Design,Synthesis And Sodium Storage Properties Of Tin-based Alloy Composite Materials

Tin-based materials are considered as one of the most promising anode materials for sodium-ion batteries because of their high theoretical capacity and pollution-free characteristics.The theoretical sodium storage capacity of Sn is 847 m Ah g^-1.However,the volume change of tin-based anode material is about 420%during the process of sodiation/desodiation.As a result,the active materials undergo pulverization and fall off from the current collectors,resulting in the instability of the capacity and the rapid capacity decay during the charge-discharge cycles.At present,there are three ways to solve the above problems:construction of nanostructures,increase of porosity,and design of heterostructures.These methods are helpful to improve the stability of electrode structure,and then improve the reversible capacity,cyclic stability,and rate performance of the electrode materials.This paper focuses on the design and synthesis of Sn-Co@C and Sn-Co@void@C and the regulation of the preparation process.The innovative results are as follows:1)The SnO₂/Co₃O₄ composite precursor was successfully prepared by the coprecipitation and thermal-derived phase separation method.The size of the precursor particles can be easily controlled.The results showed that the particles with an average diameter of 150 nm were ideal precursor for the subsequent synthesis.The precursor particles were well-formed nanocubes with smooth edges and porous surfaces.2)The Sn-Co@C composite material was successfully prepared by the St(?)ber method.The electrochemical performance of the material was compared with Sn,Sn-Co,and Sn@C.It was found that the Sn-Co@C composite material has better performance than the others.This is because the carbon shell is not easy to be broken in the sodiation process,which provides a stable surface for the formation of SEI film and improves the conductivity of the electrode;during the reaction process,the metal Co remains unchanged and acts as a buffer and an electronic conductor,and separates Sn into micro-regions,which hinders the agglomeration of Sn particles.3)The Sn-Co@void@C yolk-shell composite material was successfully prepared by using SiO₂ as self-sacrificial template.By comparing the morphologies and electro-chemical performances of Sn@void@C,Sn-Co@C and Sn-Co@void@C,it was revealed that Sn-Co@void@C composite has better electrochemical performance.This showed that the void space introduced between the carbon shell and alloy core could further accommodate the volume change of the active material.4)By exploring the influence of the amount of SiO₂ template and the amount of monomer organic molecules in the St(?)ber method on the volume of the void space and the thickness of the carbon layer,as well as studying the sodium storage performance,the preparation process of the synthesis method was optimized.