Robust three-dimensional carbon conductive network in a NaVPO4F cathode used for superior high-rate and ultralong-lifespan sodium-ion full batteries

摘要

Polyanion-type compounds, used as promising cathode materials for sodium-ion batteries (SIBs), have attracted great attention because of their suitable operating voltage, stable framework and good thermal stability. However, they suffer from inherent low conductivity, poor high-rate capability and unsatisfactory cycle stability. Herein, in order to overcome these deficiencies, a feasible strategy, which integrates high conductivity reduced graphene oxide (rGO) with the representative vanadium-based fluorophosphates to form a 3D carbon network constructed in NaVPO4F, is proposed and investigated. Based on microstructural and morphological characterization, the NaVPO4F nanoparticles are successfully synthesized and uniformly embedded in a robust rGO carbon network. Ascribed to the multifunctional structure design, the reaction kinetics of NaVPO4F were significantly improved, as demonstrated by the electrochemical impedance spectroscopy, cyclic voltammetry at varied scan rates and galvanostatic intermittent titration technique. Moreover, the hard carbon (HC) and the NaVPO4F@rGO composite are employed as the anode and the cathode, respectively, to fabricate a sodium-ion full battery, which exhibits an excellent high-rate capability (75.1 mA h g(-1)at 15C) and an outstanding cycling stability (0.0115% capacity decay per cycle over 1500 cycles at 5C rate). This study provides a feasible and effective method to develop high-performance polyanion-type electrode materials for SIBs.