The Preparation And Application Of Nanostructured Fe₂O₃/Carbon Composites For Lithium Ion Batteries

Rechargeable lithium ion batteries as the most potential energy storage equipment with the advantages of large capacity,long life,low self-discharge rate,are gradually loved by the public.However,the low theoretical capacity(372 mAh g^-1)and working voltage of commercial graphite electrode have limited its application.Graphene and carbon nanotube electrode materials have been studied and reported,but their capacity is still low.Fe₂O₃ as a clean and non-pollution new energy material,has the advantages of a high theoretical capacity(1005 mAh g^-1),low price and high corrosion resistance,but also has its own shortcomings of volume expansion,agglomeration,rapid decay of lithium storage capacity and poor conducticity during the cycle process.To slove this problem,based on the strategy of compositon control,three types of carbon materials including mesoporous carbon,porous carbon and graphene,were separately synthesized as a kind of substrate to load Fe₂O₃,which can improve the cyclic stability of the electrode materials.1.Fe₂O₃/mesoporous carbon composites were prepared by self-assembly method using F-127 as a pore forming agent.The morphology and structure of the samples were detected and investigated.Mesoporous carbon can supply large specific surface area and pore volume.It was found that Fe₂O₃ with the content of 26.3%?denoted Fe₂O₃/OMCs-1?can be distributed homogeneously in the mesoporous carbon.The electrochemical performance of the composites was tested and found that Fe₂O₃/OMCs-1 is the best.Afer 120 cycles,the capacity can achieve 789 mAh g^-1 and the rate capability is good.Through the data analysis of impedance and equivalent circuit diagram simulation,the behavior of Li⁺and electron transfer process and the growth of SEI film were revealed.It was found that the R_ctt of Fe₂O₃/OMCs-1 was small.2.Fe₂O₃/porous carbon composites were prepared by hard template method with sodium chloride as a pore forming agent.In the process of carbonization,ferrous gluconatecan also be carbonized to form a porous structure,which is conducive to the improvement of specific surface area of electrode materials.The morphology and structure of the sample were characterized and the appropriate oxidation temperature was explored.It showed that Fe can be mostly eliminated from the material at 350?in air while the porous structure can be retained.The electrochemical performance of the materials was tested which showed a high reversible capacityof 1117 mAh g^-1after 120 cycles.In the same way,impedance and equivalent circuit diagram simulation data analysis were performed,and it was found that R of Fe₂O₃/porous carbon composites was small.3.Fe₂O₃/graphene composites were fabricated by precipitation method.The morphology and structure of the samples were characterized which showed that Fe₂O₃particles with size of 30-100 nm were dispersed homogeneously on the graphene layer.Electrochemical test of the material demonstrated that Fe₂O₃/graphene composites delivered a high capacity in the early cycle process.However,with the inrease of cycle number,the capacity reduced gradually.The reason might be related to the accumulation of carbonized graphene layers,which needs further exploration and research.