We study the electrode polarization behaviour of different Na-Ca-phosphosilicate glasses by measuring the differential capacitance between blocking Pt electrodes. At low applied dc bias voltages, we detect a linear capacitance regime with interfacial capacitance values considerably larger than expected from mean-field double layer theories and also considerably larger than found for ionic liquids with similar ion concentrations. With increasing bias voltages, the differential interfacial capacitance exhibits a maximum around 1 V and a strong drop at higher voltages. We suggest that these features are caused by pseudocapacitive processes, namely by the adsorption of mobile Na + ions at the electrodes. While pseudocapacitive processes are well known in liquid electrochemistry, more detailed studies on solid electrolytes should offer perspectives for improved energy storage in solid-state supercapacitors.

The formation of surface films on lithium ion electrodes is a crucial factor for the performance and durability of the respective battery. Especially the formation of the solid electrolyte interphase (SEI) on the anodes of these cells widely determines the stability and functionality of the electrode. Therefore, a precise insight into the formation process of this layer is required. Based on temperature‐dependent electrochemical impedance spectroscopy a new approach to monitor the formation of the SEI was developed. This way the kinetics of the interphase could be described using its activation energy. Comparison of these values with the respective resistances regarding the charge turnover during the initial charging of the cell provided additional information about the course of the SEI formation. It could be shown that these findings are in good agreement with the descriptions of the mechanism of the SEI formation provided by the literature.

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.

This study presents a new approach for the interpretation of impedance spectra of large‐format lithium‐ion batteries. By application of the method of the distribution of relaxation times (DRT), all time constants contributing to the overall kinetics of a battery can be identified. By a comprehensive impedance spectroscopic investigation of the lithium‐ion cell as a function of temperature and cell potential, it can be described in a recognizable manner, which can be traced back in measurements with three electrode cells. Thereby, an unambiguous assignment of time constants to the underlying type of an electrochemical process and to the electrode of origin can be achieved. The application of these findings in aging studies can significantly increase their gain of knowledge.