Superior sodium storage of Na₃V(PO₃)₃N nanofibers as a high voltage cathode for flexible sodium-ion battery devices

The cathode materials for sodium-ion batteries are always the key issues for the ultimate success of large-scale energy storage systems. The nitrogen-dope polyanionic type material is one of the important high voltage candidates. Herein, we have developed a simple and facile method to synthesize a high voltage cathode material, Na₃V(PO₃)₃N nanofibers, via an electrospinning approach. Unexpected excellent rate performance and cyclability have been demonstrated, with a discharge capacity of 61.5 mAh g^-1achieved at a current density of 4 A g^-1. Capacity retention of 86.7% could be obtained at 0.8 A g^-1over 2000 cycles. Density functional theory calculations reveal that this material has an abnormal flat band characteristic, and its high voltage platform can be explained by the dominant V d-orbital contribution to the density of states at the Fermi level.