The Fabrication Of Fe-based Anode Material And Their Applications In Lithium Ion Batteries

With continuous improvement, LIBS have matured and been widely used in various fields. With development in technology, particularly in the field of hybrid vehicles, higher requirements have been proposed. Currently LIBS with the carbon-based material as the anode material can not meet people’s needs. Due to the high theory capacity and fairly security, Fe-based material hasbecome one of the hottest spot of new anode material investigation in recent years. But the severe volume effect of Fe-based material could happen in Li+ intercalation/deintercalation process which caused the pulverization and exfoliation of material, making the performance decay rapidly. Therefore, accompany thevolume and improve the stability of the electrode become the key piont. A large number of study showed that the performance improvement methods of Febased material mainly include preparation of hollow structure, Fe-based alloy material, nano material and composite material. However, the use of any single method can not improved the properties comprehensively, the combination of several methods, combining with other types of materials to constituting the composite material, is expected to achieve a better improvement. Based on the above considerations, the paper is mainly about the designation and modification of Fe₃O₄ from three aspects.（1） Hollow Fe₃O₄（H-Fe₃O₄） microspheres were fabricated through a facile mixed solvent solvothermal synthesis, which was performed in an ethylene glycol（EG）-diethylene glycol（DEG） mixed solvent using polyethylene glycol（PEG） as the stabilizer. The formation mechanism composed of oriented aggregation mechanism and Ostwald ripening mechanism was proposed according to the TEM and SEM analysis. Benefiting from the hollow nanostructures, which could accommodate the volume expansion of active materials, resulting in significantly improved electrochemical performance.（2） we develop a two-step synthesis strategy to fabricate 2D carbon-encapsulated hollow Fe₃O₄ nanoparticles homogeneously anchored on graphene nanosheets（H-Fe₃O₄@C/ GNS）. According to TEM and SEM of the H-Fe₃O₄@C/ GNS composites, we found that hollow Fe₃O₄ nanoparticles homogeneously anchored on graphene nanosheets, which not only improves the electrical conductivity and prevents the severe aggregation, but also assists to accommodate volume expansion. The carbon shell together with the GNS form a double-layer conductive network. The SEI film could rupture due to the catalyzing by the Fe nanocrystals formed during the lithium extraction processes, the presence of the carbon shell allows for the growth of a stable SEI. It shows excellent cycle performances at 1C and 10 C, which could meet the demand better.（3） Mn_xFe_3-xO₄/GNS composite were prepared by one-step galvanic replacement reactions at low temperature. The mechanism of the replacement process was analyzed according XRD and XPS, it shows that the substitute sequence ranges from Mn³⁺ to Mn²⁺ ion, depending on the concentration of Fe²⁺ ion. Benefiting from the hollow nanostructures and small size, it possesses a large specific area, resulting in a higher capacity and stable cycle performance.