Study On The Synthesis And Electrochemical Performance Of Molybdenum Oxide And Its Composite Materials

Lithium-ion batteries are the most advanced choice in portable electronics,electric vehicles and electrical energy storage systems.Technological improvements in rechargeable batteries are driven by the growing demand for electrodes with high energy density,excellent electrochemical and mechanical stability.As a substitute for graphite,metal oxides rich in various degrees of covalent and metal oxidation states can adjust the equilibrium potential and charging kinetics of lithium-ion batteries,and thus have great potential as high-capacity electrodes.Molybdenum oxide nanomaterials have been extensively studied and applied to solar cells,gas sensors,supercapacitors,lithium ion batteries,electrocatalysis and photocatalysis.In this paper,variously shaped molybdenum trioxide and molybdenum dioxide nanomaterials were prepared.The electrochemical properties of the prepared materials were improved by controlling the morphologies,microstructures and composite material.The details are as follows:?1?Molybdenum trioxide nanorods are directly synthesized at large scale under mild conditions?pH=0.1?by a‘‘pH adjusting''method using hydrochloric acid,using sodium molybdate?Na₂MoO₄?as the main raw material and dodecanol as the surfactant.Molybdenum trioxide nanobelts have been prepared on a large scale?pH=0.15?using dodecyl alcohol as a surfactant.Extensive structural characterization of the as-prepared samples has been performed using scanning electron microscope,transmission electron microscopy,high-resolution transmission electron microscopy,selected area electron diffraction,and X-ray diffraction.The electrochemical properties were investigated as anode material for Li-ion batteries.The results show that the coulombic efficiency of the molybdenum trioxide nanomaterial electrode can maintain a high level of performance,and presented stable cycling properties.The nanorod-like molybdenum trioxide has a high specific capacity and a nano-band trioxide molybdenum exhibits a higher specific discharge capacity than the nanorod-like molybdenum trioxide.Moreover,molybdenum trioxide nanobelts have better electrochemical performance than the rod-shaped molybdenum trioxide nanomaterial.?2?In order to improve the electrochemical performance of molybdenum trioxide nanomaterials,molybdenum trioxide/graphene composites were synthesized.The samples were characterized by X-ray powder diffractometer and scanning electron microscope,and the applications of the MoO₃ g^-1raphene in lithium ion batteries have been demonstrated by using them as anode materials.The the capacity retention and high rate of discharge capacity attenuation of the MoO₃/graphene composites were improved.It was found that the ratio of capacity retention,the capacity and cycle stability of 10%MoO₃/graphene composite nanomaterials are more superior to those of other ratios of MoO₃/graphene composites and pure MoO₃ samples.The possible reasons are that the grapheme oxide content is too high,which will affect the cycle stability of MoO₃ electrode nanomaterials.?3?Molybdenum dioxide nanoparticles have been synthesized at high yield by hydrothermal reaction.FESEM,XRD revealed the morphology,size and fine structures of the product.The specific discharge capacity of the first ring is 1166 mAh g^-1 and exceeds its theoretical specific capacity.The Coulomb efficiency after the first lap can be maintained at around 97%with good cycle performance.The improvement in electrochemical performance of molybdenum dioxide nanomaterials can be attributed to its nanostructures having a large specific surface area.?4?Molybdenum dioxide/graphite composites have been synthesized via a hydrothermal method using sodium molybdate and glucose as precursors.The final products are characterized by X-ray diffraction,scanning electron microscopy and transmission electron microscopy.The electrochemical properties of the calcined Molybdenum dioxide/graphite?500??are tested as the anode materials for lithium ion batteries.The specific capacity of MoO₂/C composites presents a tendency of increasing.When the MoO₂/C composite electrode is discharged at a density of 4000 mA g^-1,the discharge specific capacity of 215mAh g^-1 can still be maintained.The superior electrochemical properties of the MoO₂/C can be attributed to nanostructure features,which can shorten the diffusion paths of lithium ions during electrochemical cycling.