Electrode-Resolved Monitoring of the Ageing of Large-Scale Lithium-Ion Cells by using Electrochemical Impedance Spectroscopy

The ageing of large-scale lithium-ion batteries due to prolonged cycling was investigated by means of electrochemical impedance spectroscopy. The resulting spectra were analyzed by using the method of the distribution of relaxation times. Thereby, the number of distinguishable polarization processes that contribute to the overall cell electrochemistry was determined. The physical meaning of these polarization processes was clarified by the assessment of their temperature dependences as well as by comparative measurements in three-electrode setup cells. In this way, electrode-resolved interpretation of impedance spectra of large-scale lithium-ion cells without any kind of reference electrode was achieved. Based on this electrode resolution, the origin of the cell degradation due to cycling could be elucidated.