On the effect of carbon content for achieving a high performing Na3V2(PO4)3/C nanocomposite as cathode for sodium-ion batteries

Abstract An in-situ generated carbon matrix has demonstrated to be essential to provide electrical conducting properties to Na 3 V 2 (PO 4 ) 3 as cathode materials for sodium-ion cells. Na 3 V 2 (PO 4 ) 3 /C nanocomposites are synthesized by varying their eventual carbon content in order to determine the influence in the electrochemical behavior. X-ray diffraction patterns evidence the crystallinity and purity of Na 3 V 2 (PO 4 ) 3 , while Raman spectroscopy reveals the disordered character of the carbon phase. The determination of the chemical state of the carbonaceous phase unveils that an increase of the carbon content involves a decrease of carboxyl groups and a slight increase of graphitic carbon atoms, in agreement with the Raman results. The electrochemical characterization of these composites in sodium half cells reveals that carbon contents close to 7% are preferred to provide cycling stability, while the best rate performance is achieved for the sample with carbon content close to 11%. A full sodium-ion cell delivers an energy density of 320 W h kg − 1 at 2C.