Effects of calcination temperature on electrochemical properties of cathode material Na4MnV(PO4)3/C synthesized by sol-gel method for sodium-ion batteries

The effects of calcination temperature on the physical and electrochemical performance of the Na4MnV(PO4)3/C composites, which are prepared by a sol-gel method combined with the subsequent calcination in inert atmosphere, are reported in this work. The Na4MnV(PO4)3/C composites are investigated by x-ray diffraction (XRD), N2 adsorption/desorption isothermal, scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy and electrochemical measurements. The specific surface area, disorder of carbon, diffusion coefficients of Na+ (DNa) and electrochemical performance of Na4MnV(PO4)3/C composites are greatly influenced by the calcination temperature. The surface area and disorder of carbon of Na4MnV(PO4)3/C substantially decrease with the calcination temperature increasing. While the DNa and electrochemical performance of Na4MnV(PO4)3/C composites improve with the calcination temperature from 650 to 750 °C and then degrade with the calcination temperatures from 750 to 850 °C. The results reveal that the optimal calcination temperature for the Na4MnV(PO4)3/C composites is 750 °C and the corresponding Na4MnV(PO4)3/C composite possesses the highest capacity and the best rate capability and cyclability amongst all these Na4MnV(PO4)3/C composites in this work.