Synthesis Of Antimony(Sb)-based Anode Materials For Electrochemical Sodium Storage

With the great progress made for Lithium-ion batteries(LIBs)in the past three decades,and the limited global lithium resources,SIBs have been considered promising alternatives to LIBs.At present,it is an urgent demand to find and develop suitable anode materials for the practical applications of SIBs.Recently,antimony(Sb)-based compounds have been becoming a research hotspot because of several advantages when used as the anode materials for SIBs.In this thesis,we have focused on two kinds of Sb-based compounds,Sb₂O₃ and Sb₂S₃,as well as their respective composites in terms of their sodium storage performance.Sb₂O₃ and Sb₂S₃ are considered as promising anode materials for sodium ion batteries due to their low toxicity,abundant resources and high theoretical specific capacity.However,their shortcomings also exist such as low conductivity and large volume change during the sodiation/desodiation progresses.In order to solve these problems,structure design and innovative preparation method were used to synthesize kinds of nanostructures,in addition,a variety of test and characterization methods have been carried out to study the stuctures of these anodes as well as the Na storage performances and Na storage mechanism.The results show that these elaborately designed anodes can effectively improve the Na storage performance of Sb₂O₃ and Sb₂S₃,which will provide efficient approaches to solve the existing problems of Sb-based anode for practical sodium ion battery.The main achievements of this thesis work are as follows:(1)A three-dementional porous composite of Sb₂O₃ and graphene oxide(GO)is synthesized by a simple freeze-drying method.The formed three-dimentional such Sb₂O₃@GO network can not only effectively release the volume variation of Sb₂O₃during the charge and discharge processes,but also improve the conductivity of Sb₂O₃.The initial reversible capacity of Sb₂O₃@GO composite at a current density of 100m A/g is 446.6 m Ah/g,which is higher than the 358.5 m Ah/g of pure Sb₂O₃nanoparticles.The reversible capacity is decreased to 301.3 m Ah/g after 80 cycles with a capacity retention rate of 70.51%respected to the second cycle.Moreover,the rate performance of Sb₂O₃@GO is also better than that of pure Sb₂O₃.The result demonstrates that this compositing strategy can effectively improve the cyclic stability of Sb₂O₃,and the freeze-drying method adopted in this paper can also provide an inspiration for the preparation of Sb₂O₃ based composites.(2)Although the combination of Sb₂O₃ with GO improves the electrochemical performance,the cyclic stability of the anode is still insufficient,which may be due to the fact that the semi-coated structure of Sb₂O₃ by GO fails to effectively release its volume change during charging and discharging.In this section,a carbon coating strategy for Sb₂O₃ particles is developed,and a self-supporting 3D nanofiber network composite structure(Sb₂O₃@C)has been prepared using a simple electrostatic spinning method.The carbon layer can effectively release the volume change of Sb₂O₃ during the charge and discharge processes and improve the conductivity of Sb₂O₃ nanoparticles as well.The Sb₂O₃@C composite shows a discharge specific capacity up to 700 m Ah/g at a current density of 100 m A/g,even at a high current density of 1000 m A/g,a capacity of 259.5 m Ah/g can also be obtained after 1000 cycles with a retention rate of?100%compared with the first cycle at this current.This study demonstrates that the coating strategy can effectively improve the sodium storage performance of Sb₂O₃.(3)Currently,the preparation of Sb₂S₃-based anode materials is limited to the conventional hydrothermal(solvothermal)or solution method,in which toxic or costly reagent is usually involved(such as Na₂S,Sb Cl₃ or thiourea)and additionly,the process is often time consuming.In this study,a novel vaporization-condensation method is successfully developed to prepare nanocomposites between Sb₂S₃ and active carbon(YP80F carbon).During the vaporization-condensation process,Sb₂S₃ can be reformed and confined within the nanopores of YP80F carbon,obtaining a surprising high-performance anode materials(Sb₂S₃@YP samples)for SIBs.the nanopores of carbon can accommodate the large volume variation of Sb₂S₃ during charge/discharge processes and enable a fast electron/Na-ion transfer.One of these Sb₂S₃@YP samples delivers a high capacity of 799.5 m Ah/g at 1162 m A/g and maintains at 476.5 m Ah/g after 1000 cycles(based on the mass of Sb₂S₃).Moreover,this vaporization-condensation method provides a significant strategy for preparing Sb₂S₃-based anode materials for long cycle-life SIBs.(4)In order to overcome the disadvantages of Sb₂S₃ such as poor electrical conductivity and large volume variation during the charging and discharging process,Sb₂S₃ is usually combined with carbon based materials.However,the use of carbon-based materials will reduce the volume and energy density of batteries and promote the growth of metal dendrites,thus increasing the risk of battery short-circuit failure and even fire.Meanwhile,carbon-based materials themselves are relatively flammable,increasing the risk of fire as well.Therefore,reducing the use of carbon-based materials is also a current research hotspot.To solve these problem and improve the Na storage performance of Sb₂S₃,a novel Sb₂S₃/Sn O₂ bundle-like nanocomposite has been synthesized via a facile solution method followed by a hydrothermal process.When used as the anode material for SIB,this material with an unique hetero-nanostructure shows superior electrochemical performance to those of individual Sb₂S₃ and Sn O₂.The Sb₂S₃/Sn O₂ anode shows an initial reversible capacity of 711.4 m Ah/g and remains at 81.9%of the initial performance after 100 cycles at a current density of 50 m A/g.The enhanced performance is ascribed to the unique hetero nanostructure with a synergetic effect between Sb₂S₃ and Sn O₂ in Sb₂S₃/Sn O₂ composite,which can enhance both the electronic and ionic conductivities of the anode and reduce the volume change during the charge and discharge processes.The high electrochemical performance indicates that the combination of Sb₂S₃ and Sn O₂ to form a hetero nanocomposite is a promising strategy for fabricating high-performance SIB anodes.