Synthesis Of C/Fe₃O₄ And Their Applicaton In Lithium-ion Battery Anodes

As potential anode materials, Fe3O4 shows high capacity, low cost, and eco-friendliness, thus has attracted considerable attention. The capacity of lithium storage is mainly achieved through the reversible conversion reaction between lithium ion and Fe3O4: Fe3O4+8Li++8e-?3Fe+4Li2O. Despite those intriguing features, the main obstacle in developing Fe3O4 anodes lies in the severe volume change of Fe3O4 particles during lithium ion insertion/extraction, which can result in pulverization of the initial particle morphology and cause the breakdown of electrical connection of such anode materials from current collectors, thereby leading to poor cycling performance. In order to circumvent the above intractable problems, two typical approaches have been developed. One way is to synthesize nanostructured Fe3O4 materials with porous morphologies, which not only shorter path lengths for the transport of electrons and lithium ions, but also can accommodate the mechanical strain of lithium-ion insertion/extraction. The other promising strategy is to construct hybrid electrodes composed of Fe3O4 and carbon on the nanoscale, which can modify Fe3O4 and lead to good conductivity.Fe3O4 nanomaterials are synthesized with solvothermal and amine thermal combined method, and Fe3O4 with different morphology are prepared by controlling the amount of the proportion of raw material, added water and reaction time. Sphere-like Fe3O4, porous spheres Fe3O4 and nano-porous Fe3O4 are chosed as anode materials of lithium-ion batteries, and the relationship between morphology and electrochemical performance is studied. Reversible specific capacity of Fe3O4 is higher than theoretical specific capacity(926 m Ah/g) at a current density of 50 m A/g. Due to fast attenuation, after 50 cycles, the retention rate of specific capacity is less than 20%.Uniform C/Fe3O4 nanomaterials with different morphology are synthesized with hydrothermal method,and the thickness of the outer carbon shell is 2-5 nm. As anode of lithium-ion batteries, their electrochemical performance is much better than bare Fe3O4. Reversible specific capacity of C/Fe3O4 is more than 1100 m Ah/g at a current density of 50 m A/g. after 50 cycles, the retention rate of specific capacity is 64%. C/Fe3O4 is also synthesized through calcination, which get Fe3O4 with different morphology encapsulated in amorphous carbon. They have good cycling performance and rate performance as anode materials of lithium-ion batteries. C/Fe3O4 synthesized with both methods have better electrochemical performance than bare Fe3O4.Graphene nanosheets(GNs) and Fe3O4 composite materials and GNs/C@Fe3O4 nanocomposite materials are synthesized and applied in lithium-ion battery anodes. Because GNs have a good ability of lithium storage performances, composite materials have high initial capacity than bare Fe3O4. The electrochemical performance of composite materials are better than bare Fe3O4, despite they are not as good as expect.