Mg 2+ -doped Na 3 V 2 (PO 4 ) 3 /C decorated with graphene sheets: An ultrafast Na-storage cathode for advanced energy storage

NASICON-type Na3V2(PO4)3 is one of the most promising cathode materials for sodium-ion batteries, delivering about two Na+-ions extraction/insertion from/into the unit structure. However, the low electronic conductivity which leads to bad rate capability and poor cycle performance, limits its practical application for sodium-ion batteries. To overcome the kinetic problem, we attempt to prepare the carbon-coated Na3V2(PO4)3 nanocrystals further decorated by graphene sheets and doped with Mg2+ ion via the two steps of sol-gel process and solid-state treatment for the first time. Such architecture synergistically combines the advantages of two-dimensional graphene sheets and 0-dimensional Mg2+-doped Na3V2(PO4)3/C nanoparticles. It greatly increases the electron/Na+-ion transport kinetics and assures the electrode structure integrity, leading to attractive electrochemical performance. When used as sodium-ion batteries cathode, the hybrid composite delivers an initial discharge capacity of 115.2 mAh g−1 at 0.2 C rate, and retains stable discharge capacities of 113.1, 109.0, 102.4, 94.0 and 85.2 mAh g−1 at high current rates of 1, 2, 5, 10 and 20 C rate, respectively. Thus, this nanostructure design provides a promising pathway for developing high-performance Na3V2(PO4)3 material for sodium-ion batteries.