Li diffusion in lithium-silicon compounds

Project leader: Prof. Dr. Harald Schmidt Funding period: 06/2016 - 12/2020 Funding body: Deutsche Forschungsgemeinschaft.

The topic of the present application is the first systematic investigation of Li tracer diffusion in the lithium-silicon (LixSi) system. On the one hand, this is relevant for a fundamental understanding of kinetic processes at negative electrodes in lithium-ion batteries for optimized charging times, power density and maximum capacity. On the other hand, there is interest in further developing a methodology hardly used in the field of Li diffusion using an interesting model system.

Experiments will be performed on LixSi compounds as a function of Li content x, temperature and annealing time. For this purpose, different types of model systems in the form of 6LixSi/7LixSi isotopic hetrostructures deposited on Si wafer substrates with ion beam sputter deposition will be used. Comparative studies on electrochemically lithiated silicon films will complement the experiments and highlight the differences. Secondary ion mass spectrometry in depth profile mode and in lens scan mode will be used for isotope selective analysis. This allows determination of diffusion coefficients in the range of 10-10 to 10-23 m2/s. If the diffusion coefficients follow the Arrhenius law, the activation enthalpy of diffusion will be determined and analyzed with respect to possible diffusion mechanisms in theoretical literature work. The results will be compared with electrochemical GITT measurements.