Study Of The Lithium Storage Performance Of Several Chalcogenide/rGO Composites

Lithium-ion batteries(LIBs)have been widely used in portable devices,electric vehicles,military equipment,etc.Typically,graphite is used as a commercial LIB anode material.However,the low theoretical capacity of graphite(372 m Ah g^-1)can't meet the demand for small volume and large capacity storage devices.Therefore,it is necessary to develop new anode materials with high energy density,high power density and good cycle stability.In recent years,metal chalcogenides(MCs)as LIB anode materials have attracted extensive attention;for instance,Cu S,SnS₂,Fe S₂,In₂S₃,Mo S₂,and Co Se_x all show good lithium storage performance.MCs as LIB anode materials not only have the high theoretical capacity,but also may be low-cost and simply synthesized.However,there are still some problems for MCs as the anode materials for LIBs that need to be solved.For instance,there will be a large volume change during the charge and discharge process which will cause the capacity to decay rapidly,while the poor conductivity will lead to poor rate performance.To overcome these problems,the researchers have proposed some solutions,that is,synthesizing nanostructures with special morphologies,compositing with carbon materials,and heteroatomic doping.Among all kinds of reported nanomaterials as LIB anode materials,small-sized nanomaterials are unique since they have more active sites and provide the short diffusion path of Li⁺which is conducive to high power charge and discharge.However,small-sized nanomaterials are prone to agglomeration,which will lead to faster capacity decay.In this thesis,two types of stable,high-yield metal-containing ionic liquids(MILs)are used as the precursor,namely metal-chalcogenide-based and metal-halide-based ionic liquids,which play multiple roles as the reactant,stabilizer,and nitrogen and metal source.The nanocomposites of MC and reduced graphene oxide(rGO)are synthesized,that is SnS₂@rGO,In₂Se₃@NG(NG is N-doped rGO)and Zn S-NDs@SNG(SNG is S,N-co-doped rGO).The prepared materials are characterized by PXRD,TGA,TEM and XPS,etc.and the properties of as-prepared LIB electrodes were tested.Compared with conventional inorganic salt metal sources,MIL as the assembly medium can provide supramolecular interactions such as C-H··?that are beneficial to the formation of a special interface between MC nanoparticles and graphene oxide(GO).Thus,their effective combination is realized which is conducive to obtaining high performance lithium electrode materials.The research findings covered in this thesis include:Chapter 2 describes the preparation and lithium storage performance of SnS₂@rGO composites.By mixing tin powder,sulfur powder and ionic liquid(IL)at a certain molar ratio,a tin-based MIL was prepared by microwave-assisted ionothermal method which was used as the precursor for preparing the composites of?5 nm SnS₂ nanoparticles attached to rGO.The as-made LIB anodes show good cycling and rate performance with specific capacity of 1045.8 m Ah·g^-1 after 700 cycles at a current density of 500 m A g^-1.Chapter 3 reports the preparation of In₂Se₃@NG electrode and the study of their lithium storage performance.In order to verify whether the above method is applicable to other materials,e.g.,In₂Se₃,which has never been applied in LIBs,was selected.Firstly,the indium containing precursors were prepared,and the In₂Se₃ content in the composite was adjusted according to the addition of different amounts of precursors.After heat treatment,the In₂Se₃ and N-doped rGO composite materials were successfully prepared,which as the anode material shows a high reversible capacity and excellent cycling performance.Its discharge capacity is still 673.7 m Ah g^-1 after 1000 cycles at 5000 m A g^-1.This is the first time that In₂Se₃ has been used in LIB anodes.Chapter 4 describes the preparation and lithium storage performance of Zn S-NDs@SNG composite.The composite was prepared by using MIL[HMMIm][Zn Cl₄]([HMMIm]=1-hexyl-2,3-dimethylimidazolium)as the precursor,in which no organic solvent was used.Zn S nanoparticles are attached to N,S co-doped rGO in Zn S-NDs@SNG,while the material prepared without MIL shows the morphology of microspheres.Compared with other reported Zn S-carbon composites,Zn S-NDs@SNG shows outstanding cyclic properties and high capacity.At the high current density(10000m A g^-1),its specific discharge capacity can still reach 648.1 m Ah g^-1 after 5000 cycles.The work in this thesis expands the application of ionic liquids in the synthesis of inorganic functional materials.