| Low carbon economy and clean renewable energy now become significant topics over the world, due to increasing demands for energy, decreasing amount of non-renewable energy, such as petrol, coal and natural gas, as well as environment problems. With the economic development and the improvement of living standards, there is a growing emphasis on the energy development and the environment improvement. As a result, energy storage devices with high performance are urgently required to make energy utilization more efficiently. Recently, with the rapid development of the portable electronic and communication devices, such as mobile telephone, digital camera, notebook, especially for hybrid electric or all electric vehicles (HEVs or EVs), people need the lithium ion batteries with higher energy density, better cycliability and reliability. The breakthrough in the electrode materials is the key point for exploit the next generation of the lithium ion batteries. At present, a lot of research work focus on two sides:on the one hand, to ensure the lithium ion battery has good cycle stability, the point that designing the electrode materials with reasonable structure to relieve the volume expansion in the charge-discharge process was adopted; on the other hand, standpoint that preparing composite to realize the maximization of the lithium ion battery capacity was accepted. Among the various electrode materials, metaloxide/nitrogen doped carbon nanocomposites, because of their unique morphology and structure. besides, the composites with higher specific surface so as to alleviate the volume expansion effectively, is expected to more effectively increase the reversible capacity of the material. In addition, metal oxide/nitrogen doped carbon nanocomposites not only can improve the electrical conductivity of the composite, but also benefit for the rapid electron transport. meanwhile, metal oxide/nitrogen doped carbon nanocomposites achieve the complex of many ingredients to overcome the shortcoming of unsatisfied capacity of a single component.In this paper, we systematically investigate the preparation and performance of metal oxide/nitrogen doped carbon nanocomposites as anodes of lithium ion battery. Three kinds of electrode materials were successfully prepared by solvothermal, freeze drying and direct redox methods integrated with calcination, respectively. The synthesized samples were well characterized and their electrochemical performances were studied. The main achievements can be summarized as follows:1. A new strategy was presented for the synthesis of ZnO/N-doped reduced graphene oxide (N-GN) composites with different nitrogen content by a pressure-adjusted hydro thermal method in ammonia atmosphere combined with freeze drying and thermal treatment. Because N-doped GN can prevent the ZnO NPs from aggregation effectively, thus the composite can maintain the integrity of the structure and effectively improve the conductivity of electrode materials. The results demonstrate that ZnO/N-GN-3 composite with the nitrogen content of 8.7% as anode material possesses the most excellent electrochemical performance, which exhibits a reversible capacity of 1100 mA h g-1 at the current density of 0.2A g-1 after 100 cycles. The further investigation shows good rate performance of the ZnO/N-GN-3 composite.2. Co3O4/N-GN composite was successfully prepared by simple freeze-drying and thermal annealing process subsequently, with Co(NO3)2-PVA solution as precursor and graphene oxide as the supporting carbon material. A high reversible capacity of about 950 mAhg-1 is maintained without obvious decay up to 100 cycles at the current density of 0.2Ag-1, showing the high specific capacity, good cycle performance and high coulombic efficiency. The composite also shows excellent rate performance due to the better conductive networks provided by the composite.3. Fe3O4@nitrogen doped carbon (C/N) nanosphere composite was successfully prepared by hydrothermal,thermal annealing process subsequently, with FeCl3.6H2O was used as a source of iron combined with auxiliary reagents. Fe3O4@C/N hollow nanosphere composite was etched in hydrochloric acid solution, finally the double-shell Fe3O4@C/N hollow nanosphere composites were obtained. The double-shell Fe3O4@C/N hollow nanosphere composites shows good cushioning effect. As anode materials, the as-obtained double-shell Fe3O4@C/N hollow nanosphere composite with etching for 15 mins shows a reversible capacity as high as 1772 mAh g-1 after 100 cycle at the current density of 0.2Ag-1, which is potential for practical application in lithium-ion batteries. Besides, the as-obtained double-shell Fe3O4@C/N hollow nanosphere composite also exhibits high rate performance. |
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