Research On The Synthesis And Modification Of Anode Material Li₄Ti₅O₁₂ For Lithium-Ion Batteries

In the twenty-first century, the urgent energy and environmental problems force us to seriously consider to look for application of electric vehicles, such as EVs, HEVs(hybrid electric vehicles) and PHEVS (plug-in electric vehicles). Such applications require better understanding of lithium-ion batteries. The present commercial lithium-ion batteries are usually adopting carbon as the anode, however, its safety issues are not satisfying. Li4Ti5O12attracts intensive attention due to its better safety performance and cycle performance than carbon for its characteristic of "zero strain" structure and no SEI film formation during charge-discharge process. But its low electronic conductivity limits its potential commercial applicaiton. In order to improve its rate performance and cycle performance, the studies focus on the synthesis and optimization of Li4Ti5O12prepared by sol-gel process. Further preparation and electrochemical properties study of complex material Li4Ti5O12/C, doped material Li4Ti5.xCexO12and Li4Ti5O12nanoarrays were finished in this paper. The related properties of prepared materials were inverstigated by using physical testing techniques such as SEM, XRD and electrochemical methods such as charge-discharge process and electrochemical impedance spectra.The main results are listed as follows:1) Preparation of Li4Ti5O12/CAnode material Li4Ti5O12for lithium-ion battery was prepared by two-step sol-gel reaction using tetrabutyl titanate and lithium acetate as starting materials. The effects of heating temperature and calcinating time on the synthesis of Li4Ti5O12were investigated. It shows that pure Li4Ti5O12with nano-particle size can be obtained at800℃and20h during the high temperature treatment process. The sample prepared below800℃or20h contains impure phase of rutile TiO2. With the increasing of heating temperature and calcinating time, the amount of rutile TiO2reduces. The sample prepared at800℃and20h shows the best crystal characteristics and electrochemical performance. So the optimal heating condition is800℃and20h.Li4Ti5O12/C was also prepared by two-step sol-gel reaction using sugar as carbon resource. The results show all carbon coated samples have no impurity peak. Carbon from organic compounds coats on the surface of active particles as conductive network. The carbon coated samples have particle size of100-500nm, which indicate better suppression effects on crystal growth. The15%mixed sample has smaller size, just about100nm, and better rate capability and cycle performance, with capacity of168.3mAh/g at0.1C,156.1mAh/g at0.2C,136.8mAh/g at0.5C,119.7mAh/g at1C,87.7mAh/g at2C and73.5mAh/g at3C. Such improved performance is attributed to reduction of particle size and increase of electric conductivity. After60cycles at different rates, the capacity retains114.0mAh/g after30cycles at1C.2) Synthesis of Li4Ti5-xCexO12Study on doped Li4Ti5O12reveals that Ce-doped samples show pure spinel phase, except that the doped sample with x=0.2shows minor impure phase of CeC2. Doping treatment has significantly suppressed crystal growth. The doped sample with x=0.15have smaller size of about100-200nm. The doped sample with x=0.15shows better rate performance, with capacity of168.0mAh/g at0.1C,148.6mAh/g at0.2C,126.9mAh/g at0.5C,116.0mAh/g at1C,83.3mAh/g at2C and50.2mAh/g at3C. After60cycles at different rates, the capacity retains111.3mAh/g after30cycles at1C.3) Preparation of Li4Ti5O12nanoarrays The Li4Ti5O12nanoarrays can be obtained by porous anodic alumina(AAO) template, which can improve high rate charge-discharge performance. The Li4Ti5O12sol can get into channels of AAO template by vacuum absorption. After multiple depositions, Li4Ti5O12nanoarrays can be obtained by calcining the AAO temple at800℃and20h. This material can be used in micro lithium-ion batteries.