Li-ion Batteries Lab, School of Materials Science and Engineering, China University of Mining and Technology, Xuzhou 221116, China.
Phys Chem Chem Phys. 2012 Feb 28;14(8):2617-30. doi: 10.1039/c2cp23626e. Epub 2012 Jan 19.
The processes of extraction and insertion of lithium ions in LiCoO(2) cathode are investigated by galvanostatic cycling and electrochemical impedance spectroscopy (EIS) at different potentials during the first charge/discharge cycle and at different temperatures after 10 charge/discharge cycles. The spectra exhibit three semicircles and a slightly inclined line that appear successively as the frequency decreases. An appropriate equivalent circuit is proposed to fit the experimental EIS data. Based on detailed analysis of the change in kinetic parameters obtained from simulating the experimental EIS data as functions of potential and temperature, the high-frequency, the middle-frequency, and the low-frequency semicircles can be attributed to the migration of the lithium ions through the SEI film, the electronic properties of the material and the charge transfer step, respectively. The slightly inclined line arises from the solid state diffusion process. The electrical conductivity of the layered LiCoO(2) changes dramatically at early delithiation as a result of a polaron-to-metal transition. In an electrolyte solution of 1 mol L(-1) LiPF(6)-EC (ethylene carbonate) :DMC (dimethyl carbonate), the activation energy of the ion jump (which is related to the migration of the lithium ions through the SEI film), the thermal activation energy of the electrical conductivity and the activation energy of the intercalation/deintercalation reaction are 37.7, 39.1 and 69.0 kJ mol(-1), respectively.
采用恒电流循环和电化学阻抗谱（EIS）研究了在首次充放电循环过程中不同电位以及 10 次充放电循环后不同温度下锂离子在 LiCoO(2)正极中的嵌入和脱出过程。谱图在频率降低时依次呈现出三个半圆和一条略微倾斜的直线。提出了一个合适的等效电路来拟合实验 EIS 数据。通过对模拟实验 EIS 数据得到的动力学参数随电位和温度变化的详细分析，将高频、中频和低频半圆分别归因于穿过 SEI 膜的锂离子迁移、材料的电子性质和电荷转移步骤。略微倾斜的线则源于固态扩散过程。在 1 mol L(-1) LiPF(6)-EC（碳酸乙烯酯）：DMC（碳酸二甲酯）电解质溶液中，层状 LiCoO(2)在早期去锂过程中由于极化子到金属的转变而发生剧烈的电导率变化。离子跳跃的活化能（与锂离子穿过 SEI 膜的迁移有关）、电导率的热活化能和嵌入/脱嵌反应的活化能分别为 37.7、39.1 和 69.0 kJ mol(-1)。
