| Low carbon economy and clean renewable energy now become significant topics over the world, due to the increasing demands for energy, decreasing amount of non-renewable energy, such as petrol, coal and natural gas, as well as environmental problems. As a result, energy storage devices with high performance are urgently required to use energy more efficiently. Among all the energy storage devices, lithium ion batteries exhibit much more advantages, such as high voltage, high energy density, etc., thus they have been quite popularly used in portable devices since their birth, and now they are nominated as new energy source for vehicles. Besides lithium ion batteries, fuel cell is another hot topic as energy source for EVs. However the storage and transportation of hydrogen is a crucial link for its application. For development of lithium ion batteries, their high performances, i.e., safety, good cycle performance, high energy and power density and high rate performance are mainly concerned. The key step for the further development is material innovation. Besides searching for new materials with high performance and preparation of nano materials, synthesis of composites is also an effective route for the achievement mentioned above.In this dissertation, the effects of composites for the improvement of lithium ion batteries are discussed with four different composites, SSG graphite/VGCF, core-shell TiO2/C, porous TiO2/C and Ru/Li2O composites. At the main time, the composite concept has been adopted to hydrogen storage system. XRD, SEM, TEM, FTIR and XPS were used for characterization, CV, EIS and discharge-charge measurements were used for investigation of electrochemical performance. TDS was used for hydrogen storage analysis. The main contents are as following:The concept of'composites'has been used in lithium ion batteries for a long time. The electrode is composed with active material, conductive additives and binder to increase the conductivity and stability. Chapter 3 is focused on how the dispersion of SSG graphite/VGCF affects electrochemical performance of graphite electrode. With the control of technology art, two kinds of graphite electrodes were obtained, with well and poor dispersion of VGCF, respectively. They are called WF (well fabricated) and PF (Poorly fabricated) electrode afterwards. It is found that WF electrode shows high reversible capacity in first cycle and better cycling performance, however, the reversible capacity and cycling performance are poor for PF electrode. The results got from the measurements of EIS, SEM, EDX, XPS and Raman reveal that the dispersion of SSG/VGCF greatly affects the electrochemical performance of graphite electrode. When the dispersion is homogeneous, homogeneous electronic conductivity dispersion is achieved for the whole electrode, thus perfect SEI film forms in the first cycles, which could prevent further electrolyte dispersion, as well as irreversible consumption of Li, and the good cycling performance is obtained. While for PF electrode, the dispersion of VGCF and electronic conductivity are bad, no perfect SEI film forms in the first cycles, and further decomposition of electrolyte occurs in the following cycles, giving rise to bad cycling performance.Chapter 4 concerns preparation of TiO2-C nanocomposites by first adopting emulsion polymerization method to form TiO2-PAN nanocomposites, followed by calcination in inert atmosphere. CV results reveal that both nano TiO2 and TiO2-C nanocomposites present redox peaks at 1.7,2.0 V vs. Li/Li+. TiO2-C nanocomposites show better cycling performance than that of nano TiO2. EIS results indicate that after carbon coating, the charge transfer resistance decreases. The apparent diffusion efficiency of TiO2-C nanocomposites is 10 folders larger than that of nano TiO2. After carbon coating, the aggregation of nanoparticles during cycling can be suppressed, and electronic conductivity is increased, thus TiO2-C nanocomposites show better electrochemical performance.The work mentioned in Chapter 4 is preparation and electrochemical performance investigation of porous TiO2 and TiO2-C by using PS template and sucrose as carbon source. The charge-discharge results reveal that at low current rate, both porous TiO2 and TiO2-C electrodes present the similar electrochemical performance, however, when increasing the charge-discharge rate, the polarization increases greatly for porous TiO2 electrode, the charge and discharge curve increases/declines faster. After carbon coating, the polarization is suppressed, giving rise to larger reversible capacity. Furthermore, TEM micrographs of both electrodes after 30 cycles at 0.5C indicate that, both materials suffer volume expansion during cycling, however, the carbon layer of TiO2-C electrode could suppress the volume expansion and keep the stability of porous structure.Chapter 6 is about interfacial storage of lithium and hydrogen in Ru/Li2O nanocomposites. The Ru/Li2O nanocomposites were prepared by electrochemical lithiation method. The electrochemical performance of Ru/Li2O nanocomposites in the potential range between 0.05 to 1.2V vs. Li/Li+ display a capacitor performance, with excellent rate performance. They deliver 120 mAh/g at 5C (1C=120 mA/g), even 20 mAh/g at 60C. The interfacial storage mechanism could provide a bridge between lithium ion batteries and capacitor. Interfacial storage of hydrogen in Ru/Li2O nanocomposites was investigated as well for more evidence of this mechanism. To avoid the interference of H from SEI film in Ru/Li2O nanocomposites, D2 was adopted instead of H2 for absorption, and the Ru/Li2O nanocomposites were first calcined to 400℃before hydrogen adsorption. TDS was used to investigate the substance desorption. The results indicate that Ru/Li2O nanocomposites after calcination can release D2 after absorption of D2 at room temperature. In comparison, the hydrogen storage of Ru nanoparticles prepared by hydrogen reduction method and further discharging to 0.8V vs. Li/Li+ was also investigated. For Ru nanoparticles, there is no HD or D2 desorption during the TDS measurement after loading D2at room temperature. Since Li2O can not be hydrogenated, the differences of the D2 desorption between Ru-Li2O nanocomposites and Ru nanoparticles may be correlated with the interfacial 'job-sharing'storage. The above results indicate that both lithium and hydrogen could be stored at the interfaces in Ru-Li2O nanocomposites reversibly. How far hydrogen is dissociated and ionized in the proper sense of the mechanism discussed, remains to be investigated.With the results from the above four systems studied, the effects of different nanocomposites as electrode materials in lithium ion batteries can be concluded as following:First, nanocomposites with carbon components could enhance the electronic conductivity, decrease the polarization and give rise to better rate performance; Second, nanocomposites with carbon coating layer enhance the structural stability. Third, interfacial storage of lithium in nanocomposites provides a bridge between lithium ion batteries and supercapacitors. Furthermore, the interfacial storage mechanism could be used in hydrogen storage, providing more evidence for the mechanism.
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