Abstract: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.

Key words: sodium ion battery; cathode materials; capacity retention; cycle performance