The effects of Al doping on the electrochemical properties of NaVPO4F as a cathode material for sodium-ion batteries were investigated.Al-doped NaV1-xAlxPO4F(x=0,0.02)samples were prepared by a simple high temperature solid-state reaction involving VPO4 and NaF for the application of cathode material of sodium-ion batteries.The crystal structure and morphology of the material were studied by Flourier-infrared spectrometry(FT-IR),X-ray diffractometry(XRD)and scanning electron microscopy(SEM).The results show that NaV1-xAlxPO4F(x=0,0.02)has a typical monoclinic structure.The effects of Al doping on the performance of the cathode material were analyzed in terms of the crystal structure,charge-discharge curves and cycle performance.It is found that NaV0.98Al0.02PO4F shows an improved cathodic behavior and discharge capacity retention compared with the undoped samples in the voltage range of 3.0-4.5 V.The electrodes prepared from NaV0.98Al0.02PO4F deliver an initial discharge capacity of 80.4 mA·h/g and an initial coulombic efficiency of 89.2%,and the capacity retention is 85%after 30th cycle. Though the Al-doped samples have lower initial capacities,they show better cycle performance than Al-free samples.
