Carbon-Interconnected Sodium Vanadium Phosphate Microparticles: Material Characterizations and Na⁺-Storage Performances

Sodium vanadium phosphate (Na 3 V 2 (PO 4 ) 3 ) with continuous carbon-coating (NVP/C) has been regarded as one of the most promising cathode materials for sodium-ion batteries (SIBs) owing to the three-dimensional sodium superionic conductor (NASICON) structure for fast sodium-ion migrations, high theoretical energy density (ca. 400 Wh/kg), and good thermal stability (450°C). In this study, carbon-interconnected NVP/C microparticles (C@NVP/C MPs) were successfully synthesized by employing ascorbic acid and sodium-containing polymer as dual carbon sources, followed by calcination at 750°C in an argon atmosphere. The resulting C@NVP/C MPs not only exhibited great crystallinity, high purity, and size of 5-10 μm but also possessed carbon amounts of 9.9 wt. %, as confirmed through the X-ray diffractometer, scanning electron microscope, and thermogravimetric analyzer, respectively. The cyclic voltammogram revealed that the potential difference between oxidation and reduction peaks of C@NVP/C (174 mV at 0.1 mV/sec and 382 mV at 1.0 mV/sec) was less than that of the NVP/C nanoparticles (197 mV at 0.1 mV/sec and 391 mV at 1.0 mV/sec) that were synthesized without adding the sodium-containing polymer. Moreover, the same reversible capacity was delivered from C@NVP/C, i.e. , 75 mAh/g at 0.1 C. Those improved electrochemical performances could be attributed to the well-interconnection between NVP/C and carbon originating from the pyrolysis of sodium-containing polymer, creating additional electronic transportation pathways. Accordingly, the C@NVP/C MPs synthesized in the present study are reasonably anticipated to be promising cathode materials for SIBs.