Synthesis Of Iron-based Anode Materials With Micro/nano Structure And Their Lithium Storage Performances

Iron-based anode materials for lithium ion batteries has been attracted wide attentions due to its high capacity,rich resource,environmentally friendly property,low cost,etc.However,its low-conductance(comparing to carbon-based anode materials)and high-volume change during charge/discharge cycles results in a bad rate performance and serious capacity fade after long-term cycles.Nano-materials with large specific surface area has been being one of focus of related researches,as it exhibit specific physical and chemical properties.Nano-structural anode materials for Li-ion batteries can improve the electrochemical reactions,shorten the distance of charge and ions transmission,and alleviate volume effect from the intercalation/deintercalation of Li+ ions,which makes nano materials to be one of hot topics.To improved electrochemical performances of iron-based anode materials,a serial of nano-structural anode materials with special morphology has been synthesized,including nano lines,nano needles,nano rods,and nano tubes.However,such material shows some problems while using as Li-ions anode materials.Solid electrolytic interface(SEI)membrane during charge/discharge cycles will cover the surfaces of particles,which leads to a low conductance between the isolated particles.On the other hand,anode materials composed by pure nano-materials shows bad processing properties in fabricating the anode electrode comparing to the corresponding micro-materials.In this paper,flower-like iron-based anode materials(Fe S2,Fe2O3,and Fe3O4)were synthesized by sintering the iron alkoxides precursor with the same nano-structure under the atmosphere of air or N2/H2 S.The as-obtained anode materials possesses high reactivity from nanosheets of iron alkoxides,which can lower the sintering temperature and allow the product to keep the morphology of its precursor.By the way,the as-obtained anode materials with micro/nano-structure could present both high reactivity features of nanomaterials and good processing properties in fabricating the anode electrode like as micro-particles.Therefore,the as-obtained materials shows good electrochemical performances.More details are as follows:(1)Synthesis of Fe S2 with micro/nano structure and electrochemical performances:Three samples of iron/sulfur materials were prepared by sintering the flower-like micro/nano structural iron alkoxides under a mixed N2 and H2 S atmosphere at 300,450 and 800 oC.The results showed the sample sintered at 300 oC was with the structure of Fe S2,which maintained the morphology of iron alkoxides precursor and showed a well crystalline.Sample obtained at 450 oC was also with the structure of Fe S2.The surface of nanosheets within the sample exhibited a porous structure and the sample showed a well crystalline.Unfortunately,sample sintered at 800 oC was proved to be Fe9S10,which no longer possessed the original flower-like micro/nano structure of iron alkoxides precursor.Moreover XRD pattern of Fe9S10 showed an obviously low signal-to-noise ratio.Results of electrochemical tests showed that Fe S2 obtained under 300 oC exhibited an initial discharge capacity of 1484.3 m Ah g-1 at 200 m A g-1,higher than that of the other samples at 450 and 800 oC(1326.7 and 934 m Ah g-1).More importantly,after 100 times charge/discharge cycles(200 m A g-1),sample prepared under 300 oC showed a discharge capacity of 480.8 m Ah g-1,which was high than that reported in literature for pure Fe S2 sample,and almost the same as that of Fe S2/C composite.The value was far more than that of the other two samples(215.8 and 89.7 m Ah g-1).(2)Synthesis of Fe2O3 with micro/nano structure and electrochemical performances:Fe2O3 samples were prepared by sintering the flower-like micro/nano structural iron alkoxides under air at 300,450 and 800 oC.The XRD patterns showed all sintered samples were Fe2O3.The sample obtained at 300 oC could maintain the morphology of iron alkoxides precursor and showed a well crystalline.Sheet surface of Fe2O3 obtained at 450 oC exhibited a porous morphology.This sample showed a better crystalline but a lower signal-to-noise ratio comparing to the sample at 300 oC.Unfortunately,sample sintered at 800 oC was not possess the original flower-like micro/nano morphology of iron alkoxides precursor any more,and the XRD pattern showed a very low signal-to-noise ratio.Results of electrochemical tests showed that Fe2O3 obtained under 300 oC presented an initial discharge capacity of 1360.2 m Ah g-1 at 200 m A g-1,which a little lower than that of the samples at 450 and 800 oC(1411.6 and 1429.8 m Ah g-1).But after 100 times charge/discharge cycles(200 m A g-1),sample prepared under 300 oC showed a discharge capacity of 515.6 m Ah g-1,which was much high than that of the other two samples(247.6 and 206.7 m Ah g-1).(3).Synthesis.of.Fe3O4.with.micro/nano.structure.and.electrochemical.performances:Three samples of iron oxides were prepared by sintering the flower-like micro/nano structural iron alkoxides under N2 atmosphere at 300,450 and 800 oC.The XRD patterns proved that the sample sintered at 300 oC was still with the structure of Fe2O3,and the other two samples were Fe3O4.The Fe3O4 sintered at 450 oC could maintain the morphology of iron alkoxides precursor and sheets of sample were porous shape.Sample sintered at 800 oC was not possess the original flower-like micro/nano morphology of iron alkoxides precursor any more.Results of electrochemical tests showed that Fe3O4 obtained under 450 oC presented an initial discharge capacity of 1050.7 m Ah g-1 at 200 m A g-1,which a little lower than that of the samples at 800 oC(1159.3 m Ah g-1).But after 100 times charge/discharge cycles(200 m A g-1),sample prepared under 450 oC showed a discharge capacity of 505.2 m Ah g-1,which was much high than that of the sample at 800 oC(140.3 m Ah g-1).