Synthesis Of Spherical Structure Molybdenum Dioxide Nanocomposite And Their Applications In Lithium Ion Batteries

As the leading electrochemical energy storage device,lithium-ion batteries have made great achievements in the application of portable electronic products after decades of development.With the development of new energy vehicles and other emerging energy storage fields,higher requirements have been placed on the performance of electrode materials.But the traditional commercial graphite anode materials can no longer meet the needs of the current markets.As a kind of transition metal oxide,molybdenum dioxide has been expected to become the electrode material for a new generation of high-energy-density and long-lasting electric vehicles because of its relatively high specific capacity and low resistivity.However,the use of molybdenum dioxide as the negative electrode material of energy storage devices was limited by the volume effect during charge and discharge in practical applications.Therefore,the controllable design of synthetic products with hollow nanostructures and porous core-shell morphologies can effectively alleviate problems such as capacity decay.In this paper,through reasonable design,the body material of molybdenum dioxide was combined with silicon-based,carbon-based,titanium-based three functionalized nanomaterials to prepare a novel spherical structure molybdenum dioxide nano composites,showing excellent lithium storage performance.The main research contents are as follows(1)Using the synthesized silica nanospheres,molybdenum dioxide/carbon/silica(MoO2/C/SiO2)composite materials were prepared by a one-step synthesis method.The surface of the composite material was covered with cracks,and the ultrafine molybdenum dioxide nanoparticles with a size of 5-7 nm were evenly embedded in the internal structure of the silica nanospheres.The MoO2/C/SiO2 electrode sheet was assembled into a button cell and tested at a current density of 100 mA g-1.After 100 cycles,the discharge capacity maintained at 293.1 mA h g-1,showing good reversibility.Ultrafine MoO2 nanoparticles can shorten the Li+migration path and effectively prevent the agglomeration phenomenon during the battery cycle,thus improving the stability of the electrode material structure.The construction of silica and molybdenum dioxidee and the synergy effect of carbon materials in the system greatly improved the cycle stability and rate performance of the resultant lithium ion battery.(2)Through simple and effective template strategy,hollow mesoporous carbon sphere composite material(MoO2/C)supported by ultra-fine MoO2 nanoparticles were synthesized controllably.First,using tetraethyl orthosilicate as the silicon source,a core-shell structure was obtained by coating the silicon surface with a phenolic resin.Then high-temperature calcination and etching treatment promoted the formation of hollow porous carbon spheres(HMCSs).Next,Mo-PDA precursors grew into the surface pore structure of HMCSs through a one-step synthesis method.Finally,the precursors were placed in a tube furnace and calcined at high temperature to prepare MoO2/C composite materials.The prepared MoO2/C composite material inherits the hollow structure of the porous carbon sphere precursor.The ultrafine molybdenum dioxide nanoparticles show a size of 5-7 nm and were evenly embedded in the surface pores of the hollow mesoporous carbon sphere.The MoO2/C electrode sheet was assembled into a button cell and tested at a current density of 100 mA g-1.After 100 cycles,the discharge capacity maintained at 742.9 mA h g-1,which is much higher than that of commercial MoO2-Ultra-fine MoO2 nanoparticles can provide a short electron/ion transmission path,and effectively prevent the agglomeration phenomenon during the battery cycle,and avoid the collapse of the electrode structure.The synergy effect between ultrafine molybdenum dioxide nanoparticles and hollow nmesoporous carbon spheres has greatly improved the overall conductivity and rate performance of the prepared lithium ion battery.(3)Through simple and effective growth strategies,the graded porous molybdenum dioxide@titania@nitrogen-doped carbon(MoO2@TiO2@NC)nanospheres were prepared.Using polystyrene spheres as templates,the titanium dioxide was firstly coated on the surface of template by sol-gel method,and then carbonized at high temperature to obtain hollow structured TiO2.Next,MoO2 nanoparticles were hydrothermally grown inside the hollow TiO2 nanospheres,and then the surface of the spheres was coated with polydopamine.After being processed by annealing step,porous core-shell spherical structured MoO2@TiO2@NC nanocomposite was obtained.The size of the prepared core-shell structure MoO2@TiO2@NC nanospheres is about 230 nm.The molybdenum dioxide nanoparticles with a size of 10-15 nm were uniformly filled inside the hollow nanospheres.The MoO2@TiO2@NC electrode sheet was assembled into a button cell and tested at a current density of 100 mA g-1.After 100 cycles,the discharge capacity maintained at 564.4 mA h g-1,which is much higher than commercial MoO2.The MoO2@TiO2@NC electrode material with a special structure shows excellent lithium storage performance due to the construction of the titanium dioxide and molybdenum dioxide bimetal oxide system and the synergy effect between the surface carbon layer.