Synthesis Of ?-?A Group/carbon Nanocomposite Nanostructures And Their Sodium Storage Performance

Energy produce and storage technologies are essential in the daily production and life in modern society.In recent decades,the development of lithium-ion battery?LIB?technology has improved the lives of people,especially in mobile electronics and zero-emission electric vehicles.However,with the increase in the global population,the rapid consumption of limited and scarce lithium resources raises concerns,and it is currently unclear whether lithium-ion batteries alone can meet the growing demand for energy storage applications.To improve these issues,recent research has focused on alternative energy storage systems.Sodium is one of the most abundant elements on the earth.It is chemically similar to lithium,low cost and easy to obtain.Therefore,sodium ion battery?SIB?is considered to be one of the most promising energy storage and conversion equipment.At the same time,progress has been made in finding suitable anode materials for sodium ion batteries,such as carbon materials,alloy materials,and etc.Among them,transition metal chalcogenides have attracted much attention due to their high theoretical capacity,easy availability and environmental friendliness.However,there are also some problems when transition metal chalcogenides are used as anode materials of sodium ion batteries,including the conductivity is poor and the structure is easy to smash during charging and discharging,which brings poor cycle capacity and rate performance.Therefore,it is still a challenge to improve these issues and take advantage of them.This article has made many improvements in response to these issues,including designing reasonable micro-morphology and structure to promote the electron/ion transmission rate,improving its electrical conductivity and increasing specific surface area by combining with carbon materials,and also designing the solid carbon shell to prevent the collapse of the structure,increasing defects and active sites by doping heteroatoms to increase cycle capacity.The content and results are as follows:1.Synthesis of CoTe nanorods/rGO composites as anode materials for SIBs.Transition-metal sulfides and selenides have been widely studied as sodium ion batteries anode materials owing to large theoretical capacity.Nevertheless,tellurides in the same chalcogen group with higher densities and better conductivity are scarcely investigated as an electrode material for sodium ion batteries.In this work,CoTe with different morphologies were synthesized by a facile one-pot solvothermal method.Both the CoTe nanorods/reduced graphene oxide?CTNRs/rGO?composites and the CoTe nanotubes?CTNTs?exhibit an advanced performance for Na-ion storage when used as anode materials for sodium-ion batteries.The electrochemical reaction mechanism of the electrode was revealed by ex-situ X-ray diffraction,high resolution transmission electron microscopy and electron diffraction methods.Particularly,the CTNR/rGO has better performance with specific capacity of 306 m A h g^-1 at 50 mA g^-1 after 100 cycles and capacity of 200 mA h g^-1 even after 200 cycles at 0.1 A g^-1,which attribute to enlarged contact surface area,improved electrical conductivity and higher mechanical strength by hybridizing with rGO.Accordingly,the CTNR/rGO can be considered as promising anode materials for sodium-ion batteries.2.Synthesis of spindle-shaped FeS₂ enwrapped with N/S Co-doped carbon as anode materials for SIBs.Pyrite?FeS₂?has been considered as an attractive anode material for sodium ion batteries?SIBs?,which not only provided with high theoretical capacity but also has features of low cost,rich reserves and environmental benignity.However,the huge volume expansions during a charge/discharge process and unsatisfied conductivity of FeS₂ lead to the rapid capacity fading.Herein,spindle-like double-component composites constructed with FeS₂ core and nitrogen/sulfur co-doped carbon shell?FeS₂@NSC?are synthesized successfully,which can act as efficient anode materials for SIBs.Consequently.the FeS₂@NSC composites exhibit high specific capacity of 571.3,528.6 and 475.9 mA h g^-1 at the current density of 200,500 and 1000 mA g^-1 respectively after 100 cycles.The results demonstrate the strategy of components-structure designing can boost sodium-storage performances.3.Synthesis of spindle-shaped FeSe₂@C nanomaterials as anode materials for SIBs.Designing potential anode materials for sodium ion batteries with high rate and ultra-long cycle performance has attracted the attention of many researchers,and the research of size and morphology is considered to be one of the effective strategies.In this work,the FeSe₂@C composite material with a nano-scale spindle structure was successfully synthesized.After selecting a suitable voltage range and ether-based electrolyte,it showed excellent electrochemical performance as anode material for sodium ion batteries.At high current densities of 2 and 5 A g^-1,the first Coulomb efficiency exhibited 91.9%and 97.3%respectively.Also,the reversible capacity was maintained at 305.3 mA h g^-1 after 800 cycles at 2 A g^-1 and the reversible capacity is still as high as 246.9 m A h g^-1 after 1000 cycles at 5 A g^-1,showing outstanding sodium storage performance.