The KaSiLi project, carried out from 1 November 2019 to 30 April 2023, aimed to create high‑energy lithium‑ion cells that use silicon and lithium anodes to raise volumetric energy density by up to 65 % compared with conventional cells while reducing the large volume changes that occur during cycling. A key part of the effort, led by NaMLab gGmbH, was to develop an in‑situ Raman spectroscopy method capable of monitoring the formation and evolution of the solid electrolyte interphase (SEI) and other degradation processes in real time during charge and discharge.

To achieve this, the team designed and installed a custom Raman cell that could operate under inert conditions and accommodate the sensitive silicon and lithium electrodes. The cell was integrated with a Raman spectrometer that was modified to enhance the signal‑to‑noise ratio and to allow the collection of spectra from the anode, cathode, and electrolyte simultaneously. Background signals were identified and mathematically separated from the true Raman response of the battery components. The resulting setup enabled the detection of electrolyte decomposition reactions that had not previously been observed in operando studies, as well as the monitoring of lithium diffusion into and out of the silicon anode and the depletion of lithium in the electrolyte. The experiments also revealed that the voltage at which these reactions occur depends on the charge‑discharge rate, providing new insight into the kinetics of SEI growth and electrolyte stability.

The successful establishment of this in‑operando Raman technique represents a significant advance for battery research. It allows researchers to correlate structural and mechanical changes at the material level with electrochemical performance, thereby opening pathways for the systematic optimization of anodes, cathodes, and electrolytes. The knowledge gained from these studies is being transferred to the broader ExcellBattMat platform, where it will inform the design of next‑generation high‑capacity silicon‑based electrodes.

The project was a consortium effort. NaMLab gGmbH, under the leadership of Dr. Matthias Grube (reporter) and Dr. Alexander Ruf (coordinator), coordinated the work. Partners included the Technical University of Dresden’s Inorganic Chemistry 1 (AC1) and Inorganic Non‑Metallic Materials (ANW) groups, Fraunhofer Institute for Integrated Circuits (IWS), Fraunhofer Institute for Key Technologies in the Service Sector (IKTS), and the Leibniz Institute for Solid State and Materials Research (IFW). Additional analyses were performed at the Fraunhofer Institute for Photonic Microsystems (IPMS) using transmission electron microscopy and FIB‑SEM. The project was funded by the German Ministry of Education and Research under the KaSiLi program, with the project code 03XP0254C. The collaborative framework enabled the integration of expertise in electrochemistry, materials science, and advanced spectroscopy, ensuring that the technical milestones were met within the scheduled timeframe.