Phase stability of alloy-type lithium storage anode materials

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In the present project, a systematic study will be carried out that provides coherent and extensive information about potential alloy systems for Li storage anodes in Li batteries. Three project partners combine theoretical competences in the Calphad method, the thermodynamics of nanomaterials and the combination of thermodynamics and kinetics during phase transformations, as well as experimental competences in the measurement of thermodynamic properties, production of nanomaterials and characterization of nanoscaled structures.The quaternary alloy system Li-Si-Sn-C with the respective subsystems Li-Si, Li-Sn, Li-Si-C and Li-Sn-C will be investigated/established using the Calphad method. Since nanostructuring is generally accepted as a strategy to achieve an increased cycling stability in Li batteries, the contribution of grain and phase boundaries to the phase stability in the alloy systems will be modeled on the basis of excess free energies as a function of structural length scales.On the experimental side, selected alloys will be cast as ingots and nanostructured by crushing, ball-milling and subsequent sintering in an SPS system. Nanostructuring will be carried out using unique experimental equipment in a closed system with essentially oxygenfree atmosphere. The nanostructured material will be thoroughly characterized. Focus will be to determine grain size distribution, phase distribution and orientation distribution in the Transmission Electron Microscope (TEM). For this, current TEM analysis methods will be further developed and extended to ultra fine grain sizes.With the phase diagrams, the comprehensive thermodynamic description and the tools developed in this project, an estimation of cycling stability and the prediction of Li storage capacity will be possible for a large range of compositions in the above mentioned alloy system, and promising materials for Li battery alloys will be identified.