Enhancement of the Na2FePO4F@gC3N4 electrochemical performance in view of its implementation in sodium-ion batteries

Abstract

Na2FePO4F fluorophosphate has long been regarded as potential cathode material for sodium-ion batteries (SIBs) due to its undeniable economic and environmental advantages. Herein, the preparation of Na2FePO4F powder using an easier and cost-effective technique is reported. The prepared compound, using phosphoric acid as P-source, crystallizes in an orthorhombic structure with the Pbcn space group as confirmed by X-Ray Diffraction (XRD) analysis. The pristine material (refers to as PM) is combined with different percentages of graphitic carbon nitride g-C3N4 as a carbon source (15% and 20%), to build large specific surfaces, boost electronic conductivity, and achieve the optimal carbon content. Raman spectrum reveals the existence of residual carbon denoting that the in-situ carbon coating process is successful. Thermogravimetric analysis (TGA) confirmed the stability of iron fluorophosphate at temperatures of 750 °C. Scanning electron microscope (SEM), and energy-dispersive X-ray spectroscopy (EDS) are used to investigate the materials' surface morphology and particle size. The performance of 15% and 20% g-C3N4 coated materials are tested as cathodes in both pure 1 M NaClO4 in polycarbonate electrolyte and in added 5% fluoroethylene carbonate electrolyte. High cycling properties and improved electrochemical performance were revealed when compared to the additive-free electrolyte.