Study On Lithium-ion Battery And Photocatalytic Properties Of SnS₂-based Composite Materials

In recent years,all kinds of environmental problems such as global warming,the fog haze,environmental pollution,energy shortage have severely affected on people's lives,the excavation and research of clean energy become very necessary such as solar energy,wind energy etc.Lithium-ion batteries have many advantages such as high voltage,long cycle life,small self-discharge,no memory effect,safety,low environmental pollution,light weight and flexible design,and are widely used in mobile devices,mobile phones,laptops,portable small appliances,smart grids,aeronautic and aerospace engineering and electric vehicle power field.Photocatalysts have attracted widespread attention due to their strong redox ability,ability to degrade organic contaminants,reducing heavy metal chromium,without secondary pollution,and direct use the sunlight,which can contribute to solving environmental pollution,cause researchers's attention.Two-dimensional transition metal dichalcogenide compounds?TMDCs?are an emerging class of materials,they have highly attractive due to its special properties such as narrow band gaps and excellent mechanical properties make them useful to fundamental research and many other applications for nanomaterials as lithium ion batteries,photocatalytic materials,etc.Tin disulfide is composed of two layers of sulfur atoms sandwiched by a layer of tin atoms.The layers are covalently bonded and connected by van der Waals forces.The typical CdI₂-type layered structure has a wide range of application prospects,it can be used not only in the field of lithium-ion batteries,also be applied to photocatalysis,super capacitors,biosensors,and other fields.As lithium ion battery anode material,tin disulfide due to its special transformation reaction and alloying lithium storage mechanism,showing a high theoretical specific capacity,but different raw materials,the preparation technology of reaction conditions and electrode materials will affect the structure,size and morphology,the conductivity of the material is poor and big volume expansion in the process of charging and discharging,thus restricting its electrochemical performance.As a photocatalyst,tin disulfide has a narrow band gap of 2.2 eV and can be directly excited by visible light,but its high rate of electron-hole pair recombination and certain photo-corrosion limits its photocatalytic performance.Therefore,this thesis around tin sulfide to prepare tin disulfide matrix composite material by manipulating different technology,realized the controllable synthesis of material,and through the X-ray diffraction?XRD?,field emission scanning electron microscope?FE-SEM?,transmission electron microscope?TEM?,Raman spectra?Raman?,and other test to probe into the relationship of its phase composition,the material size and morphology.At the same time,the coin cell were assembled using the as-prepared sample as the active material,and through galvanostatic charge-discharge test,cyclic voltammetric curves?CV?and electrochemical impedance?EIS?test to explore the relationship of its composition,its structure structure and its electrochemical performance;as a photocatalyst,the relationship between its photocatalytic performance and its constituent structure is explored through photocatalytic test and mechanism analysis.?1?The nanoflakes self-assembly SnS₂/Ti O₂ hollow microspheres were prepared using the simple one step hydrothermal method without surface active agent.And explore the impact on the product morphology structure and electrochemical properties.It was found that the three dimensional Ti O₂/SnS₂hollow structure with a diameter of 1.5-2.0?m.To the rate performance test,the reversible discharge specific capacity is still reached to 180 mAh g^-1 at current density of 1000 mA g^-1,it also show superior electrochemical performance based on the cycling stability,retaining 180.8 mAh g^-1 after 200 cycles at the current density of 100 mA g^-1 and the first discharge specific capacity is 449.1 mAh g^-1.?2?With stannic chloride pentahydrate,thioacetamide and a certain amount of carboxyl carbon nanotubes as raw material,ethanol as the solvent,using the solvothermal approach to prepared tin disulfide package of carbon nanotubes?CNTs@SnS₂?composites,and the diameter of CNTs@Sn S₂ composite materials is bigger than the CNTs,this phenomenon show the formation of the core-shell structure.And explore the influence on the electrochemical