Metal Oxides Materials And Their Composites As Anode Materials For Lithium-ion Batteries

The graphite, with good electronic conduction and stable structure, showed stable cyclicperformance and had been used as commercial anode material for lithium-ion batteries. However,the low capacity (372mA h g-1) could not meet the requirement of high performance lithium-ionbatteries. Many researchers are focusing on new anode materials with light weight and highpower and energy density. Transition metal oxide, Si-based and Tin-based materials haveattracted much attention. Among them, metal oxides have been widely studied for their highcapacity. But large volume change during charge and discharge process will cause pulverization,resulting in the loss of electrochemical activity and commercial application. Recently,nanostructured metal oxides, which could accommodate the volume changes and pulverization,demonstrate better electrochemical performance. My research is focus on improving theperformance of lithium-ion batteries through the combination of different nanostructures andmetal oxides.In this thesis, the following three aspects were mainly studied.1. Synthesis of ZnO/MnO2sea urchin-like sleeve array and its application in anodematerials for lithium-ion batteries. ZnO nanorod array was grown directly onto the Ni foil bydydrothermal method. After electrodeposited in MnSO4solution, burr-like MnO2was covered onthe surface of ZnO, froming the sea-urching like core-shell structure. There is a gap betweenZnO and MnO2on the top of the structure, showing the sleeve structure. After studing the CVcurves of ZnO/MnO2sea urchin-like sleeve array, we found both ZnO and MnO2showedreaction peaks, which indicated both of them have a reaction of Li. With cyclic process, thedischarge plateaus of MnO2began to appear and stronger, which indicated the MnO2had morecontribution. The discharge of ZnO/MnO2reached2023mA h g-1, which is nearly the sum ofZnO nanorod (746mA h g-1) and MnO2(1374mA h g-1), and the composite effect is veryremarkable. The ZnO and MnO2supported each other and improved cyclic performance. Thecapacity is1210mA h g-1after100cycles while the ZnO and MnO2are120and500mA h g-1.After carfully studied the SEM images of different cycle number, the sleeve array will open apore on the top side graduatelly, and change to open tube array. This transformantion will gainthe usage of inside materials and enhance capacity in cycle process.2. ZnO/NiO core-shell nanorod array was prepared and tested as anode materials for lithium-ion batteries. Hierarchical ZnO/NiO core-shell nanorod arrays were prepared by a seed assistedhydrothermal method combined a chemical bath deposition assisted annealing. ZnO nanorod array presented vertical alignment, small diameter and appropriate density. NiO shell showed thewrinkled film structure. ZnO nanorod array exhibited low cyclic stability. The capacity decayedto less than200mA h g-1after50cycles at200mA g-1. ZnO/NiO core-shell nanorod arrayshowed a remarkable composite effect, delivering higher discharge capacity (525mA h g-1at200mA g-1after50cycles) and excellent cycling stability in comparison to single ZnO nanorodarray.3. NiO nanostructures with different morphology were fabricated through solvothermalmethod and annealing process. Their electrochemical property was tested as anode materials forlithium-ion batteries. Firstly, NiC2O4·2H2O with different nanostructures were deposited on Nifoam via solvothermal method. TG analyze showed that the deposition of NiC2O4·2H2O hadstages. And SEM images confirmed the basic structures still remained and the surface turnedfrom smooth to porous. Considering the factors like the kinds of solvent and change oftemperature, we found different morphology could be prepared. The ethanol could make flower-like NiO nanobelt. If a small amount of water was added, the sea anemone-like NiO nanorodwould grow on the surface of Ni foam. The grass-like NiO nanowire could obtain as thesolvothermal temperature rose. When methanol was used as solvent, compact wall-like NiOnanosheet would from. The methanol and ethanol mixed solvent could lead to the formation oftremella-like NiO nanoflake with moderate density. Among them, the tremella-like nanoflakehad relatively the best electrochemical property and presented high volumetric capacity andcyclic stability when used as anode materials for lithium-ion batteries.