Construction of high performance N-doped Na3V2(PO4)2F3/C cathode assisting by plasma enhanced chemical vapor deposition for sodium-ion batteries

Abstract

ABSTRACT One N-doped carbon coated Na3V2(PO4)2F3/C cathode for sodium-ion batteries was successfully prepared by a Plasma enhanced chemical vapor deposition (PECVD) method. N2 gas is used as the nitrogen source and it is ionized to form chemically active nitrogen ion. It can easily react with the carbon atoms in sample Na3V2(PO4)2F3/C. Research results show that the introduction of N does not affect the crystal structure of the material. The N-doped carbon layer in sample Na3V2(PO4)2F3/C becomes more and more homogeneous. The formation of the pyridinic nitrogen, pyrrolic nitrogen and graphitic nitrogen in the carbon layer can generate additional active sites to shorten the transmission distance of sodium ions, which can improve the electrochemical performance of Na3V2(PO4)2F3/C cathode. The NVPF@N-3 cathode treated by PECVD for 30 min displays excellent rate performance (109.8 mAh•g−1 at 5 C) and cyclic performance, in which the capacity retention after 1000 cycles at 10 C is 91.4% and the crystal structure of NVPF@N-3 is well maintained. This research demonstrates that the pyrolytic carbon in Na3V2(PO4)2F3/C cathode for sodium-ion batteries can be effectively doped by Nitrogen through a novel PECVD technology.