| The development of portable electronic devices such as mobile telephone, camera and notebook PC has lead to the growing demand for high power density rechargeable batteries. Recently developed lithium-ion polymer battery systems generally consist of tin composite oxide-based anodes, lithium metal oxide-based cathodes and polymer electrolytes that contain polar liquid organic solvents. Since the cathode materials, such as lithium cobalt oxide (LiCoO2), have a relatively stable performance and mature technology, considerable effort has been devoted to search suitable polymer electrolytes and anode materials for improving the performance of lithium-ion batteries.Recently, as a new class of electrolytes, ionic liquids have received considerable attention. Furthermore, ionic liquids generally show negligible vapor pressure, high ionic conductivity, good thermal and electrochemical stability. Therefore, ionic liquids are considered to promote the safety, conductivity, thermal and mechanical properties to flexible polymers. In general, there are two ways to use ionic liquids as the components of polymer electrolytes. One is to prepare polymer electrolytes by either the polymerization of vinyl monomers in ionic liquids or a simple mixing of polymers with ionic liquids. For such system, the compatibility between polymers and ionic liquids is required. The other is to obtain the polymer electrolytes containing ionic liquids by the polymerization of ionic liquid vinyl monomers. However, polymerized ionic liquids may lead to the decrease in the number of ions and the increase of glass transition temperature, and thus result in the decrease in conductivity. To overcome this problem, gel polymer electrolyte is one of the good choices. They can not only improve the conductivity, but also retain the good mechanical properties of polymer matrix.In chapter 2, we present the gel polymer electrolytes containing ionic liquid prepared by the copolymerization of acrylonitrile (AN), methyl methacrylate (MMA), poly (ethylene glycol) methyl ether methacrylate (PEGMEMA) in 1-butyl-3-methylimidazolium tetrafluoroborate (BMImBF4). IR spectra show that there is an interaction between PEO side chains of the copolymer and imidazolium cations. The AC impedance spectra obtained are analyzed using the equivalent circuit. The fitted results show that the equivalent circuit proposed can simulate the impedance response well. The TGA analysis reveals that the gel polymer electrolytes are thermally stable up to 120℃. Master curves represent that the viscoelastic properties of the system can be satisfactorily fit to the WLF equation. In comparison with Copolymer-LiClO4 complexes without ionic liquid, all the samples containing BMImBF4 exhibit higher conductivities. The existence of ionic liquid would not only alter the ability of segmental movement, but also change the free volume content in the gel system, and further affect the relaxation time and conductivity of the electrolytes. It is obvious that the introduction of ionic liquid BMImBF4 into the gel polymer electrolytes leads to the improvement of conductivity for the electrolytes. For the Copolymer-BMImBF4(50)-LiClO4 electrolytes, the conductivity reaches the value of 4×10-4 S cm-1 at room temperature when the LiClO4 concentration is 1.0 mol/kg polymer.In chapter 3, we report the gel polymer electrolytes prepared by free radical copolymerization of poly(ethylene glycol) dimethacrylate (PEGDMA) and ionic liquid N-vinylimidazolium tetrafluoroborate (VyImBF4). The copolymer poly(VyImBF4-co-PEGDMA) is selected as a polymer matrix in view of its improved flexibility with the introduction of oligomeric PEO segment. In addition, the pendant PEO chains can also decrease the plasticizer content required for gel polymer electrolytes. Upon blending of the copolymer with EC and LiClO4, it shows that the ion environment of VyIm+ and BF4- have been changed by LiClO4 but less evidently changed by EC as compared with neat copolymer. TGA indicates that these polymer electrolytes are stable until 155℃. Results show that the VyImBF4 content, the concentration of EC and LiClO4 affect the conductivity of polymer electrolytes. The temperature-dependence conductivity of the copolymer exhibits Arrhenius behavior. For our system, though the segmental movement is also important, the ionic conduction depends much more on the channels the cross-linked polymer provided than the segmental movement of the polymers. The highest conductivity is obtained with a value of 2.90×10-6 S cm-1 at room temperature for VP1/EC(25 wt.%)-LiClO4 system, corresponding to the LiClO4 concentration of 0.70 mol/kg polymer.On the other hand, as possible anodes for next generation lithium-ion batteries, tin oxide based oxide composites show great promise for their high storage capacity and low potentials for Li+ insertion. However, as is always observed, the significant capacity fading of these anodes remains a serious application issue. Such material deficiency is due to the large specific volume changes during the Li+ insertion/extraction process. Several research groups have attempted to use SnO2 or SnO in conjunction with a carbonaceous material to ease the capacity fading. One of the most promising ways is to disperse the nanosized SnO2 into a graphene monolayer matrix, where graphene acts as both structural buffer and electro-active material during the lithium insertion/extraction. It is believed that both the particle size and size distribution are important factors that affect the material performance. Generally, smaller particles and a more uniform distribution of the particles tend to experience more moderate volume changes, thereby, give improved cycling performance.Graphene, which is a single layer of carbon atoms in a closely packed honeycomb two-dimensional (2D) lattice, has extraordinary electronic and mechanical properties. It has great potential to be massively used as an engineering material. However, the fabrication methods of graphene so far, can only produce graphene sheets in limited quantities, and the entire process is sophisticated and hard to control. Therefore, now the preparation of high-quality 2D graphene is the first and most crucial step, not only for fundamental research but also for device applications in the future. In chapter 4, graphene monolayers are successfully fabricated in large quantities via a simple chemistry synthetic route involving graphite oxidation, ultrasonic exfoliation, and chemical reduction. Transmission microscopy (TEM) observations show that graphene monolayers are produced and ripple-like corrugations. X-ray diffraction (XRD) and selected area electron diffraction (SAED) confirm the ordered graphite crystal structure of graphene nanosheets. TGA analysis shows that graphene nanosheets have much lower thermal stability than natural graphite powders, but they meet the requirements of general application.In chapter 5, a novel composite, namely SnO2-Graphene, is prepared by a simple method that include in situ growth of SnO2 on the surface of graphene through hydrothermal method utilizing cetyltrimethylammonium bromide (CTAB) as structure-directing agents. It is observed that the nanocrystalline SnO2 is homogeneously distributed on the surface of graphene matrix. The nanostructured polycrystalline SnO2 is revealed by XRD and SAED. On the base of TEM images, a mechanism is proposed to explain the formation of SnO2-Graphene composite.
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