Transport von Elektronen und Molekülen durch die Festelektrolyt-Interphase in Lithium-Ionen-Batterien: Von der experimentellen Konzeption bis zur modellbasierten Interpretation
Loading...
Files
Date
relationships.isAuthorOf
Publisher
Philipps-Universität Marburg
item.page.supervisor-of-thesis
Abstract
The articles prepared as part of this work report on the passivating properties of the solid electrolyte interphase (SEI) and the underlying transport mechanisms of electrons, molecules, and ions. The combined experimental and model-based approach should contribute to the understanding of the ambivalent passivating properties of SEIs towards the molecules of the battery electrolyte and redox shuttle molecules, which are used as additives for overcharge protection in lithium-ion batteries.
In the first publication, the state of research regarding the transport of molecules, electrons and ions through SEIs was presented. The transport coefficients of lithium ions, organocarbonate molecules (as part of the electrolyte) and redox molecules were estimated with modelequations from the experimental findings of various studies of SEIs on glassy carbon, highly oriented pyrolytic graphite and composite electrodes with carbon black or graphite. The values obtained were then compared with each other. It was assumed that the transport through the SEI of redox molecules, on the one hand, and organocarbonate molecules or electrons, on the other hand, determines the reduction of these molecules. Based on this, an effective diffusion coefficient of the redox molecules and an upper limit of the effective diffusion coefficient of organocarbonate molecules could be estimated. For all electrode materials, the upper limit of the effective diffusion coefficient of the organocarbonate molecules was at least three orders of magnitude lower than the effective diffusion coefficient of the redox molecules. The studies on the reduction of redox molecules at SEI-covered electrodes were carried out at electrode potentials close to the half-step potential of the respective redox molecule and a possible potential dependence of the SEI morphology and thus also of the passivating properties was discussed. However, experimental findings on the observed ambivalence of SEI passivation towards redox and organocarbonate molecules obtained at battery operating potentials close to 0 V vs. Li+/Li were also presented. The results of this first publication were used as a basis for developing an experimental setup to experimentally investigate both the possible potential-dependent SEI passivation and the described ambivalence of passivation with regard to different types of molecules.
In the second publication, a specifically designed and developed four-electrode measurement setup was presented to address the open questions regarding the ambivalent passivating properties of SEIs towards redox and organocarbonate molecules. Using this generator-collector setup, chronoamperometric measurements of organocarbonate and redox molecule reduction (here Fc+-ions) were combined with electrochemical impedance spectroscopy. Passivation factors for organocarbonate and redox molecules were determined from the reduction currents of the respective species and from the SEI thickness determined from elastance spectra. The results suggest that the organocarbonate molecule reduction is determined by the transport of electrons, while at short SEI formation times the quasi-simultaneously measured redox molecule reduction current is much larger than that of the organocarbonate reduction. For short SEI formation times, it is concluded that the reduction of both species is determined by different transport mechanisms, the redox molecules are reduced at the electrode | SEI interface and this reduction current is determined by the transport of molecules through electrolyte-filled pores within the SEI. It is assumed that, due to a very low rate constant of organocarbonate reduction and the low organocarbonate concentration in the SEI pores, this reaction takes place at the SEI | bulk electrolyte interface and is determined by the transport of electrons through the SEI. Good estimates of the transport coefficients of molecules and electrons through the SEI were obtained from the passivation factors of the organocarbonate molecules and ferrocenium ions. Furthermore, the experiments were also carried out for SEIs at an electrode potential of 3 V vs. Li+/Li and the postulate of the potential-dependent passivation properties of the SEIs was confirmed.
In order to discuss the experimental findings of the second article with regard to the properties of the molecular species and the morphological properties of the SEI in more detail, a transport and reaction model was presented in the third article of this thesis. By means of this model, it was possible to differentiate different transport and reaction regimes as a function of the rate constant of the molecule-electron reaction and as a function of the porosity of the SEI. It was shown that this transport and reaction model is equivalent to a transmission line model. In addition, combined generator-collector experiments with electrochemical impedance spectroscopy were carried out, whereby model SEIs were formed on glassy carbon at different electrode potentials. The experimentally observed very high current density ratio of ferrocenium ion to organocarbonate molecule reduction at short SEI formation times, as well as the strong decrease of this current density ratio with increasing SEI formation times could be modelled qualitatively by simulations. The comparison of model-based and experimental results enabled good estimates of the electronic conductivity of the SEI and the transport coefficient of the molecular transport in the SEI. The electronic conductivity of the SEI shows only a very small dependence on the electrode potential. This finding gives strong indication that there is no exponential increase of the electron concentration at the electrode | SEI interface as predicted by the local Nernst equation.
Review
Metadata
Contributors
Supervisor:
Dates
Created: 2024Issued: 2025-09-15Updated: 2025-09-15
Faculty
Fachbereich Chemie
Publisher
Philipps-Universität Marburg
Language
ger
Data types
DoctoralThesis
DDC-Numbers
540
show more
Krauss, Falk Thorsten (M.Sc.): Transport von Elektronen und Molekülen durch die Festelektrolyt-Interphase in Lithium-Ionen-Batterien: Von der experimentellen Konzeption bis zur modellbasierten Interpretation. : Philipps-Universität Marburg 2025-09-15. DOI: https://doi.org/10.17192/z2025.0518.
License
This item has been published with the following license: In Copyright