Study On Controlled Preparation And Lithium-ion Battery Performance Of Ternary Transition Metal Oxide Hollow Structures

This thesis focuses on the preparation of porous yolk-shell structured Mo-doped Ni Co₂O₄ nanospheres and yolk double-shell Mn_0.5Zn_0.5Co₂O₄/C nanospheres by a self-templating solvothermal method combined with annealing process,and both materials were used in the anode of lithium-ion batteries.（1）By a simple solvothermal method,NiCoMo precursors were prepared,and Mo-doped Ni Co₂O₄ nanospheres with two different structures were obtained by controlling different temperatures during the annealing process.Specifically,porous nanospheres with a pore diameter of about 95 nm were obtained at 350°C.Porous yolk-shell structured nanospheres were obtained at 500°C.The core diameter of the porous yolk-shell nanosphere spheres is about 530 nm,the thickness of the shell is about110 nm,and the diameter of the core porosity is about 85 nm.The structure of porous yolk-shell provides a greater specific surface area to effectively buffer the volume expansion of the charge/discharge process.More importantly,the porous core of the porous yolk-shell structure nanospheres can accelerate the penetration of electrolyte and promote the transport and translocation of Li⁺and e^-.When applied to Li Bs anode materials,nanospheres with porous yolk shell structure demonstrated superior electrochemical property with high reversible capacity(The current density of 100 m A g^-1 achieved the specific capacity up to 1338 m A h g^-1),excellent rate performance(The specific capacity at the current density of 2000 m A g^-1 was 820 m A h g^-1)and stable cycle life(specific capacity of 1360 m A h g^-1 after 200 cycles at a current density of 100m A g^-1).（2）By self-templated solvothermal method to dope Mn into Zn Co₂O₄,Mn_0.5Zn_0.5Co₂O₄/C nanospheres with yolk-double shell structure were prepared.Firstly,Mn Zn Co glycerate precursors were synthesized,and then annealed at 400°C to obtain Mn_0.5Zn_0.5Co₂O₄ nanospheres with yolk shell structure.Then the Mn_0.5Zn_0.5Co₂O₄/C nanospheres with yolk-double shell structure were annealed again by coating PDA on its surface.The unique yolk-double shell structure can effectively buffer the volume expansion and reduce the diffusion path of Li⁺.The Mn_0.5Zn_0.5Co₂O₄/C nanosphere anode material had a specific capacity of 1001 m A h g^-1 when cycled 100 cycles with a current density for 200 m A g^-1.The specific capacity remained at 971 m A h g^-1 even after 150cycles at a higher current of 500 m A g^-1.Thus,Mn_0.5Zn_0.5Co₂O₄/C nanospheres as the anode material for Li Bs have outstanding electrochemical performance.Compared with Zn Co₂O₄,in Zn Co₂O₄ doped with Mn,Mn can occupy the octahedral gap of the spinel structure,which helps to enhance the pseudocapacitive properties of the anode material,accelerate ion diffusion and improve charge transfer.