Preparation Of Molybdenum-based Nanocomposite And Their Electrochemical Properties

Due to their characteristics of high energy density,long life and safety,lithium ion batteries are widely used in many fields including various portable electronic products,new energy vehicles and so on.Molybdenum?Mo?base compounds have attracted more and more attentions mainly owing to their particular characteristics of high oxidation state,multivalence and morphological diversity.However,those shortcomings of molybdenum compounds such as low conductivity and structural stability and so on,still limit their lithium storage performance.In this paper,not only the pure phase MoO2@C nanomaterials but also the C@MoS₂@C nanobelts with novel three-layer hierarchical structure and the MoS₂@C nanobelt with molybdenum disulfide nanosheet encapsulated into the armorphous carbon nanotubes were further prepared.On the other hand,their corresponding synthesis mechanism,morphology structure and lithium storage properties were also investigated in detail.The main content of this article is as follows:?1?One-dimensional MoO₃ nanobelts were prepared by hydrothermal method,then,the uniform carbon coating processes were carried out via simple organic solution thermal evaporation decomposition by using malic acid as the carbon source.The effects of the malic acids contents and annealing temperatures on the electrochemical properties of the carbon coated molybdenum oxide composite were investigated.The results showed that when the malic acid content of 0.58g added,and annealed in 400 ?,pure phase MoO2@C nanobelts were successfully obtained.The carbon layer coated on the surface of MoO2 not only could alleviate the volume effect of the nanomaterial during the charging and discharging process,but also could greatly improve the conductivity of nanomaterial.In the current density of 100mAg-1,after 100 cycles,the composite electrode delivered highly reversible capacity of 829mAhg-1,showing excellent lithium storage performance.?2?The hierarchical C@MoS₂ nanobelts with MoS₂ nanosheet growing vertically on the surface of carbon layer were prepared by using the MoO₃@C nanobelt as self-sacrificial template.Then C@MoS₂@C nanobelt with three-layer hierarchical structure was further prepared via the same organic solution thermal evaporation decomposition method by using the malic acid as the carbon source.At the current density of 200mAg-1,after 300 cycles,the composite electrode delivered the reversible capacity of 1025mAhg-1 with high coulomb efficiency up to 100%.At the current density of 500mAg-1 and 1000mAg-1,the composite electrode delivered highly reversible capacity up to 902mAhg-1 and 820mAhg-1,respectively.?3?The pure MoO₃ nanobelts were further coated by using the glucose instead of malic as the carbon source and the effects of carbonization process on subsequent hydrothermal vulcanization were studied under different annealing temperatures.The results showed that when annealed at the carbonization temperature of 300?,the subsequent vulcanization process could completely in-situ sulfidize the MoO₃ inside the carbon matrix to MoS₂ nanosheets encapsulated into carbon nanotubes,and the unique one-dimensional nanobelts architecture with MoS₂ nanosheets encapasulated into carbon nanotubes was obtained.through the construction of this architecture with MoS₂ nanosheets encapasulated into inorganic carbon nanotubes,not only could this carbon nanotube encapsulating the MoS₂ nanosheets for the unique MoS₂@C nanobelt effectively alleviate the volume effect during the charge/discharge processes,but also greatly improve the conductivity of the composite,which would facilitate their excellent lithium storage performance.At the current density of 200mAg-1,the composite delivered highly reversible capacity of 1200mAh/g after 200 cycles with coulomb efficiency of?100%.