Preparation And Electrochemical Properties Of Si/Sn/C Composite Anode Materials

In the past decades,with the development of micro-electronic technology,more and more miniaturized equipment has been applied in the fields of life application,industrial manufacturing and military industry,which has put forward high requirements for power supply.At the same time,lithium-ion power batteries have also entered the large-scale practical stage.However,the current theoretical capacity of commercial graphite anode is only 372 m A h/g,which is gradually unable to meet the current application situation of the market.The theoretical specific capacities of silicon and tin are much higher than graphite,4200 m A h/g and 994 m A h/g respectively.Silicon is one of the ideal anode materials for the next generation of lithium ion batteries.However,silicon tin based anode materials have the problem of particle breakage caused by volume expansion,which limits their commercial application.In this paper,with nano-silicon,SnCl₄·5H₂O and phenolic resin as raw materials Si-Sn@C composite materials were prepared by via vapor deposition and high-temperature carbonization Si-Sn@C/Graphite anode materials are prepared melting method and high-temperature carbonization by using nano-silicon,SnC₂O₄,graphite and phenolic resin as raw materials.The physical structure and electrochemical properties of the material are analyzed by means of SEM,TEM,XRD,BET and electrochemical measurement methods.This paper is divided into two parts:In the first part,Si-Sn@C composites materials were prepared by the following method:By via vapor deposition,nano-Si,SnCl₄·5H₂O and phenolic resins were used as raw materials to deposit ultra-fine Sn（OH）₄ nanoparticles on the surface of nano-Si,then coat the carbon layer on the outer layer of composites materials by high-temperature carbonization.In this experiment,the Si-Sn@C composite with the highest tin content achieved the most outstanding performance.With the current density of 100m A/g,The Si-Sn@C composite electrode were subjected to reversible capacity of 530m A h/g after 100 cycles.Among them,tin coated on the surface of silicon particles and the most outer layer of phenolic resin cracking carbon can effectively buffer the volume change of active substances,and promote the diffusion rate of lithium ions and electrons,which greatly improves the cyclic stability of the material.In the second part,the nanosilicon,SnC₂O₄,graphite and phenolic resin as raw materials.First,with the nano-silicon and SnC₂O₄ are mixed evenly,Si-SnO composite were prepared by means of melting method Si-Sn@C/Graphite composite was obtained by mixing Si-SnO composite and graphite and covering carbon layer.At750℃,when the Si/Snratio is 4:6 and the dosage of phenolic resin and graphite is30%wt and 40%wt,respectively,the Si-Sn@C/Graphite composites show the best properties.Therefore,the Si-Sn@C/Graphite composite delivers good electrochemical performances such as a reversible capacity of 800 m A h/g at 100 m A/g after 75 cycles.And the charge and discharge capacities of Si-Sn@C/Graphite composite materials in the initial cycle are 950.3 m A h/g and 850.6 m A h/g,respectively,and the first-cycle coulombic efficiency is 89.51%.Graphite in the composite has suitable lamellar spacing and good electrical conductivity.Cooperation with newly generated tin can improve the electrical conductivity and cyclic stability of the material.The coating of the cracked carbon layer and the uniform distribution of silicon and tin can effectively buffer the volume change of the material during the charge-discharge cycle,and improve the electrical conductivity of the material.