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

•Na3V2(PO4)3/C nanocomposites are synthesized by varying their carbon content.•Carbon contents close to 7% provide cycling stability.•Good rate performances are achieved with content close to 11%.•A full sodium-ion cell delivers an energy density of 320 W h kg− 1 at 2C.

An in-situ generated carbon matrix has demonstrated to be essential to provide electrical conducting properties to Na3V2(PO4)3 as cathode materials for sodium-ion cells. Na3V2(PO4)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 Na3V2(PO4)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.

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