Carbon-Coated Na3V2(PO4)3 Supported on Multiwalled Carbon Nanotubes for Half-/Full-Cell Sodium-Ion Batteries

Na-ion superionic conductor (NASICON)-based Na3V2(PO4)(3) is regarded as a potential cathode for sodium-ion batteries, due to the excellent thermal stability and large ion diffusion channel. Herein, multiwalled carbon nanotube-pierced Na3V2(PO4)(3) (NVP@C/MWCNT) is synthesized through a simple sol-gel approach. Tested as a cathode for sodium-ion half batteries, the as-prepared electrode displays an excellent reversible capacity (111.6 mA h g(-1) at 1 C) and superior rate capability (63.2 mA h g(-1) at 80 C). Furthermore, in situ X-ray diffraction (XRD) patterns of NVP@C/MWCNTs indicate the apparent two-phase (de-)sodiation process. In contrast, the ortho-disodium salts of tetrahydroxyquinone (o-Na2C6H2O6) are prepared as an anode, which demonstrates a reversible discharge capacity of 156.8 mA h g(-1) at 0.1 C and enhanced high-rate performance (72.1 mA h g(-1) at 20 C) for sodium-organic half batteries. When evaluated as a Na-ion full cell, a NVP@C/MWCNT || o-Na2C6H2O6 full cell shows outstanding rate capability (33.3 mA h g(-1) at 1.0 A g(-1)). Such impressive electrochemical behavior is related to the addition of multiwalled carbon nanotubes. This not only enhances electronic conductivity of NVP, but also inhibits the growth of grains, which shortens the Na+ diffusion length and increases the contact space between electrode/electrolyte.