The Application Study Of Phosphorusbased Materials As Anode For Lithium-ion Batteries

Lithium-ion batteries have been widely used in wearable intelligent electronic devices and clean energy vehicles owing to their advantages,such as high energy density,good cycling stability and long cycle life.However,due to the low theoretical specific capacity of graphite anode,the energy density of lithium-ion battery is hard to make a breakthrough.The phosphorus-based materials are more promising anode because of their high specific capacity.However,the application of phosphorus-based materials is facing challenges due to the low electronic conductivity and serious volume expansion during cycling.In this work,three types of phosphorus-based composites are designed to solve the problems of phosphorus based material during cycling.The main findings are as follows:Firstly,from the perspective of controlling the morphology and structure of red phosphorus materials,three kinds of chalcogen are successfully doped in red phosphorus and loaded in porous carbon to form chalcogen-doped P@PC composites(S-P@PC,Se-P@PC and Te-P@PC)in one step method.In the meantime,non-doped P@PC(n-P@PC)is also prepared as a comparison.High temperature can bring red phosphorus vapor into the pores of porous carbon,then red phosphorus nanoparticles embed in the deep pores of porous carbon matrix after condensation.The volume expansion stress of red phosphorus during lithiation/delithiation process can be released efficiently after forming nanostructure.Compare with n-P@PC,S-P@PC and Te-P@PC,the significantly reduced specific surface area of Se-P@PC can minimize the side reactions between composite materials and electrolyte.Therefore,the initial coulombic efficiency and cycling stability of Se-P@PC are improved.In addition,owing to the high conductivity of Se and the formation of conductive Li-Se/Li-Se-P phase during cycling,the electron transfer efficiency of Se-P@PC composite can be enhanced.Thus,the Se-P@PC composite exhibits excellent lithium storage performance among all the chalcogen-doped P@PC composite.In addition,Se-P@PC has excellent fast charge-slow discharge capacity and high lithium storage capacity in a full cell,which further indicates that the Se-P@PC material is a promising anode material.Secondly,this part of the work is started with the idea of synthesizing conversion-alloy binary phosphides.It is proposed that the excellent conductivity of Se(10^-5 S m^-1)can be used to enhance the electronic conductivity of phosphorus based materials.In order to obtain lithium anode materials with good rate performance,Se₄P₄ material is synthesized by high temperature solid phase method.Moreover,it is encapsulated in porous carbon to form Se P@C composite.The high theoretical specific capacity of P and high conductivity of Se give Se₄P₄ good lithium storage performance.And it does not need to form multi-selenide intermediates during cycle,thus the cycling performance of Se₄P₄ is enhanced.In addition,the porous carbon material can restrict the large-sized growth of Se₄P₄ material,therefore,the volume expansion stress of Se₄P₄ material can be reduced after filled in porous carbon in nanoscale.Besides,porous carbon can boost the electrical conductivity and ion diffusion rate of the Se P@C.Therefore,Se P@C electrode shows outstanding lithium storage performance.Finally,this part of the work is started with the purpose of synthesizing a ternary metal phosphoselenides.Sn PSe₃ is obtained by combining the lithium storage advantages of Sn,P and Se,so it is a promising anode material.Moreover,the free-standing film composites are prepared by suction filtration method with small-sized Sn PSe₃particle and graphene oxide dispersion(Sn PSe₃@GO)After ultrasonic of Sn PSe₃,a large number of electrochemically active sites can be exposed,so the specific capacity of Sn PSe₃ material is improved..The flexible structure of the Sn PSe₃@GO freestanding film can buffer the volume expansion stress of the Sn PSe₃ and maintain the structural stability of the Sn PSe₃@GO composite.Therefore,Sn PSe₃@GO electrode exhibited superior lithium storage performance.In addition,the redox reactions mechanism of SnPSe₃ is preliminarily determined by ex-situ XRD test.