Highly Reversible Sodium-ion Storage in NaTi₂(PO₄)₃/C Composite Nanofibers

Highlights: •NaTi₂(PO₄)₃/C composite nanofibers have been firstly synthesized by electrospinning. •NaTi₂(PO₄)₃/C composite nanofibers show outstanding electrochemical performance in sodium ion batteries. •We have calculated the D_Na+ of samples through the EIS. -- Abstract: NaTi₂(PO₄)₃/C composite nanofibers (NTP/C-F)have been prepared with success by electrospinning followed by calcination in Ar. For comparison, NaTi₂(PO₄)₃ nanofibers have also been synthesized by similar method but calcination in air. NaTi₂(PO₄)₃/C composite particles without special morphology also have been prepared by directly calcining the precursor in Ar. The samples have been characterized by scanning electron microscopy (SEM), High-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), charge-discharge test, cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS). NTP/C-F demonstrates excellent sodium ion storage properties including good rate capability and extended cycle life, much better than other two samples. It delivers the highest discharge capacities, which are about 130, 123, 122, 119, 114, 103, 87, and 63 mAh g⁻¹ at 0.1, 0.2, 0.5, 1, 2, 5, 10, and 20 C, respectively. The discharge capacity reserves as high as 97 mAh g⁻¹ after 500 cycles at 5 C, and the corresponding capacity retention is 93%. Such outstanding property is likely due to the special 1D-structure including uniform electrically conductive carbon network, which brings high electronic conductivity and rapid Na⁺ diffusion. Hence, NTP/C-F will be a potential electrode candidate for sodium ion batteries.