Characterization And Preparation Of Na₂FePO₄F Cathode Materials

Lithium-ion battery is a new type of secondary batteries developed during 1990's. Rapid progresses have been made in the research on lithium ion batteries due to its superior properties for recent years. As a new energy sources, lithium ion battery has the problem of high price and security trouble, while sodium ion battery prevails over it due to its low cost and excellent security performance, so sodium ion battery will be an attractive potential substitution for lithium ion battery. As we know the excellent performance of sodium ion battery depends deeply on the different type and preparation of anode/cathode material. While the effective research on anode material has already been done, study of cathode material with good electrochemical performance has become a key factor. In this thesis, The physical properties of a series of Na2FePO4F cathode materials synthesized by various routes are instigated and discussed in the light of structural (XRD), thermal (DTA) analyses and particle size distribution. Their microstructures were studied by transmission electron microscope (TEM) and scan electron microscope (SEM). The electrochemistry property were evaluated with cells containing the synthesized Na2FePO4F as positive electrode.The Na2FePO4F cathode materials for sodium ion battery were prepared by solid state reaction and the influence of synthesizing temperature and morphology on the electrochemical performance of Na2FePO4F powders in sodium ion batteries were systematically studied. The results indicate that Na2FePO4F synthesized at 750℃exhibited good electrochemical performance, whose first specific discharge capacity is 60mAh/g, after 20 times cycling, the average specific discharge capacity is 51.1mAh/g. Then we prepared Na2FePO4F cathode material coated with carbon by solid-state reaction. As cathode material, the first discharge capacity is 111mAh/g and the capacity reduces to 102.1mAh/g after 20 cycles. Ultrafine Na2FePO4F powders synthesized by a sol-gel process also shows a good electrochemical performance. Obviously, it is better than the material prepared by solid-state process: the first discharge capacity is 91mAh/g, after 20 cycles the specific capacity is around 81.71mAh/g. Besides, we tried to prepare arrays of nanowires using AAO...