| With the rapid development of science and technology,the lithium-ion battery composed of traditional graphite negative electrode(specific capacity 372 m Ah g-1)has gradually failed to keep up with the trend of the times.Iron-based VIA compounds have became valuable candidate materials because of their environmental friendliness and high theoretical capacity.However,in the process of assembling it into lithium-ion battery,the performance of the battery is not satisfied because of its own defects,such as poor conductivity,serious volume expansion and so on.In order to better apply it,compounding with carbon materials is a good choice,which is not only from a wide range of materials,cheap,but also improve the lithium properties of iron-based VIA compounds.In this study,iron-based oxides,iron-based sulfides and iron-based selenides were prepared and compounded with carbon materials.The morphology of the samples was analyzed by scanning electron microscope(SEM)and transmission electron microscope(TEM),the structure and composition of the samples were tested by X-ray diffraction(XRD)and X-ray photoelectron spectroscopy(XPS),and the best lithium storage conditions were explored.The specific research contents and results are as follows:(1)Using fumaric acid,Fe(NO3)3·9H2O as raw materials,MIL-88A MOFs,was synthesized by hydrothermal method and Fe/C composite was obtained by carbonization.Then mixed with selenium powder in hydrazine hydrate,the internal Fe of Fe/C was replaced to the surface by the generated Se2-,and then calcined again to obtain the composite sample of Se-doped carbon-supported Fe3O4 particles(C/Se-L-Fe3O4).The morphology and lithium electric properties of C/Se-L-Fe3O4 samples prepared at different calcination temperatures are different.When the calcination temperature is 600?,the performance of C/Se-L-Fe3O4 sample is the best.Under the condition of 1A g-1,it still has excellent capacity(942.2 m Ah g-1).This is due to the unique corn-shaped structure of the material and the good conductivity of Se-doped C.(2)Graphene oxide was synthesized by modified Hummers method,and then spherical FeS was grown on graphene sheet by hydrothermal method using Fe(NO3)3·9H2O and thiourea as raw materials and using CTAB as surfactant.The prepared FeS/rGO composite structure not only has excellent specific capacity but also shows excellent cycle stability.In this paper,the effects of the amount of graphene and CTAB on the morphology and lithium properties of the samples were discussed systematically.The experimental results show that CTAB acts as a cationic surfactant,which makes FeS grow uniformly on negatively charged graphene,and 60 mg graphene is the best dosage.The initial capacity of the first lap is 1000m Ah g-1(1A g-1).After 1100 laps,the specific capacity increases to 1300 m Ah g-1 and CE is close to 100%.Compared with the samples with uncompounded graphene and other graphene contents,the lithium-ion kinetic characteristics of FeS/rGO-60 have obvious advantages.(3)Cd-doped FeSe/C-N composites were prepared by sol-gel method.Using PVP as sol-gel material,adding certain quality of Fe(NO3)3·9H2O and Cd(NO3)2·4H2O to it,Cd-doped Fe3C/C-N was obtained by high-temperature calcination after evaporating water,and then Cd-doped FeSe/C-N composites were obtained by adding selenium powder to the tube furnace.In this dissertation,the effects of different Cd doping amount on the morphology and lithium electric properties of FeSe/C-N were studied.The results show that when the mass of Cd(NO3)2·4H2O is 0.4 g,the morphology of the sample is the best.Tested at 2 A g-1 current density,the capacity is increased to 745 m Ah g-1 after 550 laps,and the Coulomb efficiency is close to 100%.Even if the current increases to 5 A g-1,it still has the specific capacity of 438.8 m Ah g-1.Compared with the samples without Cd,the lithium-ion kinetic characteristics of Cd-doped FeSe/C-N have obvious advantages. |
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