Research On The Construction Of MoO₂-based Multi-level Structure And Lithium Storage Performance

In this thesis,by using the molybdenyl acetylacetonate as the raw material,the hierarchical MoO₂ materials with porous and hollow spheres and coral-like stucture were synthesized by template-free solventhermal method.The Mo O₂ howllow spheres composites coated by carbon and MoS₂ were also prepared in order to improve the Li storage performance.The morphology and structure of the samples were characterized.The properties of these products were also studied as the electrode materials in LIBs.The main results are as follows:Monodisperse MoO₂ hierarchically porous spheres were synthesized by a template-free solvothemal method using methanol as solvent after calcination in N₂.The as-synthesized MoO₂ spheres are assembled from primary nanoparticles of 30-40 nm in size,with a average diameter of 500-600 nm.The MoO₂ hollow spheres were synthesized through a one-step strategy useing n-butyl alcohol as solvent.The hollow nanosphere is about 400-600 nm in diameter and its shell is rough and assembled from numerous nanoparticles with a size of 30-40 nm.The unique hierarchical MoO₂ spheres exhibit excellent electrochemical performance.At current density of 100 mA g^-1,the initial discharge capacity of porous MoO₂ spheres is 1134 mA h g^-1,which retain reversible capacity of 709 mA h g^-1 after 60 cycles.The MoO₂ hollow spheres electrode deliveres the first discharge capacity of 672 mA h g^-1 and the reversible capacity drastically fades to 260 mA h g^-1 after 60 cycles.In order to improve the cycle performance of the hollow spherical MoO₂ material,carbon was subsequently coated on the surface of MoO₂ hollow microspheres through solvothermal method using MoO₂ hollow spheres and glucose as starting materials,followed by annealing in argon.Cycled after 60 times at the current density of 100 mA g^-1,specific capacity of MoO₂/C composites is 685 mA h g^-1.The hollow spheres coated with MoS₂ were also obtainde via.hydrothermal method using sodium molybdate and thioacetamide combined with an annealing treatment in inert atmosphere.The reversible specific capacity of the uniform MoO₂/Mo S₂ microspheres composite is 424 mA h g^-1after 30 cycles at a current density of 1000 mA g^-1.The rate capability is also successfully improved.Hierarchical coral-like MoO₂ were prepared via.a template-free solvothermal method by using the molybdenyl acetylacetonate as the raw materials and n-propyl alcohol as the solvent.The novel hierarchical coral is composed of branchs primary nano-particles of 20 nm.The material shows excellent lithium storage performance,delivers a maximum capacity of 827 mA h g^-1,and the reversible specific capacity is still higher than 740 mA h g^-11 after 60 charge–discharge cycles at a current density of100 mA g^-1.When cycled under the density of 500 and 1000 mA g^-1,the reversible specific capacity is 540 and 450 mA h g^-1 respectively.