Al_2O_3包覆LiMn_2O_4阴极材料的动力学研究

Kinetic study of synthesis and properties of Al_2O_3-coated LiMn_2O_4 as cathodes for Li-ion batteries

在尖晶石LiMn2O4颗粒表面包覆Al2O3,获得结构稳定、循环性能优异的锂离子蓄电池阴极材料。采用X射线衍射研究材料晶体结构,通过恒流充放电、循环伏安和交流阻抗(EIS)来研究锂离子在材料中脱嵌和嵌入的动力学机理。电极材料包覆Al2O3以后,交流阻抗图谱上显示有两个半圆和一条斜线,而未包覆的LiMn2O4只有一个半圆和一条斜线。这表明经过Al2O3包覆后,LiMn2O4活性材料与电解液的直接接触被隔断。相应的等效电路也给出,以评估反应动力学。

The surface modification of spinel LiMn2O4 by coating a thin layer of Al2O3 is an effective method to improve structural stability and cycling behavior. XRD was used to identify the crystalline phase of Al2O3-coated LiMn2O4. The kinetics of Li-ion extraction and insertion from Al2O3-coated LiMn2O4 were investigated by charge/discharge cycles, cyclic voltammetry and electrochemical impedance spectroscopy (EIS). The impedance spectra of Al2O3-coated LiMn2O4 exhibited two semicircles and a steep sloping line. In comparison, impedance spectra of pristine LiMn2O4 showed only one semicircle and a sloping line. The result indicated that Al2O3-coating separate the active cathode material from direct contact with electrolyte. Corresponding equivalent circuits were proposed to evaluate the reaction kinetics.