Synthesis And Electrochemical Properties Of Molybdenum-based Chalcogenides

The energy and environment crisis caused by the excessive use of fossil energy has seriously affected the sustainable development of the society.Clean and renewable energy sources such as solar,wind and tidal energy have the characteristics of intermittent and randomness.Electrochemical energy storage is considered to be an ideal energy storage method because of its convenience and efficiency.The energy density of lead-acid battery is low and there is heavy metal pollution.The energy density of Ni-MH battery is limited by memory effect.As anode materials for lithium-ion batteries,molybdenum-based metal sulfur compounds with high theoretical specific capacity play an important role in the development of battery.In this paper,we synthesis a series of nanostructured molybdenum-based metal sulfur compounds,such as molybdenum selenide hollow nanospheres,molybdenum selenide nanorods and molybdenum selenide nanoparticles,by solvothermal method.When used as anode materials,they show good electrochemical performance.The main contents are as follows:1.Synthesized carbon composite molybdenum selenide hollow nanospheres.Molybdenum glycerate solid spheres were synthesized using molybdenum acetylacetone,glycerol,isopropanol,molybdenum glycerate solid spheres by solvothermal method.Then,the carbon composite molybdenum selenide hollow nanospheres were synthesized,using molybdenum glycerol solid spheres as precursors,adding Se powder,hydrazine hydrate,glucose,by solvothermal method again.Based on the Kirkendal effect,the product is composed of molybdenum selenide nanosheets,As an anode material for lithium ion batteries,it shows initial discharge specific capacity of 960 m Ah g^-1 at 100 m A g^-1 current density.After 100 cycles,the specific capacity remains 800 m Ah g^-1.At a high current density of 5000 m A g^-1,it remains the specific capacity of 603 m Ah g^-1.As an anode material for sodium ion batteries,the carbon composite molybdenum selenide hollow nanospheres exhibit good lithium and sodium storage properties.When it cycles 200 times at current density of 200 m A g^-1,it remains 458 m Ah g^-1.It's because carbon materials help improve the conductivity of electrode materials and the hollow structure can alleviate the volume expansion during the progress of discharge and charge.2.Designed and synthesized molybdenum selenide(Mo Se₂)nanoparticles.Highly-uniform Mo Se₂ nanoparticles were successfully synthesized via a one-pot hydrothermal method with addition of polyvinyl pyrrolidone(PVP)following by calcination treatment.PVP serves as a surfactant preventing the over-agglomeration of Mo Se₂ nanosheets and contributing to the well-organized accumulation of Mo Se₂nanosheets into nanoparticles.When evaluated as anode for lithium ion batteries,the Mo Se₂nanoparticles show enhanced cycle stability and rate performance comparing to the Mo Se₂composite prepared without addition of PVP.After 200 cycles,the Mo Se₂ nanoparticles remain a specific capacity of 573.9 m Ah g^-1 at a rate of 200 m A g^-1 with 85%capacity retention.Meanwhile,Mo Se₂nanoparticles also showed good sodium storage performance.Under the current density of 5000 m A g^-1,Mo Se₂ nanoparticles exhibit capacity of 270m Ah g^-1.3.Carbon coated molybdenum sulfide nanorods were designed and synthesized.Molybdenum disulfide was synthesized by hydrothermal method using molybdenum trioxide-ethylenediamine(EDA)as the precursor.The raw materials of the precursor include ammonium heptamolybdate tetrahydrate and ethylenediamine.Synthesized molybdenum sulfide is rod-like structure with a diameter of about 500 nm,and the surface is burr-like,which is caused by the accumulation of molybdenum sulfide flakes.Glucose was added as a carbon source for in situ carbon coating during synthesis.In addition,layered birnessite cathode materials were synthesized by hydrothermal method,and glucose was used to encapsulate carbon in situ.Cylindrical sodium ion battery was assembled with carbon coated molybdenum sulfide nanorods as anode and carbon composite birnessite as cathode.As a result,the full battery has a capacity of 15 Ah.