Syntheses Of MoS₂ And WS₂ With Two-dimensional Layered Structure For Lithium-ion Batteries

In the 21 st century energy depletion and environmental pollution are major issues to the human society.The development and utilization of the clean,renewable energy has become the focus of the global concern.More adequates and reasonable uses of existing energy,energy storage have the same important significances with the development of new energy resources,the studies on various secondary batteries have received great attentions.Lithium ion battery has the advantages of high operating voltage,high specific energy,low self-discharge,long cycle life,outstanding low temperature performancemeanwhile,no memory effect and pollution.It is not only widely used in portable electronic products,but also the ideal power of new energy vehicles,satellites,field communications and other mobile devices.In which the development of electrode materials is the key point to improve the performance of lithium ion batteries.That is to say design and preparation of electrode materials for high performance are the hot points of current research on lithium ion batteries.This study focuses on the investigations of lithium ion anode materials,especially the two-dimensional layered transition metal sulfide.Design of experimental programs and fabrication of materials aimed to save costs,reduce environmental pollutions and improve the performance of lithium ion batteries.Among them,MoS₂,WS₂ and their composites with different carbon materials were prepared by different methods,and used as anode materials for lithium ion batteries,respectively.The structures and morphologies of these materials and their influances on the properties of lithium ion battery were studied.?1?MoS₂/rGO composites with different rGO concentrations were prepared by hydrothermal method.The weight ratio of rGO and MoS₂ is 0,1:10 and 1:20.The samples were characterized by XRD,Raman,SEM,TEM,and their electrochemical performances for lithium ion batteries were measured as well.Molybdenum sulfide is lamellar morphology and 2H phase,combined with rGO thin sheets.The devices of MoS₂/rGO?1:20?composites with less rGO content exhibit an excellent electrochemical performance.The reversible capacity is surprisely high?1056 mAh g-1?even after 240 cycles,and these batteriesalso show good rate capability.?2?MoS₂/C nanoflowers with MoS₂ nanopetals and acetylene black nanocalyxs were synthesized by an electrostatic effect modified hydrothermal method.As demonstrated by high resolution TEM image,the MoS₂ exhibits good hybridization with acetylene black at nano-scale,which leads to distinctly improvement of electronic conductivity of MoS₂.As a result,the MoS₂/C composite shows excellent electrochemical performance as conduct-free anode material for lithium ion batteries.In case of a current density of 100 mA g-1,it shows discharge capacity of 760 mAh g-1 after 100 cycles.After 50 cycles with current density change from 100 to 1600 mA g-1,it can deliver capacity of 930 mAh g-1 when reverting the current density to 100 mA g-1.?3?Porous WS₂ films have been deposited on ridge-like Ni coated Cu foils using a magnetron sputtering system,their morphologies and structures were characterized by FESEM,HRTEM and Raman.Electrochemical evaluation of batteries fabricated use these materials showed that,as negative electrode for lithium-ion batteries,the representative ridge-like Ni supported WS₂ film electrode performs a high reversible capacity and excellent rate capability which can deliver a discharge capacity as high as 1180 mAh g-1 after 100 cycles at 100 mA g-1.The capacities almost remain the same as the current density increases from 100 to 800 mA g-1.Even at 1600 mA g-1,the electrode can deliver a capacity as high as 986 mAh g-1.?4?A more environmentally friendly method was demonstrated.Materials with environmental pollution were not introduced to the whole process of the experiment.The porous foam Ni formed by reducing the oxidatied foam Ni acted as the collector,and MoS₂ has directly grown on the collector by RF magnetron sputtering,and finally realize a 3D electrode.MoS₂ on the porous foam Ni showed pompon-like structure.The samples were characterized by Raman,TEM,TEM,HR-TEM for studying the surface morphology and structure.The 3D architecture was used as an anode of lithium ion batteries.A high reversible capacity of 1341 mAh g-1 was obtained for the 140 th discharge after rate test and small current loop of 100 times.After cycling with various current densities,it can deliver a capacity of 460 mAh g-1 at a current density as high as 1000 mA g-1,indicating that the electrode prepared by such a green route can be a promising candidate for high power LIBs.