Research On The Design And Electrochemical Performance Of Composite Nanomaterials

Energy shortage and environmental pollution have greatly accelerated the development of green energy and energy storage technologies.Lithium-ion batteries are considered to be one of the best conversion and storage devices for various clean energy sources which have the advantages of high energy density,long cycle life,no memory effect,and environmental friendliness.Graphite-based materials are widely used as anode materials in commercial lithium-ion batteries.However,the low theoretical capacity（372 mA h/g）limits their use in electric vehicles and solar energy storage devices.Therefore,it is of great significance to find electrode materials with high reversible capacity and long cycle life.High-capacity transition metal oxides,transition metal sulfides,and tin-based materials have become research hotpots in lithium-ion battery anode materials.However,their large volume expansion and poor electrical conductivity have seriously hindered their practical application.Herein,we aim at the current problems of anode materials for lithium ion batteries and design various structures to prepare the corresponding nanocomposites,and also study their electrochemical properties.The work carried out in this thesis mainly includes the following aspects:（1）In₂S₃ nanosheets were grown on nitrogen-doped carbon nanorods by hydrothermal method to form In₂S₃@N-Carbon nanocomposites.In₂S₃@N-Carbon maintained a capacity of 485 mA h/g after cycling 200 times at a current density of 0.1 A/g,which was significantly higher than that of pure In₂S₃（34.6 mA h/g）.The enhanced electrochemical performance of In₂S₃@N-Carbon is attributed to the addition of nitrogen-doped carbon,which improves the conductivity of the electrode and eases the volume expansion of the electrode material.（2）The structure of sandwich carbon/tin/carbon（C/Sn/C）hollow spheres was designed using the template method.The structure effect of the novel carbon/Sn/carbon spheres on the lithium storage performances is elucidated by various means of characterization and electrochemical tests.C/Sn/C can maintain a capacity of 1100 mA h/g after 130 cycles at a current density of 0.1 A/g,which is significantly higher than Sn/C（187 mA h/g）.In addition,the high capacity of 430 mA h/g is maintained at a current density of 5 A/g.C/Sn/C hollow spheres have excellent electrochemical performance.This is due to the unique nano-constraints of the double-layered carbon shell,which has good structural stability,and the lithium plutonium capacitor energy storage also plays a role.（3）A multilayer nitrogen-doped carbon-coated Fe₃O₄/graphene nanosheet（N-carbon/Fe₃O₄/graphene）structure was designed by hydrothermal method combined with heat treatment.When evaluated as a negative electrode,the N-carbon/Fe₃O₄/graphene nanocomposites demonstrate greatly enhanced electrochemical properties compared with Fe₃O₄/graphene.The N-carbon/Fe₃O₄/graphene presents a superior reversible capacity（807mA h/g）over Fe₃O₄/graphene（540 mA h/g）.In addition,the capacity of 550 mA h/g is maintained after 700 cycles at a current density of 1 A/g.Structure-property correlation studies show that carbon riveted layers play an important role in improving the diffusion kinetics of lithium,and effective structural design promotes good electrochemical performance.（4）The TiO₂@Void@SnO₂ nanotubes were prepared by a combined method of hydrothermal process and atomic layer deposition.Compared to SnO₂（210 mA h/g）and TiO₂@SnO₂（637 mA h/g）,TiO₂@Void@SnO₂ has 798 mA h/g after 100 cycles at a current density of 100 mA/g,and superior rate performance（up to 550 mA h/g at a current density of 1 A/g）,electrochemical tests show that TiO₂@Void@SnO₂ has better performance than TiO₂@SnO₂ and SnO₂ due to its unique structural advantages.The double-layer hollow structure can adapt to volume changes and prevent SnO₂ from crushing.TiO₂ can limit the movement of SnO₂ and produce surface protection to stabilize the structure.The results of this thesis provid effective strategies for the nanostructure design of high-performance electrode materials for lithium-ion batteries in the future.