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Project leader: Prof. Dr. Harald Schmidt
Funding period: 01.01.2023 - 31.12.2024
Funding body: DFG
Responsible person: Dr. Erwin Hüger
This project proposal deals with the phenomenon of Li diffusion in lithium metal oxide compounds as cathode materials for Li-ion batteries. In this context, diffusion is important for a fundamental understanding of the kinetic processes at electrodes and battery performance (charging/discharging times, maximum capacity, side reactions). The aim is to perform the first systematic Li tracer diffusion studies in model systems of the layered structure type (LiNi0.33Mn0.33Co0.33O2; LiCoO2) and the spinel structure type (LiNi0.5Mn1.5O4; LiMn2O4). Lithium metal oxides in the form of sintered bulk materials, thin films and single crystals (LiCoO2 only) will be investigated. Tracer diffusion experiments are realized by depositing a layer enriched with 6Li isotopes on a layer with natural isotopic composition (e.g. 6LiCoO2/LiCoO2). The samples are then diffusion annealed at elevated temperature, which leads to penetration of 6Li into the film under investigation. Isotope depth profiles are determined by secondary ion mass spectrometry. Diffusion coefficients can be derived by comparing the 6Li depth profile before and after annealing with adequate solutions of the diffusion equation. The experiments are carried out as a function of temperature, structural state and Li content (e.g. Li1-xCoO2) and if the diffusion coefficients follow the Arrhenius law, the activation enthalpy of diffusion is determined and analyzed within the literature. The results are compared with those of electrochemical methods (Galvanostatic Intermittent Titration Technique) on the same type of material. The difference between the results is discussed and interpreted. The accuracy and validity of electrochemical methods for the determination of diffusion coefficients will be worked out and the work is also of interest for the further development of the tracer diffusion experiment, which is hardly used for Li-based materials despite its advantages.