properties caused by different addition content of carbon nanotubes,found that when the addition amount of carbon nanotubes was 1.0 mg mL^-1,the electrochemical performance is relatively excellent.The discharge specific capacity of CNTs@SnS₂ composite were 610,445,380,319,268 mAh g^-1 at current density of 100,200,300,500,1000 mA g^-1,respectively.After the charging and discharging of the large current density,the cycles can be carried out on the condition of the current density of100 mA g^-1,and the discharge specific capacity of CNTs@SnS₂ composite can still be maintained at 591 mAh g^-1.Under the condition of current density of 100mA g^-1,the reversible discharge specific capacity can reach 565 mAh g^-1 after200 cycles.?3?First,with stannic chloride pentahydrate,thiourea as raw material,ethanol as the solvent,using the solvothermal approach to obtain pure flower SnS₂ sample which assembled by a large number of nanoflakes,and put them into the as-prepared graphene oxide?GO?dispersion,the target product samples of SnS₂@RGO is obtained after hydrothermal reaction.And explore the influence of the introduction of graphene on the morphology and electrochemical properties of the products.SnS₂@RGO composite material has excellent electrochemical properties compared to pure Sn S₂.Under the condition of the current density of 100 mA g^-1,the reversible discharge specific capacity is 942mAh g^-1 after 100 cycles,and after the charging and discharging of large current density of 1000 mA g^-1,then return to current density for 100 mA g^-1,the reversible capacity can reach 689 mAh g^-1.?4?A simple in-situ hydrothermal method was used to synthesize SnS₂/reduced graphene oxide?SnS₂/RGO?by adding tin tetrachloride and thiourea pentahydrate in the presence of a previously prepared graphene oxide dispersion.Sn S₂/RGO nanocomposites were used as photocatalysts to test the photocatalytic reduction of hexavalent Cr?VI?aqueous solution under visible light.The Sn S₂ hexagonal nanosheets are evenly distributed on the graphene sheet and there is no obvious agglomeration phenomenon.The graphene is in the form of a thin yarn,and the SnS₂ hexagonal nanosheets are connected,and the two become three-dimensional connected systems,and the graphene can accelerate the rapid electron transfer.Promote the separation of electron-hole pairs.SnS₂/RGO nanocomposites exhibited better visible light photocatalytic activity than pure phase SnS₂ and became a promising photocatalyst for the photocatalytic reduction of heavy metal Cr?VI?.?5?SnS₂/TiO₂ nanocomposites have been synthesized via microwave assisted hydrothermal treatment of tetrabutyl titanate in the presence of SnS₂nanoplates in the solvent of ethanol at 160?for 1 h.The physical and chemical properties of SnS₂/TiO₂ were studied by XRD,FESEM,EDS,TEM,XPS and UV-vis diffuse reflectance spectra?DRS?.The photocatalytic activity of SnS₂/TiO₂ nanocomposites were evaluated by photoreduction of aqueous Cr?VI?under visible light??>420 nm?irradiation.The experimental results showed that the SnS₂/TiO₂ nanocomposites have excellent photocatalytic reduction properties of Cr?VI?aqueous compared with pure TiO₂ and SnS₂.The reduction efficiency of SnS₂/TiO₂ nanocomposites reaches⁸7%under irradiation of visible light for 150 min.?6?Three-dimensional Ag₂O and Ag co-modified flower-like SnS₂composites have been prepared by a simple hydrothermal method and photoreduction method.The physicochemical properties of three-dimensional Ag₂O and Ag-modified flower-like SnS₂ composites were carefully characterized by X-ray diffraction?XRD?,scanning electron microscopy?SEM?,transmission electron microscopy?TEM?,UV-visible diffuse reflectance spectroscopy?DRS?and X-ray photoelectron spectroscopy?XPS?.The photocatalytic performance of the as-prepared products was evaluated by decolorization of Rhodamine B solution aqueous at ambient temperature under simulated sunlight exposure.The photocatalytic results show that Ag₂O and Ag co-modified flower-like SnS₂composites have better photocatalytic activity than that of pure SnS₂.Three components of Ag₂O and Ag co-modified the flower-like Sn S₂ composites form the Z-type system.Because of its unique carrier transfer process,the redox potential of photogenerated electrons and holes can be improved.Therefore,the new Ag₂O and Ag co-modified flower-like SnS₂ composites have excellent photocatalytic properties and are expected to become reliable materials for degradation of organic pollutants in solar energy conversion process.