Lithiation mechanisms of amorphous silicon electrodes in Li-ion batteries probed by in-operando neutron reflectometry

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Rechargeable lithium-ion batteries are widely used as energy storage devices and will be essential for future demands. An important step towards this direction is the implementation of negative electrode materials with a high specific capacity like silicon (4 Ah/g). Electrode processes during charging and discharging cycles play a key role for a fundamental understanding and an optimization of these batteries. Objective of the present proposal is the experimental determination of the mechanisms of electrochemically driven lithium incorporation/extraction (homogeneous/heterogeneous) in amorphous silicon electrodes by in-operando neutron reflectometry.Potentiostat controlled experiments on electrochemical cells with thin film and volume electrodes will be done during galvanostatic charging and additionally potentiostatic charging. Based on special modelling, the results will give information on the lithiation mechanism (homogenous Li incorporation, moving phase boundary etc.) as a function of current density, electrode potential and cycle number.In addition, ex-situ experiments with secondary ion mass spectrometry (SIMS), X-ray photo electron spectroscopy (XPS), and X-ray diffractometry (GIXRD) will be applied in order to obtain additional system parameters for electrode characterization and for a reliable modelling of reflectivity patterns.The experiments should contribute to a further development of neutron reflectometry as a promising method for in-operando characterization of battery systems.