Synthesis Of Molybdenum-based Sulfide(Selenium) Nanocomposite Materials And Its Application In Lithium-ion Batteries

Among a wide variety of chemical energy sources,Li-Ion battery has become a main tream of energy storage battery because of its advantages of light weight,small size,high energy density,high safety performance and rapid charge and discharge,and Li-Ion battery has greatly promoted a mobile and fossil fuel-free society.However,with the development of electric vehicles and smart grids,the development of lithium-ion batteries are also facing new challenges,it is very vital to develop next-generation lithium-ion batteries(LIBs)with excellent performance.And lithium-ion anode materials play an important role in lithium-ion batteries.Therefore,one of the research emphases in the field of energy storage is to explore new lithium-ion anode materials.Molybdenum-based sulfur(selenium)compounds have attracted more and more interests of researchers because of their high theoretical specific capacity.However,the low conductivity and volume effect of molybdenum-based sulfur(selenium)compounds lead to its poor rate performance and cycle performance when applied to the anode materials of lithium ion batteries.In this paper,we have prepared active materials by introducing carbon matrix.core-shell structure to overcome the problems of poor conductivity and rapid capacity decay of molybdenum-based sulfur(selenium)compounds.The main research contents are as follows:(1)The Fe3O4@C@MoSe2 nanocomposite was prepared through sol-gel method and hydrothermal method,which was prepared by coating MoSe2 on the surface of core-shell Fe3O4@C.The core-shell structure of the composite material can alleviate the volume expansion of Fe3O4 during charging and discharging,and provided rich transmission channels for the diffusion of lithium ions.The carbon shell not only enhanced the overall conductivity of the material,but also improved the stability of the core and prevented the agglomeration of Fe3O4;The external molybdenum selenide nanosheets can provide more electrochemical active sites.At the current density of 100 mA g-1,Fe3O4@C@MoSe2 can reach the first discharge capacity of 1397.6 mA h g-1 and remain at 878 mA h g-1 after 70 charge-discharge cycles,with the coulombic efficiency above 99%,which showing good reversibility.At the current density of 1 A g-1,its discharge capacity can still reach 609.2 mA h g-1 after it cycled for 300 times,which showing excellent long-cycle performance.(2)The Fe3O4/MOS2@C composite was prepared through in-situ growth strategy,which was prepared by partially growing MoS2 inside the core-shell Fe3O4@C.The core-shell structure of the composite material was beneficial to slow down the volume change of Fe3O4 and MoS2 in the cyclic process.the growth of MoS2 in the cavity can provide more channels for lithium intercalation and deintercalation;carbon shell improved the overall conductivity of the material,and this synergistic effect helped to improve the structural stability and electrochemical performance of the material.At a current density of 100 mA g-1,the first discharge capacity of Fe3O4/MoS2@C can reach 1420.6 mA h g-1,and the specific discharge capacity had been basically stable after 20 cycle and still can remain at 671.6 mA h g-1 after 100 cycles,and the specific discharge capacity of Fe3O4/MoS2@C can reach 582.8 mA h g-1 after 600 cycles at a higher current density of 1.0 A g-1.Owing to the structural stability,Fe3O4/MoS2@C composite showed excellent cyclic performance.(3)Amorphous core-shell CoMoOxSy@NC nanocomposite was prepared by a simple and easy template strategy.The internal cavity can reduce the volume change of the electrode materials during charging and discharging;the amorphous structure with disordered lattice can provide more diffusion paths and more electrochemical active sites for Li+intercalation;the carbon layer doped with nitrogen atoms was helpful to increase the overall stability and conductivity of the material.At the current density of 100 mA g-1,CoMoOxSy@NC electrode material specific discharge capacity can remain at 744.2 mA h g-1 after 100 cycles.The synergistic enhancement effect of amorphous Co-Mo oxide/sulfide and the unique core-shell nanosphere structure made CoMoOxSy@NC nanocomposites show good cycle performance.