| The negative electrode material is one of the important factors that determine the high power and long life of the battery.Spinel lithium titanate(Li4Ti5O12)has been highly concerned by researchers at home and abroad because of its stable structure,good cycling performance and high safety.However,the ionic conductivity and electronic conductivity of Li4Ti5O12 samples are relatively low.At present,the ionic conductivity of Li4Ti5O12 materials prepared by hydrothermal method,sintering method and sol-gel method is about 10-8S/cm,and the electronic conductivity is 10-1010-13S/cm.In this paper,the best calcination conditions for the synthesis of Li4Ti5O12 samples were determined by analyzing the effects of calcination temperature and time on the purity,morphology and grain size of Li4Ti5O12samples,as well as the influence of calcination conditions on the conductivity and electrochemical properties of Li4Ti5O12 samples.The transport properties of Li4Ti5O12 samples were improved by coating modification,and the influence of coating conditions on the electrochemical properties of Li4Ti5O12/C samples was studied.Lithium titanate Li4Ti5O12 negative electrode materials were successfully prepared by sol gel method using butyl phthalate and lithium acetate as precursors.X-ray diffraction analysis?XRD?,scanning electron microscopy?SEM?and transmission electron microscopy?TEM?were used to characterize the phase and morphology of Li4Ti5O12.The conductivity of Li4Ti5O12 was studied by AC impedance test and potentiodynamic scanning test.When the calcination temperature is 700?and 800?,the pure phase Li4Ti5O12 can be obtained.The crystallinity of the sample increases with the increase of calcination temperature or calcination time.The characteristic peaks of Li4Ti5O12/C samples coated with carbon are all increased,which is due to the addition of carbon source,which makes the samples recrystallize at high temperature and improves the crystallinity of the samples.The crystallinity of Li4Ti5O12/C sample was the best when sucrose was used as carbon source,the amount of carbon coating was 10%,the calcination temperature was 700?,and the calcination time was 10 hoursThe conductivity was studied by AC impedance test and potentiodynamic scanning test.The results show that the crystallinity of Li4Ti5O12 sample prepared at 800? for 10 hours is the best,the transport characteristics of the sample is the best,the ionic conductivity is 8.8×10-8S/cm,the electronic conductivity is 8.53×10-10S/cm.The capacity retention rates of the samples after 10 cycles of charging and discharging were 99.1%,98.9%,98.7%,98.1%and 97.7%,respectively,at the rate of 0.5C,1C,5C,10C and 20C.The capacity retention rates of 50 cycles at 0.1C,1C and 20C are 98.7%,97.3% and 77.5%,respectively.When the carbon source is sucrose,the content of carbon coating is 10%,the calcination temperature is 700?,and the calcination time is 10 hours,the transportation and electrochemical properties of Li4Ti5O12/C samples are the best.Under this condition,the charge conductivity of Li4Ti5O12/C sample is 4.35×10-7S/cm,the electronic conductivity is9.63×10-8S/cm,and the ionic conductivity is 3.39×10-7S/cm.The first charge capacity of Li4Ti5O12/C sample battery is 186.3mAh/g,the first discharge capacity is 185.9mah/g,and the first coulomb efficiency is 99.8%.The first discharge capacity is 172.9mAh/g at 20C,and the capacity retention rate is 96.6% after 50 cycles of charging and discharging. |
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