Carbon/molybdenum Disulfide Composites:Preparation And Lithium/sodium Storage Properties

Molybdenum disulfide is earth-abundant and low-cost graphene-like layered metal sulfide.It is considered as a potential candidate anode material because it has high theoretical capacity when used as lithium/sodium storage materials.However,the electrochemical properties of MoS₂ are seriously restricted by the problems of low conductivity,easy pulverization or agglomeration in the cycling process and easy dissolution of active components.In this paper,a series of C/MoS₂nanocomposites were designed and synthesized to improve their performance of electrochemical lithium/sodium storage.These materials include:graphene/MoS₂foam,graphene-carbon nanotube/MoS₂ foam,graphitic N doped C/MoS₂,amorphous C/MoS₂,pyrrolic-N doped C/MoS₂ and other composites.The reaction mechanism of MoS₂ prepared by pyrolysis was studied.The regularities and relations between the micro-nano structure,N-atom doped and electrochemical properties are discussed.Graphene foam and graphene-carbon nanotube foam were prepared by chemical vapor deposition using nickel foam as template,and graphene/MoS₂ foam and graphene-carbon nanotube/MoS₂ foam were prepared by hydrothermal synthesis.The G-CNTs/MoS₂ composite foam displayed the lithium storage capacity of 752mAh g^-11 and the sodium storage capacity of 92 mAh g^-11 after the 200 cycles.Graphene-carbon nanotube foam is more easy to charge transfer,as well as improve the electrical conductivity of electrode,carbon nanotubes has excellent flexible to maintain integrity of the electrode structure in long circling.Inhibition of the volume change of electrode materials in the process of charging and discharging,so as to improve the electrochemical properties of compositesand enhance the lithium/sodium ion battery performance effectively.The 3DOM graphitic C and graphitic N doped C was prepared by the hard template method.The 3DOM graphitic C/MoS₂ and the 3DOM graphitic-N doped C/MoS₂ were prepared by hard template method and the thermal decomposition method.The time of infiltration can control the C/Mo proportion in the composites.By comparison,it was found that the electrochemical performance of the composite electrode was optimal when the number of infiltration was 2.The MoS₂ and the amorphous C/MoS₂ complexes were prepared by hard template method.The C/Mo ratio in 3DOM C/MoS₂ is regulated to optimize its electrochemical performance.When C content accounts for 23.95%,the composite electrode has the best electrochemical performance.As the lithium storage materials,the initial reversible capacity is 1387 mAh g^-1,and the retention rate of capacity is59.33%after 500 cycles;for sodium storage material,the initial reversible capacity is 631 mAh g^-1,and the retention rate of capacity is 77.63%after 500 cycles.The unique structure of the composite plays a key role in the stability of the electrodes in long cycling.The tight packing of amorphous C around the MoS₂ thin layer is beneficial to the conductivity of the electrode and the fixation of the Na_xS_n/Li_x S_m,to alleviate the volume expansion and internal microstress of the electrode,and enhance the cyclic stability and rate performance of the electrode.The[EMIm]Cl assisted pyrolysis method successfully grown the pyrrolic N-doped C/monolayer MoS₂ composite layer on the GO surface,and the pyrrolic N-doped C layer was insetted into the MoS₂ Van der Waals spacing.The reaction mechanism and kinetic mechanism of preparing MoS₂ from?NH₄?₂MoS₄ were studied.The most probable mechanism function differential equation and reaction mechanism of the heat decomposition endotherm of the reaction were determined by Kissinger method and Flynm-Wall-Ozawa method.The reaction mechanism of MoS₃ desulphurization to MoS₂ is three-dimensional diffusion.During?NH₄?₂MoS₄removal of hydrogen sulfide and ammonia decomposition into MoS₃,the reaction mechanism is random nucleation and subsequent growth.The electrochemical properties of the N doped C/monolayer MoS₂ composites with N element doped content of 9.32%,pydinic N of 57.2%and carbon content of13.7%were obtained by optimizing the process.The initial reversible specific capacity was 1169 mAh g^-1,showed a capacity of 862 mAh g^-11 and the delivering73.74%capacity retention after 500 cycles.The electrode also has excellent sodium storage performance with an initial reversible capacity of 661 mAh g^-1,showed a capacity of 570 mAh g^-11 and the delivering 86.36%capacity retention after 500cycles.