Kraftwerk Batterie 2022
Title: Comparison of ultrasonic frequency response and puls transmission measurements for the characterization of lithium ion cells
Authors: Andreas Oberbauer, Sebastian Ludwig, Andreas Jossen (Technical University of Munich (TUM), School of Engineering and Design (ED), Chair of Electrical Energy Storage Technology)
Category: Cell characterization
Field of research: Characterization methods
A comprehensive characterization of aged lithium-ion cells is important to understand underlying ageing effects, evaluate operating strategies and possibly extend cell lifetime. As a contribution to achieve this, a variety of ultrasonic based methods have been proposed in the literature, where the cells are characterized based on changes of their mechanical properties [1–3]. Most methods use ultrasonic pulses, and observe signal features such as the pulses’ time of flight, in the transmitted or reflected signal. For this work, in a more general approach, the ultrasonic frequency response over a wide frequency interval was measured during cycling of the cell.
The results are compared to a pulse based method and it is shown that the results of both methods are in good agreement while the frequency response measurement potentially contains more information about internal changes in the cell.
For the comparison of both methods, a prismatic cell was cycled with C/10 and both measurements where performed at various states of charge. For both methods, the excitation signal was applied to the cell and the transmitted signal was measured on the opposite side. For the pulse-based method, we used a raised cosine pulse signal and investigated the frequency dependency by a varying the center frequency of the raised cosine. For the measurement of the frequency response, we used a sinusoidal signal and measured the transmission for 500 excitation frequencies between 50 kHz and 1 MHz.
We compare both measurements based on the transmitted amplitude and time of flight or evaluated phase information respectively. We show that the two methods lead to similar results for both signal properties. However, the frequency response shows a much more pronounced dependency on the excitation frequency and cell state of charge than the pulse method. Therefore, we assume that the frequency response measurement may retrieve more information about internal changes in the cell and is a promising method for the characterization of aged lithium ion cells. Moreover, the comparison confirms the linearity of the system. This this will be exploited in a linear model approach which is subject to future work.
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