Synthesis Of Molybdenum-based Sulfur Compounds By Gas Phase And Their Electrochemical Properties

With the increasing utilization of renewable resources,the development of new energy vehicles in electronic equipment is increasing rapidly,and the demand for energy storage equipment is getting higher.Lithium ion battery get the attention of the scientific researchers as a kind of high energy density,high security and long cycle life of the energy storage equipment.The commercialized graphite anode material cannot meet the demand of high density energy storage because of its low theoretical capacity(372 mAh g^-1).Therefore,it is urgent to find a new type of negative electrode material to replace the graphite to meet people's needs.The transition metal sulfide compounds'?MoS₂,MoSe₂?structure are similar to graphite and have the merits of high capacity(the theoretical specific capacity of MoS₂ is 670 mAh g^-1;the theoretical specific capacity of MoSe₂ is422 mAh g^-1),environmentally friendliness and pollution-free,are considered as good substitute for graphite.However,due to the semiconductor properties of this material,their electrochemical properties are limited by low lithium ion diffusion coefficient.In our work,carbon-encased MoSe₂ nanosheets-constructed hollow microspheres,Py-Mo reshaped growth of Mo Se₂ nanoflakes and the pitaya-like CoMoSe₄ are successfully synthesized to improve the conductivity of MoSe₂ and the speed of lithium ion diffusion.Exploring and adjusting the growth of MoSe₂.Electrochemical performance demonstrate that the synthesized MoSe₂-based compounds exhibit high specific capacity,excellent rate capability,and good long cycling performance.The main contents are as follows:?1?Carbon-encased MoSe₂ nanosheets-constructed hollow microspheres:hollow microspheres of PDA-Mo have been synthesized via the redox reaction of dopamine and ammonium molybdate in aqueous under alkaline condition.The presence of catechins in dopamine react with ammonium molybdate complex can make the C,N elements well doped into the materials.The synthesized MoSe₂/C anode material possess a high specific surface area of 162.2 m2g^-1 with plenty of meso-pores,increases the contact area between the anode and electrolyte,enhances the diffusion of electrons and Li-ion.The MoSe₂/C exhibit enhanced electrochemical properties,including high specific capacity(1567.3mAh g^-1 at 0.1 A g^-1),good rate capability(597.3 mAh g^-1 at 10 A g^-1)and well long cycling performance(1313.1 mAh g^-1 at 1 A g^-1 after 100 cycles).The enhanced Li-ion storage properties of the MoSe₂/C can be attributed to the hollow microspheres and the high specific area.?2?Py-Mo reshaped growth of MoSe₂ nanoflakes:MoSe₂/C nanoflakes are synthesized by pyrrole and phosphomolybdic acid react at room temperature formed the Py-Mo precursor and then selenylation at high temperature after deal with oxalic acid.We found that the MoSe₂/C nanoflakes have a layered structure with a back shape.The electrochemical performance shows that this MoSe₂/C nanoflakes have excellent electrochemical properties.It has the capacity of 1381.7 mAh g^-1 at the current density of0.1 A g^-1 and excellent rate performance(708.6 mAh g^-11 at 10 A g^-1).Besides,this MoSe₂/C nanoflakes have amazing long cycle life capacity of 976.4 A g^-1 at 1 A g^-1 after100 cycles.The outstanding properties can be ascribed to the unique structure.The MoSe₂/C nanoflakes can relief the volume change in the process of charging and discharging,and exposed more active sites favored by Li-ion diffusion.?3?The synthesis and the investigated electrochemical performance of pitaya-like CoMoSe₄:MoSe₂ has a high specific capacity and excellent rate performance,but its conductivity is poor and limited its electrochemical properties;CoSe₂ is also a layered material and has good conductivity,but its volume changes greatly during charging and discharging.Therefore,the precursor is synthesized via hydrothermal approach.The CoMoSe₄ is synthesized via high temperature calcination.At the surface of pitaya-like CoMoSe₄ there are some lamellar structures,provide a fast channel for the transfer of Li-ion.The electrochemical test shows that this material have good capacity(1209.5 mAh g^-1 at 0.1 A g^-1),good rate performance(366.7 mAh g^-1 at 10 A g^-1),long cycle life(653.1mAh g^-1 at 1 A g^-1 after 100 cycles).This excellent properties can be attribute to the lamellar structure,and the CoSe₂ can increase the conductivity therefore improve the electrochemical property of the material.