Synthesis Of Metal Sulfides/Graphene Composites And Their Electrochemical Lithium Storage Performance

Lithium ion batteries?LIBs?with high energy density,long service life and no memory effect have become dominant power sources for portable electronic devices and electric vehicles.The physical and chemical property of electrode materials wherein is a determining factor for the energy density and performance of LIBs.Metal sulfides such as nickel sulfides,cobalt sulfides,tin disulfide and antimony trisulfide have been actively investigated as possible candidates for anode materials due to their high capacity,low cost and abundant reserves.The low electronic conductivity and the electrode pulverization caused by volume change during lithium ions insertion/extraction process,which would lead to their poor cyclic stability and rate capability.In order to resolve these drawbacks,one of the effective methods is to fabricate composite with carbon nanomaterials?such as carbon nanotubes and graphene sheets?.Graphene with high electrical conductivity,giant charge mobility,large theoretical specific surface area,excellent flexibility and chemical stability become an ideal substrate for the growth of other nanomaterials.The graphene can not only provide an elastic space to buffer the volume change of the electrode materials during the repetitive charge/discharge process,but also facilitate the faster electron transport during electrode reaction process.In this paper,a series of metal sulfide/graphene composite nanomaterials were synthesized by hydrothermal method,then make experimental characterization and electrochemical tests,we discuss the formation mechanism of nanocomposites,lithium storage mechanism and the reason for improvement of electrochemical properties.The results indicate that the as-prepared materials as the anode material of lithium ion battery display excellent lithium storage performance,the main research conclusions as follows:?1?NiS₂/graphene anode material:First,graphene oxide sheets were prepared from natural graphite power by the modified Hummers method.The NiS₂/graphene composite was synthesized via a hydrothermal reaction between NiCl2 and L-cysteine in the presence of graphene oxide sheets.The sphere-like NiS₂ nanoparticles range from 30 to70 nm in diameterare well dispersed on the corrugated graphene nanosheets.Electrochemical measurements demonstrate that in comparison with the pristine NiS₂,NiS₂/graphene composite not only delivers high reversible specific capacity of 1200 mAh/g at a current density of 100 mA/g with excellent cycling stability,but also exhibits significantly enhanced rate capability of 740 mAh/g at a current density of 1000 mA/g.In particular,NiS₂/graphene can retain the reversible capacity of 813 mAh/g after 1000 cycles at a current density of 500 mA/g?2?SnCoS₄/graphene anode material:The SnCoS₄/graphene composite was synthesized via a hydrothermal reaction between CoCl2,SnCl4 and L-cysteine in the presence of graphene oxide sheets.The result composite was characterized by XRD,SEM and TEM.Electrochemical measurements demonstrate that in comparison with CoS₂/graphene and SnS₂/graphene,the as-prepared SnCoS₄/graphene composite exhibits a high reversible capacity of 1350 mAh/g after 200 cycles at 100 mA/g with long cycle life and desirable rate capability.The reversible capacity of 845 mAh/g can be preserved after 2000 cycles at 2000 mA/g.?3?SnS₂-Sb₂S₃/graphene anode material:The SnS₂-Sb₂S₃/graphene composite was synthesized via a hydrothermal reaction between SbCl3,SnCl4 and L-cysteine in the presence of graphene oxide sheets.Electrochemical measurements demonstrate that in comparison with Sb₂S₃/graphene and SnS₂/graphene,the as-prepared SnS₂-Sb₂S₃/graphene composite exhibits a high reversible capacity of 1125 mAh/g after 100 cycles at a current density of 100 mA/g.When the current density increase to 1000 mA/g,its reversible capacity is 950 mAh/g,indicating an excellent rate performance.