Li Diffusion in Lithium Silicon Compounds

• Applicant: Professor Dr. Harald Schmidt
• Subject Area: Thermodynamics and Kinetics as well as Properties of Phases and Microstructure of Materials
• Term: from 2016 to 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 316931911

Topic of the present proposal is the realization of the first systematic lithium tracer diffusion investigations in the system lithium-silicon (LixSi). This is of relevance for a fundamental understanding of kinetic processes at negative electrode materials in lithium-ion batteries for optimized charging times, power densities and maximum capacity. Further it is important to further develop a methodology, not very widely used in the area of Li diffusion, using an interesting model system. The experiments will be carried out on Li¬¬xSi samples as a function of Li concentration x, temperature, annealing time, and production method (sputter deposition, electrochemically). For this, different model systems in form of 6LixSi/7LixSi isotope heterostructures will be deposited on silicon substrates by ion-beam sputtering. Complementary investigations on electrochemically lithiated silicon layers will complete the experiments and identify the differences. For isotope selective analysis, secondary ion mass spectrometry (SIMS) in depth profile mode and/or alternatively in line scan mode will be used. This will allow a quantification of diffusivities between 10-10 and 10-23 m2/s. Diffusivities will be measured in a range between room temperature and 500 °C as a function of temperature. If the diffusivities follow the Arrhenius law, the activation enthalpy of diffusion will determined and analysed concerning different diffusion mechanisms in the framework of literature. The results should be compared to electrochemical GITT measurements. The results should be analysed in a comparative way.

• DFG Programme: Research Grants