Porous Na3V2(PO4)3 enwrapped by dual carbon substrate from phenol formaldehyde with superior electrochemical performance

Abstract

Low electronic conductivity and poor cycling stability at high rates have limited the practical application of Na₃V₂(PO₄)₃ (NVP). In this study, NVP coated with phenol–formaldehyde-derived porous carbon and citric acid-derived amorphous carbon (NVP/C-P) is prepared by a two-step sol–gel method. The porous carbon skeleton not only enhances the conductivity of the material by forming a conductive graphited framework but also buffers the stress impact of high currents on the electrode material, ensuring excellent rate performance and cycling stability even at high current densities. Due to the unique porous skeleton, the specific surface area of NVP/C-P is significantly enlarged, resulting in a favourable contacting effects between electrode and electrolyte. In addition, the abundant mesoporous structure in the sample can be utilized for Na⁺ storage, contributing to pseudocapacitance. Hence, NVP/C-P can exhibit a high initial specific capacity of 132.8 mAh/g at 0.1C, significantly exceeding the theoretical value of 117.6 mAh/g. Furthermore, it can release a value of 53.7 mAh/g at 100C, maintaining a specific capacity of 50.8 mAh/g after cycling for 3000 cycles with a super high retention rate of 94.5 %. The structural evolution and sodium storage mechanism during charge and discharge processes of the modified sample NVP/C-P are investigated by ex-situ XRD, confirming its excellent stability and reversibility. The after-cycled XRD/SEM/CV/EIS demonstrate NVP/C-P possesses relatively dominant kinetic characteristics and crystal/morphological stability, further verifying the great advantages of the modification by dual-carbon substrate and porous skeleton for NVP/C-P.