| Lithium ion batteries have been already used in portable electronic devices widely due to the superior advantages, e.g. high voltage, high specific capacity, high energy density, environmental friendlyness, no memory effect, longer cycle life and so on. The performances of the cathode materials have a direct influence on LIBs, which are the key materials for LIBs. In addition, the performance of graphene composites as anodes in LIBs is greatly improved due to the specific structure and excellent properties of graphene. In this paper, we synthesized LiFePO4through solvothermal method, and prepared porous ceria,(ceria, tin dioxide)/graphene composites using hydrothermal and microwave method, respectively. The details are as following:(1)Rhombus LiFePO4was synthesized through solvothermal method with the raw materials of LiOH·H2O, FeSO4·7H2O, H3PO4and L-Vc. LiFePO4/C was obtained as the glucose was used as carbon source. The phase, morphology and structure of the sample were characterized by XRD, SEM and TEM, and the electrochemical properties were tested on the cell tester. We also investigated the influence on its structure and morphology by using different molar ratio of the raw materials, different mass of PEG20000. The results demonstrate that the optimum molar ratio of the raw materials is nLi:nFe:nP:nvc=3:1:1:0.5, and the mass of PEG20000is0.4g. The discharge capacity of LiFePO4/C prepared at the best condition is151.1mAh/g at0.1C, and the first coulombic efficiency is93.87%. The rate performance and CV testing also indicate that LiFePO4/C has a superior rate capability and cyclic stability.(2)Porous CeO2was obtained by a hydrothermal method with a subsequent calcination while GO was used as a template, CeO2was characterized by XRD, SEM, TEM and BET. The adsorptive, electro-catalysis and battery performance testing was used to illustrate that the material exhibits an outstanding adsorptive ability to organic dyestuff, a better electro-catalysis capability to L-cys and has a certain practical application in LIBs. CeO2/graphene composites were obtained through a microwave-assisted method and characterized by XRD, SEM and TEM. Microwave-assisted method is a rapid, low-cost and ideal method to synthesize graphene composites without subsequent calcinations process.(3)Tin dioxide/graphene nano-composites were obtained through a hydrothermal method using SnCl2as tin source. We can see clearly the tin dioxide nano-particles were deposited on the graphene sheets with an average diameter of～13run. The battery performance testing results were:the first discharge capacity is2576.5mAh/g at200mAh/g and its coulombic efficiency is57%, the charge and discharge capacity were993.2mAh/g and1002.4mAh/g after50cycles, respectively, much higher than the theoretical capacity of graphite (372mAh/g). The rate capability of the composites also demonstrates that the materials could still retain a higher electrochemical activity even undergoing discharge-charge cycling at a high current density. The CV testing was used to study the mechanism of the reaction. |
