Stability of lithium electrolyte interphase enabling rechargeable lithium-metal batteries

Weber, Felix Martin; Figgemeier, Egbert (Thesis advisor); Eichel, Rüdiger-A. (Thesis advisor)

Aachen : RWTH Aachen University (2023)
Book, Dissertation / PhD Thesis

In: Aachener Beiträge des ISEA 168
Page(s)/Article-Nr.: 1 Online-Ressource : Illustrationen, Diagramme

Dissertation, Rheinisch-Westfälische Technische Hochschule Aachen, 2023


The improvement of energy storage systems is a critical factor while changing the world’senergy supply from fossil fuels to renewable electric solutions. The use of metallic lithium as an anode in batteries has the ability to significantly increase the energy density compared to today’s lithium-ion batteries (LIBs). The application of the material is mainly limited by the poor chemical compatibility of metallic lithium and commonly used liquid electrolyte. Whilst solutions for the chemical compatibility were found for LIBs in the last decades, the chemical reactions at the metal/electrolyte interphase are not yet understood, nor controlled. This thesis focuses on the electrolyte decomposition of an electrolyte from ethylene carbonate (EC) and ethyl methyl carbonate (EMC), defined as baseline electrolyte (BE), at lithium metal surfaces and strategies to minimize the decomposition reactions during storage as well as during charging and discharging of lithium-metal batteries (LMBs). For analysis of the interphase, scanning electrochemical microscopy (SECM) was optimized to allow long-term observation of the changes of the surface. The application of the often use dredox mediator 2, 5-di-tert-butyl-1, 4-dimethoxybenzene (DBDMB) was found to be not feasible and the effectiveness of ferrocene was carefully evaluated and successfully established. It was discovered that with a BE no stable and passivating surface layer on lithiumis formed and that the ongoing reactions fully decompose the electrolyte. The addition of well known electrolyte additives from the field of LIBs reduces the decomposition reactions during contact. This concept further improves the charging and discharging behavior, whilst the vinylene carbonate (VC)-based surface layer is more efficient than the fluoroethylene carbonate (FEC)-based one. The concept of flexible surface layers was transferred and new potential additives were designed. Their effect was analyzed with the help of a layer model developed in this thesis. In a final approach, the lithium/electrolyte interphase was stabilized through coating of lithium with graphite. The lithium intercalates into the graphite, but no reaction of this species with the electrolyte was observed. The apparent selective passivation leads to a fully conducting surface and the absence of an insulating surface layer even when in contact with electrolyte. This proves that the coating successfully shields the lithium metal from the electrolyte and suppresses the surface reactions that are responsible for the formation of a surface layer. Upon plating, the passivating effect is reduced and patterns of insulating material form on the surface. In the thesis, different strategies for lithium passivation are developed and analyzed, resulting in knowledge that is required to control the reactions of the electrolyte with the metallic lithium for enabling rechargeable LMBs.


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