The Lillint project, funded by the Federal Ministry for Economic Affairs and Climate Protection under grant 13XP0225C, ran from 1 April 2019 to 30 September 2022 at the Forschungszentrum Jülich GmbH, Institute for Energy and Climate Research (IEK‑9). The research team, led by Prof. Dr. Florian Hausen and Beatrice Wolff, employed a doctoral candidate to carry out the experimental work. Travel expenses covered attendance at international conferences, notably the International Meeting of Lithium Batteries (IMLB 2022) in Sydney, and were largely offset by material exchanges with partner laboratories. The project’s objectives were to deepen the understanding of the solid‑electrolyte interphase (SEI) that forms at the interface between metallic lithium electrodes and liquid electrolytes, and to investigate lithium stripping and plating processes that can lead to dendrite formation.

The core experimental approach involved atomic force microscopy (AFM) in Peak Force Tapping mode, a probe‑gentle technique that records force–distance curves at each pixel to extract both topography and mechanical stiffness. Commercial lithium foil from Honjo Metal Co. was used without further surface preparation, and its native roughness was found to be only a few nanometers, sufficient for high‑resolution AFM imaging. Two electrolytes were examined: 1.2 M LiPF₆ in an EC/EMC (3:7 weight ratio) solvent system, and the same electrolyte with a 5 % weight addition of vinyl‑ene carbonate (VC). After electrolyte addition, the lithium surface displayed a stripe pattern attributed to rolling during foil manufacturing, but the overall roughness remained in the nanometer regime, confirming the suitability of the material for in‑situ AFM studies.

To observe SEI evolution under realistic electrochemical conditions, the AFM was integrated into a glove‑box‑compatible three‑electrode cell. This configuration allowed real‑time monitoring of lithium deposition and dissolution while maintaining an inert atmosphere. Although specific quantitative stiffness values are not reported in the excerpt, the methodology enabled mapping of local mechanical properties across the SEI, providing insight into its heterogeneity and potential failure points.

Complementary to the AFM work, the project planned to correlate electron spin resonance (ESR) spectroscopy with the microscopic observations. ESR is sensitive to distinct lithium‑based species and can reveal changes in the chemical composition of the SEI during cycling. By combining ESR and AFM, the team aimed to link macroscopic growth phenomena, such as dendrite formation, to nanoscale morphological and mechanical changes.

The project’s scientific output included two comprehensive review articles summarizing the state of the art at the outset, and several peer‑reviewed papers detailing the AFM findings and the in‑situ cell design. Planned publications were also outlined, reflecting the ongoing dissemination of results. The collaboration extended beyond the core team, involving exchanges of materials and expertise with partner laboratories, which helped reduce costs and broaden the experimental scope.

Overall, the Lillint project advanced the characterization of the lithium‑electrolyte interface by integrating high‑resolution AFM with in‑situ electrochemical measurements and spectroscopic analysis. The findings contribute to a more detailed understanding of SEI stability and lithium plating behavior, which are critical for improving the safety and capacity of lithium‑ion batteries.