Study On Titanium Oxide As High Performance Anode Material For Lithium Ion Battery

Titanium oxides have been regarded as potential candidates for anode materialsof lithium ion batteries, owing to their advantages including high charge-dischargevoltage, good chemical stability, zero volume strain during the charge and dischargeprocess, and open channel for lithium-ion insertion and extraction. However, the lowelectron conductivity of lithium titanium oxide adversely has restricted its ability offast charge and discharge. With regards to the disadvantages of several titaniumoxides, we prepared nanostructure electrode materials with different structure byemploying strategies of sol-gel and hydrolysis methods. In this thesis, TG（Thermogravimetry analysis）, XRD （X-ray diffraction）, SEM （Scanning ElectronMicroscopy）, TEM （Transmission Electron Microscopy）, CV （Cyclic Voltammetry）、DC（Discharge and Charge test）、EIS （Electrochemical impedance spectroscopy）measurements are performed to characterize the morphologies, structures andelectrochemical performance of the as-derived samples.Firstly, we report a facile approach for synthesizing nanocrystalline Li₄Ti₅O₁₂via sol-gel process by employing a nonionic surfactant tri-block copolymer （pluronicF127） as the chelating agent. In the strong acid condition of our experiment, thealkylene oxide segments of F127could form crown-ether-type complexes with Ti⁴⁺and Li+through coordination bonds, bringing the reaction partners sufficiently closetogether. Therefore, a pure-phase Li₄Ti₅O₁₂could be obtained at a relative lowtemperature of700oC. SEM and TEM measurements indicate that the as-derivedLi₄Ti₅O₁₂has a cubic morphology, high crystallinity and a uniform particle sizedistribution of around100nm. Nanocrystal Li₄Ti₅O₁₂is tested as an anode materialfor lithium ion batteries, exhibiting excellent electrochemical performance. Thespecific charge capacities of the cell are165mAhg^-1、150mAhg^-1、131mAhg^-1and108mAhg^-1at5C,10C,20C and40C, respectively.The titanium gel precursor is further calcined under Ar atmosphere on the basisof employing a nonionic surfactant tri-block copolymer （pluronic F127） as thechelating agent. The grain growth of Li₄Ti₅O₁₂is effectively restrained by the carbongenerated from the carbonization of F127in the caclination process, and a smallparticle size of Li₄Ti₅O₁₂（²0nm） is successfully obtained at the calcinationtemperature of750oC. The electrical conductivity is further enhanced to be8.2103S m1due to the formed carbon-network on the surface of the sample. The as-derivednanocrystalline Li₄Ti₅O₁₂is tested as anode material for lithium ion battery, exhibiting excellent rate capability and cycle performance. The specific chargecapacities of the cell are160mAhg^-1、155mAhg^-1、139mAhg^-1and123mAhg^-1at5C,10C,20C and40C, respectively.Moreover, mesoporous anatase TiO₂nanocrystalline with uniform pore sizedistribution, large surface area and high thermal stability was prepared via sol-gelapproach by employing room temperature ionic liquids （RTILs）. We studied theinfluence of the calcination temperature and the carbon-chain length of RTILs on theperformance of the as-derived TiO₂. The result indicates that the long carbon-chainionic liquids showed superior function of template and stabilizing agent. Meanwhile,RTILs play a critical role in stabilizing the crystal structure of anatase TiO₂in oursynthesis. The mesoporous anatase TiO₂shows a large surface area of112m2g1.The as-derived mesoporous anatase TiO₂nanocrystalline is tested as an anodematerial for lithium ion batteries, exhibiting excellent rate capability and cycleperformance. The cell exhibits a reversible capacity of140mAhg^-1and118mAhg1at the current density of5C and10C. Meanwhile, the cell demonstrates goodcapacity retentions and high coulombic efficiencies （¹00%） at all current rates.Finally, we report the synthesis of “flower” rutile TiO₂through a facile one-pothydrolysis route by employing titanium tetrachloride as the titanium source and1-hexadecyl-3-methyl imidazolium bromine (C₁₆mimBr) as the structure-directingagent. The rutile TiO₂particle features flower-like nanostructure with the averagesize of400nm comprised with numerous well-defined and straight nanorods. Thenanorods with a diameter of around6nm are oriented radially from the central regiontoward edges of the particle. The dandelions-like nanostructure exposes plenty ofvertical cross-section of c-axis, which could enlarge the effective contact area for thetransport of Li+. Meanwhile, the well-connected nanorod-crystals provide acontinuous pathway for the diffusion of lithium ions and electrons in the titaniascaffold. The as-derived “flower” rutile TiO₂is tested as anode material for lithiumion batteries, exhibiting excellent rate capability and cycle performance. The chargeand discharge measurement indicates that about0.72Li+could be reversibly insertedand extracted into the TiO₂structure, corresponding to the capacity of242mAhg^-1.Meanwhile, the cell exhibits a reversible capacity of170mAhg^-1、144mAhg^-1and116mAhg^-1at the current density of5C,10C and20C respectively. Furthermore,we successfully obtain rutile TiO₂/graphene composite by in-situ synthesis route. Theas-derived composite is tested as an anode material for lithium ion batteries,exhibiting excellent rate capability and cycle stability. The cell exhibits a reversiblecapacity of186mAhg^-1、171mAhg^-1and140mAhg^-1at the current density of5C, 10C and20C respectively. Meanwhile, the cell demonstrates high coulombicefficiency of¹00%at all current rates.