Nanocharacterization with lithium tracing for Li-ion batteries

Lithium-ion batteries (LIBs) have become a cornerstone of modern technologies, underpinning the widespread adoption of portable electronics, electric mobility, and the integration of renewable energy into power grids. While significant progress has been achieved through the development of advanced electrode materials, further gains in performance, lifetime, and safety are increasingly constrained by an incomplete understanding of the complex physicochemical processes occurring within battery electrodes during operation. Modern LIB electrodes are intrinsically heterogeneous and hierarchical, and their structure, chemistry, and interfacial properties evolve dynamically with cycling. Addressing these challenges requires advanced characterization techniques capable of probing lithium distribution and transport with high spatial resolution and chemical sensitivity across multiple length scales.
This thesis focuses on the development and application of advanced correlative characterization methodologies, with a particular emphasis on focused ion beam–secondary ion mass spectrometry (FIB-SIMS), to investigate lithium transport, redistribution, and degradation phenomena in silicon–carbon–based anodes. A comprehensive experimental workflow is established that enables high-resolution, high-sensitivity elemental analysis throughout the full electrode thickness and down to sub-particle length scales. This methodology allows routinely correlative sub-nanometric morphological analysis by electron microscopy and a sub-15 nm chemical analysis by FIB-SIMS of complex battery electrodes minimizing topographical artifacts.
Using this methodology, degradation processes in Si–C/graphite anodes are systematically investigated. FIB-SIMS analyses reveal a distinctive degradation pattern characterized by a core–shell structure at the particle level, where a relatively intact core is surrounded by a chemically and morphologically degraded shell. This spatially resolved insight establishes a direct link between electrochemical aging and heterogeneous lithium redistribution within individual particles and across the electrode.
Lithium transport mechanisms are further elucidated through lithium isotope labeling experiments combined with correlative FIB-SIMS and complementary bulk techniques as inductively coupled plasma mass spectrometry (ICP-MS) and solid state nuclear magnetic resonance (ssNMR). These measurements provide direct evidence of substantial lithium exchange within both the active material and the solid electrolyte interphase (SEI) at early life stages as well as after extended cycling. At the same time, enhanced lithium retention is observed in the degraded shell regions compared to non-aged active material, highlighting the role of degradation-induced heterogeneity in long-term lithium trapping.
Finally, the impact of a controlled prelithiation strategy was examined using a physical vapor deposition (PVD) approach. Post-mortem FIB-SIMS analyses demonstrate effective lithium incorporation into the active material after activation and a sustained increase in lithium inventory throughout the cell’s life. These findings correlate with improved electrochemical performance, including higher capacity and reduced capacity fade compared to non-prelithiated electrodes.