In battery systems with high terminal voltages, many cells have to be connected in series. Since the weakest cell in this chain defines the overall performance of the complete string, the monitoring of the cell performance is vital to the system performance. Also, the imminent breakdown of one cell has to be detected early to maintain the availability of the battery system. So the detection of the upcoming failure of one cell in the battery string is a key function of a system diagnosis, which should use a cheap an reliable method for the detection.
The content of this work deals with the investigation of two analysis methods for determining the internal resistance of lithium-ion batteries in comparison to the cell voltage. Old and defective lithium-ion batteries can be identified via the internal resistance. This can be done using direct current pulses and electrochemical impedance spectroscopy. In the first step, both methods are simulated on a MATLAB/Simulink model and then measured on real cells. The simulation and measurements are both carried out first on individual cells and then on series connections. Finally, the results of the simulation and the measurements are linked together in a qualitative comparison.