Na₃V₂(PO₄)₃/C Composite Prepared by Sol-Gel Method as Cathode for Sodium Ion Batteries

Na 3 V 2 (PO 4 ) 3 (NVP) composites were prepared by a facile sol-gel method. The optimal synthetic conditions were systematically investigated by orthogonal test method and single factor of calcination temperature, which had maximum effect on the electrochemical properties of the sample. The optimal Na 3 V 2 (PO 4 ) 3 /C (denoted as Opt-NVP/C) has been prepared under the condition of the calcination temperature at 800°C, the molar ratio of NVP to C as 1:1, sol-gel reaction temperature at 80°C and the calcination time of 16 h. The capacity retention decreased by only 2% from the initial value of 106.7 mAh g −1 to 104.5 mAh g −1 after 100 cycles at 0.2C. Enhanced electrochemical performance can be attributed to reduced polarization and stable operating voltage window. The high purity and crystallinity at the proper calcination temperature and porous particles morphologies are related to lower polarization and higher Na + diffusion coefficient, respectively.