Preparation Of Ternary Molybdenum-based Metal Oxide Hierarchical Structures And Their Lithium Storage Properties

Ternary molybdenum-based metal oxides are considered as a kind of promising anode material for lithium-ion batteries because they provide a high theoretical specific capacity close to 1000 m A h g^-1.The synergistic effect resulted from the two different metals in the same crystal lattice makes the ternary molybdenum-based metal oxides exhibit high electrochemical activity.The investigations were done involving in the ternary molybdenum-based metal oxides as the anode material for lithium-ion batteries as follows:(1)Five kinds of ternary molybdenum-based metal oxides anode materials(Mn MoO₄,Fe₂(MoO₄)₃,Co MoO₄,NiMoO₄,Cu MoO₄)with spherical hierarchical structure were successfully prepared by simple solvothermal method using organic complex salts as precursors.Among them,the porous Co MoO₄ microspheres exhibited the best lithium storage performance.After 50 charge and discharge cycles,at a current density of 0.4 A g^-1,the reversible specific capacity remained 731.4 m A h g^-1.(2)By simply changing the p H value of the reaction system and reaction time,two hollow Co MoO₄hierarchical structures were obtained,namely hollow hydrangea-like and hollow spherical Co MoO₄,and their growth mechanism was discussed in detail.Both hollow hierarchical structures Co MoO₄ exhibited excellent lithium storage performance,and the hollow hydrangea-like Co MoO₄ showed slightly higher capacity than spherical Co MoO₄.At a current density of 0.4 A g^-1,the reversible capacities of hydrangea-like and spherical Co MoO₄ were 997.8 and 925.4 m A h g^-1,respectively,after 50 charge and discharge cycles.(3)Hollow spherical Co MoO₄/C composite material was successfully prepared by a simple secondary hydrothermal method using inexpensive glucose as a carbon source.The reversible specific capacity of the composite was maintained at 734 m A h g^-1 after200 cycles at a current density of 0.4 A g^-1.It was still as high as 438 m A h g^-1 after1000 charge and discharge cycles at a current density of 1 A g^-1,which is significantly higher than the cycle life of hollow spherical Co MoO₄.It should be attributed to the introduction of carbon that increases the structural stability of the overall material.(4)The polydopamine was used as the carbon source to prepare the layered coral-like Co MoO₄@C composite via dopamine polymerization at room temperature,combined with the subsequent sintering treatment.The composite exhibited superior lithium storage performance,and the reversible specific capacity was maintained at1126.9 m A h g^-1 after 560 cycles at a current density of 0.4 A g^-1.Even at a large current density of 5 A g^-1,the reversible specific capacity was still as high as 132.2 m A h g^-1after 10,000 charge and discharge cycles.The excellent lithium storage properties maybe attributed to synergistic effect of the unique hierarchical structure and carbon coating of Co MoO₄@C composite.