超声辅助TiO_2包覆尖晶石LiMn_2O_4及电化学性能研究

Ultrasonic Assisted Coating of TiO_2 on LiMn_2O_4 and Its Electrochemical Properties

采用超声辅助溶液法在尖晶石LiMn2O4表面包覆TiO2。通过X射线衍射、扫描电子显微镜、恒电流充放电、交流阻抗技术分析合成材料的结构、形貌及电化学性能。结果表明:TiO2包覆LiMn2O4与LiMn2O4具有相似的X射线衍射结果,衍射峰尖锐,样品颗粒大小均匀,无明显团聚。室温下0.2C充放电时,表面包覆1%TiO2的LiMn2O4首次放电比容量为123.51 mAh·g-1,略低于未包覆LiMn2O4的124.02 mAh·g-1,但在2C和4C高倍率时,表面包覆1%TiO2的LiMn2O4比容量分别为105.54和80.73 mAh·g-1,远高于未包覆的79.76和66.37 mAh·g-1。室温及55℃下以0.2C倍率循环50后,表面包覆1%TiO2的LiMn2O4容量保持率分别为91.69%和87.36%,远高于未包覆LiMn2O4的86.58%和78.02%。室温下以1C倍率循环100次后,表面包覆1%TiO2的容量保持率比未包覆LiMn2O4高出3.75%。表面包覆TiO2后LiMn2O4的循环性能得到了大大的提高,尤其是高温循环性能。

TiO2 coated LiMn2 O4 was prepared by ultrasonic assisted solution method.The structural,surface morphology and electrochemical performance of synthesized materials were characterized by X-ray diffraction,scanning electron microscope,galvanostatic charge-discharge technique and AC impedance spectroscopy.The results showed that LiMn2 O4 and TiO2-coated LiMn2 O4 had the similar X-ray diffraction patterns and sharper diffraction peaks.The powders were uniform and no serious aggregation could be observed.When cycled at charge-discharge rate of 0.2C at room temperature,the initial discharge specific capacity of LiMn2 O4 coated with 1%TiO2 was 123.51 mAh · g-1,which was a bit smaller than 124.02 mAh · g-1 for the uncoated one.When cycled at charge-discharge rates of 2C and 4C,the specific capacity of LiMn2 O4 coated with 1%TiO2 was 105.54 and 80.73 mAh · g-1,which was much higher than 79.76 and 66.37 mAh · g-1 for the LiMn2 O4.When cycled at room temperature and 55 ℃ for 50 times at the charge-discharge rate of 0.2C,the capacity retention of TiO2 coated LiMn2 O4 was 91.69% and 87.36%,which was much higher than 86.58% and 78.02% for the uncoated LiMn2 O4.When the charge-discharge rate reached 1C,the capacity retention of 1% TiO2 coated LiMn2 O4 became 3.75% higher than the uncoated one after cycling 100 times at room temperature.Coating of TiO2 on LiMn2 O4 significantly improved the cyclability of LiMn2 O4 especially at high temperature.