Construction Of Three-dimensional Graphitic Carbon/transition Metal Sulfide Composites For Lithium Storage

With the increasing demand for clean and renewable energy,the rapid development of energy storage technology,it has become one of the hottest issues to study high-performance,high-efficiency energy storage equipment.Lithium-ion batteries?LIBs?have been widely studied and used in miniaturized electronic equipment and hybrid electric vehicles and so on,owning to their high energy density and excellent cycle stability.At present,the commercial graphite materials are mainly anode materials of LIBs,it cannot meet the demand for high-performance batteries thanks to the low theoretical capacity(372 mAh g^-1).Therefore,it has become one of the problems that need to be solved to develop high-performance anode materials in current LIBs.Transition metal sulfides?such as iron sulfide,molybdenum disulfide,etc.?based on the conversion reaction mechanism have been extensively studied due to their high theoretical capacity.However,it also possesses poor cycle stability because of the poor conductivity and large volume expansion and particle packing during the charge and discharge cycle,which restricting its development and application in the field of electrochemical energy storage.In order to solve the problem of transition metal sulfides,the three-dimensional porous composite structure was constructed.We will study the effects of composite microstructure,composition and bonding form on the electrochemical properties of transition metal sulfides.Reasonable structure is an effective method to alleviated volume expansion and accumulation agglomeration of transition metal sulfide during charge and discharge.Meanwhile,it could improve the electrochemical performance to realize high specific capacity,good rate performance and excellent cycle stability of LIBs.The main contents are as follows:1.Polyvinylpyrrolidone was employed as the carbon precursor and metal nitrate as catalyst,a three-dimensional porous graphitized carbon/iron composite was prepared by high-temperature carbonization treatment,and a three-dimensional graphitized carbon@FeS composite was prepared by further sulfuration.The composite has a stable three-dimensional network structure,and the FeS nanoparticles are uniformly embedded in the carbon network.As an anode for LIBs,it exhibits excellent electrochemical performance.It delivers high specific discharge capacity of 1077.2mAh g^-1 at 0.1 A g^-1,maintains excellent rate capacity of 820 mAh g^-1 even at high current densities of 0.5 A g^-1 after 175 cycles.2.Carbon nanofibers were used as the structural support,and carbon nanofiber/graphitized carbon@FeS composite was prepared through carbonization and sulfuration process by using polyvinylpyrrolidone and metal salt as the precursors.The carbon nanosheets are interlaced in the surface and pores of the carbon nanofibers.Meanwhile,the FeS particles are evenly dispersed on the surface of the carbon skeleton.The stable structure and carbon coating can effectively buffer the volume expansion of FeS.When used as anode for LIBs,the composite exhibits capacity is still stable at1021 mAh g^-1 at a current density of 0.1 A g^-1 after 100 cycles,which possess excellent cycle stability.3.By further oxidizing the prepared three-dimensional graphitized carbon/iron composite material,a graphitized carbon/Fe₂O₃ composite material was prepared.The three-dimensional graphitized carbon/Fe₂O₃@MoS₂ composite by hydrothermal method.MoS₂ nanosheets can be uniformly dispersed on the surface of the carbon skeleton,and the thickness of MoS₂ nanosheet is about 2-3 nm.When used as anode for LIBs,the composite material has a reversible capacity of 920.7 mAh g^-1 after 240cycles at a current density of 0.1 A g^-1,which exhibits stable cycle performance.And PVP can effectively improve the rate performance.