新型晶态氧化锡纳米材料的制备、表征及在锂离子电池中的应用/Synthesis and Characterization Novel Crystalline Ti

2018-10-01 13:05:41

crystal TiN oxide monoxide 氧化亚


Synthesis of nanomaterials with controlled morphology, size, chemical composition, crystal structure, and in large quantity has received considerable attention because of their putative applications in nanotechnology. Being a promising semiconducting material, tin-based oxide materials have attracted much attention due to its important applications in high energy density rechargeable lithium batteries, storage of solar energy, gas sensors and organic synthesis. Great endeavors have been devoted to the synthesis of tin oxide materials with different dimensions and morphologies. And the research in tin-based oxide materials now is mainly focused on the syntheses of novel structures and functionalization. This thesis concentrated on the controllable synthesis of tin-based oxide materials with special morphology, and the application of tin monoxide materials as anode material for lithium secondary batteries.
The thesis developed a facile solution-based chemical route to tin monoxide materials with controllable morphology by using different salts, organic compounds and surfactants as structure-directing agents. Different additive reduces the chemical potential in the formation of tin monoxide via different route, and consequently influences the morphology and crystal structure of the products. The results show that CTAB has superior structure-directing function, which can effectively restrain the crystal growth along the [001] direction. As a result, single crystalline tin monoxide with nanosheet-like morphology is obtained. Moreover, it is found that the crystal lattices expand proportionally with the addition of CTAB. However, most inorganic additives such as tri-sodium citrate direct the growth via a different mechanism. They prefer to coordinate with the intermediate product, stannous hydroxide species, to reduce the growth rate. Thus the plane with lowest surface energy appears easily, leading to tin monoxide covered by {110} crystal planes.
To improve the physical and chemical performances of the tin monoxide materials, metal heteroatoms are successfully doped into the crystal lattices with the facile solution-based chemical route. Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, La, Ce, Al, Sn (IV) and Pb doped tin monoxide crystals are all successfully fabricated, which further confirms the generality of the synthesis route. Structural analysis shows that the crystal lattice parameters change regularly with the electron configuration, ionic radius and coordination number of the doped elements. The crystal defect increases remarkably with the doped heteroatoms, and the defects arrange orderly and exhibit a long periodic structure. The (1/2){110} reflections which is not available for tin monoxide thus appear.
Based on the tin monoxide nanosheets, tin oxide is produced by thermal calcination. The resulted tin oxide also has 2D nanosheet morphology and is dominated by the {101} crystal plane. However, the liquid tin metal appears during the formation of tin oxide, which roughens the surface of the nanosheets. Tin oxide doped with Cu and Ni can also be synthesized in this method. Structural analysis reveals that the crystal defects increase and prefer to arrange in long periodic structure. SAED patterns show the Ni-doped tin oxide nanosheets have the (1/2){101} reflections. It is also found that the crystal surface becomes smooth with the doping of the heteroatoms.
The application of the tin monoxide nanosheets in lithium ion battery anode material is investigated. The tin monoxide nanosheets fabricated by using CTAB as the structure-directing agent display a high reversible capacity, and the capacity can be improved to 830 mA h/g by increasing the CTAB addition, which is much higher than that of the fully lithiated graphite (372 mA h/g). It is suggested that the loosely packed {001} surfaces and expanded lattice of the as-prepared tin monoxide nanosheets render a high reversible capacity. However, the crystal structure is destroyed completely by the lithium-ion insertion and extraction, therefore deteriorate the capacity. It is found that the heteroatom doping may be promising in improve the cycling performance. When using tin monoxide doped with Cu, 50.5% reversible capacity is left after ten cycles. It is proposed that the doped Cu can prevent the aggregation of the tin species and increase the conductivity, thus offering advantages in the cycling performance.