Synthesis And Modification Of Na₃V₂?PO₄?₃ As A Cathode Material For Sodium-ion Batteries

In this work,Na3V2(PO4)3 was synthesized via ball mill method with Na2CO3,NH4VO3, NH4H2PO4 as the raw material. Carbon coating, metal ion doping were used to modify the electrochemical performance. The crystalline structure, morphology and electrochemical performance for each as-prepared material were characterized by XRD, SEM, TEM and charge-discharge measurements. The CV and impedance performance were tested on Autolab.Na3V2(PO4)3/C was synthesized via ball mill method with PVA as carbon source.When the PVA ' s mass fraction was 10%,the Na3V2(PO4)3/C exhibited the best cycling performance and rate capability. At 0.5C, the initial discharge capacity was 113.2mAh/g (theoretical capacity is 118 mAh/g), the capacity retention rate was 88.8% after being discharged at 0.5C and cycled for 100 times.Na3V2(PO4)3/C was synthesized by sol-gel method with citric acid as carbon source.The initial charge capacity was 117.7 mA h g-1, discharge capacity was 104.23 mA h g-1,so the sample exhibited a highly coulombic efficiency of 88.6%. The discharge capacity was 97.29 mA h g-1 after 50 cycles. The capacity retention rate was 93.3%.But the capacity faded rapidly, the capacity retention rate was only 80.4% after cycled for 100 times. The capacity retention rate need to be improved.Na3V2-xCox(PO4)3/C (x=0.05, 0.10, 0.13) samples were prepared by sol-gel method with cobalt nitrate as cobalt source. The result showed that Co-doping was benefit to improve the cyclic stability. The initial charge capacity of Na3Vi.9Co0.1(PO4)3/C was 109.93 mA h g-1, and the discharge capacity was 104.78 mA h g-1. The first coulombic efficiency reached 95.3%. It was better than Na3V2(PO4)3/C.Na3V2-xAlx(PO4)3/C (x=0,0.10,0.15,0.20) samples were synthesized by sol-gel method with aluminium nitrate as aluminium source. The result showed that Al-doping could enhance the initial discharge effectively. With the Al3+ content increased,the initial discharge capacity of the samples were reached to the highest, then decreased,but all of them were higher than Na3V2(PO4)3/C. Na3V1.85Al0.15(PO4)3/C exhibited the best cycle performance and rate performance. The capacity retention rate reached to 99.4%, almost no faded.