Synthesis And Sodium Storage Properties Study Of Ni-Sn @C Nanocomposites

Due to the wide resources and low price of sodium,sodium ion batteries have become the focus of future research on new energy storage devices.Among the many options for anode materials,metallic tin has become one of the research hotspots because of its high capacity.However,metal tin has a large volume change during the sodium ion storage process,which leads to its poor cycle stability.Aiming at this problem,this thesis mainly designs and synthesizes a variety of Ni-Sn@C nanocomposite materials by combining nanomodification,alloying and carbon composite methods to improve the electrochemical performance of tin-based anode materials.The main research content as follows:(1)Using cheap sodium chloride as a template,a simple freeze-drying and low-temperature sintering step was used to successfully synthesize a composite material(Ni₃Sn₂@PNC and Ni₃Sn₄@PNC)with Ni-Sn quantum dots embedded on porous carbon nanosheets.The research results show that Ni₃Sn₄@PNC exhibits high capacity(the specific capacity remains 232.7 mAh g^-1 after 100 cycles at a current density of 100 mA g^-1)and excellent cycle stability(the capacity retention rate reaches 81.6%after 1000 cycles at 400mA g^-1),which can be used as the first choice of Ni-Sn alloy anode material.This work proves that the use of nanomaterials and porous nano-carbon composites can improve the electrochemical performance of Sn-based alloys.(2)The study found that Ni₃Sn₂ material as the negative electrode of sodium ion battery has low capacity and poor stability.Therefore,this paper adopts carbon composite method to improve its electrochemical performance.The composite material(Ni₃Sn₂@C)with Ni₃Sn₂ particles attached to the porous structure of the carbon skeleton was synthesized by simple microwave reaction and low-temperature heating in two steps.As a negative electrode material for SIB,Ni₃Sn₂@C exhibits excellent cycle stability.The first charge reversible capacity is 240.0 mAh g^-1 at 400 mA g^-1.After 500 cycles,the capacity retention rate reaches 77.5%compared with the 10th cycle.The excellent electrochemical performance of the Ni₃Sn₂@C anode material is attributed to the carbon framework ensuring structural stability and buffering large volume changes,enhancing the conductivity of the material;the large specific surface area(294.6 cm² g^-1)of the composite material provides more reactive sites increase the capacity of the material;single-phase Ni₃Sn₂ nanoparticles shorten the diffusion path of sodium ions and improve the rate performance of the material.(3)On the basis of previous work,P element was introduced to try to increase the sodium storage capacity of Ni-Sn@C material.In this paper,a hollow spherical Ni-Sn-P@C heterojunction composite material was synthesized by solvothermal and co-precipitation methods.Used as a negative electrode material for sodium ion batteries,Ni-Sn-P@C has a first charge capacity of 730.0 and 626.7 mAh g^-1 at current densities of 100 and 400 mA g^-1,but the cycle stability needs to be improved,mainly the material The unstable structure of the battery leads to a faster capacity decay during the battery cycle.How to improve the stability of materials is the focus of the next research.