Hydrothermal Synthesis and Electrochemical Properties of Na3V2(PO4)2O2F Cathode for Sodium-Ion Batteries

Na3V2(PO4)(2)O2F (NVPOF) sodium ion battery cathode materials were prepared by hydrothermal method, and the morphology, structure and electrochemical properties were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and galvanostatic charge/discharge (GCD). The results showed that as. prepared pure phase NVPOF had regular tetraprisms morphology, which was 1 similar to 3 mu m in length, 300 nm similar to 1 mu m in width, and the ratio of length to width was 2 similar to 3. NVPOF showed two pairs of stable charging and discharging platforms, the discharge specific capacities of NVPOF were 124.2 and 70.5 mAh.g(-1) at 0.2C and 2C at room temperature, and de. creased to 105.8 and 59.6 mAh.g(-1) after 100 cycles, the capacity retention rate were about 85.2% and 84.5% while the Coulombic efficiency was more than 97%. In addition, NVPOF also had good electrochemical performance at low temperature (0 degrees C). By coating reduced graphene oxide (rGO) to increase the electrical conductivity, NVPOF@ rGO presented high specific discharge capacities of 124.4 and 88.4 mAh. g(-1) at 0.2C and 2C at room tem. perature. The specific capacity was still 78.7 mAh.g(-1) after 200 cycles at 2C, and the capacity retention rate was as high as 89% while the Coulomb efficiency was always about 99%, showing excellent rate and cycling performance.