Separation der Kathodenalterung in Lithium-Ionen-Batteriezellen mittels elektrochemischer Impedanzspektroskopie

Wünsch, Martin; Sauer, Dirk Uwe (Thesis advisor); Kurrat, Michael (Thesis advisor)

Aachen : ISEA (2019, 2020)
Book, Dissertation / PhD Thesis

In: Aachener Beiträge des ISEA 134
Page(s)/Article-Nr.: 1 Online-Ressource (xvi, 177 Seiten) : Illustrationen, Diagramme

Dissertation, Rheinisch-Westfälische Technische Hochschule Aachen, 2019

Abstract

In the present work, three different cell types (lithium-ion-cells) have been cyclically aged under different conditions. In particular, 3-electrode-cells on a laboratory scale, automotive prismatic cells (PHEV2) and large-sized pouch cells are used. The latter are also applied in the automotive sector. During aging, different states of charge and states of health were set to measure electrochemical impedance spectra and derive specific parameters. The corresponding aging phenomena could be assigned via a post-mortem-analysis. Therefore, primarily optical emission spectrometry using inductively coupled plasma and scanning electron microscopy were used. In laboratory cells, which contain a lithium reference electrode, it was noticeable that the cathode imdepance influences the full cell impedance crucially in case of a NMC111 | graphite chemistry. Contrary to that, anode spectra are relatively insensitive to the state of charge and aging of the cell. Thus, the dynamics of the charge transfer resistances (CTR) of an overall cell impedance are dominated by the cathode. Hence, it could be used to evaluate the state of the NMC. Investigating prismatic cells, it became obvious that the sensitivity of the charge transfer resistance is transferable to larger automotive cells. Furthermore, the CTR can be used for the evaluation of particle cracking in the cathode. Additionally, it is dependent on the selected temperature and C-rate in course of cyclization. During the cyclic aging of pouch cells, a significant influence of the external applied mechanical stress on the lifetime was identified. In addition, a parameter is derived from the real part of the impedance, that indicates an optimal tension concept of battery cells early.