| Because the spinel lithium titanate has good structural stability, high safety and reliability, excellent anti-overcharge performance, long cycle life, abundant raw material sources and many other advantages, it will become a new generation of anode materials for lithium-ion energy storage batteries which are widely used in electric cars, hybrid cars and other energy storage fields those require high security, high stability and long cycle life. However, the large-scale commercial application of lithium titanate still exist the restricted factors currently. The reason is that the poor ions and electronic conductivity of Li4Ti5O12leading to its poor high-rate performance, and the tap density of Li4Ti5O12is low, also leading to a low volume energy density, these shortcomings seriously hinder the application of the lithium titanate. So how to improve the electrochemical performance of Li4Ti5O12materials has become a main research focus in the current researchers.Usually the preparation method plays a key role in the performance of materials. In the work, two kinds of Li4Ti5O12anode materials for lithium-ion batteries were prepared through two different process of hydrothermal(solvothermal) method. The microstructure and morphology of the samples were characterized by test such as XRD, SEM, FTIR and Raman. And their electrochemical performance were studied through testing of galvanostatic charge/discharge cycling, CV and EIS.The first method is one step to synthesis of Li4Ti5O12nanoparticles by semi-aqueous thermal method. Using bultyl titanate and Li0H-H2O as the source of titanium and lithium. The effect of different solvents on the electrochemical properties was investigated. By comparison, the sample synthesized in trimethylamine-water system shows the best performance. In addition, in this solvent system, the effect of reaction temperature, reaction time and PH on the electrochemical properties was investigated. It showed that under alkalescence trimethylamine-water system, The sample systhesized at220℃for24h then heated at700℃for2h has the best electrochemical performance. The sample presents the granule. At charge/discharge rate of0.1C,0.5C,1C and IOC, the initial discharge capacity was173.58mAh-g-1,148.77mAh·g1,138.35mAh·g-1and102.82mAh·g-1, the capacity retention rate can up to97.32%,95.84%,91.60%and87.20%in each charge/discharge rate after20cycles.The second process is two steps to synthesis of Li4Ti5O12nanospheres by solvothermal method. With butyl titanate, ethylene glycol, acetone as raw material, the spherical precursor was synthesized by sol-gel method firstly. Then mixed the precursor and amount of LiOH·H2O. The Li4Ti5O12nanospheres was synthesized by the solvothermal method subsequently. The study found that the right amount of butyl titanate to prepare the precursor is2mL(Vbuty1titanate:Vethylene glycol=1:25), and the precursor is the titanium glycolate with good spherical morphology. After optimization of reaction temperature, it can be found that spherical Li4Ti5O12with500-800nm can be obtained at180℃for12h reaction. The samples having the best performance and the charge-discharge cycle characteristics. At charge/discharge rate of0.1C,0.5C,1C,5C and IOC, the initial discharge capacity was174.21mAh-g-1,167.62mAh-g’,157.05mAh-g-1,136.58mAh-g-1and116.05mAh-g-1。the capacity retention rate can up to99.03%,98.16%,97.14%,96.18%and94.73%after30cycles。The spherical Li4Ti5O12/Ag composite materials were synthesized by solvothermal method based on the second preparation process. It also studied the influence of different amount of Ag coating on the properties of materials. The results showed that when the Ag content is5wt.%of Li14Ti5O12/Ag, its rate capability and cycle performance relative to the optimal. At charge/discharge rate of0.5C,1C,5C and10C, the initial discharge capacity was186.34mAh-g-1,172.47mAh-g-1,154.12mAh-g-1and136.06mAh-g=1。After30cycles under the high rate of10C, the retention rate of capacity of the sample can still remained96.14%. |
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