Double-Nanocarbon Synergistically Modified Na₃V₂(PO₄)₃: An Advanced Cathode for High-Rate and Long-Life Sodium-Ion Batteries

An advanced cathode material, nitrogen-doped carbon-coated Na₃V₂(PO₄)₃ hybriding with multiwalled carbon nanotubes (CNTs) composite, namely double-nanocarbon synergistically modified Na₃V₂(PO₄)₃ of sodium ion battery, was fabricated through a simple sol–gel approach. According to the systemical analysis of experimental results on this composite structure, it is found that N-doping not only increases Na-ion migration velocity across the carbon-coated layer but also improves the electric conductivity of the carbon layer. More importantly, the CNTs 3D conducting network could significantly accelerate the electron transport between multiple particles of Na₃V₂(PO₄)₃, due to the intimate contacts between active materials and CNTs. Consenquently, the electrochemical properties of this double-nanocarbon-modified Na₃V₂(PO₄)₃ are significantly enhanced, especially the high-rate capability and long cycle life. For instance, its initial capacity of 94.5 mAh g^–1 at 0.2 C decreases to 70 mAh g^–1 at 70 C, and the capacity retention is 74%. Moreover, when dischage rate increases to a higher 30 C, the capacity retention is still as high as 87% after 300 cycles