The localisation and quantitative analysis of lithium (Li) in battery materials, components, and full cells are scientifically highly relevant, yet challenging tasks. The methodical developments of MeV ion beam analysis (IBA) presented here open up new possibilities for simultaneous elemental quantification and localisation of light and heavy elements in Li and other batteries. It describes the technical prerequisites and limitations of using IBA to analyse and solve current challenges with the example of Li-ion and solid-state battery-related research and development. Here, nuclear reaction analysis and Rutherford backscattering spectrometry can provide spatial resolutions down to 70 nm and 1% accuracy. To demonstrate the new insights to be gained by IBA, SiO_x-containing graphite anodes are lithiated to six states-of-charge (SoC) between 0–50%. The quantitative Li depth profiling of the anodes shows a linear increase of the Li concentration with SoC and a match of injected and detected Li-ions. This unambiguously proofs the electrochemical activity of Si. Already at 50% SoC, we derive C/Li = 5.4 (< LiC₆) when neglecting Si, proving a relevant uptake of Li by the 8 atom % Si (C/Si ≈ 9) in the anode with Li/Si ≤ 1.8 in this case. Extrapolations to full lithiation show a maximum of Li/Si = 1.04 ± 0.05. The analysis reveals all element concentrations are constant over the anode thickness of 44 µm, except for a ~6-µm-thick separator-side surface layer. Here, the Li and Si concentrations are a factor 1.23 higher compared to the bulk for all SoC, indicating preferential Li binding to SiO_x. These insights are so far not accessible with conventional analysis methods and are a first important step towards in-depth knowledge of quantitative Li distributions on the component level and a further application of IBA in the battery community.

Silicon is a promising candidate for next-generation lithium-ion battery anodes due to its superior gravimetric capacity, derived from its alloying reaction with lithium. Given the correlation between electrochemical and optical properties, optical inspection provides a non-invasive method for probing lithiation dynamics. In this study, the state of lithiation (SoL) was systematically linked with optical response through both ex situ and in situ measurements. Reflectance consistently decreased as lithium content increased within the silicon lattice, a trend validated across multiple experimental setups. For instance, a spatial lithium gradient, introduced by varying electrode sizes in coin cells, was successfully visualized via reflectance mapping. This approach also suggests a scalable quality-control strategy for prelithiation, the process of alloying silicon with lithium. The areal lithiation uniformity of prelithiated silicon anodes was evaluated, demonstrating the potential of this spectroscopic method for real-time inspection in roll-to-roll manufacturing. Additionally, the physical mechanism of reflectance changes was explored. Surface roughness measurements and density functional theory (DFT) calculations indicate that reduced reflectance at higher SoL is due to increased light scattering from particle expansion and bandgap narrowing. Overall, this spectroscopic method enables both a fundamental understanding of silicon lithiation and a practical framework for industrial-scale quality control.