Study On The Modified Preparation And Electrochemical Property Of Li₄Ti₅O₁₂ Anode Materials For Lithium Ion Batteries

The spinel Li₄Ti₅O₁₂ is a type of popular candidate as anode materials for LIBs due to its fast lithium ion diffusion kinetics following an insertion reaction mechanism.It shows relatively high lithium insertion and extraction voltage plateau?¹.55 V vs.Li/Li⁺?.The negligible volume expansion?⁰.2%?of Li₄Ti₅O₁₂ is beneficial to the insertion and desertion of lithium ions for ultralong cycling life.However,its rate performance is restricted by large polarization at high current rate because of its low electrical conductivity?10¹3 S cm-¹?.In this thesis,many methods have been investigated to improve the electrochemical performance of Li₄Ti₅O₁₂ based anode material,for example,nanostructure,carbon coating and composited with conductive material.Concrete research content is as follows:?1?Firstly,we select a titanium-based metal organic framework?MOF?as precursor to prepare unique porous TiO₂ nano-tablet.By introducing subsequent wet-chemical lithiation and post-annealing,anatase TiO₂ nanoparticles are transformed into porous Li₄Ti₅O₁₂ nano-tablet.Li₄Ti₅O₁₂ nano-tablet delivers a high reversible capacity of 158 mAh g^-1 at 0.1 A g^-1,and excellent cycling stability of maintaining a capacity of 122 mAh g-¹ after 1000 cycles at 1 A g-¹ between 1.0 V and 2.5 V.?2?We use PVDF as carbon resource to synthesize fluorine-doped carbon encapsulated Li₄Ti₅O₁₂ nanoflowers assembled by nanosheet.Under the current density of 0.1 A g^-1,F-C-Li₄Ti₅O₁₂nanoflowers discharge capacity is 179 mAh g-¹,when the current density increased to 7 A g-¹,the discharge specific capacity is 120 mAh g^-1,far higher than Li₄Ti₅O₁₂ nanoflowers without fluorine doped carbon coated layer(when the current density for 7 A g-¹,the discharge specific capacity is 105mAh g^-1).Fluorine-doped carbon encapsulated Li₄Ti₅O₁₂ nanoflower displays superior rate and cyclic properties.?3?MXene is used as titanium source and conducting medium,developing a novel strategy for the in-situ synthesis of layered-stacked Li₄Ti₅O₁₂-MXene composite.The synergistic effect of Li₄Ti₅O₁₂ and MXene greatly improved the electrochemical properties of Li₄Ti₅O₁₂-MXene composite.Moreover,a high discharge capacity of 178 mAh g-¹ after 500 cycles can be maintained at a current density of 5 A g-¹.