Controllable Preparation And Energy Storage Properties Of Transition Metal Chalcogenide Materials

The rapid development of clean,safe and efficient energy storage system is considered as one of the necessary ways to control energy consumption and carbon dioxide emissions during the"14th Five-Year Plan"period.Since the first commercial lithium-ion batteries(LIBs)was invented by Sony in 1991,they have dominated people's everyday lives from 3C products to the electric vehicles,and then to large-scale energy storage.However,as the rapid development of economy and society,the price of LIBs is unavoidably increasing due to the limited resrouces and uneven distribution in the earth.In comparison with lithium,sodium possesses similar physical and chemical properties,more abundant resources,and potentially low cost.Especially,sodium ion batteries(SIBs)share the identical rocking-chair mechanism as LIBs,which means that the fruitful research experiences obtained from LIBs in the past thirty years could be used in developing SIBs.More importantly,the commercially used electrode material production equipment in LIBs can also be applied in assembly of SIBs,which will greatly reduce the manufacture cost of SIBs.Based on the above-mentioned merits,SIBs might be an ideal choice for large-scale energy storage system.Apart from the organic SIBs,the aqueous Zinc ion batteries(AZIBs)also demonstrates the advantages of high safety,low price,environmental friendliness and easy manufacturing,which attracts much attention in recent years.Tought the great achievements obtained,these two systems have to face the challenges of exploiting high-performance electrode materials to meet the ever-growing demand for better capacity and rate capability.Among potential electrode materials,transition metal chalcogenides have attracted wide attention due to their excellent physical and chemical properties.In this thesis,we select transition metal chalcogenides as the research object and design several kinds of transition metal chalcogenidesto satisfy the requirements of different storage systems for better electrode materials.We also develop a variety of effective strategies to enhance the electrochemical performance which lays a theoretical foundation for further application.The main conclusions can be summarized as following:Firstly,we prepare VS₂nanosheets with flower-like morphology by hydrothermal method.Via optimization of ether-based electrolyte and decreasing the lowest voltage to 0.3 V,VS₂ could deliver a reversible specific capacity of 600 m A h g^-1,two sodium ions insertion and extraction,which is much better than that of using carbonate-based eletrolyte(?250 m A h g^-1).Furthermore,the anode delivers an improved rate capability with capacity rentention of 277 m A h g^-1 at a high current density of 20 A g^-1 owing to the unique flower-like morphology with high contact area between the VS₂ and electrolyte,The kinetics analysis suggests that the high rate performance can be attributed to the contribution of intercalation pseudocapacitive.Secondly,we successfully synthesize the pine-needle-like CuS assembled by the cross-linked nanotubes via condensation reflux method together with their sodium ion storage properties and working principle.The proposed synthesis method owns the merits of low heat consumption,short preparation period and low cost.Benefiting from the high specific surface area,CuS provide a reversible specific capacity of520m Ah g^-1 and high capacity rentention of 90%after 100 cycles,which is better than irregular-shaped CuS particles(370 m A h g-1).In addition,the as-preared CuS belongs to covellite phase exhibiting high electronic conductivity.At a current density of 20 A g^-1,the reversible capacity is achieved as 317 m A h g^-1.DFT calculation further elucidate the intrinsic metallic behavior before and after the adsorption of Na atoms.Thirdly,as is known to all,transition metal sulfides is unstable in water and not suitble as the electorde material for aqueous ion batteries.We,for the firs time,find that VS₂ is spontaneously oxidized in aqueous environment.We take advantage of this shortcoming to prepare the VS₂/VO_x heterostructure via the in-situ electrochemical oxidation,and evaluate its Zn²⁺and NH₄⁺ion storage properties.The reversible specific capacity is achieved as 300 m A h g^-1 at the current density of 0.05 A g^-1.And even the current density increases to 10 A g^-1,VS₂/VO_x heterostructure could still deliver a capacity of 150 m A h g^-1.Morover,when being applied in an ammonium ion battery,the reversible capacity is 150 m A h g^-1at 0.1 A g^-1,higher than that of reported NH₄⁺ion storage materials.In addition,we found that the generation of ionic bonding is responsible for the excellent performance of ammonium ion storage.Finally,we use the in-situ electrochemical oxidation method to generate more electrochemical acive sites in the bulk phase of V₂O₃ and obtain V_2-xO₃ with cation defects.When V_2-xO₃ is employed as the cathode for aqueous zinc ion battery,the reversible specific capacity can reach 515 m A h g^-1at the current density of 0.05 A g^-1,much higher than that of V₂O₃(100 m A h g^-1).When in an aqueous ammonium ion battery,the reversible capacity is 300 m A h g^-1 at 0.1 A g^-1,the highest among reported ammonium ion storage materials.In addition,the introduction of defects could improve the ability of ion transport and accelerate the reaction kinetics,the excellent rate performance is achieved.The fabrication of defects through in-situ electrochemical oxidation provides a new way to solve the problem of low capacity of transition metal chalcogenides.In summary,in this thesis,we develop several kinds of transiton metal chalcogenides with excellent electrochemical performance.We propose a series of strategies such as in-situ electrochemical oxidation to construct the heterostructure,defect engineering and regualtion of state of charge to realize the effective improvement of electrochemical performance.We also reveal the ion storage process and working mechanism.Our work can provide a theoretical basis and guidance for the application of transition metal chalcogenides.