Investigate the Aging Behavior of Lithium-Ion Battery by Ac Impedance

• Main Authors: Chuan -Tse Lin, 林權澤
• Other Authors: JING-SHAN DO
• Format: Others
• Language: zh-TW
• Published: 2012
• Online Access: http://ndltd.ncl.edu.tw/handle/94970425327029225176

碩士 === 國立勤益科技大學 === 化工與材料工程系 === 100 === The aging behaviors of commercial 18650 cylindrical lithium-ion battery are studied in this paper. The equivalent circuit models are firstly established, and then the optimal equivalent circuit is obtained by fitting the Ac impedance spectroscopy to understand the battery aging mechanisms. The galvanostatic charge/discharge process is experimentally used to aging the batteries, the battery aging bahaviors are investigated at the appropriate battery aging stages in terms of the ac impedance, cyclic voltammetry(CV), scanning electron microscope (SEM), X-ray diffraction analysis (XRD) and Raman spectroscopy techniques, respectively. Finally, a suitable equivalent circuit model for impedance analysis and the aging mechanisms for commercial 18650 lithium-ion battery are obtained and established. Four equivalent circuit models are proposed for fitting the ac impedance spectroscopies of aging batteries in this thesis. The most reasonable equivalent circuit is obtained to be model IV given in the followings: The capacity fading of battery is obtained to be 54.3 % for 1300 charge/discharge cycles with 1 C-rate. Based on ac impedance, cyclic voltammetry, SEM, Raman spectroscopy, XRD and EDX analysis, the main battery aging mechanisms are proposed: (1) The formation and deposition of solid electrolyte membrane (SEI) on both the positive and negative electrode surfaces by decomposition of the electrolyte and combination with lithium ion. Increasing the SEI layer the rates of intercalation of Li ion, charge transfer and mass transfer decrease and causes the decrease in the battery charge/discharge efficiency. (2) The dissolution of the active materials (LiNiO2, LiCoO2, LiMn2O4) of positive electrode and the Cu current collector of negative electrode in the charge/discharge process results in the detachment of graphite conductive agent. Hence the decrease in electrochemical activity of positive electrode and the impedances of battery result in the decrease in the capacity of battery. (3) The change in crystal properties and the decrease in the conductivity of the active materials of positive electrode cause the battery capacity fading.