Synthesis Of Double-Walled Hollow Spherical Tin-Based Anode Materials And Study Of Their Lithium/Sodium Storage Properties

The advancement of society,the depletion of fossil fuels prompts people to focus on green clean energy and efficient energy storage and conversion devices.Since they have a high energy density,a long cycle life,and are eco-friendly,lithium-ion batteries are frequently employed.Sodium-ion battery is considered as a potential substitute for lithium-ion battery because of their lower battery cost and abundant resources.At present,commercial graphite carbon is used as the main anode material because of its good cycle stability and low price.Unfortunately,due to its poor theoretical capacity,its uses are limited(372 mAh g^-1).The tin base material is one of the most potential anode materials because of its high theoretical specific capacity,low price and plenty of reserves.The tin-based anode material has a serious volume effect,and the charging and discharging process will produce a large stress,leading to the structural collapse of the electrode material and affecting its cycle performance.In this paper,three kinds of tin-based anode materials with double-layer hollow spheres structures were designed and synthesized by using the limited domain sacrificial template method.The volume effect of the active material may be substantially reduced by the double-layer hollow spheres construction,which also enhances the battery’s cycle performance.The following are specific research contents:1.Synthesis of double-layer hollow spherical SnO₂@Void@HCSs composites and their lithium/sodium storage propertiesFirstly,by adjusting the concentration of NaOH and the etching time,SiO₂ cores in SiO₂@mesoporous carbon（SiO₂@HCSs）were partially etched to obtain SiO₂ cores of different diameters,and nanogaps were formed between SiO₂ cores and carbon spheres.Then,using SiO₂@Void@HCSs as the precursor and using Na₂SnO₃ as the tin source by the limited domain template sacrifice method,SnO₂ was hydrolyzed to generate SnO₂ and SiO₂ core was etched.The size of the SiO₂ template can be modified.The size controllable SnO₂ hollow sphere can be obtained to construct the double-layer hollow spheres structure with nanovoids SnO₂@Void@HCSs.When SnO₂@Void@HCSs is used as the cathode material for LIBs and SIBs,the discharge capacity is 749.2 mAh g^-1 and 335.6 mAh g^-1,respectively,after 500 cycles at 1 A g^-1 current density.By observing the microstructure changes of SnO₂@Void@HCSs composite material after charge and discharge,the mechanism of lithium/sodium storage of the material was analyzed,and the structural characteristics of the double-layer hollow spheres structure in the process of lithium/sodium storage were expounded.The double-layer hollow spheres structure not only effectively reduces the volume expansion of SnO₂ but also provides active sites with high specific surface area,promoting the movement of ions and electrons.The excellent electrochemical performance shows that the structure has a broad application prospect of energy storage,and provides a useful strategy for the rational design of the double-layer hollow spheres structure.2.Synthesis of double-layer hollow spherical SnO₂/SnS@Void@HCSs composites and their lithium/sodium storage propertiesThe partially vulcanized SnO₂/SnS@Void@HCSs composite with double-layer hollow spheres structure in the previous chapter was obtained by using SnO₂@Void@HCSs composite as the precursor and sulfur powder as the S source under high-temperature calcination in N₂ atmosphere.The composite retains the original double-layer hollow spheres structure,and there are nano-voids between the SnO₂/SnS hollow spheres and mesoporous carbon spheres,which provides the possibility to mitigate the volume effect of the material in the future.The composite performed electrochemically quite well.At 0.1 A g^-1 of current density after 100 cycles,the reversible specific capacity of lithium/sodium storage of SnO₂/SnS@Void@HCSs composite could still reach 939.8 mAh g^-1 and 335.6 mAh g^-1.The material has a high surface area,which speeds up the ion transport rate.The material has a high surface area,which speeds up the ion transport rate.The excellent electrochemical performance of the material is due to the synergistic effect between the construction of the double-layer hollow structures and the ternary composite material,which provides more active sites for Li+/Na+,accelerates the reaction rate,and effectively improves the multiplier performance and cycling performance.3.Synthesis of double-layer hollow spherical SnSe₂@Void@HCSs composites and their lithium/sodium storage propertiesUsing SnO₂@Void@HCSs composite with double wall hollow sphere structure as a precursor and selenium powder as Se source,SnO₂ was in situ derived into SnSe₂ in Ar/H₂ atmosphere.After high-temperature selenizationthe,the SnSe₂@Void@HCSs composite was successfully synthesized by retaining the original double wall hollow sphere structure.When SnSe₂@Void@HCSs is used as the cathode material of lithium-ion battery,the specific capacity of initial discharge and the reversible charge is about 1177.1mAh g^-1,780.8 mAh g^-1,and the coulomb efficiency is 67.4%.When SnSe₂@Void@HCSs is used as the anode material of the sodium ion battery,the specific capacity of the initial discharge first circle is about 792.6 mAh g^-1,and the specific capacity of the reversible charge is 665.3 mAh g^-1.After 500 cycles at current density of 1 A g^-1,the reversible capacity of SnSe₂@Void@HCSs for lithium/sodium storage remained at 434 mAh g^-1 and 370.8 mAh g^-1,respectively.The construction of the double-wall hollow sphere structure and the doping of the Se element not only provide a large activation space and lithium/sodium storage sites,but also provide an effective buffer space for the volume expansion of the material,and effectively improve the cycle stability of the battery.