Structure and Performance of Li4Ti5O12 Microspheres Synthesized by Solvothermal Methods as Anode Material for Lithium Secondary Batteries
|School||Nanjing University of Aeronautics and Astronautics|
|Course||Physical and chemical|
|Keywords||anode material solvothermal methods spherical Li4Ti5O12 hollow microspheres mesoporous microspheres|
In this paper, spherical Li4Ti5O12, Li4Ti5O12hollow microspheres and mesoporous Li4Ti5O12microspheres anode materials were synthesized by using solvothermal methods, and the phase andmorphology structure of Li4Ti5O12sample were characterized by X-ray diffraction, Scanning electronmicroscope and transmission electron microscope. In particular, the capacity and cycle performanceof Li4Ti5O12material were tested and analyzed by electrochemical testing method. The main researchcontents of this paper are listed as follows:（1） The spherical Li4Ti5O12was prepared by accommodating the mole ratio of titanium to lithium,solvothermal reaction times and subsequent heat treatment temperature. The resultant products havebeen proved to be a spinel Li4Ti5O12by XRD and the SEM image shows that the particle size ofspherical Li4Ti5O12was about1μm. The first discharge of the spherical Li4Ti5O12shows a capacity of167.3mAh/g at a rate of0.1C, and the capacity decreased to162.4mAh/g after20cycles, the capacityretention rate is97.1%. When the charge and discharge rate was1C, the discharge capacity wasdecreased from142.9mAh/g to114.1mAh/g after20cycles, the capacity retention rate droped to79.8%. When the rate increased to5C, the discharge capacity was decreased from142.9mAh/g to114.1mAh/g after20cycles, the capacity retention rate has reduced to51.4%.（2） Furthermore, Li4Ti5O12hollow microspheres were synthesized with the addition of NH4HCO3in solvothermal reaction. Through SEM test, the Li4Ti5O12material exhibited a structure of hollowmicrospheres with rich porous. The first discharge of Li4Ti5O12hollow microspheres at the rate of0.1C presented a capacity of168.6mAh/g, approaching to the theoretical capacity of Li4Ti5O12material. The first discharge capacity of Li4Ti5O12hollow microspheres decreased with the charge anddischarge rate increase from0.1C to10C, the first discharge shows a capacity of168.6mAh/g,153.4mAh/g,144.8mAh/g,117.6mAh/g,94.1mAh/g, respectively. After50cycles under differentrates, the obvious capacity decrease of Li4Ti5O12hollow microspheres did not occur except thecapacity loss resulting from the trace water adsorbing on the surface of new prepared electrode at rateof0.1C.（3）With the addition of oxalic acid to suppress tetra-n-butyl titanate’s hydrolysis, tetra-n-butyltitanate and lithium acetate were mixed in water/ethanol solution. Finally, mesoporous Li4Ti5O12microspheres has been prepared template-free by solvothermal process in ethanol-water mixedsolution and subsequent heat treatment. Li4Ti5O12mesoporous microspheres assembled bynanoparticle have a particle size of1um, and the BET surface areas of mesoporous Li4Ti5O12 microspheres are as high as80.65m2/g with average pore size and porous volume19.3nm and0.38cm3/g, respectively. When charge and discharge at rates of0.5C,1C,2C,5C,10C, respectively,Li4Ti5O12mesoporous microspheres showed different first discharge capacity of173.6mAh/g,162.1mAh/g,153.4mAh/g,141mAh/g,114.3mAh/g, respectively. After50cycles under different rates, thecapacity of Li4Ti5O12mesoporous microspheres remained95.8%,97.8%,96.6%,94.7%,94.5%,respectively, which shows that Li4Ti5O12mesoporous microspheres have a better rate performancethan spherical Li4Ti5O12and Li4Ti5O12hollow microspheres.