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

Highlights: • Na₄MnV(PO₄)₃/C (NMVP/C) was prepared by sol-gel route plus calcination in N₂ stream. • Calcination temperature impacts on physical and electrochemical properties of NMVP/C. • The optimal calcination temperature is 750 °C in the range of 650–850 °C. • The optimal NMVP/C has higher capacity and better rate capability and cyclability. • The optimal NMVP/C has discharge capacity of 108 mAh/g (0.2C) and 81.3 mAh/g (20C). -- Abstract: 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⁺ (D_Na) 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 D_Na 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.