In situ redox reaction induced firmly anchoring of Na3V2(PO4)2F3 on reduced graphene oxide & carbon nanosheets as cathodes for high stable sodium-ion batteries

NASICON-type Na3V2(PO4)2F3 is considered as one of the most promising cathodes for sodium-ion batteries due to its high operating potential, fast ion transport and superior structural stability. However, its poor rate capability and insufficient cyclability hinder its future practical applications. Herein, a hybrid of Na3V2(PO4)2F3 nanoparticles firmly anchoring on reduced graphene oxide & carbon (rGO&C) nanosheets is synthesized through an in situ redox reaction. The ethylenediamine and oxalic acid not only could induce the nucleation of Na3V2(PO4)2F3 along the surface of rGO, but also act as carbon sources of amorphous carbon, serving as binders to firmly and densely couple Na3V2(PO4)2F3 with the three-dimensional continuous conductive network constructed by rGO nanosheets. The composite displays excellent rate capability and remarkable cycling stability (capacity retention of 81.9% for 1000 cycles at 30 C), due to the 2D rGO&C nanosheets and anchored ultrafine Na3V2(PO4)2F3 nanoparticles shorten diffusion length of the ions and electrons, the firm connectivity between Na3V2(PO4)2F3 and rGO&C nanosheets enables high structure stability to relieve the stress and strain generated during the cycling. The strategy can be extended to prepare other NASICON vanadium phosphates cathodes materials for advanced batteries.