Synthesis Of Ti-based Anode Materials For Lithium Ion Battery And The Performance

Lithium ion batteries are one of the most important energy storage and conversion technologies with prominent advantages of high energy and power density as well as long cycling life, and they have been widely applied in portable electronic devices, communication facilities, stationary energy storage systems and ever-enlarging markets of electric vehicles. Among various applicable materials, Ti-based oxides have demonstrated their potential anode candidates for Lithium ion batteries due to the excellent cycling stability, high safety, and the environmental friendliness. However, there is still a challenge to improve their high-rate performance. Therefore, the development of high-rate electrode materials becomes the focus of our research. This work can be divided into three parts, the effects of the structure and morphology of Ti-based materials, the embedded-metal, and the incorporation of graphene on the electric properties of the Ti-based materials when they were used as the anode of the lithium ion batteries. The details include:TiO2microspheres were designed and synthesized via one-pot hydrothermal process. Through well designed calcination, TiO2microspheres with various amounts of carbon-residue, such as the core/shell C@TiO2, hollow neat H-TiO2, and hollow C/TiO2composites were obtained. When these microspheres were used as anode materials for lithium ion batteries, the comparison results indicated the lithium storage performances were significantly influenced by the structure and the carbon-residue. With a thin shell of TiO2nanoparticles and carbon-residues, the capacity of hollow C/TiO2-400composite maintained as143.3mAh g-1at0.5C (83.5mA g-1) after100cycles. The cycle voltammograms (CV) and electrochemical impedance spectroscopy (EIS) analysis results further revealed that lithium ion insertion/extraction processes were reversible, the diffusion coefficient of lithium ion in the hollow C/TiO2-400composites was much higher than those of others, because the hollow structure can act as the ion-buffering reservoir and facilitate lithium ion transfer from both sides of the shell, moreover, the carbon-residue in the shell improved the conductivity as well. Ordered mesoporous TiO2-C-Cu composites with Cu nanoparticles embedded were prepared via an evaporation induced of self-assembly (EISA). The characterization results revealed that the self-assembly composites were composed of the ordered mesoporous structure with about5nm diameter channels and a large surface area of161.9m2g-1. Cu nanoparticles were highly dispersed in the wall. When the composites were used as the anode for lithium ion batteries, the lithium storage performances were effectively improved by "Cu-embedded" nanoparticles at low current density. The reversible capacities of TiO2-C-Cu could be stable as150.0mAh·g-1at the current density of33.4mA g-1, much better than that without "Cu-embedded" Moreover, the CV and EIS analysis further revealed that the electrochemical performances were significantly improved by "Cu-embedded", as well as by the existence of ordered mesoporous channels. Accordingly, incorporating metals into TiO2composites would be a convenient and economic method to improve lithium insertion/extraction characteristics.The exfoliation of graphene oxide (GO) was achieved by the intercalation of imidazole ionic liquids (ILs) of3-methyl-l-octylimidazolium chloride ([Omim]Cl) and1-Butyl-3-methylimidazolium chloride ([Bmim]Cl). With longer alkyl chain,[Omim]Cl showed a superior exfoliation of GO. When this exfoliated GO-[Omim]Cl was used as the carrier, LTO/graphene-IL nanocomposites were obtained via the microwave-assisted hydrothermal reaction. The crystalline LTO nanoparticles with an average size of20nm grown on the graphene sheet provided a high electrode/electrolyte contact area, which enhanced the electron transport and shortened the path for lithium ion transfer. When used as the anodic material for the lithium ion battery, the LTO/graphene-IL nanocomposites exhibited excellent reversible capacity of159mAh g-1at0.5C after100cycles, and a high-rate performance (162mAh g-1at0.2C;148.5mAh g-1at20C, and162mAh g-1at0.2C, again). The EIS analysis results further revealed that the Rs and Rct of LTO/graphene-IL were both lower and the diffusion coefficient is50times larger than that of LTO and LTO/graphene without graphene or ILs.In brief, both carbons and metals can effectively improve the conductivity of Ti-based materials; the nanostructure can provide a short path for lithium ion transfer; the hollow spheres, the mesoporous channels as well as the graphene network can significantly facilitate the lithium insertion/extraction.