Evaluation of Thermal and Mechanical Damage of Lithium Ion Battery by Electrochemical Impedance Spectroscopy

Purpose: Health and safety of lithium ion batteries have become important issue due to increasing reports on explosion and firing accident during use. In this research, mechanical and thermal damages of a lithium ion battery were evaluated by applying alternative current electrochemical impedance spectroscopy.BR Methods: Nyquist plot was obtained for the isothermally exposed batteries to 85℃, 100℃ and 120℃ as well as mechanically twisted and bended lithium polymer batteries, respectively. Ohmic, SEI (secondary electrolytic interface), and charge transfer resistance were extracted and compared among them.BR Results: Nyquist plot of both thermally exposed and mechanically deformed batteries were observed to shift toward high resistance region. SEI resistance value increased with thermal exposure, which is attributed to the decomposition reaction of lithium salt over 60℃. For the mechanically deformed battery, Ohmic resistance increased, while little change in SEI resistance was observed.BR Conclusion: SEI resistance and Ohmic resistance value extracted from the Nyquist plot can be applied as a state-of-health monitoring indicator of the lithium ion batteries used under thermal exposure or mechanical deformation condition, respectively.