Facile Synthesis Of Novel High Performance Li₄Ti₅O₁₂ Anode Materials And Electrochemical Properties

Spinel Li₄Ti₅O₁₂is one of the most promis ing lithium ion batteries anodematerials. However, due to the low electronic conductivity of the material, Li₄Ti₅O₁₂perform poor high rate electrochemical performance. In recent years, manyliteratures show that special morphology structure such as nanomaterials andmicro-nano hierarchical materials can reduce the diffusion path of Li⁺, promoteelectron conductivity, expand the area of contacting with the electrolyte, whichsignificantly enhance the high rate performance of the electrode material.Meanwhile, delicate morphology structures of nanomaterials may produce somefavorable properties for photo and electric reactions, such as pseudo-capacitanceeffects, reported in relevant literatures. Therefore, the main content of this thesis isto synthesize nano or micro-nano hierarchical Li₄Ti₅O₁₂anode material with specialmorphologys. Characterize the morphologys and structures of the as-obtainedsamples, followed by the electrochemical properties tests. Finally, study and proposepossible morphology formation mechanisms. Find the relationship between differentmorphologies and electrochemical performance.Li₄Ti₅O₁₂samples are controllablely prepared through solvothermal methodwith mixed solvents of ethanol and water. Different morphologys are achieved byadjusting the lithium source, reaction temperature, sintering temperature, the mixingratios of the solvent component, and different surfactants. The morphologys andelectrochemical properties are characterized to determine the best parameters of thesolvothermal method.Herein, Li₄Ti₅O₁₂nanosheets stacked by ultrathin nanoflakes with a thicknessof³nm and perfect Li₄Ti₅O₁₂microspheres integrated with2-3nm nanocrystalswere obtained with the determined optimum parameters through solvothermalmethod. XRD, FESEM and HRTEM were employed to characterize the structuresand morphologies of Li₄Ti₅O₁₂with morphologys metioned above, respectively. Onthe basis of time-dependent experiments, possible morphology evolution andchemical reaction mechanisms are proposed. Measure the electrochemical propertiesof samples with different morphologies through the charge and dischargeperformance test, cyclic voltammetry and EIS.The results indicate that Li₄Ti₅O₁₂nanosheets stacked by ultrathin nanoflakesrepresent better electrochemical proformance. It is attributed to the morphology ofultrathin nanoflakes stacked Li₄Ti₅O₁₂anode material makes the material separatefrom each other but still be inconnected. The morphology form a three-dimensionalnetwork and ensure the contact area between the electrolyte and anode materials, benefit the electron conductivity and Li⁺diffusion. Meanwhile there may be pseudo-capacitance effect exist between the nanoflakes. So that the hierarchical Li₄Ti₅O₁₂nanosheets presents the initial discharge capacity of up to175.9mAhg^-1 at thecurrent rate of0.5C, and substantially maintain the coulombic efficiency of100%during100cycles. And the material showed high stability, reversibility and excellentrate performance even increase the current rate to20C. While the nanocrystallineswith little sizes integrated to the perfect microspherical Li₄Ti₅O₁₂combined witheach other very tightly, which embarrass the contacting area with the electrolyte,thus influence their electrochemical properties of high rate.