Preparation And Electrochemical Properties Of Carbon And Carbon - Nitrogen Co - Doped Titanium Dioxide Nanotubes

Compared to traditional energy storage system, such as Lead-acid batteries, Cadmium nickel batteries and Nickel-metal hydride batteries, lithium-ion batteries have the advantage of high-energy storage density, high voltage, long cycle life and no memory effect. Many advanced Lithium-ion batteries negative materials, including Si, which have a high theoretical capacity value of4200mAhg-1, but easy cause large volume change during insertion and extraction of Li+, leading to active material pulled off from electrode. In addition, graphite is widely used commercial material, but its low operating voltage is too close to Li electroplating voltage to form a solid electrolyte interface, raising concerns over safety and loss of capacity.Titanium dioxide (TiO2) which attracted great interest by many scientists and researchers is considered as a promising negative electrode for Li-ion batteries due to its small volume change(<4%), good cyclic stability, high discharge voltage plateau and abundant in nature etc. But it presents poor electron transfer ability which attributed to its semi-conductor nature limits its real performance in Li-ion batteries. Many researches have indicated that the conductivity of TiO2can be promoted by doping heterogeneous elements and then improve the performance of Li-ion batteries. In this work, we will adopt well-alined, pore size-tuned TiO2arrays as templates to achieve "heterogeneous elements doped nanotubes arrays" with heterogeneous elements such as C、N by ionic penetration (liquid carburizing, gas nitriding). Then these doped materials will be assembled into Li-ion battery as electrodes and its electrochemical properties will be tested. After that the effect of doped elements to TiO2nanostructure arrays will be investigated and the changes of physical and chemical properties of materials will be analyzed. The differences between charge/discharge capacity and EIS among all the as-prepared materials will be compared and determine the best optimized configuration of materials.TiO2nanotube arrays fabricated in different electrolytes by anodization, which were used to the half-cell battery negative material to test their electrochemical property after annealing in air at450℃. The initial discharge capacity, capacity retention(87.2%) after thirty cyclicing of nanotube anodized in organic solvent were higher than that of the two types of nanotube anodized in aqueous electrolytes. In adition, the AC Impedance value of nanotube anodized in organic solvent is much smaller than that the others.On the basis of the previous work, we first prepared TiO2nanotube uesd NH4F and H3PO4solution as electrolyte, through soaked in glycol, then obtained the C-doped TiO2nanotube after calcined at450℃. Moreover, C-N-doped TiO2nanotube arrays were first anodized in organic solvent, then as-grown sample were calcined at450℃in vacuum tube furnace, under a flow of dry N2, with a heating rate of5℃/min.I used heterogeneous elements (C、N)doped nanotube as electrode and test their electrochemical properties. Compared with undoped samples, its found that heterogeneous elements doped sample obviously improved the initial discharge capacity of lithium batteries, the coulomb efficiency, cycle stability, capacity retention and AC Impedance, etc,.