Development of a new Electrochemical Impedance Spectroscopy Approach for Monitoring the Solid Electrolyte Interphase Formation

Abstract

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.

Impedance Characterization of an LCO-NMC/Graphite Cell: Ohmic Conduction, SEI Transport and Charge-Transfer Phenomenon

“…Illig et al also find a process exhibiting a small variation with the SoC, which has been assigned to the interface between the active material and the current collector due to the low activation energy they obtained [25]. Moreover, some other studies that relate the processes occurring at such high frequencies to the current collector interfaces [28,29,32,36,39] The characteristic frequency of the semicircle appearing at higher frequencies (P2_PE in Figure 4) is located between 60 kHz and 100 kHz ( Figure 6c). On the one hand, we find that the resistance slightly increases in the entire SoC range but increases faster at very low SoCs, especially when the cell is fresh (Figure 6a).…”

“…Illig et al also find a process exhibiting a small variation with the SoC, which has been assigned to the interface between the active material and the current collector due to the low activation energy they obtained [25]. Moreover, some other studies that relate the processes occurring at such high frequencies to the current collector interfaces [28,29,32,36,39] also indicate that, in general, those processes show a low variability with the SoC [29,32,39]. Thus, because of the high characteristic frequency and the low variability with the SoC, we determine that P2_PE has to correspond to the interface between the LCO-NMC active material particles and the aluminum current collector.…”

“…Concretely, the characteristic frequency mostly stays between 10 kHz and 60 kHz depending on the evaluated SoC and aging level. In the literature, processes which take place above 1 kHz are commonly related to particle-to-particle interfaces or to the interfaces between active material particles and current collectors [28,32,36], but in some cases they have also been attributed to the SEI layer [28,37,38]. Thus, one might think that the physical origin of P2_NE should correspond to one of those.…”

On the Interpretation of Impedance Spectra of Large‐Format Lithium‐Ion Batteries and Its Application in Aging Studies

“…Electrochemical impedance spectroscopy (EIS) is a powerful tool for the investigation of complex electrochemical systems, which has been applied in numerous studies on lithium‐ion batteries . Its main advantage is its ability to depict all electrical and electrochemical loss processes that contribute to the overall performance of the considered electrochemical system.…”

Impedance Spectroscopic Investigation of the Impact of Erroneous Cell Assembly on the Aging of Lithium‐Ion Batteries

“…A powerful tool for a more profound characterization of lithium‐ion cells is electrochemical impedance spectroscopy (EIS) . Numerous studies applied this technique to gain in‐depth knowledge on their degeneration behavior .…”