TiO₂-Based Anode Materials Derived From Pyrolysis Of Single Molecule Precursors And Their Lithium Storage Properties

TiO₂ was regarded as a promising anode material for next-generation lithium-ion batteries because of its low cost,environmental friendness,structural stability,and high safety.However,TiO₂,as a semiconducting metal oxide,has poor electronic conductivity and low Li⁺diffusivity,resulting in its poor rate performance as an anode material.This drawback limits its practical application.Usually,the electrochemical properties of TiO₂ can be improved by the combination of materials with high conductivity,doping of heteroatoms into the crystal lattice and preparation of nanoscale TiO₂.Based on these considerations,this paper mainly focus on the investigation on the preparation of TiO₂-based materials with special morphology,composition and phase structure,that is,one-dimensional porous titania with different phases and anatase/N-doped carbon nanocomposite?TiO₂-NPs/NC?by direct pyrolysis of single source precursor under different experimental conditions.Also,the unique electrochemical performances of the as-prepared TiO₂-based samples as anode materials were studied in detail,to achieve TiO₂-based anode materials with excellent performances.The main research content of this thesis can be summarized as follows:1)The preparation conditions and electrochemical properties,as well as the lithium-ion storage mechanism of three different phase structures such as pure anatase,anatase/rutile nanocomposite and anatase/TiO₂-B nanocomposite were investigated;2)The electrochemical properties of TiO₂-NPs/NC nanocomposites prepared from the pyr-olysis of single source precursor at different temperatures were studied;3)The lithium-ion storage mechanism and dynamic characters,as well as the charge-dischar ge performances of the as-prepared TiO₂-NPs/NC nanocomposite were investigated and discussed.Five experimental results and/or conclusions were summarized as follows:1)TiO₂-based anode materials with different phase structures and special composition can be prepared by the pyrolysis of single molecule precursor by controlling the experimental conditions.2)Compared with the electrochemical properties of the three TiO₂-based anode materials with different phase structures?pure anatase,anatase/rutile and anatase/TiO₂-B?,it was found that anatase/TiO₂-B nanocomposite exhibited the best electrochemical performances.3)By careful study and analysis the electrochemical properties of TiO₂-NPs/NC nanocom-posites prepared from different calcination temperatures,it was found that the TiO₂-NPs/NC nanocomposite obtained from pyrolysis of a single molecule precursor at 550 ^oC exhibited the best electrochemical performances.4)An analysis of the lithium storage mechanism and dynamic characters by the voltamme-tric sweeps indicated that the total lithium storage capability of the as-prepared TiO₂-NPs/NC nanocomposite were attributed to the synerstigistic roles of pseudocapacitive behavior at the surface of the material and the lithium intercalation processes?Faraday mechanism?.Furthermore,the ultrafine TiO₂ nanopaticles affored the high lithium ion diffusion coefficient(D_Li+).5)The as-prepared TiO₂-NPs/NC nanocomposite with small specific surface area could also exhibit good rate performance,cycling stability and high specific capacity.The specific capacities of this material reached 360,270,220,160 and 125 mAh g^-1 under the current density of 0.3,1.0,2.0,4.0 and 6.0 A g^-1,respectively.After 1000 cycles under high current density of 4.0 and 6.0 A g^-1,the capacity retention was up to 93.3%and 94.0%,respectively.The superior electrochemical performance of the TiO₂-NPs/NC anode material is believed to be derived from the synergistic roles of the high electric conductivity provided by the NC matrix and ultrafine anatase particles which can mitigate the diffusion path for both electrons and ions and tolerate high strain.