Core/shell nanostructured Na3V2(PO4)3/C/TiO2 composite nanofibers as a stable anode for sodium-ion batteries

Abstract

Na3V2(PO4)3/C/TiO2 (NVP/C/TiO2) composite nanofibers with core/shell nanostructure are prepared by coaxial electrospinning plus heat treatment method. The physical and electrochemical performances of NVP/C/TiO2 nanofibers are investigated by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and electrochemical tests. The results show that the composite nanofibers are made of TiO2/C nanoparticles shell and Na3V2(PO4)3/C nanofibers core with embedded TiO2/C nanoparticles. NVP/C/TiO2 nanofibers exhibite much better electrochemical performance than both TiO2/C and Na3V2(PO4)3/C nanofibers prepared by coaxial electrospinning method. The core-shelled NVP/C/TiO2 nanofibers delivere a reversible capacity of 196.1 mAh g−1 at 0.2C (35.6 mA g−1) in the voltage of 0.01–3.0 V (vs.Na+/Na), which is higher than the theoretical capacity of 178 mAh g−1 for Na3V2(PO4)3 and that of TiO2/C composite. NVP/C/TiO2 also displays excellent cycle stability and rate capability. Even at a high rate of 20C, it can still release a high reversible charge capacity of 109 mAh g−1 and retain a capacity of more than 70 mAh g−1 after 1500 cycles. The special microstructure and synergetic effects of Na3V2(PO4)3, conductive carbon and ultrafine TiO2 are responsible for the excellent electrochemical performance. This facile strategy exhibits superiority in fabricating core-shell nanostructured composite nanofibers as promising electrode materials for energy storage devices.