Lithium Tracer Diffusion in Lithium-Metal-Oxide Compounds for Battery Cathodes

• Applicant: Professor Dr. Harald Schmidt
• Subject Area: Thermodynamics and Kinetics as well as Properties of Phases and Microstructure of Materials
• Term: since 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 413672097

The present 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 kinetic processes at electrodes and of basic battery performance (charging/discharging times, maximum capacities, side reactions). The aim of the proposal is to carry out the first systematic Li tracer diffusion studies in model systems of layered (LiNi0.33Mn0.33Co0.33O2; LiCoO2) and spinel (LiNi0.5Mn1.5O4; LiMn2O4) structure types. Lithium-metal-oxides in form of sintered bulk material, thin films and single crystals (LiCoO2 only) are investigated. Tracer diffusion experiments will be done by depositing a thin 6Li isotope enriched layer on top of the samples with natural isotope composition (e.g. 6LiCoO2/LiCoO2). Afterwards the samples are diffusion annealed, leading to a penetration of 6Li into the film under investigation. Isotope depth profiles are recorded by Secondary Ion Mass Spectrometry. By comparison of the 6Li depth profile before and after annealing to adequate solutions of the diffusion equation, diffusivities can be derived. The experiments will be done as a function of temperature, of the structural state, and of Li content (e. g. Li1-xCoO2). If the diffusivities follow the Arrhenius law, the activation enthalpy of diffusion will be determined and analysed in the framework of literature. The results will be compared to those of electrochemical methods (Galvanostatic Intermittent Titration Technique) on the same type of material. The difference between the results will be discussed and interpreted. The exactness and validity of electrochemical methods for diffusivity determination should be elaborated. The work is also of relevance for an advancement of a methodical approach of tracer diffusion that is rarely used for Li based materials.

• DFG Programme: Research Grants