The Sodium Storage Performance Of Yolk@Shell Structured Titanium Dioxides With Rich Oxygen Vacancies

Sodium ion batteries?SIBs?play a significant role in the field of large-scale energy storage due to the advantages of abundant sodium resources,low cost,and high energy conversion efficiency.Exploiting high-performance SIBs anode materials are the most important things to promote the development of SIBs technology.Titanium dioxide?TiO₂?has plenty of advantages:abundance,low cost,structural stability,safety,and environmental friendliness.For the specific application in SIBs,TiO₂ possesses high theoretical specific capacity,suitable Na⁺accommodation sites,and good cycling stability,which indicate that TiO₂ would be a suitable candidate as an anode material for SIBs.However,the intrinsic electrical conductivity and ion diffusivity of TiO₂ are relatively low due to its semi-conductor properties,which require further optimizations and enhancements of its sodium storage performance.Most of the previous reported methods,including carbon coating and foreign element doping,are tedious and complex.Therefore,it is of great significance to employ a facile and efficient synthetic method to obtain high-performance TiO₂ anode materials.In this thesis,two kinds of sodium ion batteries anode materials including yolk@shell structured anatase TiO₂ microspheres with rich oxygen vacancies(denoted as yolk@shell TiO_2-x)as well as its composites with tin(yolk@shell TiO_2-x/Sn)are designed and synthesized through a facile spray-pyrolysis-assisted method.Afterwards,we characterize the structure and morphology properties of the samples.The sodium storage performance of both two samples are analyzed and studied in detail.The specific research content and results are as follows:?1?Firstly,the TiO₂/C composite microspheres are obtained by spray pyrolysis using the water-soluble titanium?IV?bis?ammonium lactato?dihydroxide?TiBALDH?solution as titanium sources.Then,the TiO₂/C composite microspheres are calcined under air and hydrogen atmosphere successively to produce the final product yolk@shell TiO_2-x.?2?The sodium storage performance of the yolk@shell TiO_2-x anode are tested.The as-synthesized yolk@shell TiO_2-x demonstrates a high reversible capacity(230.7mAh g^-1 after 200 cycles at 50 mA g^-1)and remarkable long-cycling stability(capacity retention of 91.7%after 1000 cycles at 1000 mA g^-1).In the meanwhile,electrochemical measurements?such as electrochemical impedance spectroscopy analysis?and density functional theory calculations are also employed to investigate the influence of the introduction of oxygen defects on the sodium storage performance.And the results reveal that introducing oxygen vacancies in TiO₂ enhances the electrical conductivity,lowers the sodiation energy barrier,and facilitates Na⁺diffusion kinetics.The in-situ XRD,ex-situ SEM and XRD results also prove its structural stability.?3?The composites of yolk@shell TiO_2-x and tin were further designed and synthesized,which are obtained by using the simaliar spray-pyrolysis-assisted methods with adding the tin methyl sulfonate into the precursor solutions.And then we characterize their structure,morphology,and sodium storage performance.The yolk@shell TiO2-x/Sn anode also demonstrates distinct improved cycling specific capacity and stability.When tested at the current density of 100 mA g^-1,the yolk@shell TiO_2-x/Sn electrode performs a high discharge specific capacity of 471.4 mAh g^-1.The electrode can still possess a high specific capacity of²00 mAh g^-1 after 120 cycles.