In-Situ Neutron Depth Profiling Studies (Measurements and Simulations) to Characterize the Surface of Silicon Anodes and Complementary Neutron Techniques for in-Situ and Operando Characterization
Authors: Gilles Ralph , Grossmann Lukas , Vacik Jiri , Cannavo Antonino , Ceccio Giovanni 
Published: December 2024

In-situ methods for characterizing electrochemical systems are becoming increasingly important to understand the mechanism of lithiation and delithiation processes. The characterization of surfaces that have been under electrochemical influence is of great interest because many electrochemical processes originate here and are therefore crucial for cell performance. Pure silicon anodes with their large volume expansion, which leads to a short service life, can be modified at WACKER company by partial lithiation of microscale silicon particles [1]. Such anode types promise higher specific capacity. Neutron depth profiling (NDP) is a very well suitable technique to study the Li quantity with depth dependence on the first micrometers. The NDP method uses the capture reaction of Li atoms and neutrons with subsequent decay into ions of well-defined energies. The depth at which ions are created in the material is defined from their energy loss through the material to the detector with an accuracy of tens of nanometers [2, 3]. After formation different lithiation stages of SiG anodes are presented and compared with simulations. The lithiation process involving SEI formation, electrode swelling and phase transformation from crystalline to amorphous is presented. In the second part, a brief overview of other neutron techniques for in-situ and operando characterization of individual battery components or entire cells is given [4].
References:
[1] M. Graf, C. Berg, R. Bernhard, S. Haufe, J. Pfeiffer, H.A. Gasteiger, Effect and Progress of the Amorphization Process for Microscale Silicon Particles under Partial Lithiation as Active Material in Lithium-Ion Batteries, Journal of the Electrochemical Society (2022), 169, 020536.
[2] M. Trunk, L. Werner, R. Gernhäuser, B. Märkisch, Z. Revay, H. A. Gasteiger, M. Wetjen, R. Gilles,Materials science application of neutron depth profiling at the Prompt Gamma-ray Activation Analysis (PGAA) of Heinz Maier-Leibnitz Zentrum, Materials Characterization (2018), 146, 127.
[3] I. Pivarnikova, M. Flügel, N. Paul, A. Cannavo, G. Ceccio, J. Vacik, P. Müller-Buschbaum, M. Wohlfahrt-Mehrens, R. Gilles, T. Waldmann, Preferential sputtering of Si/graphite anodes from Li-ion cells with GD-OES and its validation with NDP, Journal of Power Sources (2024), 594, 233972.
[4] R. Gilles, How neutrons facilitate research into gas turbines and batteries from development to engineering applications, Journal of Surface Investigations: X-Ray, Synchrotron and Neutron Techniques (2020), 14, Suppl. 1, S69.
Acknowledgements:
The German Federal Ministry for Economic Affairs and Climate Action (BMWK) is acknowledged for the support of the project under funding number 03EI3046F. The authors thank WACKER Chemie AG for providing the raw material for the silicon anode electrodes. Thanks to J. Dickmanns and Clara Berg from Technical University Munich for sample preparation. The NDP measurements were carried out at the infrastructures ‘CANAM’ and ‘Reactors LVR-15 and LR-0’ supported by the Ministry of Education, Youth and Sports of the Czech Republic.