Preparation,Modification And Electrochemical Properties Of Lithium Titanate Anode Materials For Lithium Ion Batteries

Lithium titanate(Li₄Ti₅O₁₂,LTO)as one of the most promising anode materials for high-power lithium ion batteries?LIBs?,exhibits excellent safety due to long cycling life thanks to its?zero-strain?feature during charge-discharge process and good thermal stability.However,the low conductivity of LTO limits its high rate performance.Therefore,LTO was modified by adjusting the structure,coating of conductive materials and doping of ions.In this paper,tetrabutyl titanate?TBT?and lithium hydroxide?LiOH?were used as raw materials to prepare LTO microspheres?LTOS?,with"micro/nano structure"by hydrothermal and further calcination method,and the mechanism of the preparation process was studied.On this basis,LTOS was modified by multi-walled carbon nanotubes?MWCNTs?coating and bromine doping methods,in order to further improve the electrochemical performance of the material.The main findings are as follows:?1?LTOS microspheres consisting of a stack of primary nano-crystalline grains were prepared by CTAB-assisted hydrothermal process and further calcination,The effects of Li⁺and OH^-on the hydrolysis process of TBT were discussed by changing the species of cations and anions,and the role of CTAB in the system were studied,Formation mechanism of LTOS was put forward.When LiOH aqueous solution was added to TBT/CTAB ethylene glycol solution,the nucleophilic substitution reaction between OH^-and TBT took place,the?Ti-O^-was formed and then?Ti-O^-as a nucleus to form negatively charged colloidal particles.The types of cations mainly affected the size of the resulting colloidal particles,and the size of the resulting colloidal particles was mainly influenced by the type of cations.The positively charged cationic surfactant CTAB is adsorbed on the surface of colloidal particles by electrostatic interaction to form a microsphere.In the meantime,the whole particle structure does not destroy because of the surface protection provided by CTAB.Finally,CTAB were decomposed during the subsequent calcination process and LTOS were obtained.Moreover,LTOS microspheres exhibit excellent electrochemical performance.Even at 60C,the specific capacity is 157mAh·g^-1.moreover,The capacity retention reaches 93%after 500 cycles at 10C.?2?LTOS/multiwalled carbon nanotubes?MWCNTs?composites with different contents of MWCNTs have been prepared by electrostatic self-assembly.First,the positive charges on the surface of MUCNTs were introduced by the hydrophobic interaction between the long alkane chains of CTAB and MWCNTs.In addition,the surface charge of LTOS is negative.Therefore,electrostatic attraction occurs between LTOS and CTAB-functionalized MWCNTs when they approach,and LTOS/MWCNTs composites are obtained after removing CTAB by calcination.Notably,LTOS/MWCNTs composites with 10wt.%MWCNTs exhibit superior electrochemical performances.Their specific capacities at 5C,10C,20C,40C and 60C are 170,168,167,165 and 160mAh·g^-1,respectively,Even at 80C and 90C,the specific capacities are still as high as 154 and 152mAh·g^-1.Moreover,The specific capacity retains 140mAh g^-1after 2000 cycles at 10C.The excellent performance of LTOS/MWCNTs composites is mainly owing to the conductive network forming by MWCNTs connecting different LTOS,acting as highway for the fast transmission of electrons and ions during charge-discharge process.?3?Br-doping LTOS were prepared by hydrothermal process and further calcination.The effect of Br-doping on the electrochemical performance of LTOS was studied.The results show that Br-doping significantly improves the electrochemical performance of LTOS.Li₄Ti₅O_11.8Br_0.2 composites exhibit excellent electrochemical properties.Even at120C,the specific capacities are still as high as 122mAh·g^-1.The excellent high-rate properties of materials benefit from O^2-was occupied by Br^-,and Ti⁴⁺is transformed into Ti³⁺,therefore,A free electron will be given as the charge compensation,the conductivity of the material can be improved effectively.