The Research On Metal Sulfides Of Anode Materials For Sodium-ion Battery

Lithium-ion batteries?LIBs?have been widely used in portable electronic devices such as mobile phones,tablets and notebook computers for the past 20 years due to its high energy density,environmental friendliness and long cycle life.According to lithium resources are mainly distributed in the Americas,the crustal reserves are low and the price is expensive,it is difficult to meet the people's growing needs of life.At the same time,the sodium and lithium have similar physical and chemical properties because of in the same group.Due to the sodium reserves are very rich and low price,sodium-ion batteries?SIBs?have received widespread attention.Electrode materials is one of the most critical factors for building high performance sodium-ion batteries.In recent years,two-dimensional layered transition metal sulfides have attracted great interest in energy storage.Such materials have a layered structure similar to graphite:they are joined by covalent bonds within the layers,and the layers are connected by weak Van Der Waals Forces.Our thesis mainly focuses on the preparation,structure,morphology and composition of transition metal sulfides and their composites,and further studies their electrochemical properties and the Na storage mechanism as electrode materials for sodium-ion batteries.The specific work includes the following parts:1.The flower-like Sb₂S₃/PPy spheres were synthesized by solvothermal method.Due to the radius of sodium ion is much larger than lithium ion,the sodium ion intercalation and deintercalation in the process of charge and discharge has a great damage to the material structure,and the conductivity of pure Sb₂S₃ is not well.It is coated with a layer of conductive polymer polypyrrole on the surface of the material in order to improve the conductivity and cycle stability.From the electrochemical data,it can be concluded that the flower-like Sb₂S₃/PPy spheres material can exhibit a high specific capacity as SIBs anode.In addition,the specific capacity of flower-like Sb₂S₃/PPy spheres can reach 236 mAh g^-1 at the current density of 800 mA g^-1,showing an outstanding electrochemical performance and cyclic stability.2.Mn-MoS₂ nanotubes were synthesized by self-assembly solvothermal method.The effects of different solvents and different solvent time on the morphology of the materials were investigated.The product synthesis mechanism of the structure by control the reaction time?1 h,4 h,8 h?was tested by the XRD and TEM.These Mn-MoS₂ nanotubes have a large specific surface area and an open two-dimensional structure,whcih can provide more sodium ion deintercalation sites and increase the contact area with the electrolyte.As an anode electrode material of SIBs,it exhibits high specific capacity,outstanding cycle stability and excellent rate characteristics.We also measure CV curves to calculates the sodium ion diffusion coefficient to determine the capacitance behavior.3.The core-shell structure of binary metal sulfide--CuCo₂S₄ was also obtained by solvothermal method.It is found that the formation and growth process of the core-shell structure are closely related to the reaction time of the precursor,so we discuss the growth mechanism of the core-shell structure CuCo₂S₄.When it was used as the anode for SIBs,the electrochemical performance was not satisfactory.Therefore,we explored the electrochemical performance of LIBs.Through the electrochemical meatures,the porous core-shell CuCo₂S₄ material has good electrochemical performance and cycle performance,the specific capacity can be obtained of 773.7 mAh g^-11 at the current density of 1 A g^-1 after 1000 cycles,Even at a high current density of 10 A g^-1,the specific capacity is 358.4 mAh g^-11 after 1000cycles.These good electrochemical properties are due to its unique porous core-shell structure in LIBs.4.Nanoporous CuO/Cu composites were successfully prepared by de-alloying method.This nano-porous structure can provide a large number of active reaction sites for Na⁺and shorten the diffusion migration path of Na⁺.Nanoporous CuO/Cu composites have good electrical conductivity.The nanoporous structure is a continuous channel of about 20⁵0 nm,which can effectively maintain the volume expansion during the Na⁺insertion/extraction process,and shorten the Na⁺diffusion path.All above mentioned in order to improve Na⁺storage capacity.Moreover,the nanoporous structure can improve its contact area with the electrolyte.When used as the anode of sodium ion battery,the CuO/Cu initial specific capacity is 580 mAh g^-1at a current density of 500 mA g^-1.After 200 cycles,it can maintain a specific capacity of 200 mAh g^-1,which can be used as a better anode material for sodium ion batteries.