, a reversible capacity of 92.5 mA h g−1 at 5 C after 300 cycles could be achieved realizing a high capacity retention of 93.5%. The results indicate that it is vital to select the suitable sodium source to prepare Na3V2(PO4)3 with favorable performance.