| Titanium dioxide(TiO2) has been widely studied as anode material of lithium ion batteries(LIBs), due to its low cost, non-toxicity, abundance as well as structural stability during lithium insertion/extraction, free of electrochemical Li deposition and decomposition of organic electrolyte which is vital for the safety of power-type LIBs. However, the Li storage performance of LIBs with TiO2 in all polymorphs as anode material is severely limited because of its slow lithium ion diffusion rate and poor electronic conductivity. Many researches have been devoted to overcoming this disadvantage, including synthesizing nano-sized TiO2 to reduce ionic and electronic transportation distance, incorporating second phase with high electronic conductivity and substituting a small quantity of Ti4+ or O2- sites with metal cation or non-metal anion.Nanotube titanic acid(NTA) has attracted lots of interest over the past 10 years because of its one-dimension tubular structure with muti-walls, which makes it own large specific surface area and stronger ion-exchange ability. Previous studies have recovered that when calcined at elevated temperature, nanotube titanic acid turns into anatase TiO2, accompanied with a process of dehydration. Also, novel TiO2 with defects of oxygen vacancy can be prepared via manipulating the dehydration process. Based on the abovementioned and using nanotube titanic acid as precursor to prepare TiO2 as the anode material of LIBs, the major research contents are as follows:(1) TiO2 nanoparticles with oxygen vacancy defects existed only in the bulk or both in the surface and bulk phase were prepared by treating NTA in air and H2 atmosphere, respectively. The crystal structure, morphology, electron resonance spectrum and X-ray photoelectron spectrum of as-prepared products were investigated. The influence of surface oxygen vacancies and bulk oxygen vacancies on the electrochemical properties of products was investigated. It was found that the surface oxygen vacancies can act as physical space for Li-ion storage so as to improve the specific capacity of the electrode, while the bulk oxygen vacancies can improve the rate performance of the electrode.(2) Tubular TiO2 with large specific surface area was obtained by calcining nanotube titanic acid under vacuum. As-prepared tubular TiO2 makes it feasible to increase the contact area between active material and electrolyte, thereby providing efficient access for Li-ion. The generated defects of oxygen vacancy during the process of calcination process effectively improve electrical conductivity of the as-prepared tubular TiO2, thereby resulting in excellent electrochemical properties. In order to have a good knowledge of the relationship between pseudo capacitance and electrochemical property, we preliminarily analyzed the contribution of pseudo capacitance and bulk lithium-ion insertion via dissecting cyclic voltammograms of tubular TiO2 at various scan rates. It turns out that Li+ insertion/extraction process is a diffusion controlled process and it delivers pseudo capacitance at high charge/discharge current density.(3) Since the electrochemical properties of Li4Ti5O12 are improved by being coated with TiN, we studied the synthesis of TiO2/TiN at different reaction conditions and evaluated the electrochemical properties of the products. It was found that a amount of TiO2 is formed when TiN is calcined at 340℃, but the rate performance of the products is poor because of the large particle size and the small bonding force between Ti N and TiO2. The structure and morphology of TiN nanoparticles remain nearly unchanged when they undergo hydrothermal reaction at lower temperature, but the nanoparticles are transformed to rod-like structure when the concentration of alkali liquid is raised and the reaction temperature and the reaction time are elevated. In a word, although TiN exhibits good rate performance, it seems not to be a desired lithium ion storage material. |
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