Fabrication And Properties Of Transition Metal Oxides As Anode Materials For Lithium-ion Battery

Compared with other rechargeable batteries,lithium-ion batteries have a higher energy density for more battery life in a lighter package and have no memory effect.As an energy storage device,lithium-ion batteries have broad market prospect.With the rapid development of mobile information terminal products and new energy vehicles industry,lithium-ion batteries with high-performance are urgently needed.To develop new anode materials with high capacity and good stability is an effective way to prove the performance of lithium-ion batteries.Transition metal oxides have attracted much attention because of their higher theoretical capacity than that of commercial lithium-ion battery graphite anode material.However,the high capacity is accompanied by low electronic conductivity and huge volume change upon cycling,which restricts the application of transition metal oxides.Several ways have been developed to optimize the electrochemical properties of transition metal oxides,such as preparing unique structural materials and constructing hybrid material systems.In this thesis,transition metal oxides and their composites with unique structure were prepared through the optimization of the synthesis process.In addition,the electrochemical properties of the products were characterized.The main contents are as follows:?1?Nanosheets-based NiO microspheres were prepared by ethanol/water mixing solvent thermal method under a relatively low temperature combined with subsequent heat treatment.The morphologies of the obtained NiO precursors under different reaction conditions are quite different.The results shows that the precursor with optimal morphology can be synthesized when the ethanol/water volume ratio is 1:1.Characterization results show NiO microspheres are constructed from the assembly of nanosheets.Moreover,NiO microspheres exhibit hollow structure and have a large specific surface area of 101.84 m2/g.NiO microspheres deliver a reversible specific capacity of 415 mAh/g at a current density of 100 mA/g after 100 cycles.Moreover,NiO microspheres exhibit good rate performance even at a very high rate.?2?Nanosheets-based NiO/ZnO microspheres were prepared through a simple hydrothermal method combined with subsequent heat treatment.Characterization results show NiO/ZnO microspheres are constructed from the assembly of nanosheets,and have a large specific surface area of 82.41 m2/g.ZnO or NiO microspheres were also prepared in the same way for comparison.The nanosheets-based NiO/ZnO microspheres show a remarkable composite effect,exhibiting a higher specific capacity?508 mAh/g at 100 mA/g after 50 cycles?and excellent cycling stability in comparison to those of pure ZnO or NiO microspheres.?3?A novel yolk-shell Co₃O₄@C composite was successfully prepared through a coating method with Co₃O₄ submicrospheres as the cores.This process involved the hydrothermal preparation of Co₃O₄ submicrospheres,the coating of silica shell layer on the surface of Co₃O₄ submicrospheres through St?ber method,the coating of carbon layer on the surface of silica layer through the hydrothermal carbonization of glucose,and the etching of silica layer by immersing in sodium hydroxide solution.Characterization results show the carbon content of yolk-shell Co₃O₄@C composite is about 10.5 wt%.This novel yolk-shell structure could provide interstitial void space to accommodate the huge volume change of Co₃O₄ and prevent the aggregation of particles by the shell during charging/discharging process.thus improving the cycling performance of the composite.Also,the existence of carbon layer can improve the electron conductivity of the composite,thus improving the electrochemical performance of the composite.As an anode material for lithium-ion batteries,this Co₃O₄@C composite exhibits high capacity,good cycling stability.It delivers a higher specific capacity of approximately 605 mAh/g at a low current density of 100mA/g after 50 cycles than that of pure Co₃O₄?468 mAh/g?.