Na3V2(PO4)3/C nanofiber bifunction as anode and cathode materials for sodium-ion batteries

Na3V2(PO4)(3)/C composite nanofibers are prepared successfully through a coaxial electrospinning technique and subsequent calcination. The diameter of the prepared nanofibers is uniformly distributed (about 100200 nm), and the composite nanofibers (NF-NVP/C) contain Na3V2(PO4)(3) nanofibers and carbon nanofibers, and Na3V2(PO4)(3) nanoparticles with diameters of 5-10 nm are embedded into the composite nanofibers. The NF-NVP/C anode exhibits a high reversible capacity 189.9 mAh/g at a current rate of 0.2 C (1 C=118 mA/g) in the voltage range of 0.01-3.00 V (vs. Na+/Na). Even at high rates of 5 and 10 C, this anode displays discharge capacities of 105.1 and 80.4 mAh/g at the second cycle and capacity retentions of 83 and 77% after 200 and 500 cycles, respectively. A sodium-ion full cell with NF-NVP/C as the electroactive material of both positive and negative electrodes presents two average operating voltages at 0.5 and 1.5 V and delivers a reversible capacity of 106.2 mAh/g at a current density of 100 mA/g in a voltage range of 0.01-4.00 V. The outstanding electrochemical performance is attributed to the unique nanofiber structure and uniform distribution of NVP nanoparticles in the highly conductive carbon matrix.