Preparation Of Graphene-based Nanocomposites And Their Application In Li-ion Battery

Li-ion batteries (LIB) have attracted great research interest due to high electromotive force, high energy density and long cycle life. And the positive and negative electrode material is the key part in the battery, which determine the batteries performance. LiNi1/3Mn1/3Co1/3O2has been shown to be one of the most promising alternative cathode materials in terms of operating voltage, high specific capacity, cyclic stability. Lu4Ti5O12has a flat discharge plateau, structural stability. It’s promising for high rate battery applications.Graphene has also attracted a lot of attention in recent years, owing to its high electronic conductivity and excellent structural stability, large surface area. Graphene has been used as a conductive medium for the development of highly efficient LIB electrodes in some papers. In order to improve the cycling performance and rate capability of the LIB, the electrode materials based on graphene is prepared in this thesis. The materials was characterized by Scan Electron Microscope(SEM), X-ray Diffraction(XRD) and investigated by constant current charge-discharge test.The LiNi1/3Mn1/3Co1/3O2/graphene composite with diffenent content of graphene is synthesized in this paper. The result shows that2.5w.t.%has a discharge capacity205.4mAh/g at0.1C,150mAh/g at0.5C. It also has a good cycle performance.The spinel Li4Ti5O12was synthesized by solid reaction. The discharge capacity is113.5mAh/g at0.1C,72mAh/g at1C. In order to improve its performance, Li4Ti5O12and graphite oxide was prepared, under the optimized synthetic conditions (calcination temperature is500℃), the composite has much better performance than the pristine Li4Ti5O12. The discharge capacity at0.1C is122.1mAh/g, the capacity retention is95.9%after40cycles. The The higher temperature makes further reduction of graphene.The nano flower-like Li4Ti5O12was synthesized by hydrothermal method, under the optimized synthetic conditions(hydrothermal time is24h, calcination temperature is550℃), the results show that the discharge capacity is160mAh/g at0.1C,127mAh/g at1C. It shows a higher capacity than Li4Ti5O12prepared by solid reaction. Because the nano flower-like structure shorten the diffusion path of lithium ions. The Li4Ti5O12/graphene composite is in situ synthesized by hydrothermal method. The discharge capacity reached150mAh/g at1C,125mAh/g event at5C. The composite shows an excellent performance.