Preparation And Electrochemical Performance Study Of Novel Sn-based Anode Materials For Lithium-ion Batteries

Lithium ion batteries have been widely used in portable electronic devices due to its many advantages such as high energy density,high working potential,environment friendly and long cycle life,and so on.In recent years,as the development of the electric vehicles and hybrid electric vehicles,the energy density of lithium ion batteries have needed to be further improved.Anode materials are an important part of the lithium ion batteries,which performance has a significant influence on the performance of lithium ion batteries.However,graphite,the commercial anode materials can not meet the demand for high energy density lithium ion batteries because of its relatively low theoretical capacity.Tin-based anode materials have shown significant potential replace to graphite for lithium ion batteries due to its high capacity.But the huge volume change resulting in poor cycle life during the change and discharge process was the key issue hinder its commercial application.To improve the performances of Sn-based anodes,preparing the Sn-based composite anode by a facile ball milling method,the influence of template and added MoS₂ on the micro structure and electrochemcial performance of the composite materials were also investigated.(1)Using the metal tin as the tin sources,sodium chloride as the template,citric acid as the carbon sources,preparing the Sn/SnO_x/C composite by a facile ball milling method.This composite present a nano sheet-type structure and the Sn/SnO_x nanoparticles embedded in carbon nanosheet.The composite shows superior rate and cycle performance as the anode materials for lithium ion batteries,the reversible specific capacity can be maintained 385mAh/g under the current density of 5.0A/g;after 200 cycles,a specific capacity of 577mAh/g was also obtained at a current density of 500mA/g.The high capacity and stable cycle performance could be attributed to the structure of composite,the carbon nanosheet can effectively not only avoid the direct exposure of Sn/SnO_x nanoparticles to the electrolyte but also buffer the volume expansion during the charge and discharge process,resulting in superior elecrtochemical performance of the composite.(2)Sodium molybdate dihydrate as the molybdenum sources,thiourea as the sulfur source,sodium chloride as the template,citric acid as the carbon sources,commercial tin powders as tin sources,preparing the Sn@SnO_x@MoS₂@C composite by ball milling method and in situ vapor deposition.With assistance of sodium chloride,MoS₂@C nanosheets can be in situ synthesized and success encapsulated Sn@SnO_x nanoparticles.Sn@SnO_x@MoS₂@C composite with outstanding electrochemical performance when as anode material for lithium ion batteries.The specific capacity still up 500 mAh/g under current density of 5.0A/g and a high capacity of 530mAh/g was achieved after 800 cycles at current density of 2.0A/g,exhibited extremely excellent cycling performance at high current density.The Sn@SnO_x@MoS₂@C composite shows excellent electrochemical performance could be attributed to MoS₂@C nanosheets can not only buffer the volume expansion of the Sn@SnO_x nanoparticles but also effectively avoid the direct exposure of Sn@SnO_x nanoparticles to the electrolyte,that can preserve the structural stabilization of the composite during the cycling process.(3)Commercial tin powders as the tin sources,sodium chloride as the template,citric acid as the carbon sources,added as-prepared MoS₂,prepared Sn/SnO_x/MoS₂/C composite after ball milling and calcination.With assistance of sodium chloride,the Sn/SnO_x nanoparticles and MoS₂ nanoparticles diepersed in carbon nanosheet martix.The Sn/SnO_x/MoS₂/C composite exhibited excellent electrochemical performance as anode materials for lithium ion batteries,have a high capacity of 698mAh/g at a current density of 5.0A/g after 800 cycles,Sn/SnO_x/MoS₂/C composite also have a high capacity of 725.3 mAh/g at current density of 3.0A/g.The Sn/SnO_x/MoS₂/C anode material has a superior electrochemical performances ascribed to the following factors:on one hand,the carbon nanosheets can not only accommodate the volume expansion of Sn/SnO_x nanoparticles but also prevent the nanoparticles from directly contact with electrolyte,on the other hand,the MoS₂ can enhance the mechanical strength of the carbon nanosheets,offer a mass of active sites to host lithium ions and then greatly shorten the diffusion distance of electrons and ions,resulting in high specific capacity and superior rate performance.