Na2FePO4F/C composite synthesized via a simple solid state route for lithium-ion batteries

Abstract

Using low-cost FePO4·2H2O as iron source, Na2FePO4F/C composite is prepared by alcohol-assisted ball milling and solid-state reaction method. The XRD pattern of Na2FePO4F/C composite demonstrates sharp peaks, indicating high crystalline and phase purity. The SEM and TEM images reveal that diameter of the spherical-like Na2FePO4F/C particles ranges from 50 to 300 nm, and HRTEM image shows that the surface of Na2FePO4F/C composite is uniformly coated by carbon layer with a average thickness of about 3.6 nm. The carbon coating constrains the growth of the particles and effectively reduces the agglomeration of nanoparticles. Using lithium metal as anode, the composite delivers a discharge capacities of 102.8, 96.4 and 90.3 mA·h/g at rates of 0.5C, 1C and 2C, respectively. After 100 cycles at 0.5C, a discharge capacity of 98.9 mA·h/g is maintained with capacity retention of 96.2%. The Li+ diffusion coefficient (D) of Na2FePO4F/C composite is calculated as 1.71×10−9 cm2/s. This study reveals that the simple solid state reaction could be a practical and effective synthetic route for the industrial production of Na2FePO4F/C material.