Modification Design And Lithium Storage Performance Study Of Spinel Li₄Ti₅O₁₂

Lithium-ion batteries,as a dominant type of energy storage device,has long been the focus of new energy research and development.Lithium titanate(Li₄Ti₅O₁₂)is considered as a safe and stable anode material for lithium-ion batteries due to its stable voltage platform and"zero strain"characteristics during the charge/discharge.However,the low theoretical capacity(175 m Ah·g^-1)and intrinsically low electronic conductivity and ionic conductivity,lead to its poor high-rate performance,serious polarization,thus impeding its intensive application.Based on this,this paper mainly modified LTO by introducing oxygen vacancies and in-situ constructing heterogeneous structures,aiming to improve its low electronic conductivity and high-rate performance.The main research contents are as follows:（1）First,oxygen vacancies are introduced into commercial LTO by heat treatment under Ar/H₂（5%）.LTO with oxygen vacancy showed better performance than sample before treatment,especially under high current density.Density functional theory calculation results show that increasing oxygen vacancy concentration can improve the electronic conductivity,reduce the diffusion barrier of lithium ions,resulting in a fast electrochemical kinetics process.As expected,LTO with more oxygen vacancies（HLTO）showed much better high-rate performance than pristine LTO,with a reversible capacity of 85.1 m Ah·g^-1 at a very high charge-discharge rate of 30 C,while LTO only had 59.9m Ah·g^-1.HLTO also showed a higher reversible capacity than LTO in the long cycling test at 20 C current density.（2）Then,the Li₄Ti₅O₁₂/rutile TiO₂（LTO/RT）heterogeneous nanorods with tunable oxide phases were prepared in situ by annealing the electrospinning nanofiber precursor containing titanium isopropoxide.Density functional theory calculation shows that the LTO/RT heterostructure can not only enhance the adsorption of lithium atoms,reduce the diffusion barrier of lithium atoms,but also promote the spontaneous electron transfer at the interface.Compared with phase-pure LTO and RT,LTO/RT has smaller charge transfer resistance and faster Li⁺migration at the phase boundary.Therefore,LTO/RT showed superior lithium storage performance with a capacity of 160.3 m Ah·g^-1after 200 cycles at 1 C and 125.5 m Ah·g^-1 after 500 cycles at 10 C.After 1000 cycles at30 C,the capacity retention rate reached 90.3%,which was better than that of pure LTO,RT and commercial LTO products.