| Lithium-ion batteries(LIBs),a kind of important energy storage devices,have been widely used on portable devices because of their high energy density and long cycle life.With the rapid development of electric vehicles and smart grids,the demand for LIBs with better performance is becoming more and more urgent.The anodic material is one of the core components of the LIBs,which directly influences the electrochemical performance of the whole battery.As a branch of the negative electrode material of the LIBs,iron oxides are one of the hottest research materials because of their high theoretical capacities,low costs,rich resources,and pollution-free However,iron oxides anode materials have a large volume expansion in the process of lithium intercalation,resulting in the crushing of the electrode material,which always led to a poor cycle performance.To solve the above problem,we designed the iron oxide/carbon nanocomposite material with the hollow core-shell structure to control the volume expansion of the iron oxide during the charging and discharging process,thereby improving the cycle performance.By using the template method,four nanocomposite materials,including core-shell tubular Fe3O4/carbon,core-shell chain Fe3O4/carbon,double-hollow chain Fe2SiO4/carbon,and core-shell cube Fe3O4/carbon,are prepared,respectively.Compared with the corresponding pure phase materials,the four nanocomposite materials exhibit higher capacity and better cycle stability.In this paper,the specific research contents are as follows(1)The Fe2O3@SiO2@phenolic resin composite was prepared by a hydrothermal method via utilizing Fe2O3 nanotube,tetraethoxysilane(TEOS),resorcinol and formaldehyde as precursors.After the carbonization treatment and the removal of SiO2,the Fe3O4@void@C nanotubular composite was obtained.By controlling the amount of TEOS in the hydrothermal process,the thickness of the SiO2 coating layer could be controlled,and the control of the cavity size could be finally realized.In addition,the influence of the size of the cavity in the composite for the performance of LIBs was studied.The results showed that,when the amount of TEOS is 1.4 mL,the obtained Fe3O4@void@C-1.4 composite had the better electrochemical performance.(2)Using Fe3O4 mesoporous microspheres,TEOS,resorcinol and formaldehyde as precursors,Fe3O4@SiO2@phenolic resin composites were prepared by hydrothermal method After the carbonization treatment and the removal of SiO2;the final product was obtained.The effect of carbonization temperature on the crystal form and structure of the product was studied.The core-shell Fe3O4@void@C chain-like composite was obtained by carbonization at 600?.After the carbonization at 700?,800? and 900?,the composites with double hollow Fe2SiO4@C chain-like structure with different cavity sizes were obtained.With the increase of carbonization temperature,the internal cavity gradually increased,while the external cavity gradually decreased.The properties of the composites as anode materials for LIBs were further studied.The results showed that all the samples showed good cyclic stability.(3)Fe2O3@polydopamine was prepared by using Fe2O3 cubic block and dopamine hydrochloride as precursor.Fe3O4@N-doped C cubic composite was obtained by further carbonization treatment.Finally,the core-shell Fe3O4@N-Doped C-x composites with different cavity sizes were obtained by etching Fe3O4.The effect of pickling time on cavity size was studied.The properties of the composites as anode materials for LIBs were further studied.The results showed that the sample obtained by 2 mol/L HCl etching for 5 hours at 30? has the better electrochemical performance. |
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