Impact of deformation on electrochemical impedance spectroscopy analysis methods and continued operation of Li-ion batteries

Crashes involving electric vehicles (EVs) can deform batteries due to mechanical loads. Electrochemical impedance spectroscopy (EIS) is increasingly used as a non-invasive method that can potentially detect changes in battery behavior due to deformation. However, different methods are available to investigate the impedance spectra. Therefore, this publication provides a comparison of the commonly used methods (Nyquist plot, Kramers-Kronig relations, electric circuit model and distribution of relaxation times) in their ability to detect deformation of batteries. It also examines the information that can be gained from each method to investigate the underlying mechanisms responsible for observed changes. All methods were able to detect changes in EIS measurements performed on batteries before and after deformation to different extents, which was induced by different impactor sizes. To further investigate the influence of deformation, the batteries were subjected to cycling at high C-rates (3C-Charge and 4C-Discharge). During cycling no safety critical events (e.g. increased temperature, smoke) were observed. However, cycling did result in battery failure, probably caused by a micro short circuit (MSC). These results provide a foundation for determining which EIS analysis methods are effective in detecting deformation of batteries. It also serves as a reference for understanding potential failure mechanism that may occur when deformed batteries continue to be operated.